Subject: [regext] Benjamin Kaduk's Discuss on draft-ietf-regext-rdap-sorting-and-paging-17: (with DISCUSS and COMMENT)

From: Benjamin Kaduk via Datatracker <[email-masked]>
Date: Wed, 23 Sep 2020 14:40:24 -0700

Benjamin Kaduk has entered the following ballot position for
draft-ietf-regext-rdap-sorting-and-paging-17: Discuss

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----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

Should we say something about which order the sorting criteria are
applied (first to last vs last to first) when multiple sortItems are
specified in a query?

I recognize that in the HATEOS model, the actual JSONPaths reported by
the server should be used by the client to determine what a given sort
property does, but it also seems like it would be confusing for this
document to specify (e.g.) an "email" property with specific JSONPath,
and then have a server go off and use "email" to mean something else,
even if that is just the addition of "pref" as discussed at the end of
Section 2.3.1.  Do we want to try to have the properties defined by this
document be universally defined and encourage the use of new/different
property names for variations on them?  (The answer may well be "no",
but the answer is not intuitively clear to me.)  To put it another way,
is the list in Section 2.3.1 normative, or just an example?

----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

Section 1

   However, there are some drawbacks associated with the use of the HTTP
   header.  First, the header properties cannot be set directly from a
   web browser.  Moreover, in an HTTP session, the information on the
   status (i.e. the session identifier) is usually inserted in the
   header or a cookie, while the information on the resource
   identification or the search type is included in the query string.
   The second approach is therefore not compliant with the HTTP standard
   [RFC7230].  As a result, this document describes a specification
   based on the use of query parameters.

A few more words (section number from 7230?) on why the second approach
is not compliant with HTTP might help the reader, though it isn't
stricly necessary (we're not using it, after all).

Section 2.1

      *  "jsonPath": "String" (OPTIONAL) the JSONPath of the RDAP field
         corresponding to the property;

What is this path relative to?  (Does the client have to know from the
other context what type of object it refers to?)

      *  "links": "Link[]" (OPTIONAL) an array of links as described in
         [RFC8288] containing the query string that applies the sort
         criterion.

Just to check: this is going to have the same structure for a Link
object that draft-ietf-regext-rdap-partial-response does?  (I am not
coming up with a great way to deduplicate the definitions, off the top
of my head.)

   o  "pageSize": "Numeric" (OPTIONAL) a numeric value representing the
      number of objects returned in the current page.  It MUST be
      provided if and only if the total number of objects exceeds the
      page size.  This property is redundant for RDAP clients because
      the page size can be derived from the length of the search results
      array but, it can be helpful if the end user interacts with the
      server through a web browser;

If it's redundant, we should probably say something about error handling
for when the things that are supposed to be identical have different
values.

Section 2.3

   Except for sorting IP addresses, servers MUST implement sorting
   according to the JSON value type of the RDAP field the sorting
   property refers to.  That is, JSON strings MUST be sorted
   lexicographically and JSON numbers MUST be sorted numerically.  If IP
   addresses are represented as JSON strings, they MUST be sorted based
   on their numeric conversion.

There are more JSON types than string and number; are those other types
garanteed to not appear in sortable RDAP fields?  (I can't see how such
a guarantee could be made, given that servers can define their own
sorting properties.)

   If the "sort" parameter reports an allowed sorting property, it MUST
   be provided in the "currentSort" field of the "sorting_metadata"
   element.

nit: is "reports" the best word to describe this behavior (which, IIUC,
is "present in the query component of the request URL"?

Section 2.3.1

   In the "sort" parameter ABNF syntax, property-ref represents a
   reference to a property of an RDAP object.  Such a reference could be
   expressed by using a JSONPath.  The JSONPath in a JSON document

nit: is there a missing word here ("a JSONPath expression")?

   o  Note that some of the object specific properties are also defined
      as query paths.  The object specific properties include:

nit: the list structure in this item does not seem parallel to the
structure of the first item.

      as two representations of the same value.  By default, the
      unicodeName value MUST be used while sorting.  When the
      unicodeName is unavailable, the value of the ldhName MUST be used
      instead;

I'm not entirely sure how much value "by default" adds here.  Would the
meaning be different if we said "The unicodeName value MUST be used
while sorting if it is present; when the unicodeName is unavailable, the
value of the ldhName is used instead"?

   o  The jCard "sort-as" parameter MUST be ignored for the sorting
      capability described in this document;

It's a little bit of a juxtaposition to refer to jCard here in the prose
but vcard in the table.

   o  Even if a nameserver can have multiple IPv4 and IPv6 addresses,
      the most common configuration includes one address for each IP
      version.  Therefore, the assumption of having a single IPv4 and/or
      IPv6 value for a nameserver cannot be considered too stringent.

I disagree with the flat assertion that it "cannot be considered too
stringent".  It can be so considered, as a matter of difference of
opinion; what is appropriate to do here is to say that this
document/protocol makes the assumption (especially since we go on to
describe the exception-handling procedure when the assumption is
violated).

   o  Multiple events with a given action on an object might be
      returned.  If this occurs, sorting MUST be applied to the most
      recent event;

This makes a lot of sense as the default and I don't propose changing it
now, but I do wonder how hard it would be to add support later for
sorting on (say) the oldest event instead.

   The "jsonPath" field in the "sorting_metadata" element is used to
   clarify the RDAP field the sorting property refers to.  The mapping
   between the sorting properties and the JSONPaths of the RDAP fields
   is shown below:
   [...]
      name

         $.domainSearchResults[*].unicodeName

This seems to ignore the subtlety regarding unicodeName vs ldhName.  Is
there a way it could be expressed in JSONPath?

   o  Nameserver

      name

         $.domainSearchResults[*].unicodeName

Presumably this is supposed to be nameserverSearchResults?

Section 2.4

I think we want another introductory paragraph like:

% The cursor parameter is used by the server to preserve information
% about the pagination state of a given query's results across calls to
% the search API, so that successive requests by the client can return
% page N, N+1, N+2, etc.  Its value is only required to be interpretable
% by the server and could be implemented, for example, as an opaque
% database lookup key.  If a server does use a method for generating
% cursor values that involves internal structure, such as the one
% described below, