Subject: API Draft

From: James Kempf <[email-masked]>
Date: Tue, 30 Mar 1999 11:07:29 -0800 (PST)

Date: Thu, 25 Mar 1999 14:33:54 -0800 (PST)
From: James Kempf <[email-masked]>
Subject: API Draft
To: [email-masked]
MIME-Version: 1.0

The IESG had a few suggestions to change in the API draft, and I've corrected
a few typos and such. I've attached a copy of draft-ietf-srvloc-api-09.txt,
and changes are listed below. I'd like to get a sense of whether the
working group feels these changes are significant enough to go through
another working group and IETF last call, or whether we can go ahead
and submit 09 for informational status. If we can simply go ahead and
submit the 09 draft, we can finish up all the SLP RFCs at once.

Here are the changes from 08:

- Removed all uses of MUST, SHOULD, and MAY where they simply duplicate
the wording from the protocol or service scheme standard documents.

- Fixed spelling errors.

- Removed the designation of '(' and ')' as reserved characters in
the configuration file grammar. This was a relic of the old
DA address and scope syntax.

- Changed reference of CONFIG_DA_RETRY to CONFIG_RETRY and CONFIG_DA_MAX
to CONFIG_RETRY_MAX. This was a relic of SLPv1.

- Clarified that the net.slp.MTU configuration property refers to 
the total datagram packet size, including IP and TCP or UDP header.

- Clarified that the net.slp.interfaces property should not be set
unless either broadcast is being used on the subnets connected
to the interfaces, instead of multicast, or packets are not being
routed between interfaces.

- Removed the extra newline at the end of the ser-reg production 
in the registration file grammer.

- Changed the return type of SLPGetRefreshInterval() from int to
unsigned short.

- Clarified that the SLP configuration properties file syntax is
slightly different from java.util.Properties file syntax, and so
the java.util.Properties file reader can't be used to read in
SLP configuration properties, although the SLP properties are
stored in java.util.Properties.

		jak

Service Location Working Group                               James Kempf
INTERNET DRAFT                                              Erik Guttman
5 April  1999                                           Sun Microsystems

                      An API for Service Location
                      draft-ietf-svrloc-api-09.txt

Status of This Memo

   This document is a submission by the Service Location Working Group
   of the Internet Engineering Task Force (IETF).  Comments should be
   submitted to the [email-masked] mailing list.

   Distribution of this memo is unlimited.

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at
   any time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at:

      http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at:

      http://www.ietf.org/shadow.html.

Kempf, Guttman              Expires 5 October 1999              [Page i]

Internet Draft            Service Location API             5 April  1999

Abstract

   The Service Location Protocol (SLP) provides a new way for clients to
   dynamically discovery network services.  With SLP, it is simple to
   offer highly available services that require no user configuration or
   assistance from network administrators prior to use.  This document
   describes standardized APIs for SLP in C and Java.  The APIs are
   modular and are designed to allow implementations to offer just the
   feature set needed.  In addition, standardized file formats for
   configuration and serialized registrations are defined, allowing SLP
   agents to set network and other parameters in a portable way.  The
   serialized file format allows legacy services to be registered with
   SLP directory agents in cases where modifying the legacy service
   program code is difficult or impossible, and to portably exchange a
   registration database.

Kempf, Guttman             Expires 5 October 1999              [Page ii]

Internet Draft            Service Location API             5 April  1999

                                Contents

Status of This Memo                                                    i

Abstract                                                              ii

 1. Introduction                                                       1
     1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . .    1
     1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . .    2

 2. File Formats                                                       4
     2.1. Configuration File Format . . . . . . . . . . . . . . . .    5
           2.1.1. DA configuration  . . . . . . . . . . . . . . . .    6
           2.1.2. Static Scope Configuration  . . . . . . . . . . .    7
           2.1.3. Tracing and Logging . . . . . . . . . . . . . . .    8
           2.1.4. Serialized Proxy Registrations  . . . . . . . . .    9
           2.1.5. Network Configuration Properties  . . . . . . . .    9
           2.1.6. SA Configuration  . . . . . . . . . . . . . . . .   11
           2.1.7. UA Configuration  . . . . . . . . . . . . . . . .   12
           2.1.8. Security  . . . . . . . . . . . . . . . . . . . .   13
     2.2. Multihomed Machines . . . . . . . . . . . . . . . . . . .   13
     2.3. Serialized Registration File  . . . . . . . . . . . . . .   14
     2.4. Processing Serialized Registration and Configuration Files  15

 3. Binding Independent Implementation Considerations                 16
     3.1. Multithreading  . . . . . . . . . . . . . . . . . . . . .   16
     3.2. Asynchronous and Incremental  . . . . . . . . . . . . . .   16
     3.3. Type Checking for Service Types . . . . . . . . . . . . .   16
     3.4. Refreshing Registrations  . . . . . . . . . . . . . . . .   17
     3.5. Configuration File Processing . . . . . . . . . . . . . .   17
     3.6. Attribute Types . . . . . . . . . . . . . . . . . . . . .   17
     3.7. Removal of Duplicates . . . . . . . . . . . . . . . . . .   17
     3.8. Character Set Encoding  . . . . . . . . . . . . . . . . .   18
     3.9. Error Semantics . . . . . . . . . . . . . . . . . . . . .   18
    3.10. Modular Implementations . . . . . . . . . . . . . . . . .   21
    3.11. Handling Special Service Types  . . . . . . . . . . . . .   21
    3.12. Scope Discovery and Handling  . . . . . . . . . . . . . .   22

 4. C Language Binding                                                23
     4.1. Constant Types  . . . . . . . . . . . . . . . . . . . . .   24
           4.1.1. URL Lifetimes . . . . . . . . . . . . . . . . . .   24
           4.1.2. Error Codes . . . . . . . . . . . . . . . . . . .   24
           4.1.3. SLPBoolean  . . . . . . . . . . . . . . . . . . .   25
     4.2. Struct Types  . . . . . . . . . . . . . . . . . . . . . .   26
           4.2.1. SLPSrvURL . . . . . . . . . . . . . . . . . . . .   26
           4.2.2. SLPHandle . . . . . . . . . . . . . . . . . . . .   27

Kempf, Guttman             Expires 5 October 1999             [Page iii]

Internet Draft            Service Location API             5 April  1999

     4.3. Callbacks . . . . . . . . . . . . . . . . . . . . . . . .   27
           4.3.1. SLPRegReport  . . . . . . . . . . . . . . . . . .   28
           4.3.2. SLPSrvTypeCallback  . . . . . . . . . . . . . . .   28
           4.3.3. SLPSrvURLCallback . . . . . . . . . . . . . . . .   29
           4.3.4. SLPAttrCallback . . . . . . . . . . . . . . . . .   31
     4.4. Opening and Closing an SLPHandle  . . . . . . . . . . . .   32
           4.4.1. SLPOpen . . . . . . . . . . . . . . . . . . . . .   32
           4.4.2. SLPClose  . . . . . . . . . . . . . . . . . . . .   33
     4.5. Protocol API  . . . . . . . . . . . . . . . . . . . . . .   34
           4.5.1. SLPReg  . . . . . . . . . . . . . . . . . . . . .   34
           4.5.2. SLPDereg  . . . . . . . . . . . . . . . . . . . .   35
           4.5.3. SLPDelAttrs . . . . . . . . . . . . . . . . . . .   36
           4.5.4. SLPFindSrvTypes . . . . . . . . . . . . . . . . .   37
           4.5.5. SLPFindSrvs . . . . . . . . . . . . . . . . . . .   39
           4.5.6. SLPFindAttrs  . . . . . . . . . . . . . . . . . .   40
     4.6. Miscellaneous Functions . . . . . . . . . . . . . . . . .   42
           4.6.1. SLPGetRefreshInterval . . . . . . . . . . . . . .   42
           4.6.2. SLPFindScopes . . . . . . . . . . . . . . . . . .   42
           4.6.3. SLPParseSrvURL  . . . . . . . . . . . . . . . . .   43
           4.6.4. SLPEscape . . . . . . . . . . . . . . . . . . . .   44
           4.6.5. SLPUnescape . . . . . . . . . . . . . . . . . . .   45
           4.6.6. SLPFree . . . . . . . . . . . . . . . . . . . . .   46
           4.6.7. SLPGetProperty  . . . . . . . . . . . . . . . . .   46
           4.6.8. SLPSetProperty  . . . . . . . . . . . . . . . . .   47
     4.7. Implementation Notes  . . . . . . . . . . . . . . . . . .   48
           4.7.1. Refreshing Registrations  . . . . . . . . . . . .   48
           4.7.2. Syntax for String Parameters  . . . . . . . . . .   48
           4.7.3. Client Side Syntax Checking . . . . . . . . . . .   48
           4.7.4. System Properties . . . . . . . . . . . . . . . .   49
           4.7.5. Memory Management . . . . . . . . . . . . . . . .   49
           4.7.6. Asynchronous and Incremental Return Semantics . .   49
     4.8. Example . . . . . . . . . . . . . . . . . . . . . . . . .   50

 5. Java Language Binding                                             54
     5.1. Introduction  . . . . . . . . . . . . . . . . . . . . . .   54
     5.2. Exceptions and Errors . . . . . . . . . . . . . . . . . .   55
           5.2.1. Class ServiceLocationException  . . . . . . . . .   55
     5.3. Basic Data Structures . . . . . . . . . . . . . . . . . .   56
           5.3.1. Interface ServiceLocationEnumeration  . . . . . .   56
           5.3.2. Class ServiceLocationAttribute  . . . . . . . . .   57
           5.3.3. Class ServiceType . . . . . . . . . . . . . . . .   59
           5.3.4. Class ServiceURL  . . . . . . . . . . . . . . . .   62
     5.4. SLP Access Interfaces . . . . . . . . . . . . . . . . . .   65
           5.4.1. Interface Advertiser  . . . . . . . . . . . . . .   65
           5.4.2. Interface Locator . . . . . . . . . . . . . . . .   67
     5.5. The Service Location Manager  . . . . . . . . . . . . . .   71
           5.5.1. Class ServiceLocationManager  . . . . . . . . . .   71
     5.6. Service Template Introspection  . . . . . . . . . . . . .   72
           5.6.1. Abstract Class TemplateRegistry . . . . . . . . .   72

Kempf, Guttman             Expires 5 October 1999              [Page iv]

Internet Draft            Service Location API             5 April  1999

           5.6.2. Interface ServiceLocationAttributeVerifier  . . .   75
           5.6.3. Interface ServiceLocationAttributeDescriptor  . .   77
     5.7. Implementation Notes  . . . . . . . . . . . . . . . . . .   80
           5.7.1. Refreshing Registrations  . . . . . . . . . . . .   80
           5.7.2. Parsing Alternate Transports in ServiceURL  . . .   80
           5.7.3. String Attribute Values . . . . . . . . . . . . .   80
           5.7.4. Client Side Syntax Checking . . . . . . . . . . .   80
           5.7.5. Language Locale Handling  . . . . . . . . . . . .   81
           5.7.6. Setting SLP System Properties . . . . . . . . . .   81
           5.7.7. Multithreading  . . . . . . . . . . . . . . . . .   82
           5.7.8. Modular Implementations . . . . . . . . . . . . .   82
           5.7.9. Asynchronous and Incremental Return Semantics . .   82
     5.8. Example . . . . . . . . . . . . . . . . . . . . . . . . .   83

 6. Internationalization Considerations                               85
     6.1. service URL . . . . . . . . . . . . . . . . . . . . . . .   85
     6.2. Character Set Encoding  . . . . . . . . . . . . . . . . .   86
     6.3. Language Tagging  . . . . . . . . . . . . . . . . . . . .   86

 7. Security Considerations                                           86

 8. Acknowledgements                                                  87

 9. Full Copyright Statement                                          89

1. Introduction

   The Service Location API is designed for standardized access to the
   Service Location Protocol (SLP). The APIs allow client and service
   programs to be be written or modified in a very simple manner to
   provide dynamic service discovery and selection.  Bindings in the
   C and Java languages are defined in this document.  In addition,
   standardized formats for configuration files and for serialized
   registration files are presented.  These files allow SLP agents
   to configure network parameters, to register legacy services that
   have not been SLP enabled, and to portably exchange registration
   databases.

1.1. Goals

   The overall goal of the API is to enable source portability of
   applications that use the API between different implementations of
   SLP. The result should facilitate the adoption of SLP, and conversion
   of clients and service programs to SLP.

Kempf, Guttman              Expires 5 October 1999              [Page 1]

Internet Draft            Service Location API             5 April  1999

   The goals of the C binding are to create a minimal but complete
   access to the functionality of the SLP protocol, allowing for simple
   memory management and limited code size.

   The Java API provides for modular implementations (where unneeded
   features can be omitted) and an object oriented interface to the
   complete set of SLP data and functionality.

   The standardized configuration file and serialized file formats
   provide a simple syntax with complete functional coverage of
   the protocol, but without system dependent properties and secure
   information.

1.2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119  [1].

      Service Location Protocol (SLP)

         The underlying protocol allowing dynamic and scalable service
         discovery.  This protocol is specified in the Service Location
         Protocol Version 2 [7].

      SLP framework

         When a 'Service Location framework' is mentioned, it refers to
         both the SLP implementation and interface implementation; i.e.
         whatever provides the SLP functionality to user level programs.
         This includes remote agents.

      Directory Agent (DA)

         A service that automatically gathers service advertisements
         from SAs in order to provide them to UAs.

      User Agent (UA)

         This is the Service Location process or library that allows
         SLP requests to be made on behalf of a client process.  UAs
         automatically direct requests to DAs when they exist.  In their
         absence, UAs make requests to SAs.

      Service Agent (SA)

         This is the Service Location process or library that allows
         service software to register and deregister itself with the SLP

Kempf, Guttman              Expires 5 October 1999              [Page 2]

Internet Draft            Service Location API             5 April  1999

         framework.  SAs respond to UA service requests, detect DAs and
         register service advertisements with them.

      SA Server

         Many operating system platforms only allow a single process to
         listen on a particular port number.  Since SAs are required
         to listen on a multicast address for SLP service requests,
         implementations of the SLP framework on such platforms that
         want to support multiple SAs on one machine need to arrange for
         a single process to do the listening while the advertising SAs
         communicate with that process through another mechanism.  The
         single listening process is called an SA server.  SA servers
         share many characteristics with DAs, but they are not the same.

      Service Advertisement

         A URL possibly combined with service attributes.  These are
         made available to UAs by SAs, either directly or via a DA.

      Locale

         The language localization that applies to strings passed into
         or returned from the SLP API. The Locale is expressed using a
         Language Tag [6].  All attribute strings are associated with a
         particular locale.  The locale is completely orthogonal to the
         ANSI C locale.  The SLP locale is mapped into the Java locale
         in the Java API.

      Service Template

         A document that describes the syntax of the URL for a given
         service type and a definition of all service attributes
         including the meaning, defaults, and constraints on values the
         attributes may take.  See [8] for more information on service
         templates.

      The service:  URL

         A service of a particular type announces its availability
         with a service:  URL that includes its service access point
         (domain name or IP address, and possibly its port number) and
         optionally basic configuration parameters.  The syntax of the
         service:  URL is defined in the service template.  Other URL's
         can be used in service advertisements if desired.

Kempf, Guttman              Expires 5 October 1999              [Page 3]

Internet Draft            Service Location API             5 April  1999

      Service Attributes

         The attributes associated with a given service.  The values
         that can be assigned to service attributes are defined by the
         service template.

      Scope

         A string used to control the availability of service
         advertisements.  Every SLP Agent is configured with one or more
         scope strings.  Scopes are assigned by site administrators to
         group services for many purposes, but chiefly as a means of
         scalability.  DAs store only services advertised having a scope
         string matching the scopes with which they are configured.

      Naming Authority (NA)

         This is a 'suffix' to the service type string.  It completely
         changes the meaning of the service type.  NAs are used
         for private definitions of well known Service Types and
         experimental Service Type extensions.  The default NA is
         "IANA", which must not be explicitly included.  Service types
         with the IANA naming authority are registered with the Internet
         Assigned Numbers Authority (see [8] for more information on the
         registration procedure).

2. File Formats

   This section describes the configuration and serialized registration
   file formats.  Both files are defined in the UTF-8 character set [3].

   Attribute tags and values in the serialized registration file
   require SLP reserved characters to be escaped.  The SLP reserved
   characters are `(', `)', `,', `\', `!', `<', `=', `>', `~' and
   control characters (characters with UTF codes less than 0x0020 and
   the character 0x007f, which is US-ASCII DEL). The escapes are formed
   exactly as for the wire protocol, i.e.  a backslash followed by two
   hex digits representing the character.  For example, the escape
   for ',' is '\2c'.  In addition, the characters `\n', `\r', `\t',
   and `_' are prohibited from attribute tags by the SLP wire syntax
   grammar. [7]

   In serialized registration files, escaped strings beginning with
   `\ff`, an encoding for a nonUTF-8 character, are treated as opaques.
   Exactly as in the wire protocol, syntactically correct opaque
   encodings consist of a string beginning with `\ff` and containing
   *only* escaped characters that are transformed to bytes.  Such
   strings are only syntactically correct in the serialized registration

Kempf, Guttman              Expires 5 October 1999              [Page 4]

Internet Draft            Service Location API             5 April  1999

   file as attribute values.  In other cases, whenever an escape is
   encountered and the character is not an SLP reserved character, an
   error is signaled.

   Escaped characters in URLs in serialized registration files use the
   URL escape convention. [2].

   Property names and values in the configuration file have a few
   reserved characters that are involved in file's lexical definition.
   The characters '.'  and '=' are reserved in property names and
   must be escape.  The characters ',', '(', and ')' are reserved in
   property values and must be escaped.  In addition, scope names in the
   net.slp.useScopes property use the SLP wire format escape convention
   for SLP reserved characters.  This simplifies implementation, since
   the same code can be used to unescape scope names as is used in
   processing the serialized registration file or for formatting wire
   messages.

   On platforms that only support US-ASCII and not UTF-8, the upper
   bit of bytes incoming from the configuration and registration
   files determines whether the character is US-ASCII or not US-ASCII.
   According to the standard UTF-8 encoding, the upper bit is zero if
   the character is US-ASCII and one if the character is multibyte
   and thus not US-ASCII. Platforms without intrinsic UTF-8 support
   are required to parse the multibyte character and store it in an
   appropriate internal format.  Support for UTF-8 is required to
   implement the SLP protocol (see [7]), and can therefore be used in
   file processing as well.

   The location and name of the configuration file is system-dependent,
   but implementations of the API are encouraged to locate it together
   with other configuration files and name it consistently.

2.1. Configuration File Format

   The configuration file format consists of a newline delimited list
   of zero or more property definitions.  Each property definition
   corresponds to a particular configurable SLP, network, or other
   parameter in one or more of the three SLP agents.  The file format
   grammar in ABNF [5] syntax is:

      config-file   =  line-list
      line-list     =  line / line line-list
      line          =  property-line / comment-line
      comment-line  =  ( "#" / ";" ) 1*allchar newline
      property-line =  property newline
      property      =  tag "=" value-list

Kempf, Guttman              Expires 5 October 1999              [Page 5]

Internet Draft            Service Location API             5 April  1999

      tag           =  prop / prop "." tag
      prop          =  1*tagchar
      value-list    =  value / value "," value-list
      value         =  int / bool /
                       "(" value-list ")" / string
      int           =  1*DIGIT
      bool          =  "true" / "false" / "TRUE" / "FALSE"
      newline       =  CR / ( CRLF )
      string        =  1*stringchar
      tagchar       =  DIGIT / ALPHA / tother / escape
      tother        =  %x21-%x2d / %x2f /
                       %x3a / %x3c-%x40 /
                       %x5b-%x60 / %7b-%7e
                       ; i.e., all characters except `.',
                       ; and `='.
      stringchar    =  DIGIT / ALPHA / sother / escape
      sother        =  %x21-%x29 / %x2a-%x2b /
                       %x2d-%x2f / %x3a-%x40 /
                       %x5b-%x60 / %7b-%7e
                       ; i.e., all characters except `,'
      allchar       =  DIGIT / ALPHA / HTAB / SP
      escape        =  "\" HEXDIG HEXDIG
                       ; Used for reserved characters

   With the exception of net.slp.useScopes, net.slp.DAAddresses,
   and net.slp.isBroadcastOnly, all other properties can be changed
   through property accessors in the C and Java APIs.  The property
   accessors only change the property values in the running agent
   program and do not affect the values in the configuration file.  The
   net.slp.useScopes and net.slp.DAAddresses properties are read-only
   because they control the agent's view of the scopes and DAs and
   are therefore critical to the function of the API scope discovery
   algorithm.  Attempts to modify them are unlikely to yield productive
   results, and could harm the ability of the agent to find scopes and
   use DAs.  The net.slp.isBroadcastOnly property is read-only because
   the API library needs to configure networking upon start up and
   changing this property might invalidate the configuration.  Whether
   the local network uses broadcast or multicast is not likely to change
   during the course of the program's execution.

   The properties break down into the following subsections describes an
   area and its properties.

2.1.1. DA configuration

   Important configuration properties for DAs are included in this
   section.  These are:

Kempf, Guttman              Expires 5 October 1999              [Page 6]

Internet Draft            Service Location API             5 April  1999

      net.slp.isDA

         A boolean indicating if the SLP server is to act as a DA. If
         false, not run as a DA. Default is false.

      net.slp.DAHeartBeat

         A 32 bit integer giving the number of seconds for the
         DA heartbeat.  Default is 3 hours (10800 seconds).  This
         property corresponds to the protocol specification parameter
         CONFIG_DA_BEAT [7].  Ignored if isDA is false.

      net.slp.DAAttributes

         A comma-separated list of parenthesized attribute/value list
         pairs that the DA must advertise in DAAdverts.  The property
         must be in the SLP attribute list wire format, including
         escapes for reserved characters. [7]

2.1.2. Static Scope Configuration

   These properties allow various aspects of scope handling to be
   configured.

      net.slp.useScopes

         A value-list of strings indicating the only scopes a UA or SA
         is allowed to use when making requests or registering, or the
         scopes a DA must support.  If not present for the DA and SA,
         then in the absence of scope information from DHCP, the default
         scope "DEFAULT" is used.  If not present for the UA, and there
         is no scope information available from DHCP, then the user
         scoping model is in force.  Active and passive DA discovery
         or SA discovery are used for scope discovery, and the scope
         "DEFAULT" is used if no other information is available.  If a
         DA or SA gets another scope in a request, a SCOPE_NOT_SUPPORTED
         error should be returned, unless the request was multicast, in
         which case it should be dropped.  If a DA gets another scope in
         a registration, a SCOPE_NOT_SUPPORTED error must be returned.
         Unlike other properties, this property is "read-only", so
         attempts to change it after the configuration file has been
         read are ignored.  See Section 3.12 for the algorithm the API
         uses in determining what scope information to present.

      net.slp.DAAddresses

         A value-list of IP addresses or DNS resolvable host names
         giving the SLPv2 DAs to use for statically configured UAs and

Kempf, Guttman              Expires 5 October 1999              [Page 7]

Internet Draft            Service Location API             5 April  1999

         SAs.  Ignored by DAs (unless the DA is also an SA server).
         Default is none.  Unlike other properties, this property is
         "read-only", so attempts to change it after the configuration
         file has been read are ignored.

         The following grammar describes the property:

               addr-list     =  addr / addr "," addr-list
               addr          =  fqdn / hostnumber
               fqdn          =  ALPHA / ALPHA *[ anum / "-" ] anum
               anum          =  ALPHA / DIGIT
               hostnumber    =  1*3DIGIT 3("." 1*3DIGIT)

         An example is:

                sawah,mandi,sambal

         IP addresses can be used instead of host names in networks
         where DNS is not deployed, but network administrators are
         reminded that using IP addresses will complicate machine
         renumbering, since the SLP configuration property files
         in statically configured networks will have to be changed.
         Similarly, if host names are used, implementors must be careful
         that a name service is available before SLP starts, in other
         words, SLP cannot be used to find the name service.

2.1.3. Tracing and Logging

   This section allows tracing and logging information to be printed by
   the various agents.

      net.slp.traceDATraffic

         A boolean controlling printing of messages about traffic with
         DAs.  Default is false.

      net.slp.traceMsg

         A boolean controlling printing of details on SLP messages.
         The fields in all incoming messages and outgoing replies are
         printed.  Default is false.

Kempf, Guttman              Expires 5 October 1999              [Page 8]

Internet Draft            Service Location API             5 April  1999

      net.slp.traceDrop

         A boolean controlling printing details when a SLP message is
         dropped for any reason.  Default is false.

      net.slp.traceReg

         A boolean controlling dumps of all registered services upon
         registration and deregistration.  If true, the contents
         of the DA or SA server are dumped after a registration or
         deregistration occurs.  Default is false.

2.1.4. Serialized Proxy Registrations

   These properties control the reading and writing of serialized
   registrations.

      net.slp.serializedRegURL

         A string containing a URL pointing to a document containing
         serialized registrations that should be processed when the DA
         or SA server starts up.  Default is none.

2.1.5. Network Configuration Properties

   The properties in this section allow various network configuration
   properties to be set.

      net.slp.isBroadcastOnly

         A boolean indicating if broadcast should be used instead of
         multicast.  Like the net.slp.useScopes and net.slp.DAAddresses
         properties, this property is "read-only", so attempts to change
         it after the configuration file has been read are ignored.
         Default is false.

      net.slp.passiveDADetection

         A boolean indicating whether passive DA detection should be
         used.  Default is true.

      net.slp.multicastTTL

         A positive integer less than or equal to 255, giving the
         multicast TTL. Default is 255.

Kempf, Guttman              Expires 5 October 1999              [Page 9]

Internet Draft            Service Location API             5 April  1999

      net.slp.DAActiveDiscoveryInterval

         A 16 bit positive integer giving the number of seconds
         between DA active discovery queries.  Default is 900 seconds
         (15 minutes).  This property corresponds to the protocol
         specification parameter CONFIG_DA_FIND [7].  If the property is
         set to zero, active discovery is turned off.  This is useful
         when the DAs available are explicitly restricted to those
         obtained from DHCP or the net.slp.DAAddresses property.

      net.slp.multicastMaximumWait

         A 32 bit integer giving the maximum amount of time to perform
         multicast, in milliseconds.  Default is 15000 ms (15 sec.).
         This property corresponds to the CONFIG_MC_MAX parameter in the
         protocol specification [7].

      net.slp.multicastTimeouts

         A value-list of 32 bit integers used as timeouts, in
         milliseconds, to implement the multicast convergence
         algorithm.  Each value specifies the time to wait before
         sending the next request, or until nothing new has
         been learned from two successive requests.  Default
         is:  3000,3000,3000,3000,3000.  In a fast network the
         aggressive values of 1000,1250,1500,2000,4000 allow better
         performance.  This property corresponds to the CONFIG_MC_RETRY
         parameter in the protocol specification [7].  Note that the
         net.slp.DADiscoveryTimeouts property must be used for active DA
         discovery.

      net.slp.DADiscoveryTimeouts

         A value-list of 32 bit integers used as timeouts, in
         milliseconds, to implement the multicast convergence algorithm
         during active DA discovery.  Each value specifies the time
         to wait before sending the next request, or until nothing
         new has been learned from two successive requests.  This
         property corresponds to the protocol specification parameter
         CONFIG_RETRY [7].  Default is:  2000,2000,2000,2000,3000,4000.

      net.slp.datagramTimeouts

         A value-list of 32 bit integers used as timeouts, in
         milliseconds, to implement unicast datagram transmission to
         DAs.  The nth value gives the time to block waiting for a reply
         on the nth try to contact the DA. The sum of these values is
         the protocol specification property CONFIG_RETRY_MAX [7].

Kempf, Guttman             Expires 5 October 1999              [Page 10]

Internet Draft            Service Location API             5 April  1999

      net.slp.randomWaitBound

         A 32 bit integer giving the maximum value for all random
         wait parameters, in milliseconds.  Default is 1000 (1
         sec.).  This value corresponds to the protocol specification
         parameters CONFIG_START_WAIT, CONFIG_REG_PASSIVE, and
         CONFIG_REG_ACTIVE [7].

      net.slp.MTU

         A 16 bit integer giving the network packet MTU, in bytes.
         This is the maximum size of any datagram to send, but the
         implementation might receive a larger datagram.  The maximum
         size includes IP, and UDP or TCP headers.  Default is 1400.

      net.slp.interfaces

         Value-list of strings giving the IP addresses of network
         interfaces on which the DA or SA should listen on port 427 for
         multicast, unicast UDP, and TCP messages.  Default is empty,
         i.e.  use the default network interface.  The grammar for this
         property is:

               addr-list     =  hostnumber / hostnumber "," addr-list
               hostnumber    =  1*3DIGIT 3("." 1*3DIGIT)

         An example is:

                  195.42.42.42,195.42.142.1,195.42.120.1

         The example machine has three interfaces on which the DA should
         listen.

         Note that since this property only takes IP addresses, it will
         need to be changed if the network is renumbered.

2.1.6. SA Configuration

   This section contains configuration properties for the SA. These
   properties are typically set programmatically by the SA, since they
   are specific to each SA.

Kempf, Guttman             Expires 5 October 1999              [Page 11]

Internet Draft            Service Location API             5 April  1999

      net.slp.SAAttributes

         A comma-separated list of parenthesized attribute/value list
         pairs that the SA must advertise in SAAdverts.  The property
         must be in the SLP attribute list wire format, including
         escapes for reserved characters. [7]

2.1.7. UA Configuration

   This section contains configuration properties for the UA. These
   properties can be set either programmatically by the UA or in the
   configuration file.

      net.slp.locale

         A RFC 1766 Language Tag [6] for the language locale.  Setting
         this property causes the property value to become the default
         locale for SLP messages.  Default is "en".  This property is
         also used for SA and DA configuration.

      net.slp.maxResults

         A 32 bit integer giving the maximum number of results to
         accumulate and return for a synchronous request before the
         timeout, or the maximum number of results to return through a
         callback if the request results are reported asynchronously.
         Positive integers and -1 are legal values.  If -1, indicates
         that all results should be returned.  Default value is -1.

         DAs and SAs always return all results that match the
         request.  This configuration value applies only to UAs, that
         filter incoming results and only return as many values as
         net.slp.maxResults indicates.

      net.slp.typeHint

         A value-list of service type names.  In the absence of any
         DAs, UAs perform SA discovery for finding scopes.  These SA
         discovery requests may contain a request for service types as
         an attribute.

         The API implementation will use the service type names supplied
         by this property to discover only those SAs (and their scopes)
         which support the desired service type or types.  For example,
         if net.slp.typeHint is set to "service:imap,service:pop3" then
         SA discovery requests will include the search filter:

Kempf, Guttman             Expires 5 October 1999              [Page 12]

Internet Draft            Service Location API             5 April  1999

                (|(service-type=service:imap)(service-type=service:pop3))

         The API library can also use unicast to contact the discovered
         SAs for subsequent requests for these service types, to
         optimize network access.

2.1.8. Security

   The property in this section allows security for all agents to be set
   on or off.  When the property is true, then the agent must include
   security information on all SLP messages transacted by that agent.
   Since security policy must be set network wide to be effective, a
   single property controls security for all agents.  Key management
   and management of SLP SPI strings [7] are implementation and policy
   dependent.

      net.slp.securityEnabled

         A boolean indicating whether the agent should enable
         security for URLs, attribute lists, DAAdverts, and SAAdverts.
         Each agent is responsible for interpreting the property
         appropriately.  Default is false.

2.2. Multihomed Machines

   On multihomed machines, the bandwidth and latency characteristics on
   different network interfaces may differ considerably, to the point
   where different configuration properties are necessary to achieve
   optimal performance.  The net.slp.interfaces property indicates which
   network interfaces are SLP enabled.  An API library implementation
   may support configuration customization on a per network interface
   basis by allowing the interface IP address to be appended to the
   property name.  In that case, the values of the property are only
   used for that particular interface, the generic property (or defaults
   if no generic property is set) applies to all others.

   For example, if a configuration has the following properties:

      net.slp.interfaces=125.196.42.41,125.196.42.42,125.196.42.43
      net.slp.multicastTTL.125.196.42.42=1

   then the network interface on subnet 42 is restricted to a TTL of 1,
   while the interfaces on the other subnets have the default multicast
   radius, 255.

Kempf, Guttman             Expires 5 October 1999              [Page 13]

Internet Draft            Service Location API             5 April  1999

   The net.slp.interfaces property must only be set if there is no
   routing between the interfaces.  If the property is set, the DA
   (if any) and SAs should advertise with the IP address or host name
   appropriate to the interface on the interfaces in the list.  If
   packets are routed between the interfaces, then the DA and SAs should
   only advertise on the default interface.  The property should also
   be set if broadcast is used rather than multicast on the subnets
   connected to the interfaces.  Note that even if unicast packets are
   not routed between the interfaces, multicast may be routed through
   another router.  The danger in listening for multicast on multiple
   interfaces when multicast packets are routed is that the DA or SA
   may receive the same multicast request via more than one interface.
   Since the IP address is different on each interface, the DA or SA
   cannot identify the request as having already being answered via
   the previous responder's list.  The requesting agent will end up
   getting URLs that refer to the same DA or service but have different
   addresses or host names.

2.3. Serialized Registration File

   The serialized registration file contains a group of registrations
   that a DA or SA server (if one exists) registers when it starts up.
   These registrations are primarily for older service programs that do
   not internally support SLP and cannot be converted, and for portably
   exchanging registrations between SLP implementations.  The character
   encoding of the registrations is required to be UTF-8.

   The syntax of the serialized registration file, in ABNF format [5],
   is as follows:

      ser-file      =  reg-list
      reg-list      =  reg / reg reg-list
      reg           =  creg / ser-reg
      creg          =  comment-line ser-reg
      comment-line  =  ( "#" / ";" ) 1*allchar newline
      ser-reg       =  url-props [slist] [attr-list] newline
      url-props     =  surl "," lang "," ltime [ "," type ] newline
      surl          =  ;The registration's URL. See
                       ; [8] for syntax.
      lang          =  1*8ALPHA [ "-" 1*8ALPHA ]
                       ;RFC 1766 Language Tag see [6].
      ltime         =  1*5DIGIT
                       ; A positive 16-bit integer
                       ; giving the lifetime
                       ; of the registration.
      type          =  ; The service type name, see [7]
                       ; and [8] for syntax.

Kempf, Guttman             Expires 5 October 1999              [Page 14]

Internet Draft            Service Location API             5 April  1999

      slist         =  "scopes" "=" scope-list newline
      scope-list    =  scope-name / scope-name "," scope-list
      scope         =  ; See grammar of [7] for
                       ; scope-name syntax.
      attr-list     =  attr-def / attr-def attr-list
      attr-def      =  ( attr / keyword ) newline
      keyword       =  attr-id
      attr          =  attr-id "=" attr-val-list
      attr-id       =  ;Attribute id, see [7] for syntax.
      attr-val-list =  attr-val / attr-val "," attr-val-list
      attr-val      =  ;Attribute value, see [7] for syntax.
      allchar       =  char / WSP
      char          =  DIGIT / ALPHA / other
      other         =  %x21-%x2f / %x3a-%x40 /
                       %x5b-%x60 / %7b-%7e
                       ; All printable, nonwhitespace US-ASCII
                       ; characters.
      newline       =  CR / ( CRLF )

   The syntax for scope names, attribute tags, and attribute values
   requires escapes for special characters as specified in [7].  DAs
   and SA servers that process serialized registrations must handle
   them exactly as if they were registered by an SA. In the url-props
   production, the type token is optional.  If the type token is present
   for a service:  URL, a warning is signaled and the type name is
   ignored.  If the maximum lifetime is specified (65535 sec.), the
   registration is taken to be permanent, and is continually refreshed
   by the DA or SA server until it exits.  Scopes can be included in a
   registration by including an attribute definition with tag "scopes"
   followed by a comma separated list of scope names immediately after
   the url-props production.  If the optional scope list is present,
   the registrations are made in the indicated scopes; otherwise, they
   are registered in the scopes with which the DA or SA server was
   configured through the net.slp.useScopes property.

   If the scope list contains scopes that are not in the
   net.slp.useScopes property (provided that property is set) or
   are not specified by DHCP, the API library should reject the
   registration and issue a warning message.

2.4. Processing Serialized Registration and Configuration Files

   Implementations are encouraged to make processing of configuration
   and serialized files as transparent as possible to clients of
   the API. At the latest, errors must be caught when the relevant
   configuration item is used.  At the earliest, errors may be caught
   when the relevant file is loaded into the executing agent.  Errors

Kempf, Guttman             Expires 5 October 1999              [Page 15]

Internet Draft            Service Location API             5 April  1999

   should be reported by logging to the appropriate platform logging
   file, error output, or log device, and the default value substituted.
   Serialized registration file entries should be caught and reported
   when the file is loaded.

   Configuration file loading must be complete prior to the initiation
   of the first networking connection.  Serialized registration must be
   complete before the DA accepts the first network request.

3. Binding Independent Implementation Considerations

   This section discusses a number of implementation considerations
   independent of language binding, with language specific notes where
   applicable.

3.1. Multithreading

   Implementations of both the C and Java APIs are required to make API
   calls thread-safe.  Access to data structures shared between threads
   must be co-ordinated to avoid corruption or invalid access.  One way
   to achieve this goal is to allow only one thread at a time in the
   implementing library.  Performance in such an implementation suffers,
   however.  Therefore, where possible, implementations are encouraged
   to allow multiple threads within the SLP API library.

3.2. Asynchronous and Incremental

   The APIs are designed to encourage implementations supporting
   asynchronous and incremental client interaction.  The goal is to
   allow large numbers of returned service URLs, service types, and
   attributes without requiring the allocation of huge chunks of memory.
   The particular design features to support this goal differ in the two
   language bindings.

3.3. Type Checking for Service Types

   Service templates [8] allow SLP registrations to be type checked for
   correctness.  Implementations of the API are free to make use of
   service type information for type checking, but are not required to
   do so.  If a type error occurs, the registration should terminate
   with TYPE_ERROR.

Kempf, Guttman             Expires 5 October 1999              [Page 16]

Internet Draft            Service Location API             5 April  1999

3.4. Refreshing Registrations

   SLP advertisements carry an explicit lifetime with them.  After
   the lifetime expires, the DA flushes the registration from its
   cache.  In some cases, an application may want to have the URL
   continue being registered for the entire time during which the
   application is executing.  The API includes provision for clients
   to indicate whether they want URLs to be automatically refreshed.
   Implementations of the SA API must provide this automatic refreshing
   capability.  Note that a client which uses this facility should
   explicitly deregister the service URL before exiting, since the API
   implementation may not be able to assure that the URL is deregistered
   when the application exits, although it will time out in the DA
   eventually.

3.5. Configuration File Processing

   DAs, SAs and UAs processing the configuration file, and DAs and SA
   servers processing the serialized registration file are required
   to log any errors using whatever underlying error mechanism is
   appropriate for the platform.  Examples include writing error
   messages to the standard output, writing to a system logging device,
   or displaying the errors to a logging window.  After the error is
   reported, the offending property must be set to the default and
   program execution continued.  An agent MUST NOT fail if a file format
   error occurs.

3.6. Attribute Types

   String encoded attribute values do not include explicit type
   information.  All UA implementations and those SA and DA
   implementations that choose to support type checking should use the
   type rules described in [8] in order to convert from the string
   representation on the wire to an object typed appropriately.

3.7. Removal of Duplicates

   The UA implementation SHOULD always collate results to remove
   duplicates during synchronous operations and for the Java API. During
   asynchronous operation in C, the UA implementation SHOULD forgo
   duplicate elimination to reduce memory requirements in the library.
   This allows the API library to simply take the returned attribute
   value list strings, URL strings, or service type list strings
   and call the callback function with it, without any additional
   processing.  Naturally, the burden of duplicate elimination is thrown
   onto the client in this case.

Kempf, Guttman             Expires 5 October 1999              [Page 17]

Internet Draft            Service Location API             5 April  1999

3.8. Character Set Encoding

   Character string parameters in the Java API are all represented in
   Unicode internally because that is the Java-supported character
   set.  Characters buffer parameters in the C API are represented
   in UTF-8 to maintain maximum compatibility on platforms that only
   support US-ASCII and not UTF-8.  API functions are still required to
   handle the full range of UTF-8 characters because the SLP protocol
   requires it, but the API implementation can represent the characters
   internally in any convenient way.  On the wire, all characters are
   converted to UTF-8.  Inside URLs, characters that are not allowed by
   URL syntax [2] must be escaped according to the URL escape character
   convention.  Strings that are included in SLP messages may include
   SLP reserved characters and can be escaped by clients through
   convenience functions provided by the API. The character encoding
   used in escapes is UTF-8.

   Due to constraints in SLP, no string parameter passed to the C or
   Java API may exceed 64K bytes in length.

3.9. Error Semantics

   All errors encountered processing SLP messages should be logged.
   For synchronous calls, an error is only reported on a call if no
   successful replies were received from any SLP framework entity.  If
   an error occurred among one of several successful replies, then the
   error should be logged and the successful replies returned.  For
   asynchronous calls, an error occurring during correspondence with a
   particular remote SLP agent is reported through the first callback
   (in the C API) or enumeration method invocation (in the Java API)
   after the error occurs, which would normally report the results of
   the correspondence.  This allows the callback or client code to
   determine whether the operation should be terminated or continue.  In
   some cases, the error returned from the SLP framework may be fatal
   (SLP_PARSE_ERROR, etc.).  In these cases, the API library terminates
   the operation.

   Both the Java and C APIs contain language specific error code
   mechanisms for returning error information.  The names of the error
   codes are consistent between the two implementations, however.

   The following error codes are returned from a remote agent (DA or SA
   server):

      LANGUAGE_NOT_SUPPORTED

         No DA or SA has service advertisement or attribute information
         in the language requested, but at least one DA or SA indicated,

Kempf, Guttman             Expires 5 October 1999              [Page 18]

Internet Draft            Service Location API             5 April  1999

         via the LANGUAGE_NOT_SUPPORTED error code, that it might have
         information for that service in another language.

      PARSE_ERROR

         The SLP message was rejected by a remote SLP agent.  The API
         returns this error only when no information was retrieved, and
         at least one SA or DA indicated a protocol error.  The data
         supplied through the API may be malformed or a may have been
         damaged in transit.

      INVALID_REGISTRATION

         The API may return this error if an attempt to register a
         service was rejected by all DAs because of a malformed URL or
         attributes.  SLP does not return the error if at least one DA
         accepted the registration.

      AUTHENTICATION_ABSENT

         If the SLP framework supports authentication, this error arises
         when the UA or SA failed to send an authenticator for requests
         or registrations in a protected scope.

      INVALID_UPDATE

         An update for a non-existing registration was issued, or the
         update includes a service type or scope different than that in
         the initial registration, etc.

   The following errors result from interactions with remote agents or
   can occur locally:

      AUTHENTICATION_FAILED

         If the SLP framework supports authentication, this error arises
         when a authentication on an SLP message failed.

      SCOPE_NOT_SUPPORTED

         The API returns this error if the SA has been configured with
         net.slp.useScopes value-list of scopes and the SA request did
         not specify one or more of these allowable scopes, and no
         others.  It may be returned by a DA or SA if the scope included
         in a request is not supported by the DA or SA.

Kempf, Guttman             Expires 5 October 1999              [Page 19]

Internet Draft            Service Location API             5 April  1999

      REFRESH_REJECTED

         The SA attempted to refresh a registration more frequently
         than the minimum refresh interval.  The SA should call the
         appropriate API function to obtain the minimum refresh interval
         to use.

   The following errors are generated through a program interacting with
   the API implementation.  They do not involve a remote SLP agent.

      NOT_IMPLEMENTED

         If an unimplemented feature is used, this error is returned.

      NETWORK_INIT_FAILED

         If the network cannot initialize properly, this error is
         returned.

      NETWORK_TIMED_OUT

         When no reply can be obtained in the time specified by the
         configured timeout interval for a unicast request, this error
         is returned.

      NETWORK_ERROR

         The failure of networking during normal operations causes this
         error to be returned.

      BUFFER_OVERFLOW

         An outgoing request overflowed the maximum network MTU size.
         The request should be reduced in size or broken into pieces and
         tried again.

      MEMORY_ALLOC_FAILED

         If the API fails to allocate memory, the operation is aborted
         and returns this.

      PARAMETER_BAD

         If a parameter passed into an interface is bad, this error is
         returned.

Kempf, Guttman             Expires 5 October 1999              [Page 20]

Internet Draft            Service Location API             5 April  1999

      INTERNAL_SYSTEM_ERROR

         A basic failure of the API causes this error to be returned.
         This occurs when a system call or library fails.  The operation
         could not recover.

      HANDLE_IN_USE

         In the C API, callback functions are not permitted to
         recursively call into the API on the same SLPHandle, either
         directly or indirectly.  If an attempt is made to do so, this
         error is returned from the called API function.

      TYPE_ERROR

         If the API supports type checking of registrations against
         service type templates, this error can arise if the attributes
         in a registration do not match the service type template for
         the service.

   Some error codes are handled differently in the Java API. These
   differences are discussed in Section 5.

   The SLP protocol errors OPTION_NOT_UNDERSTOOD, VERSION_NOT_SUPPORTED,
   INTERNAL_ERROR, MSG_NOT_SUPPORTED, AUTHENTICATON_UNKNOWN, and
   DA_BUSY_NOW should be handled internally and not surfaced to clients
   through the API.

3.10. Modular Implementations

   Subset implementations that do not support the full range of
   functionality are required to nevertheless support every interface
   in order to maintain link compatibility between compliant API
   implementations and applications.  If a particular operation is not
   supported, a NOT_IMPLEMENTED error should be returned.  The Java API
   has some additional conventions for handling subsets.  Applications
   that are expected to run on a wide variety of platforms should be
   prepared for subset API implementations by checking returned error
   codes.

3.11. Handling Special Service Types

   The service types service:directory-agent and service:service-agent
   are used internally in the SLP framework to discover DAs and SAs.
   The mechanism of DA and SA discovery is not normally exposed to the
   API client; however, the client may have interest in discovering
   DAs and SAs independently of their role in discovering other

Kempf, Guttman             Expires 5 October 1999              [Page 21]

Internet Draft            Service Location API             5 April  1999

   services.  For example, a network management application may want
   to determine which machines are running SLP DAs.  To facilitate
   that, API implementations must handle requests to find services and
   attributes for these two service types so that API clients obtain the
   information they expect.

   In particular, if the UA is using a DA, SrvRqst and AttrRqst for
   these service types must be multicast and not unicast to the DA,
   as is the case for other service types.  If the requests are not
   multicast, the DA will respond with an empty reply to a request for
   services of type service:service-agent and with its URL only to a
   request for services of type service:directory-agent.  The UA would
   therefore not obtain a complete picture of the available DAs and SAs.

3.12. Scope Discovery and Handling

   Both APIs contain an operation to obtain a list of currently known
   scope names.  This scope information comes from a variety of places:
   DHCP, the net.slp.useScopes property, unicast to DAs configured via
   DHCP or the net.slp.DAAddresses property, and active and passive
   discovery.

   The API is required to be implemented in a way that re-enforces the
   administrative and user scoping models described in [7].  SA clients
   only support the administrative scoping model.  SAs must know a
   priori what DAs they need to register with since there is typically
   no human intervention in scope selection for SAs.  UAs must support
   both administrative and user scoping because an application may
   require human intervention in scope selection.

   API implementations are required to support administrative scoping
   in the following way.  Scopes configured by DHCP and scopes of DAs
   configured by DHCP have first priority (in that order) and must be
   returned if they are available.  The net.slp.useScopes property has
   second priority, and scopes discovered through the net.slp.useScopes
   property must be returned if this property is set and there are
   no scopes available from DHCP. If scopes are not available from
   either of these sources and the net.slp.DAAddresses property is set,
   then the scopes available from the configured DAs must be returned.
   Note that if both DAs and scopes are configured, the scopes of the
   configured DAs must match the configured scope list; otherwise
   and error is signaled and agent execution is terminated.  If no
   configured scope information is available, then an SA client has
   default scope, "DEFAULT", and a UA client employs user scoping.

   User scoping is supported in the following way.  Scopes discovered
   from active DA discovery, and from passive DA discovery all must be
   returned.  If no information is available from active and passive DA

Kempf, Guttman             Expires 5 October 1999              [Page 22]

Internet Draft            Service Location API             5 April  1999

   discovery, then the API library may perform SA discovery, using the
   service types in the net.slp.typeHint property to limit the search
   to SAs supporting particular service types.  If no net.slp.typeHint
   property is set, the UA may perform SA discovery without any
   service type query.  In the absence of any of the above sources of
   information, the API must return the default scope, "DEFAULT".  Note
   that the API must always return some scope information.

   SLP requires that SAs must perform their operations in all scopes
   currently known to them. [7].  The API enforces this constraint by
   not requiring the API client to supply any scopes as parameters to
   API operations.  The API library must obtain all currently known
   scopes and use them in SA operations.  UA API clients should use a
   scope obtained through one of the API operations for finding scopes.
   Any other scope name may result in a SCOPE_NOT_SUPPORTED error from a
   remote agent.  The UA API library can optionally check the scope and
   return the error without contacting a remote agent.

4. C Language Binding

   The C language binding presents a minimal overhead implementation
   that maps directly into the protocol.  There is one C language
   function per protocol request, with the exception of the SLPDereg()
   and SLPDelAttrs() functions, which map into different uses of the
   SLP deregister request.  Parameters are for the most part character
   buffers.  Memory management is kept simple by having the client
   allocate most memory and requiring that client callback functions
   copy incoming parameters into memory allocated by the client code.
   Any memory returned directly from the API functions is deallocated
   using the SLPFree() function.

   To conform with standard C practice, all character strings passed to
   and returned through the API are null terminated, even though the
   SLP protocol does not use null terminated strings.  Strings passed
   as parameters are UTF-8 but they may still be passed as a C string
   (a null terminated sequence of bytes.)  Escaped characters must be
   encoded by the API client as UTF-8.  In the common case of US-ASCII,
   the usual one byte per character C strings work.  API functions
   assist in escaping and unescaping strings.

   Unless otherwise noted, parameters to API functions and callbacks
   are non-NULL. Some parameters may have other restrictions.  If
   any parameter fails to satisfy the restrictions on its value, the
   operation returns a PARAMETER_BAD error.

Kempf, Guttman             Expires 5 October 1999              [Page 23]

Internet Draft            Service Location API             5 April  1999

4.1. Constant Types

4.1.1. URL Lifetimes

4.1.1.1. Synopsis

   typedef enum {
     SLP_LIFETIME_DEFAULT = 10800,
     SLP_LIFETIME_MAXIMUM = 65535
   } SLPURLLifetime;

4.1.1.2. Description

   The SLPURLLifetime enum type contains URL lifetime values, in
   seconds, that are frequently used.  SLP_LIFETIME_DEFAULT is 3 hours,
   while SLP_LIFETIME_MAXIMUM is about 18 hours and corresponds to the
   maximum size of the lifetime field in SLP messages.

4.1.2. Error Codes

4.1.2.1. Synopsis

   typedef enum {
     SLP_LAST_CALL                    = 1,
     SLP_OK                           = 0,
     SLP_LANGUAGE_NOT_SUPPORTED       = -1,
     SLP_PARSE_ERROR                  = -2,
     SLP_INVALID_REGISTRATION         = -3,
     SLP_SCOPE_NOT_SUPPORTED          = -4,
     SLP_AUTHENTICATION_ABSENT        = -6,
     SLP_AUTHENTICATION_FAILED        = -7,
     SLP_INVALID_UPDATE               = -13,
     SLP_REFRESH_REJECTED             = -15,
     SLP_NOT_IMPLEMENTED              = -17,
     SLP_BUFFER_OVERFLOW              = -18,
     SLP_NETWORK_TIMED_OUT            = -19,
     SLP_NETWORK_INIT_FAILED          = -20,
     SLP_MEMORY_ALLOC_FAILED          = -21,
     SLP_PARAMETER_BAD                = -22,
     SLP_NETWORK_ERROR                = -23,
     SLP_INTERNAL_SYSTEM_ERROR        = -24,
     SLP_HANDLE_IN_USE                = -25,
     SLP_TYPE_ERROR                   = -26

Kempf, Guttman             Expires 5 October 1999              [Page 24]

Internet Draft            Service Location API             5 April  1999

   } SLPError ;

4.1.2.2. Description

   The SLPError enum contains error codes that are returned from API
   functions.

   The SLP_OK code indicates that the no error occurred during the
   operation.

   The SLP_LAST_CALL code is passed to callback functions when the API
   library has no more data for them and therefore no further calls will
   be made to the callback on the currently outstanding operation.  The
   callback can use this to signal the main body of the client code
   that no more data will be forthcoming on the operation, so that
   the main body of the client code can break out of data collection
   loops.  On the last call of a callback during both a synchronous and
   asynchronous call, the error code parameter has value SLP_LAST_CALL,
   and the other parameters are all NULL. If no results are returned
   by an API operation, then only one call is made, with the error
   parameter set to SLP_LAST_CALL.

4.1.3. SLPBoolean

4.1.3.1. Synopsis

   typedef enum {
      SLP_FALSE = 0,
      SLP_TRUE = 1

   } SLPBoolean;

4.1.3.2. Description

   The SLPBoolean enum is used as a boolean flag.

Kempf, Guttman             Expires 5 October 1999              [Page 25]

Internet Draft            Service Location API             5 April  1999

4.2. Struct Types

4.2.1. SLPSrvURL

4.2.1.1. Synopsis

   typedef struct srvurl {
     char *s_pcSrvType;
     char *s_pcHost;
     int   s_iPort;
     char *s_pcNetFamily;
     char *s_pcSrvPart;
   } SLPSrvURL;

4.2.1.2. Description

   The SLPSrvURL structure is filled in by the SLPParseSrvURL() function
   with information parsed from a character buffer containing a service
   URL. The fields correspond to different parts of the URL. Note that
   the structure is conformant with the standard Berkeley sockets
   struct servent, with the exception that the pointer to an array of
   characters for aliases (s_aliases field) is replaced by the pointer
   to host name (s_pcHost field).

      s_pcSrvType

         A pointer to a character string containing the service
         type name, including naming authority.  The service type
         name includes the "service:" if the URL is of the service:
         scheme. [7]

      s_pcHost

         A pointer to a character string containing the host
         identification information.

      s_iPort

         The port number, or zero if none.  The port is only available
         if the transport is IP.

      s_pcNetFamily

         A pointer to a character string containing the network address
         family identifier.  Possible values are "ipx" for the IPX

Kempf, Guttman             Expires 5 October 1999              [Page 26]

Internet Draft            Service Location API             5 April  1999

         family, "at" for the Appletalk family, and "" (i.e.  the empty
         string) for the IP address family.

      s_pcSrvPart

         The remainder of the URL, after the host identification.

   The host and port should be sufficient to open a socket to the
   machine hosting the service, and the remainder of the URL should
   allow further differentiation of the service.

4.2.2. SLPHandle

4.2.2.1. Synopsis

   typedef void* SLPHandle;

   The SLPHandle type is returned by SLPOpen() and is a parameter to all
   SLP functions.  It serves as a handle for all resources allocated on
   behalf of the process by the SLP library.  The type is opaque, since
   the exact nature differs depending on the implementation.

4.3. Callbacks

   A function pointer to a callback function specific to a particular
   API operation is included in the parameter list when the API function
   is invoked.  The callback function is called with the results of the
   operation in both the synchronous and asynchronous cases.  The memory
   included in the callback parameters is owned by the API library, and
   the client code in the callback must copy out the contents if it
   wants to maintain the information longer than the duration of the
   current callback call.

   In addition to parameters for reporting the results of the operation,
   each callback parameter list contains an error code parameter and a
   cookie parameter.  The error code parameter reports the error status
   of the ongoing (for asynchronous) or completed (for synchronous)
   operation.  The cookie parameter allows the client code that starts
   the operation by invoking the API function to pass information
   down to the callback without using global variables.  The callback
   returns an SLPBoolean to indicate whether the API library should
   continue processing the operation.  If the value returned from
   the callback is SLP_TRUE, asynchronous operations are terminated,
   synchronous operations ignore the return (since the operation is
   already complete).

Kempf, Guttman             Expires 5 October 1999              [Page 27]

Internet Draft            Service Location API             5 April  1999

4.3.1. SLPRegReport

4.3.1.1. Synopsis

   typedef void SLPRegReport(SLPHandle hSLP,
                             SLPError errCode,
                             void *pvCookie);

4.3.1.2. Description

   The SLPRegReport callback type is the type of the callback function
   to the SLPReg(), SLPDereg(), and SLPDelAttrs() functions.

4.3.1.3. Parameters

      hSLP

         The SLPHandle used to initiate the operation.

      errCode

         An error code indicating if an error occurred during the
         operation.

      pvCookie

         Memory passed down from the client code that called the
         original API function, starting the operation.  May be NULL.

4.3.2. SLPSrvTypeCallback

4.3.2.1. Synopsis

   typedef SLPBoolean SLPSrvTypeCallback(SLPHandle hSLP,
                                         const char* pcSrvTypes,
                                         SLPError errCode,
                                         void *pvCookie);

Kempf, Guttman             Expires 5 October 1999              [Page 28]

Internet Draft            Service Location API             5 April  1999

4.3.2.2. Description

   The SLPSrvTypeCallback type is the type of the callback function
   parameter to SLPFindSrvTypes() function.  If the hSLP handle
   parameter was opened asynchronously, the results returned through
   the callback MAY be uncollated.  If the hSLP handle parameter was
   opened synchronously, then the returned results must be collated and
   duplicates eliminated.

4.3.2.3. Parameters

      hSLP

         The SLPHandle used to initiate the operation.

      pcSrvTypes

         A character buffer containing a comma separated, null
         terminated list of service types.

      errCode

         An error code indicating if an error occurred during the
         operation.  The callback should check this error code before
         processing the parameters.  If the error code is other than
         SLP_OK, then the API library may choose to terminate the
         outstanding operation.

      pvCookie

         Memory passed down from the client code that called the
         original API function, starting the operation.  May be NULL.

4.3.2.4. Returns

   The client code should return SLP_TRUE if more data is desired,
   otherwise SLP_FALSE.

4.3.3. SLPSrvURLCallback

4.3.3.1. Synopsis

   typedef SLPBoolean SLPSrvURLCallback(SLPHandle hSLP,
                                        const char* pcSrvURL,
                                        unsigned short sLifetime,

Kempf, Guttman             Expires 5 October 1999              [Page 29]

Internet Draft            Service Location API             5 April  1999

                                        SLPError errCode,
                                        void *pvCookie);

4.3.3.2. Description

   The SLPSrvURLCallback type is the type of the callback function
   parameter to SLPFindSrvs() function.  If the hSLP handle parameter
   was opened asynchronously, the results returned through the
   callback MAY be uncollated.  If the hSLP handle parameter was
   opened synchronously, then the returned results must be collated and
   duplicates eliminated.

4.3.3.3. Parameters

      hSLP

         The SLPHandle used to initiate the operation.

      pcSrvURL

         A character buffer containing the returned service URL.

      sLifetime

         An unsigned short giving the life time of the service
         advertisement, in seconds.  The value must be an unsigned
         integer less than or equal to SLP_LIFETIME_MAXIMUM.

      errCode

         An error code indicating if an error occurred during the
         operation.  The callback should check this error code before
         processing the parameters.  If the error code is other than
         SLP_OK, then the API library may choose to terminate the
         outstanding operation.

      pvCookie

         Memory passed down from the client code that called the
         original API function, starting the operation.  May be NULL.

4.3.3.4. Returns

   The client code should return SLP_TRUE if more data is desired,
   otherwise SLP_FALSE.

Kempf, Guttman             Expires 5 October 1999              [Page 30]

Internet Draft            Service Location API             5 April  1999

4.3.4. SLPAttrCallback

4.3.4.1. Synopsis

   typedef SLPBoolean SLPAttrCallback(SLPHandle hSLP,
                                      const char* pcAttrList,
                                      SLPError errCode,
                                      void *pvCookie);

4.3.4.2. Description

   The SLPAttrCallback type is the type of the callback function
   parameter to SLPFindAttrs() function.

   The behavior of the callback differs depending on whether
   the attribute request was by URL or by service type.  If the
   SLPFindAttrs() operation was originally called with a URL, the
   callback is called once regardless of whether the handle was opened
   asynchronously or synchronously.  The pcAttrList parameter contains
   the requested attributes as a comma separated list (or is empty if no
   attributes matched the original tag list).

   If the SLPFindAttrs() operation was originally called with a service
   type, the value of pcAttrList and calling behavior depend on whether
   the handle was opened asynchronously or synchronously.  If the handle
   was opened asynchronously, the callback is called every time the API
   library has results from a remote agent.  The pcAttrList parameter
   MAY be uncollated between calls.  It contains a comma separated list
   with the results from the agent that immediately returned results.
   If the handle was opened synchronously, the results must be collated
   from all returning agents and the callback is called once, with the
   pcAttrList parameter set to the collated result.

4.3.4.3. Parameters

      hSLP

         The SLPHandle used to initiate the operation.

      pcAttrList

         A character buffer containing a comma separated, null
         terminated list of attribute id/value assignments, in SLP wire
         format; i.e.  "(attr-id=attr-value-list)" [7].

Kempf, Guttman             Expires 5 October 1999              [Page 31]

Internet Draft            Service Location API             5 April  1999

      errCode

         An error code indicating if an error occurred during the
         operation.  The callback should check this error code before
         processing the parameters.  If the error code is other than
         SLP_OK, then the API library may choose to terminate the
         outstanding operation.

      pvCookie

         Memory passed down from the client code that called the
         original API function, starting the operation.  May be NULL.

4.3.4.4. Returns

   The client code should return SLP_TRUE if more data is desired,
   otherwise SLP_FALSE.

4.4. Opening and Closing an SLPHandle

4.4.1. SLPOpen

4.4.1.1. Synopsis

   SLPError SLPOpen(const char *pcLang, SLPBoolean isAsync, SLPHandle *phSLP);

4.4.1.2. Description

   Returns a SLPHandle handle in the phSLP parameter for the language
   locale passed in as the pcLang parameter.  The client indicates
   if operations on the handle are to be synchronous or asynchronous
   through the isAsync parameter.  The handle encapsulates the language
   locale for SLP requests issued through the handle, and any other
   resources required by the implementation.  However, SLP properties
   are not encapsulated by the handle; they are global.  The return
   value of the function is an SLPError code indicating the status of
   the operation.  Upon failure, the phSLP parameter is NULL.

   An SLPHandle can only be used for one SLP API operation at a time.
   If the original operation was started asynchronously, any attempt
   to start an additional operation on the handle while the original
   operation is pending results in the return of an SLP_HANDLE_IN_USE
   error from the API function.  The SLPClose() API function terminates
   any outstanding calls on the handle.  If an implementation is

Kempf, Guttman             Expires 5 October 1999              [Page 32]

Internet Draft            Service Location API             5 April  1999

   unable to support a asynchronous( resp.  synchronous) operation,
   due to memory constraints or lack of threading support, the
   SLP_NOT_IMPLEMENTED flag may be returned when the isAsync flag is
   SLP_TRUE (resp.  SLP_FALSE).

4.4.1.3. Parameters

      pcLang

         A pointer to an array of characters containing the RFC 1766
         Language Tag [6] for the natural language locale of requests
         and registrations issued on the handle.

      isAsync

         An SLPBoolean indicating whether the SLPHandle should be opened
         for asynchronous operation or not.

      phSLP

         A pointer to an SLPHandle, in which the open SLPHandle is
         returned.  If an error occurs, the value upon return is NULL.

4.4.2. SLPClose

4.4.2.1. Synopsis

   void SLPClose(SLPHandle hSLP);

4.4.2.2. Description

   Frees all resources associated with the handle.  If the handle was
   invalid, the function returns silently.  Any outstanding synchronous
   or asynchronous operations are cancelled so their callback functions
   will not be called any further.

4.4.2.3. Parameters

      SLPHandle

         A SLPHandle handle returned from a call to SLPOpen().

Kempf, Guttman             Expires 5 October 1999              [Page 33]

Internet Draft            Service Location API             5 April  1999

4.5. Protocol API

4.5.1. SLPReg

4.5.1.1. Synopsis

   SLPError SLPReg(SLPHandle   hSLP,
                   const char  *pcSrvURL,
                   const unsigned short usLifetime,
                   const char  *pcSrvType,
                   const char  *pcAttrs
                   SLPBoolean  fresh,
                   SLPRegReport callback,
                   void *pvCookie);

4.5.1.2. Description

   Registers the URL in pcSrvURL having the lifetime usLifetime with the
   attribute list in pcAttrs.  The pcAttrs list is a comma separated
   list of attribute assignments in the wire format (including escaping
   of reserved characters).  The usLifetime parameter must be nonzero
   and less than or equal to SLP_LIFETIME_MAXIMUM. If the fresh flag is
   SLP_TRUE, then the registration is new (the SLP protocol FRESH flag
   is set) and the registration replaces any existing registrations.
   The pcSrvType parameter is a service type name and can be included
   for service URLs that are not in the service:  scheme.  If the URL is
   in the service:  scheme, the pcSrvType parameter is ignored.  If the
   fresh flag is SLP_FALSE, then an existing registration is updated.
   Rules for new and updated registrations, and the format for pcAttrs
   and pcScopeList can be found in [7].  Registrations and updates take
   place in the language locale of the hSLP handle.

   The API library is required to perform the operation in all scopes
   obtained through configuration.

4.5.1.3. Parameters

      hSLP

         The language specific SLPHandle on which to register the
         advertisement.

      pcSrvURL

         The URL to register.  May not be the empty string.

Kempf, Guttman             Expires 5 October 1999              [Page 34]

Internet Draft            Service Location API             5 April  1999

      usLifetime

         An unsigned short giving the life time of the service
         advertisement, in seconds.  The value must be an unsigned
         integer less than or equal to SLP_LIFETIME_MAXIMUM and greater
         than zero.

      pcSrvType

         The service type.  If pURL is a service:  URL, then this
         parameter is ignored.

      pcAttrs

         A comma separated list of attribute assignment expressions for
         the attributes of the advertisement.  Use empty string, "" for
         no attributes.

      fresh

         An SLPBoolean that is SLP_TRUE if the registration is new or
         SLP_FALSE if a reregistration.

      callback

         A callback to report the operation completion status.

      pvCookie

         Memory passed to the callback code from the client.  May be
         NULL.

4.5.1.4. Returns

   If an error occurs in starting the operation, one of the SLPError
   codes is returned.

4.5.2. SLPDereg

4.5.2.1. Synopsis

   SLPError SLPDereg(SLPHandle  hSLP,
                     const char *pcURL,
                     SLPRegReport callback,
                     void *pvCookie);

Kempf, Guttman             Expires 5 October 1999              [Page 35]

Internet Draft            Service Location API             5 April  1999

4.5.2.2. Description

   Deregisters the advertisement for URL pcURL in all scopes where the
   service is registered and all language locales.  The deregistration
   is not just confined to the locale of the SLPHandle, it is in all
   locales.  The API library is required to perform the operation in all
   scopes obtained through configuration.

4.5.2.3. Parameters

      hSLP

         The language specific SLPHandle to use for deregistering.

      pcURL

         The URL to deregister.  May not be the empty string.

      callback

         A callback to report the operation completion status.

      pvCookie

         Memory passed to the callback code from the client.  May be
         NULL.

4.5.2.4. Returns

   If an error occurs in starting the operation, one of the SLPError
   codes is returned.

4.5.3. SLPDelAttrs

4.5.3.1. Synopsis

   SLPError SLPDelAttrs(SLPHandle   hSLP,
                        const char  *pcURL,
                        const char  *pcAttrs,
                        SLPRegReport callback,
                        void *pvCookie);

Kempf, Guttman             Expires 5 October 1999              [Page 36]

Internet Draft            Service Location API             5 April  1999

4.5.3.2. Description

   Delete the selected attributes in the locale of the SLPHandle.  The
   API library is required to perform the operation in all scopes
   obtained through configuration.

4.5.3.3. Parameters

      hSLP

         The language specific SLPHandle to use for deleting attributes.

      pcURL

         The URL of the advertisement from which the attributes should
         be deleted.  May not be the empty string.

      pcAttrs

         A comma separated list of attribute ids for the attributes to
         deregister.  See Section 9.8 in [7] for a description of the
         list format.  May not be the empty string.

      callback

         A callback to report the operation completion status.

      pvCookie

         Memory passed to the callback code from the client.  May be
         NULL.

4.5.3.4. Returns

   If an error occurs in starting the operation, one of the SLPError
   codes is returned.

4.5.4. SLPFindSrvTypes

4.5.4.1. Synopsis

   SLPError SLPFindSrvTypes(SLPHandle    hSLP,
                            const char  *pcNamingAuthority,
                            const char  *pcScopeList,
                            SLPSrvTypeCallback callback,

Kempf, Guttman             Expires 5 October 1999              [Page 37]

Internet Draft            Service Location API             5 April  1999

                            void *pvCookie);

   The SLPFindSrvType() function issues an SLP service type request
   for service types in the scopes indicated by the pcScopeList.  The
   results are returned through the callback parameter.  The service
   types are independent of language locale, but only for services
   registered in one of scopes and for the indicated naming authority.

   If the naming authority is "*", then results are returned for all
   naming authorities.  If the naming authority is the empty string,
   i.e.  "", then the default naming authority, "IANA", is used.  "IANA"
   is not a valid naming authority name, and it is a PARAMETER_BAD error
   to include it explicitly.

   The service type names are returned with the naming authority intact.
   If the naming authority is the default (i.e.  empty string) then
   it is omitted, as is the separating ".".  Service type names from
   URLs of the service:  scheme are returned with the "service:" prefix
   intact. [7] See [8] for more information on the syntax of service
   type names.

4.5.4.2. Parameters

      hSLP

         The SLPHandle on which to search for types.

      pcNamingAuthority

         The naming authority to search.  Use "*" for all naming
         authorities and the empty string, "", for the default naming
         authority.

      pcScopeList

         A pointer to a char containing comma separated list of scope
         names to search for service types.  May not be the empty
         string, "".

      callback

         A callback function through which the results of the operation
         are reported.

Kempf, Guttman             Expires 5 October 1999              [Page 38]

Internet Draft            Service Location API             5 April  1999

      pvCookie

         Memory passed to the callback code from the client.  May be
         NULL.

4.5.4.3. Returns

   If an error occurs in starting the operation, one of the SLPError
   codes is returned.

4.5.5. SLPFindSrvs

4.5.5.1. Synopsis

   SLPError SLPFindSrvs(SLPHandle  hSLP,
                        const char *pcServiceType,
                        const char *pcScopeList,
                        const char *pcSearchFilter,
                        SLPSrvURLCallback callback,
                        void *pvCookie);

4.5.5.2. Description

   Issue the query for services on the language specific SLPHandle and
   return the results through the callback.  The parameters determine
   the results

4.5.5.3. Parameters

      hSLP

         The language specific SLPHandle on which to search for
         services.

      pcServiceType

         The Service Type String, including authority string if any, for
         the request, such as can be discovered using SLPSrvTypes().
         This could be, for example "service:printer:lpr" or
         "service:nfs".  May not be the empty string.

Kempf, Guttman             Expires 5 October 1999              [Page 39]

Internet Draft            Service Location API             5 April  1999

      pcScopeList

         A pointer to a char containing comma separated list of scope
         names.  May not be the empty string, "".

      pcSearchFilter

         A query formulated of attribute pattern matching expressions in
         the form of a LDAPv3 Search Filter, see [4].  If this filter
         is empty, i.e.  "", all services of the requested type in the
         specified scopes are returned.

      callback

         A callback function through which the results of the operation
         are reported.

      pvCookie

         Memory passed to the callback code from the client.  May be
         NULL.

4.5.5.4. Returns

   If an error occurs in starting the operation, one of the SLPError
   codes is returned.

4.5.6. SLPFindAttrs

4.5.6.1. Synopsis

   SLPError SLPFindAttrs(SLPHandle   hSLP,
                         const char *pcURLOrServiceType,
                         const char *pcScopeList,
                         const char *pcAttrIds,
                         SLPAttrCallback callback,
                         void *pvCookie);

4.5.6.2. Description

   This function returns service attributes matching the attribute ids
   for the indicated service URL or service type.  If pcURLOrServiceType
   is a service URL, the attribute information returned is for that
   particular advertisement in the language locale of the SLPHandle.

Kempf, Guttman             Expires 5 October 1999              [Page 40]

Internet Draft            Service Location API             5 April  1999

   If pcURLOrServiceType is a service type name (including naming
   authority if any), then the attributes for all advertisements of that
   service type are returned regardless of the language of registration.
   Results are returned through the callback.

   The result is filtered with an SLP attribute request filter string
   parameter, the syntax of which is described in [7].  If the filter
   string is the empty string, i.e.  "", all attributes are returned.

4.5.6.3. Parameters

      hSLP

         The language specific SLPHandle on which to search for
         attributes.

      pcURLOrServiceType

         The service URL or service type.  See [7] for URL and service
         type syntax.  May not be the empty string.

      pcScopeList

         A pointer to a char containing a comma separated list of scope
         names.  May not be the empty string, "".

      pcAttrIds

         The filter string indicating which attribute values to return.
         Use empty string, "", to indicate all values.  Wildcards
         matching all attribute ids having a particular prefix or suffix
         are also possible.  See [7] for the exact format of the filter
         string.

      callback

         A callback function through which the results of the operation
         are reported.

      pvCookie

         Memory passed to the callback code from the client.  May be
         NULL.

Kempf, Guttman             Expires 5 October 1999              [Page 41]

Internet Draft            Service Location API             5 April  1999

4.5.6.4. Returns

   If an error occurs in starting the operation, one of the SLPError
   codes is returned.

4.6. Miscellaneous Functions

4.6.1. SLPGetRefreshInterval

4.6.1.1. Synopsis

   unsigned short SLPGetRefreshInterval();

4.6.1.2. Description

   Returns the maximum across all DAs of the min-refresh-interval
   attribute.  This value satisfies the advertised refresh interval
   bounds for all DAs, and, if used by the SA, assures that no
   refresh registration will be rejected.  If no DA advertises a
   min-refresh-interval attribute, a value of 0 is returned.

4.6.1.3. Returns

   If no error, the maximum refresh interval value allowed by all DAs
   (a positive integer).  If no DA advertises a min-refresh-interval
   attribute, returns 0.  If an error occurs, returns an SLP error code.

4.6.2. SLPFindScopes

4.6.2.1. Synopsis

   SLPError SLPFindScopes(SLPHandle hSLP,
                          char** ppcScopeList);

4.6.2.2. Description

   Sets ppcScopeList parameter to a pointer to a comma separated list
   including all available scope values.  The list of scopes comes from
   a variety of sources:  the configuration file's net.slp.useScopes
   property, unicast to DAs on the net.slp.DAAddresses property, DHCP,

Kempf, Guttman             Expires 5 October 1999              [Page 42]

Internet Draft            Service Location API             5 April  1999

   or through the DA discovery process.  If there is any order to the
   scopes, preferred scopes are listed before less desirable scopes.
   There is always at least one name in the list, the default scope,
   "DEFAULT".

4.6.2.3. Parameters

      hSLP

         The SLPHandle on which to search for scopes.

      ppcScopeList

         A pointer to char pointer into which the buffer pointer is
         placed upon return.  The buffer is null terminated.  The memory
         should be freed by calling SLPFree().

4.6.2.4. Returns

   If no error occurs, returns SLP_OK, otherwise, the appropriate error
   code.

4.6.3. SLPParseSrvURL

4.6.3.1. Synopsis

   SLPError SLPParseSrvURL(char *pcSrvURL
                           SLPSrvURL** ppSrvURL);

4.6.3.2. Description

   Parses the URL passed in as the argument into a service URL structure
   and returns it in the ppSrvURL pointer.  If a parse error occurs,
   returns SLP_PARSE_ERROR. The input buffer pcSrvURL is destructively
   modified during the parse and used to fill in the fields of the
   return structure.  The structure returned in ppSrvURL should be freed
   with SLPFreeURL().  If the URL has no service part, the s_pcSrvPart
   string is the empty string, "", i.e.  not NULL. If pcSrvURL is not
   a service:  URL, then the s_pcSrvType field in the returned data
   structure is the URL's scheme, which might not be the same as the
   service type under which the URL was registered.  If the transport is
   IP, the s_pcTransport field is the empty string.  If the transport is
   not IP or there is no port number, the s_iPort field is zero.

Kempf, Guttman             Expires 5 October 1999              [Page 43]

Internet Draft            Service Location API             5 April  1999

4.6.3.3. Parameters

      pcSrvURL

         A pointer to a character buffer containing the null terminated
         URL string to parse.  It is destructively modified to produce
         the output structure.

      ppSrvURL

         A pointer to a pointer for the SLPSrvURL structure to receive
         the parsed URL. The memory should be freed by a call to
         SLPFree() when no longer needed.

4.6.3.4. Returns

   If no error occurs, the return value is SLP_OK. Otherwise, the
   appropriate error code is returned.

4.6.4. SLPEscape

4.6.4.1. Synopsis

   SLPError SLPEscape(const char* pcInbuf,
                      char** ppcOutBuf,
                      SLPBoolean isTag);

4.6.4.2. Description

   Process the input string in pcInbuf and escape any SLP reserved
   characters.  If the isTag parameter is SLPTrue, then look for bad
   tag characters and signal an error if any are found by returning the
   SLP_PARSE_ERROR code.  The results are put into a buffer allocated by
   the API library and returned in the ppcOutBuf parameter.  This buffer
   should be deallocated using SLPFree() when the memory is no longer
   needed.

4.6.4.3. Parameters

      pcInbuf

         Pointer to he input buffer to process for escape characters.

Kempf, Guttman             Expires 5 October 1999              [Page 44]

Internet Draft            Service Location API             5 April  1999

      ppcOutBuf

         Pointer to a pointer for the output buffer with the SLP
         reserved characters escaped.  Must be freed using SLPFree()
         when the memory is no longer needed.

      isTag

         When true, the input buffer is checked for bad tag characters.

4.6.4.4. Returns

   Return SLP_PARSE_ERROR if any characters are bad tag characters and
   the isTag flag is true, otherwise SLP_OK, or the appropriate error
   code if another error occurs.

4.6.5. SLPUnescape

4.6.5.1. Synopsis

   SLPError SLPUnescape(const char* pcInbuf,
                        char** ppcOutBuf,
                        SLPBoolean isTag);

4.6.5.2. Description

   Process the input string in pcInbuf and unescape any SLP reserved
   characters.  If the isTag parameter is SLPTrue, then look for
   bad tag characters and signal an error if any are found with the
   SLP_PARSE_ERROR code.  No transformation is performed if the input
   string is an opaque.  The results are put into a buffer allocated by
   the API library and returned in the ppcOutBuf parameter.  This buffer
   should be deallocated using SLPFree() when the memory is no longer
   needed.

4.6.5.3. Parameters

      pcInbuf

         Pointer to he input buffer to process for escape characters.

Kempf, Guttman             Expires 5 October 1999              [Page 45]

Internet Draft            Service Location API             5 April  1999

      ppcOutBuf

         Pointer to a pointer for the output buffer with the SLP
         reserved characters escaped.  Must be freed using SLPFree()
         when the memory is no longer needed.

      isTag

         When true, the input buffer is checked for bad tag characters.

4.6.5.4. Returns

   Return SLP_PARSE_ERROR if any characters are bad tag characters and
   the isTag flag is true, otherwise SLP_OK, or the appropriate error
   code if another error occurs.

4.6.6. SLPFree

4.6.6.1. Synopsis

   void SLPFree(void* pvMem);

4.6.6.2. Description

   Frees memory returned from SLPParseSrvURL(), SLPFindScopes(),
   SLPEscape(), and SLPUnescape().

4.6.6.3. Parameters

      pvMem

         A pointer to the storage allocated by the SLPParseSrvURL(),
         SLPEscape(), SLPUnescape(), or SLPFindScopes() function.
         Ignored if NULL.

4.6.7. SLPGetProperty

4.6.7.1. Synopsis

   const char* SLPGetProperty(const char* pcName);

Kempf, Guttman             Expires 5 October 1999              [Page 46]

Internet Draft            Service Location API             5 April  1999

4.6.7.2. Description

   Returns the value of the corresponding SLP property name.  The
   returned string is owned by the library and MUST NOT be freed.

4.6.7.3. Parameters

      pcName

         Null terminated string with the property name, from
         Section 2.1.

4.6.7.4. Returns

   If no error, returns a pointer to a character buffer containing the
   property value.  If the property was not set, returns the default
   value.  If an error occurs, returns NULL. The returned string MUST
   NOT be freed.

4.6.8. SLPSetProperty

4.6.8.1. Synopsis

   void SLPSetProperty(const char *pcName,
                       const char *pcValue);

4.6.8.2. Description

   Sets the value of the SLP property to the new value.  The pcValue
   parameter should be the property value as a string.

4.6.8.3. Parameters

      pcName

         Null terminated string with the property name, from
         Section 2.1.

      pcValue

         Null terminated string with the property value, in UTF-8
         character encoding.

Kempf, Guttman             Expires 5 October 1999              [Page 47]

Internet Draft            Service Location API             5 April  1999

4.7. Implementation Notes

4.7.1. Refreshing Registrations

   Clients indicate that they want URLs to be automatically
   refreshed by setting the usLifetime parameter in the SLPReg()
   function call to SLP_LIFETIME_MAXIMUM. This will cause the API
   implementation to refresh the URL before it times out.  Although
   using SLP_LIFETIME_MAXIMUM to designate automatic reregistration
   means that a transient URL can't be registered for the maximum
   lifetime, little hardship is likely to occur, since service URL
   lifetimes are measured in seconds and the client can simply use a
   lifetime of SLP_LIFETIME_MAXIMUM - 1 if a transient URL near the
   maximum lifetime is desired.  API implementations MUST provide this
   facility.

4.7.2. Syntax for String Parameters

   Query strings, attribute registration lists, attribute deregistration
   lists, scope lists, and attribute selection lists follow the syntax
   described in [7] for the appropriate requests.  The API directly
   reflects the strings passed in from clients into protocol requests,
   and directly reflects out strings returned from protocol replies to
   clients.  As a consequence, clients are responsible for formatting
   request strings, including escaping and converting opaque values to
   escaped byte encoded strings.  Similarly, on output, clients are
   required to unescape strings and convert escaped string encoded
   opaques to binary.  The functions SLPEscape() and SLPUnescape() can
   be used for escaping SLP reserved characters, but perform no opaque
   processing.

   Opaque values consist of a character buffer containing a
   UTF-8-encoded string, the first characters of which are the nonUTF-8
   encoding '\ff'.  Subsequent characters are the escaped values for the
   original bytes in the opaque.  The escape convention is relatively
   simple.  An escape consists of a backslash followed by the two
   hexadecimal digits encoding the byte.  An example is '\2c' for the
   byte 0x2c.  Clients handle opaque processing themselves, since the
   algorithm is relatively simple and uniform.

4.7.3. Client Side Syntax Checking

   Client side API implementations may do syntax checking of scope
   names, naming authority names, and service type names, but are
   not required to do so.  Since the C API is designed to be a
   thin layer over the protocol, some low memory SA implementations
   may find extensive syntax checking on the client side to be

Kempf, Guttman             Expires 5 October 1999              [Page 48]

Internet Draft            Service Location API             5 April  1999

   burdensome.  If syntax checking uncovers an error in a parameter, the
   SLP_PARAMETER_BAD error must be returned.  If any parameter is NULL
   and is required to be nonNULL, SLP_PARAMETER_BAD is returned.

4.7.4. System Properties

   The system properties established in the configuration file are
   accessible through the SLPGetProperty() and SLPSetProperty()
   functions.  The SLPSetProperty() function only modifies properties
   in the running process, not in the configuration file.  Properties
   are global to the process, affecting all threads and all handles
   created with SLPOpen.  Errors are checked when the property is used
   and, as with parsing the configuration file, are logged.  Program
   execution continues without interruption by substituting the default
   for the erroneous parameter.  With the exception of net.slp.locale,
   net.slp.typeHint, and net.slp.maxResults, clients of the API should
   rarely be required to override these properties, since they reflect
   properties of the SLP network that are not of concern to individual
   agents.  If changes are required, system administrators should modify
   the configuration file.

4.7.5. Memory Management

   The only API functions returning memory specifically requiring
   deallocation on the part of the client are SLPParseSrvURL(),
   SLPFindScopes(), SLPEscape(), and SLPUnescape().  This memory should
   be freed using SLPFree() when no longer needed.  Character strings
   returned via the SLPGetProperty() function should NOT be freed, they
   are owned by the SLP library.

   Memory passed to callbacks belongs to the library and MUST NOT be
   retained by the client code.  Otherwise, crashes are possible.
   Clients are required to copy data out of the callback parameters.  No
   other use of the parameter memory in callback parameters is allowed.

4.7.6. Asynchronous and Incremental Return Semantics

   If a handle parameter to an API function was opened asynchronously,
   API function calls on the handle check the other parameters, open the
   appropriate operation and return immediately.  In an error occurs in
   the process of starting the operation, an error code is returned.  If
   the handle parameter was opened synchronously, the API function call
   blocks until all results are available, and returns only after the
   results are reported through the callback function.  The return code
   indicates whether any errors occurred both starting and during the
   operation.

Kempf, Guttman             Expires 5 October 1999              [Page 49]

Internet Draft            Service Location API             5 April  1999

   The callback function is called whenever the API library has results
   to report.  The callback code is required to check the error code
   parameter before looking at the other parameters.  If the error code
   is not SLP_OK, the other parameters may be invalid.  The API library
   has the option of terminating any outstanding operation on which an
   error occurs.  The callback code can similarly indicate that the
   operation should be terminated by passing back SLP_FALSE. Callback
   functions are not permitted to recursively call into the API on the
   same SLPHandle.  If an attempt is made to recursively call into
   the API, the API function returns SLP_HANDLE_IN_USE. Prohibiting
   recursive callbacks on the same handle simplifies implementation of
   thread safe code, since locks held on the handle will not be in place
   during a second outcall on the handle.  On the other hand, it means
   that handle creation should be fairly lightweight so a client program
   can easily support multiple outstanding calls.

   The total number of results received can be controlled by setting the
   net.slp.maxResults parameter.

   On the last call to a callback, whether asynchronous or synchronous,
   the status code passed to the callback has value SLP_LAST_CALL. There
   are four reasons why the call can terminate:

      DA reply received

         A reply from a DA has been received and therefore nothing more
         is expected.

      Multicast terminated

         The multicast convergence time has elapsed and the API library
         multicast code is giving up.

      Multicast null results

         Nothing new has been received during multicast for a while and
         the API library multicast code is giving up on that (as an
         optimization).

      Maximum results

         The user has set the net.slp.maxResults property and that
         number of replies has been collected and returned

4.8. Example

   This example illustrates how to discover a mailbox.

Kempf, Guttman             Expires 5 October 1999              [Page 50]

Internet Draft            Service Location API             5 April  1999

   A POP3 server registers itself with the SLP framework.  The
   attributes it registers are "USER", a list of all users whose mail is
   available through the POP3 server.

   The POP3 server code is the following:

   SLPHandle slph;
   SLPRegReport errCallback = POPRegErrCallback;

   /* Create an English SLPHandle, asynchronous processing. */

   SLPError err = SLPOpen("en", SLP_TRUE, &slph);

   if( err != SLP_OK ) {

     /* Deal with error. */

   }

   /* Create the service: URL and attribute parameters. */

   const char* surl = "service:pop3://mail.netsurf.de"; /* the URL */

   const char *pcAttrs = "(user=zaphod,trillian,roger,marvin)"

   /* Perform the registration. */

   err = SLPReg(slph,
                surl,
                SLP_LIFETIME_DEFAULT,
                ppcAttrs,
                errCallback,
                NULL);

   if (err != SLP_OK ) {

      /*Deal with error.*/

   }

   The errCallback reports any errors:

   void
   POPRegErrCallback(SLPHandle hSLP,
                     SLPError errCode,
                     unsigned short usLifetime,
                     void* pvCookie) {

Kempf, Guttman             Expires 5 October 1999              [Page 51]

Internet Draft            Service Location API             5 April  1999

      if( errCode != SLP_OK ) {

        /* Report error through a dialog, message, etc. */

      }

      /*Use lifetime interval to update periodically. */

    }

   The POP3 client locates the server for the user with the following
   code:

   /*
    * The client calls SLPOpen(), exactly as above.
    */

   const char *pcSrvType   = "service:pop3"; /* the service type  */
   const char *pcScopeList = "default";      /* the scope         */
   const char *pcFilter    = "(user=roger)"; /* the search filter */
   SLPSrvURLCallback srvCallback =           /* the callback      */
                                   POPSrvURLCallback;

   err = SLPFindSrvs(slph,
                     pcSrvType, pcScopeList, pcFilter,
                     srvCallback, NULL);

   if( err != SLP_OK ) {

       /* Deal with error. */

   }

   Within the callback, the client code can use the returned POP
   service:

  SLPBoolean
  POPSrvURLCallback(SLPHandle hSLP,
                    const char* pcSrvURL,
                    unsigned short sLifetime,
                    SLPError errCode,
                    void* pvCookie) {

     if( errCode != SLP_OK ) {

        /* Deal with error. */

     }

Kempf, Guttman             Expires 5 October 1999              [Page 52]

Internet Draft            Service Location API             5 April  1999

     SLPSrvURL* pSrvURL;

     errCode = SLPParseSrvURL(pcSrvURL, &pSrvURL);

     if (err != SLP_OK ) {

       /* Deal with error. */

     } else {

       /* get the server's address */

       struct hostent *phe = gethostbyname(pSrvURL.s_pcHost);

       /* use hostname in pSrvURL to connect to the POP3 server
        *     . . .
        */

       SLPFreeSrvURL((void*)pSrvURL);  /* Free the pSrvURL storage */
     }

     return SLP_FALSE;                 /* Done! */
   }

   A client that wanted to discover all the users receiving mail at the
   server uses with the following query:

   /*
    * The client calls SLPOpen(), exactly as above. We assume the
    * service: URL was retrieved into surl.
    */

   const char *pcScopeList = "default";      /* the scope            */
   const char *pcAttrFilter    = "use";      /* the attribute filter */
   SLPAttrCallback attrCallBack =            /* the callback         */
                                  POPUsersCallback

   err =
     SLPFindAttrs(slph,
                  surl,
                  pcScopeList, pcAttrFilter,
                  attrCallBack, NULL);

   if( err != SLP_OK ) {

        /* Deal with error. */

   }

Kempf, Guttman             Expires 5 October 1999              [Page 53]

Internet Draft            Service Location API             5 April  1999

   The callback processes the attributes:

   SLPBoolean
   POPUsersCallback(const char* pcAttrList,
                    SLPError errCode,
                    void* pvCookie) {

     if( errCode != SLP_OK ) {

       /* Deal with error. */

     } else {

       /* Parse attributes. */

     }

     return SLP_FALSE;  /* Done! */

   }

5. Java Language Binding

5.1. Introduction

   The Java API is designed to model the various SLP entities in
   classes and objects.  APIs are provided for SA, UA, and service type
   template access capabilities.  The ServiceLocationManager class
   contains methods that return instances of objects implementing
   SA and UA capability.  Each of these is modeled in an interface.
   The Locator interface provides UA capability and the Advertiser
   interface provides SA capability.  The TemplateRegistry abstract
   class contains methods that return objects for template introspection
   and attribute type checking.  The ServiceURL, ServiceType, and
   ServiceLocationAttribute classes model the basic SLP concepts.  A
   concrete subclass instance of TemplateRegistry is returned by a class
   method.

   All SLP classes and interfaces are located within a single package.
   The package name should begin with the name of the implementation and
   conclude with the suffix "slp".  Thus, the name for a hypothetical
   implementation from the University of Michigan would look like:

                             edu.umich.slp

   This follows the Java convention of prepending the top level DNS
   domain name for the organization implementing the package onto the
   organization's name and using that as the package prefix.

Kempf, Guttman             Expires 5 October 1999              [Page 54]

Internet Draft            Service Location API             5 April  1999

5.2. Exceptions and Errors

   Most parameters to API methods are required to be non-null.  The
   API description indicates if a null parameter is acceptable, or
   if other restrictions constrain a parameter.  When parameters
   are checked for validity (such as not being null) or their
   syntax is checked, an error results in the RuntimeException
   subclass IllegalArgumentException being thrown.  Clients of the
   API are reminded that IllegalArgumentException, derived from
   RuntimeException, is unchecked by the compiler.  Clients should
   thus be careful to include try/catch blocks for it if the relevant
   parameters could be erroneous.

   Standard Java practice is to encode every exceptional condition as a
   separate subclass of Exception.  Because of the relatively high cost
   in code size of Exception subclasses, the API contains only a single
   Exception subclass with different conditions being determined by an
   integer error code property.  A subset, appropriate to Java, of the
   error codes described in Section 3 are available as constants on the
   ServiceLocationException class.  The subset excludes error codes such
   as MEMORY_ALLOC_FAILED.

5.2.1. Class ServiceLocationException

5.2.1.1. Synopsis

   public class ServiceLocationException
   extends Exception

5.2.1.2. Description

   The ServiceLocationException class is thrown by all methods when
   exceptional conditions occur in the SLP framework.  The error
   code property determines the exact nature of the condition, and an
   optional message may provide more information.

5.2.1.3. Fields

   public static final short LANGUAGE_NOT_SUPPORTED = 1
   public static final short PARSE_ERROR = 2
   public static final short INVALID_REGISTRATION = 3
   public static final short SCOPE_NOT_SUPPORTED = 4
   public static final short AUTHENTICATION_ABSENT = 6

Kempf, Guttman             Expires 5 October 1999              [Page 55]

Internet Draft            Service Location API             5 April  1999

   public static final short AUTHENTICATION_FAILED = 7
   public static final short INVALID_UPDATE = 13
   public static final short REFRESH_REJECTED = 15
   public static final short NOT_IMPLEMENTED = 16
   public static final short NETWORK_INIT_FAILED 17
   public static final short NETWORK_TIMED_OUT = 18
   public static final short NETWORK_ERROR = 19
   public static final short INTERNAL_SYSTEM_ERROR = 20
   public static final short TYPE_ERROR = 21
   public static final short BUFFER_OVERFLOW = 22

5.2.1.4. Instance Methods

   public short getErrorCode()

   Return the error code.  The error code takes on one of the static
   field values.

5.3. Basic Data Structures

5.3.1. Interface ServiceLocationEnumeration

   public interface ServiceLocationEnumeration
    extends Enumeration

5.3.1.1. Description

   The ServiceLocationEnumeration class is the return type for all
   Locator SLP operations.  The Java API library may implement this
   class to block until results are available from the SLP operation,
   so that the client can achieve asynchronous operation by retrieving
   results from the enumeration in a separate thread.  Clients use the
   superclass nextElement() method if they are unconcerned with SLP
   exceptions.

5.3.1.2. Instance Methods

   public abstract Object next() throws ServiceLocationException

Kempf, Guttman             Expires 5 October 1999              [Page 56]

Internet Draft            Service Location API             5 April  1999

   Return the next value or block until it becomes available.

   Throws:

      ServiceLocationException

         Thrown if the SLP operation encounters an error.

      NoSuchElementException

         If there are no more elements to return.

5.3.2. Class ServiceLocationAttribute

5.3.2.1. Synopsis

   public class ServiceLocationAttribute
     extends Object implements Serializable

5.3.2.2. Description

   The ServiceLocationAttribute class models SLP attributes.  Instances
   of this class are returned by Locator.findAttributes() and are
   communicated along with register/deregister requests.

5.3.2.3. Constructors

   public ServiceLocationAttribute(String id,Vector values)

   Construct a service location attribute.  Errors in the id or values
   vector result in an IllegalArgumentException.

   Parameters:

      id

         The attribute name.  The String can consist of any Unicode
         character.

Kempf, Guttman             Expires 5 October 1999              [Page 57]

Internet Draft            Service Location API             5 April  1999

      values

         A Vector of one or more attribute values.  Vector contents
         must be uniform in type and one of Integer, String, Boolean,
         or byte[].  If the attribute is a keyword attribute, then the
         parameter should be null.  String values can consist of any
         Unicode character.

5.3.2.4. Class Methods

   public static String escapeId(String id)

   Returns an escaped version of the id parameter, suitable for
   inclusion in a query.  Any reserved characters as specified in [7]
   are escaped using UTF-8 encoding.  If any characters in the tag are
   illegal, throws IllegalArgumentException.

   Parameters:

      id

         The attribute id to escape.  ServiceLocationException is thrown
         if any characters are illegal for an attribute tag.

   public static String escapeValue(Object value)

   Returns a String containing the escaped value parameter as a string,
   suitable for inclusion in a query.  If the parameter is a string,
   any reserved characters as specified in [7] are escaped using UTF-8
   encoding.  If the parameter is a byte array, then the escaped string
   begins with the nonUTF-8 sequence `\ff` and the rest of the string
   consists of the escaped bytes, which is the encoding for opaques.
   If the value parameter is a Boolean or Integer, then the returned
   string contains the object converted into a string.  If the value
   is any type other than String, Integer, Boolean or byte[], an
   IllegalArgumentException is thrown.

   Parameters:

      value

         The attribute value to be converted into a string and escaped.

Kempf, Guttman             Expires 5 October 1999              [Page 58]

Internet Draft            Service Location API             5 April  1999

5.3.2.5. Instance Methods

   public Vector getValues()

   Returns a cloned vector of attribute values, or null if the attribute
   is a keyword attribute.  If the attribute is single-valued, then the
   vector contains only one object.

   public String getId()

   Returns the attribute's name.

   public boolean equals(Object o)

   Overrides Object.equals().  Two attributes are equal if their
   identifiers are equal and their value vectors contain the same number
   of equal values as determined by the Object equals() method.  Values
   having byte[] type are equal if the contents of all byte arrays in
   both attribute vectors match.  Note that the SLP string matching
   algorithm [7] MUST NOT be used for comparing attribute identifiers or
   string values.

   public String toString()

   Overrides Object.toString().  The string returned contains a
   formatted representation of the attribute, giving the attribute's
   id, values, and the Java type of the values.  The returned string is
   suitable for debugging purposes, but is not in SLP wire format.

   public int hashCode()

   Overrides Object.hashCode().  Hashes on the attribute's identifier.

5.3.3. Class ServiceType

5.3.3.1. Synopsis

Kempf, Guttman             Expires 5 October 1999              [Page 59]

Internet Draft            Service Location API             5 April  1999

   public class ServiceType extends Object implements Serializable

5.3.3.2. Description

   The ServiceType object models the SLP service type.  It parses a
   string based service type specifier into its various components, and
   contains property accessors to return the components.  URL schemes,
   protocol service types, and abstract service types are all handled.

5.3.3.3. Constructors

   public ServiceType(String type)

   Construct a service type object from the service type specifier.
   Throws IllegalArgumentException if the type name is syntactically
   incorrect.

   Parameters:

      type

         The service type name as a String.  If the service type is from
         a service:  URL, the "service:" prefix must be intact.

5.3.3.4. Methods

   public boolean isServiceURL()

   Returns true if the type name contains the "service:" prefix.

   public boolean isAbstractType()

   Returns true if the type name is for an abstract type.

   public boolean isNADefault()

Kempf, Guttman             Expires 5 October 1999              [Page 60]

Internet Draft            Service Location API             5 April  1999

   Returns true if the naming authority is the default, i.e.  is the
   empty string.

   public String getConcreteTypeName()

   Returns the concrete type name in an abstract type, or the empty
   string if the service type is not abstract.  For example, if the type
   name is "service:printing:ipp", the method returns "ipp".  If the
   type name is "service:ftp", the method returns "".

   public String getPrincipleTypeName()

   Returns the abstract type name for an abstract type, the protocol
   name in a protocol type, or the URL scheme for a generic URL. For
   example, in the abstract type name "service:printing:ipp", the method
   returns "printing".  In the protocol type name "service:ftp", the
   method returns "ftp".

   public String getAbstractTypeName()

   If the type is an abstract type, returns the fully formatted abstract
   type name including the "service:" and naming authority but without
   the concrete type name or intervening colon.  If not an abstract
   type, returns the empty string.  For example, in the abstract type
   name "service:printing:ipp", the method returns "service:printing".

   public String getNamingAuthority()

   Return the naming authority name, or the empty string if the naming
   authority is the default.

   public boolean equals(Object obj)

   Overrides Object.equals().  The two objects are equal if they are
   both ServiceType objects and the components of both are equal.

   public String toString()

Kempf, Guttman             Expires 5 October 1999              [Page 61]

Internet Draft            Service Location API             5 April  1999

   Returns the fully formatted type name, including the "service:" if
   the type was originally from a service:  URL.

   public int hashCode()

   Overrides Object.hashCode().  Hashes on the string value of the
   ``service'' prefix, naming authority, if any, abstract and concrete
   type names for abstract types, protocol type name for protocol types,
   and URL scheme for generic URLs.

5.3.4. Class ServiceURL

5.3.4.1. Synopsis

   public class ServiceURL extends Object implements Serializable

5.3.4.2. Description

   The ServiceURL object models the advertised SLP service URL. It
   can be either a service:  URL or a regular URL. These objects are
   returned from service lookup requests, and describe the registered
   services.  This class should be a subclass of java.net.URL but can't
   since that class is final.

5.3.4.3. Class Variables

   public static final int NO_PORT = 0

   Indicates that no port information is required or was returned for
   this URL.

   public static final int LIFETIME_NONE = 0

   Indicates that the URL has a zero lifetime.  This value is never
   returned from the API, but can be used to create a ServiceURL object
   to deregister, delete attributes, or find attributes.

Kempf, Guttman             Expires 5 October 1999              [Page 62]

Internet Draft            Service Location API             5 April  1999

   public static final int LIFETIME_DEFAULT = 10800

   The default URL lifetime (3 hours) in seconds.

   public static final int LIFETIME_MAXIMUM = 65535

   The maximum URL lifetime (about 18 hours) in seconds.

   public static final int LIFETIME_PERMANENT = -1

   Indicates that the API implementation should continuously re-register
   the URL until the application exits.

5.3.4.4. Constructors

   public ServiceURL(String URL,int lifetime)

   Construct a service URL object having the specified lifetime.

   Parameters:

      URL

         The URL as a string.  Must be either a service:  URL or a valid
         generic URL according to RFC 2396 [2].

      lifetime

         The service advertisement lifetime in seconds.  This value may
         be between LIFETIME_NONE and LIFETIME_MAXIMUM.

5.3.4.5. Methods

   public ServiceType getServiceType()

   Returns the service type object representing the service type name of
   the URL.

Kempf, Guttman             Expires 5 October 1999              [Page 63]

Internet Draft            Service Location API             5 April  1999

  public final void setServiceType(ServiceType type)
  throws ServiceLocationException

   Set the service type name to the object.  Ignored if the URL is a
   service:  URL.

   Parameters:

      type

         The service type object.

   public String getTransport()

   Get the network layer transport identifier.  If the transport is IP,
   an empty string, "", is returned.

   public String getHost()

   Returns the host identifier.  For IP, this will be the machine name
   or IP address.

   public int getPort()

   Returns the port number, if any.  For non-IP transports, always
   returns NO_PORT.

   public String getURLPath()

   Returns the URL path description, if any.

   public int getLifetime()

   Returns the service advertisement lifetime.  This will be a positive
   int between LIFETIME_NONE and LIFETIME_MAXIMUM.

Kempf, Guttman             Expires 5 October 1999              [Page 64]

Internet Draft            Service Location API             5 April  1999

   public boolean equals(Object obj)

   Compares the object to the ServiceURL and returns true if the two are
   the same.  Two ServiceURL objects are equal if their current service
   types match and they have the same host, port, transport, and URL
   path.

   public String toString()

   Returns a formatted string with the URL. Overrides Object.toString().
   The returned URL has the original service type or URL scheme, not the
   current service type.

   public int hashCode()

   Overrides Object.hashCode().  Hashes on the current service type,
   transport, host, port, and URL part.

5.4. SLP Access Interfaces

5.4.1. Interface Advertiser

5.4.1.1. Synopsis

   public interface Advertiser

5.4.1.2. Description

   The Advertiser is the SA interface, allowing clients to register new
   service instances with SLP, to change the attributes of existing
   services, and to deregister service instances.  New registrations
   and modifications of attributes are made in the language locale
   with which the Advertiser was created, deregistrations of service
   instances are made for all locales.

5.4.1.3. Instance Methods

   public abstract Locale getLocale()

Kempf, Guttman             Expires 5 October 1999              [Page 65]

Internet Draft            Service Location API             5 April  1999

   Return the language locale with which this object was created.

   public abstract void register(ServiceURL URL,
                                 Vector attributes)
   throws ServiceLocationException

   Register a new service with SLP having the given attributes.

   The API library is required to perform the operation in all
   scopes obtained through configuration.

   Parameters:

      URL

         The URL for the service.

      attributes

         A vector of ServiceLocationAttribute objects describing the
         service.

   public abstract void deregister(ServiceURL URL)
   throws ServiceLocationException

   Deregister a service from the SLP framework.  This has the effect
   of deregistering the service from every language locale.  The API
   library is required to perform the operation in all scopes obtained
   through configuration.

   Parameters:

      URL

         The URL for the service.

   public abstract void
   addAttributes(ServiceURL URL,
                 Vector attributes)
   throws ServiceLocationException

Kempf, Guttman             Expires 5 October 1999              [Page 66]

Internet Draft            Service Location API             5 April  1999

   Update the registration by adding the given attributes.  The API
   library is required to perform the operation in all scopes obtained
   through configuration.

   Parameters:

      URL

         The URL for the service.

      attributes

         A Vector of ServiceLocationAttribute objects to add to the
         existing registration.  Use an empty vector to update the URL
         alone.  May not be null.

   public abstract void
   deleteAttributes(ServiceURL URL,
                    Vector attributeIds)
   throws ServiceLocationException

   Delete the attributes from a URL for the locale with which the
   Advertiser was created.  The API library is required to perform the
   operation in all scopes obtained through configuration.

   Parameters:

      URL

         The URL for the service.

      attributeIds

         A vector of Strings indicating the ids of the attributes
         to remove.  The strings may be attribute ids or they
         may be wildcard patterns to match ids.  See [7] for the
         syntax of wildcard patterns.  The strings may include SLP
         reserved characters, they will be escaped by the API before
         transmission.  May not be the empty vector or null.

5.4.2. Interface Locator

5.4.2.1. Synopsis

   public interface Locator

Kempf, Guttman             Expires 5 October 1999              [Page 67]

Internet Draft            Service Location API             5 April  1999

5.4.2.2. Description

   The Locator is the UA interface, allowing clients to query the SLP
   framework about existing service types, services instances, and about
   the attributes of an existing service instance or service type.
   Queries for services and attributes are made in the locale with which
   the Locator was created, queries for service types are independent of
   locale.

5.4.2.3. Instance Methods

   public abstract Locale getLocale()

   Return the language locale with which this object was created.

   public abstract ServiceLocationEnumeration
   findServiceTypes(String namingAuthority,
                    Vector scopes)
   throws ServiceLocationException

   Returns an enumeration of ServiceType objects giving known service
   types for the given scopes and given naming authority.  If no service
   types are found, an empty enumeration is returned.

   Parameters:

      namingAuthority

         The naming authority.  Use "" for the default naming authority
         and "*" for all naming authorities.

      scopes

         A Vector of scope names.  The vector should be selected from
         the results of a findScopes() API invocation.  Use "DEFAULT"
         for the default scope.

   public abstract ServiceLocationEnumeration
   findServices(ServiceType type,
                Vector scopes,

Kempf, Guttman             Expires 5 October 1999              [Page 68]

Internet Draft            Service Location API             5 April  1999

                String searchFilter)
   throws ServiceLocationException

   Returns a vector of ServiceURL objects for services matching the
   query, and having a matching type in the given scopes.  If no
   services are found, an empty enumeration is returned.

   Parameters:

      type

         The SLP service type of the service.

      scopes

         A Vector of scope names.  The vector should be selected from
         the results of a findScopes() API invocation.  Use "DEFAULT"
         for the default scope.

      searchFilter

         An LDAPv3 [4] string encoded query.  If the filter is empty,
         i.e.  "", all services of the requested type in the specified
         scopes are returned.  SLP reserved characters must be escaped
         in the query.  Use ServiceLocationAttribute.escapeId() and
         ServiceLocationAttribute.escapeValue() to construct the query.

   public abstract ServiceLocationEnumeration
   findAttributes(ServiceURL URL,
                  Vector scopes,
                  Vector attributeIds)
   throws ServiceLocationException

   For the URL and scope, return a Vector of ServiceLocationAttribute
   objects whose ids match the String patterns in the attributeIds
   Vector.  The request is made in the language locale of the Locator.
   If no attributes match, an empty enumeration is returned.

   Parameters:

      URL

         The URL for which the attributes are desired.

Kempf, Guttman             Expires 5 October 1999              [Page 69]

Internet Draft            Service Location API             5 April  1999

      scopes

         A Vector of scope names.  The vector should be selected from
         the results of a findScopes() API invocation.  Use "DEFAULT"
         for the default scope.

      attributeIds

         A Vector of String patterns identifying the desired attributes.
         An empty vector means return all attributes.  As described
         in [7], the patterns may include wildcards to match substrings.
         The strings may include SLP reserved characters, they will be
         escaped by the API before transmission.

   public abstract ServiceLocationEnumeration
   findAttributes(ServiceType type,
                  Vector scopes,
                  Vector attributeIds)
   throws ServiceLocationException

   For the type and scope, return a Vector of all ServiceLocationAttribute
   objects whose ids match the String patterns in the attributeIds
   Vector regardless of the Locator's locale.  The request is made
   independent of language locale.  If no attributes are found, an empty
   vector is returned.

   Parameters:

      serviceType

         The service type.

      scopes

         A Vector of scope names.  The vector should be selected from
         the results of a findScopes() API invocation.  Use "DEFAULT"
         for the default scope.

      attributeIds

         A Vector of String patterns identifying the desired
         attributes.  An empty vector means return all attributes.
         As described in [7], the patterns may include wildcards to
         match all prefixes or suffixes.  The patterns may include SLP
         reserved characters, they will be escaped by the API before
         transmission.

Kempf, Guttman             Expires 5 October 1999              [Page 70]

Internet Draft            Service Location API             5 April  1999

5.5. The Service Location Manager

5.5.1. Class ServiceLocationManager

5.5.1.1. Synopsis

    public class ServiceLocationManager
    extends Object

5.5.1.2. Description

   The ServiceLocationManager manages access to the service location
   framework.  Clients obtain the Locator and Advertiser objects
   for UA and SA, and a Vector of known scope names from the
   ServiceLocationManager.

5.5.1.3. Class Methods

   public static int getRefreshInterval()
   throws ServiceLocationException

   Returns the maximum across all DAs of the min-refresh-interval
   attribute.  This value satisfies the advertised refresh interval
   bounds for all DAs, and, if used by the SA, assures that no
   refresh registration will be rejected.  If no DA advertises a
   min-refresh-interval attribute, a value of 0 is returned.

   public static Vector findScopes()
   throws ServiceLocationException

   Returns an Vector of strings with all available scope names.  The
   list of scopes comes from a variety of sources, see Section 2.1 for
   the scope discovery algorithm.  There is always at least one string
   in the Vector, the default scope, "DEFAULT".

   public static Locator
   getLocator(Locale locale)
   throws ServiceLocationException

Kempf, Guttman             Expires 5 October 1999              [Page 71]

Internet Draft            Service Location API             5 April  1999

   Return a Locator object for the given language Locale.  If the
   implementation does not support UA functionality, returns null.

   Parameters:

      locale

         The language locale of the Locator.  The default SLP locale is
         used if null.

   public static Advertiser
   getAdvertiser(Locale locale)
   throws ServiceLocationException

   Return an Advertiser object for the given language locale.  If the
   implementation does not support SA functionality, returns null.

   Parameters:

      locale

         The language locale of the Advertiser.  The default SLP locale
         is used if null.

5.6. Service Template Introspection

5.6.1. Abstract Class TemplateRegistry

5.6.1.1. Synopsis

   public abstract class TemplateRegistry

5.6.1.2. Description

   Subclasses of the TemplateRegistry abstract class provide
   access to service location templates [8].  Classes implementing
   TemplateRegistry perform a variety of functions.  They manage the
   registration and access of service type template documents.  They
   create attribute verifiers from service templates, for verification
   of attributes and introspection on template documents.  Note that
   clients of the Advertiser are not required to verify attributes
   before registering (though they may get a TYPE_ERROR if the

Kempf, Guttman             Expires 5 October 1999              [Page 72]

Internet Draft            Service Location API             5 April  1999

   implementation supports type checking and there is a mismatch with
   the template).

5.6.1.3. Class Methods

   public static TemplateRegistry getTemplateRegistry();

   Returns the distinguished TemplateRegistry object for performing
   operations on and with service templates.  Returns null if the
   implementation doesn't support TemplateRegistry functionality.

5.6.1.4. Instance Methods

   public abstract void
   registerServiceTemplate(ServiceType type,
                           String documentURL,
                           Locale locale,
                           String version)
   throws ServiceLocationException

   Register the service template with the template registry.

   Parameters:

      type

         The service type.

      documentURL

         A string containing the URL of the template document.  May not
         be the empty string.

      locale

         A Locale object containing the language locale of the template.

      version

         The version number identifier of template document.

   public abstract void

Kempf, Guttman             Expires 5 October 1999              [Page 73]

Internet Draft            Service Location API             5 April  1999

   deregisterServiceTemplate(ServiceType type,
                             Locale locale,
                             String version)
   throws ServiceLocationException

   Deregister the template for the service type.

   Parameters:

      type

         The service type.

      locale

         A Locale object containing the language locale of the template.

      version

         A String containing the version number.  Use null to indicate
         the latest version.

   public abstract
   String findTemplateURL(ServiceType type,
                          Locale locale,
                          String version)
   throws ServiceLocationException

   Returns the URL for the template document.

   Parameters:

      type

         The service type.

      locale

         A Locale object containing the language locale of the template.

      version

         A String containing the version number.  Use null to indicate
         the latest version.

Kempf, Guttman             Expires 5 October 1999              [Page 74]

Internet Draft            Service Location API             5 April  1999

   public abstract
   ServiceLocationAttributeVerifier
   attributeVerifier(String documentURL)
   throws ServiceLocationException

   Reads the template document URL and returns an attribute verifier
   for the service type.  The attribute verifier can be used for
   verifying that registration attributes match the template, and for
   introspection on the template definition.

   Parameters:

      documentURL

         A String containing the template document's URL. May not be the
         empty string.

5.6.2. Interface ServiceLocationAttributeVerifier

5.6.2.1. Synopsis

   public interface ServiceLocationAttributeVerifier

5.6.2.2. Description

   The ServiceLocationAttributeVerifier provides access to service
   templates.  Classes implementing this interface parse SLP template
   definitions, provide information on attribute definitions for
   service types, and verify whether a ServiceLocationAttribute object
   matches a template for a particular service type.  Clients obtain
   ServiceLocationAttributeVerifier objects for specific SLP service
   types through the TemplateRegistry.

5.6.2.3. Instance Methods

   public abstract ServiceType getServiceType()

   Returns the SLP service type for which this is the verifier.

   public abstract Locale getLocale()

Kempf, Guttman             Expires 5 October 1999              [Page 75]

Internet Draft            Service Location API             5 April  1999

   Return the language locale of the template.

   public abstract String getVersion()

   Return the template version number identifier.

   public abstract String getURLSyntax()

   Return the URL syntax expression for the service:  URL.

   public abstract String getDescription()

   Return the descriptive help text for the template.

   public abstract ServiceLocationAttributeDescriptor
   getAttributeDescriptor(String attrId)

   Return the ServiceLocationAttributeDescriptor for the attribute
   having the named id.  If no such attribute exists in this template,
   return null.  This method is primarily for GUI tools to display
   attribute information.  Programmatic verification of attributes
   should use the verifyAttribute() method.

   public abstract Enumeration
   getAttributeDescriptors()

   Returns an Enumeration allowing introspection on the attribute
   definition in the service template.  The Enumeration returns
   ServiceLocationAttributeDescriptor objects for the attributes.
   This method is primarily for GUI tools to display attribute
   information.  Programmatic verification of attributes should use the
   verifyAttribute() method.

   public abstract void
   verifyAttribute(
     ServiceLocationAttribute attribute)

Kempf, Guttman             Expires 5 October 1999              [Page 76]

Internet Draft            Service Location API             5 April  1999

   throws ServiceLocationException

   Verify that the attribute matches the template definition.  If the
   attribute doesn't match, ServiceLocationException is thrown with the
   error code as ServiceLocationException.PARSE_ERROR.

   Parameters:

      attribute

         The ServiceLocationAttribute object to be verified.

   public abstract void
   verifyRegistration(
     Vector attributeVector)
   throws ServiceLocationException

   Verify that the Vector of ServiceLocationAttribute objects matches
   the template for this service type.  The vector must contain all the
   required attributes, and all attributes must match their template
   definitions.  If the attributes don't match, ServiceLocationException
   is thrown with the error code as ServiceLocationException.PARSE_ERROR

   Parameters:

      attributeVector

         A Vector of ServiceLocationAttribute objects for the
         registration.

5.6.3. Interface ServiceLocationAttributeDescriptor

5.6.3.1. Synopsis

   public interface
   ServiceLocationAttributeDescriptor

5.6.3.2. Description

   The ServiceLocationAttributeDescriptor interface provides
   introspection on a template attribute definition.  Classes
   implementing the ServiceLocationAttributeDescriptor interface return

Kempf, Guttman             Expires 5 October 1999              [Page 77]

Internet Draft            Service Location API             5 April  1999

   information on a particular service location attribute definition
   from the service template.  This information is primarily for GUI
   tools.  Programmatic attribute verification should be done through
   the ServiceLocationAttributeVerifier.

5.6.3.3. Instance Methods

   public abstract String getId()

   Return a String containing the attribute's id.

   public abstract String getValueType()

   Return a String containing the fully package-qualified Java type of
   the attribute.  SLP types are translated into Java types as follows:

      STRING

         "java.lang.String"

      INTEGER

         "java.lang.Integer"

      BOOLEAN

         "java.lang.Boolean"

      OPAQUE

         "[B" (i.e.  array of byte, byte[])

      KEYWORD

         empty string, ""

 public abstract String getDescription()

   Return a String containing the attribute's help text.

   public abstract Enumeration

Kempf, Guttman             Expires 5 October 1999              [Page 78]

Internet Draft            Service Location API             5 April  1999

   getAllowedValues()

   Return an Enumeration of allowed values for the attribute type.
   For keyword attributes returns null.  For no allowed values (i.e.
   unrestricted) returns an empty Enumeration.

   public abstract Enumeration
   getDefaultValues()

   Return an Enumeration of default values for the attribute type.
   For keyword attributes returns null.  For no allowed values (i.e.
   unrestricted) returns an empty Enumeration.

   public abstract boolean
   getRequiresExplicitMatch()

   Returns true if the "X"" flag is set, indicating that the attribute
   should be included in an any Locator.findServices() request search
   filter.

   public abstract boolean getIsMultivalued()

   Returns true if the "M" flag is set.

   public abstract boolean getIsOptional()

   Returns true if the "O"" flag is set.

   public abstract boolean getIsLiteral()

   Returns true if the "L" flag is set.

   public abstract boolean getIsKeyword()

   Returns true if the attribute is a keyword attribute.

Kempf, Guttman             Expires 5 October 1999              [Page 79]

Internet Draft            Service Location API             5 April  1999

5.7. Implementation Notes

5.7.1. Refreshing Registrations

   A special lifetime constant, ServiceURL.LIFETIME_PERMANENT, is
   used by clients to indicate that the URL should be automatically
   refreshed until the application exits.  The API implementation
   should interpret this flag as indicating that the URL lifetime is
   ServiceURL.LIFETIME_MAXIMUM, and MUST arrange for automatic refresh
   to occur.

5.7.2. Parsing Alternate Transports in ServiceURL

   The ServiceURL class is designed to handle multiple transports.  The
   standard API performs no additional processing on transports other
   than IP except to separate out the host identifier and the URL path.
   However, implementations are free to subclass ServiceURL and support
   additional methods that provide more detailed parsing of alternate
   transport information.  For IP transport, the port number, if any,
   is returned from the getPort() method.  For non-IP transports, the
   getPort() method returns NO_PORT.

5.7.3. String Attribute Values

   In general, translation between Java types for attribute values and
   the SLP on-the-wire string is straightforward.  However, there are
   two corner cases.  If the Java attribute value type is String and
   the value of the string has an on-the-wire representation that is
   inferred by SLP as an integer, the registered attribute value may not
   be what the API client intended.  A similar problem could result if
   the Java attribute value is the string "true" or "false", in which
   case the on-the-wire representation is inferred to boolean.  To
   handle these corner cases, the Java API prepends a space onto the
   string.  So, for example, if the string attribute value is "123",
   the Java API transforms the value to "123 ", which will have an
   on-the-wire representation that is inferred by SLP to be string.
   Since appended and prepended spaces have no effect on query handling,
   this procedure should cause no problem with queries.  API clients
   need to be aware, however, that the transformation is occurring.

5.7.4. Client Side Syntax Checking

   The syntax of scope names, service type names, naming authority
   names, and URLs is described in [7] and [8].  The various methods
   and classes taking String parameters for these entities SHOULD
   type check the parameters for syntax errors on the client side,

Kempf, Guttman             Expires 5 October 1999              [Page 80]

Internet Draft            Service Location API             5 April  1999

   and throw an IllegalArgumentException if an error occurs.  In
   addition, character escaping SHOULD be implemented before network
   transmission for escapable characters in attribute ids and String
   values.  This reduces the number of error messages transmitted.
   The ServiceLocationAttribute class provides methods for clients to
   obtain escaped attribute id and value strings to facilitate query
   construction.

5.7.5. Language Locale Handling

   The Locator and Advertiser interfaces are created with a Locale
   parameter.  The language locale with which these objects are created
   is used in all SLP requests issued through the object.  If the Locale
   parameter is null, the default SLP locale is used.  The default SLP
   locale is determined by, first, checking the net.slp.locale System
   property.  If that is unset, then the default SLP locale [7] is used,
   namely "en".  Note that the default SLP locale may not be the same as
   the default Java locale.

5.7.6. Setting SLP System Properties

   SLP system properties that are originally set in the configuration
   file can be overridden programmatically in API clients by simply
   invoking the System.getProperties() operation to get a copy of the
   system properties, modifying or adding the SLP property in question,
   then using System.setProperties() to set the properties to the
   modified Property object.  Program execution continues without
   interruption by substituting the default for the erroneous parameter.
   Errors are checked when the property is used and are logged.

   The SLP configuration file cannot be read with the java.util.Properties
   file reader because there are some syntactic differences.  The SLP
   configuration file syntax defines a different escape convention
   for non-ASCII characters than the Java syntax.  However, after the
   file has been read, the properties are stored and retrieved from
   java.util.Properties objects.

   Properties are global for a process, affecting all threads
   and all Locator and Advertiser objects obtained through the
   ServiceLocationManager.  With the exception of the net.slp.locale,
   net.slp.typeHint, and net.slp.maxResults properties, clients should
   rarely be required to override these properties, since they reflect
   properties of the SLP network that are not of concern to individual
   agents.  If changes are required, system administrators should modify
   the configuration file.

Kempf, Guttman             Expires 5 October 1999              [Page 81]

Internet Draft            Service Location API             5 April  1999

5.7.7. Multithreading

   Thread-safe operation is relatively easy to achieve in Java.  By
   simply making each method in the classes implementing the Locator
   and Advertiser interfaces synchronized, and by synchronizing access
   to any shared data structures within the class, the Locator and
   Advertiser interfaces are made safe.  Alternatively, finer grained
   synchronization is also possible within the classes implementing
   Advertiser and Locator.

5.7.8. Modular Implementations

   While, at first glance, the API may look rather heavyweight, the
   design has been carefully arranged so that modular implementations
   that provide only SA, only UA, or only service template access
   capability, or any combination of the three, are possible.

   Because the objects returned from the ServiceLocationManager.getLocator()
   and ServiceLocationManager.getAdvertiser() operations are interfaces,
   and because the objects returned through those interfaces are in
   the set of base data structures, an implementation is free to omit
   either UA or SA capability by simply returning null from the instance
   creation operation if the classes implementing the missing function
   cannot be dynamically linked.  API clients are encouraged to check
   for such a contingency, and to signal an exception if it occurs.
   Similarly, the TemplateRegistry concrete subclass can simply be
   omitted from an implementation that only supports UA and/or SA
   clients, and the TemplateRegistry.getRegistry() method can return
   null.  In this way, the API implementation can be tailored for the
   particular memory requirements at hand.

   In addition, if an implementation only supports the minimal subset of
   SLP [7], the unsupported Locator and Advertiser interface operations
   can throw an exception with ServiceLocationException.NOT_IMPLEMENTED
   as the error code.  This supports better source portability between
   low and high memory platforms.

5.7.9. Asynchronous and Incremental Return Semantics

   The Java API contains no specific support for asynchronous operation.
   Incremental return is not needed for the Advertiser because service
   registrations can be broken up into pieces when large.  Asynchronous
   return is also not needed because clients can always issue the
   Advertiser operation in a separate thread if the calling thread can't
   block.

Kempf, Guttman             Expires 5 October 1999              [Page 82]

Internet Draft            Service Location API             5 April  1999

   The Locator can be implemented either synchronously or
   asynchronously.  Since the return type for Locator calls is
   ServiceLocationEnumeration, a Java API implementation that supports
   asynchronous semantics can implement ServiceLocationEnumeration
   to dole results out as they come in, blocking when no results are
   available.  If the client code needs to support other processing
   while the results are trickling in, the call into the enumeration to
   retrieve the results can be done in a separate thread.

   Unlike the C case, collation semantics for return of attributes when
   an attribute request by service type is made require that the API
   collate returned values so that only one attribute having a collation
   of all returned values appear to the API client.  In practice, this
   may limit the amount of asynchronous processing possible with the
   findAttributes() method.  This requirement is imposed because memory
   management is much easier in Java and so implementing collation as
   part of the API should not be as difficult as in C, and it saves the
   client from having to do the collation.

5.8. Example

   In this example, a printer server advertises its availability to
   clients.  Additionally, the server advertises a service template for
   use by client software in validating service requests:

  //Get the Advertiser and TemplateRegistry.

  Advertiser adv = null;
  TemplateRegistry tr = null

  try {

    adv = ServiceLocationManager.getAdvertiser("en");

    tr = TemplateRegistry.getTemplateRegistry();

  } catch( ServiceLocationException ex ) { } //Deal with error.

  if( adv == null ) {

    //Serious error as printer can't be registered
    //  if the implementation doesn't support SA
    //  functionality.

  }

  //Get the printer's attributes, from a file or

Kempf, Guttman             Expires 5 October 1999              [Page 83]

Internet Draft            Service Location API             5 April  1999

  //  otherwise. We assume that the attributes
  //  conform to the template, otherwise, we
  //  could register the template here and verify
  //  them.

  Vector attributes = getPrinterAttributes();

  //Create the service: URL for the printer.

  ServiceURL printerURL =
    new ServiceURL(
      "service:printer:lpr://printshop/color2",
      ServiceURL.LIFETIME_MAXIMUM);

  try {

    //Register the printer.

    adv.register(printerURL, attributes);

    //If the template registry is available,
    //  register the printer's template.

    if( tr != null ) {
      tr.registerServiceTemplate(
        new ServiceType("service:printer:lpr"),
        "http://shop.arv/printer/printer-lpr.slp",
        new Locale("en",""),
        "1.0");

   }

  } catch( ServiceLocationException ex ) { } //Deal with error.

   Suppose a client is looking for color printer.  The following code is
   used to issue a request for printer advertisements:

  Locator loc = null;
  TemplateRegistry tr = null;

  try {

    loc = ServiceLocationManager.getLocator("en");

  } catch( ServiceLocationException ex ) { } //Deal with error.

  if( loc == null ) {

Kempf, Guttman             Expires 5 October 1999              [Page 84]

Internet Draft            Service Location API             5 April  1999

    //Serious error as client can't be located
    //  if the implementation doesn't support
    //  UA functionality.

  }

  //We want a color printer that does CMYK
  //  and prints at least 600 dpi.

  String query = "(&(marker-type=CMYK)(resolution=600))";

  //Get scopes.

  Vector scopes = ServiceLocationManager.findScopes();

  Enumeration services;

  try {

    services =
      loc.findServices(new ServiceType("service:printer"),scopes,query);

  } catch { } //Deal with error.

  if (services.hasMoreElements() ) {

    //Printers can now be used.
    ServiceURL surl = (ServiceURL) services.next();

    Socket sock = new Socket(surl.getHost, surl.getPort());

    // Use the Socket...

  }

6. Internationalization Considerations

6.1. service URL

   The service URL itself must be encoded using the rules set forth
   in [2].  The character set encoding is limited to specific ranges
   within the UTF-8 character set [3].

   The attribute information associated with the service URL must be
   expressed in UTF-8.  See [8] for attribute internationalization
   guidelines.

Kempf, Guttman             Expires 5 October 1999              [Page 85]

Internet Draft            Service Location API             5 April  1999

6.2. Character Set Encoding

   Configuration and serialized registration files are encoded in the
   UTF-8 character set [3].  This is fully compatible with US-ASCII
   character values.  C platforms that do not support UTF-8 are required
   to check the top bit of input bytes to determine whether the incoming
   character is multibyte.  If it is, the character should be dealt
   with accordingly.  This should require no additional implementation
   effort, since the SLP wire protocol requires that strings are encoded
   as UTF-8.  C platforms without UTF-8 support need to supply their own
   support, if only in the form of multibyte string handling.

   At the API level, the character encoding is specified to be Unicode
   for Java and UTF-8 for C. Unicode is the default in Java.  For C, the
   standard US-ASCII 8 bits per character, null terminated C strings are
   a subset of the UTF-8 character set, and so work in the API. Because
   the C API is very simple, the API library needs to do a minimum of
   processing on UTF-8 strings.  The strings primarily just need to be
   reflected into the outgoing SLP messages, and reflected out of the
   API from incoming SLP messages.

6.3. Language Tagging

   All SLP requests and registrations are tagged to indicate in which
   language the strings included are encoded.  This allows multiple
   languages to be supported.  It also presents the possibility that
   error conditions result when a request is made in a language that is
   not supported.  In this case, an error is only returned when there is
   data available, but not obtainable in the language requested.

   The dialect portion of the Language Tag is used on 'best effort'
   basis for matching strings by SLP. Dialects that match are preferred
   over those which don't.  Dialects that do not match will not prevent
   string matching or comparisons from occurring.

7. Security Considerations

   Security is handled within the API library and is not exposed
   to API clients except in the form of exceptions.  The
   net.slp.securityEnabled, property determines whether an SA
   client's messages are signed, but a UA client should be prepared for
   an authentication exception at any time, because it may contact a DA
   with authenticated advertisements.

   An adversary could delete valid service advertisements, provide false
   service information and deny UAs knowledge of existing services
   unless the mechanisms in SLP for authenticating SLP messages are

Kempf, Guttman             Expires 5 October 1999              [Page 86]

Internet Draft            Service Location API             5 April  1999

   used.  These mechanisms allow DAAdverts, SAAdverts, Service URLs and
   Service Attributes to be verified using digital cryptography.  For
   this reason, all SLP agents should be configured to use SLP SPIs.
   See [7] for a description of how this mechanism works.

8. Acknowledgements

   The authors would like to thank Don Provan for his pioneering work
   during the initial stages of API definition.

Kempf, Guttman             Expires 5 October 1999              [Page 87]

Internet Draft            Service Location API             5 April  1999

References

    [1] S. Bradner.  Key Words for Use in RFCs to Indicate Requirement
        Levels.  RFC 2119, March 1997.

    [2] T. Berners-Lee, R. Fielding, and L. Masinter.  Uniform Resource
        Locators (URL): Generic Syntax and Semantics.  RFC 2396, August,
        1998.

    [3] F. Yerfeau  UTF-8, a transformation format of ISO 10646.  RFC
        2279  January 1998.

    [4] T. Howes  The String Representation of LDAP Search Filters  RFC
        2254  December 1997.

    [5] D. Crocker and P Overell.  Augmented BNF for Syntax
        Specifications:  ABNF.  RFC 2234  November 1997.

    [6] H. Alvestrand.  Tags for the Identification of Languages.  RFC
        1766  March 1995.

    [7] E. Guttman, C. Perkins, J. Veizades, and M. Day.  Service
        Location Protocol.  draft-ietf-svrloc-protocol-v2-12.txt  A work
        in progress  Feburary 1999.

    [8] E. Guttman, C. Perkins, J. Kempf  Service Templates and service:
        Schemes  draft-ietf-svrloc-service-scheme-14.txt  A work in
        progress  Feburary 1999.

Kempf, Guttman             Expires 5 October 1999              [Page 88]

Internet Draft            Service Location API             5 April  1999

9. Full Copyright Statement

   Copyright (C) The Internet Society (1997).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However,
   this document itself may not be modified in any way, such as by
   removing the copyright notice or references to the Internet Society
   or other Internet organizations, except as needed for the purpose
   of developing Internet standards in which case the procedures
   for copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

Kempf, Guttman             Expires 5 October 1999              [Page 89]

Internet Draft            Service Location API             5 April  1999

Authors' Addresses

   Questions about this memo can be directed to:

James Kempf                                  Erik Guttman
Sun Microsystems                             Sun Microsystems
901 San Antonio Rd.                          Bahnstr. 2
Palo Alto, CA, 94303                         74915 Waibstadt
USA                                          Germany
+1 650 786 5890                              +49 7263 911 701
+1 650 786 6445 (fax)
[email-masked]                          [email-masked]

Kempf, Guttman             Expires 5 October 1999              [Page 90]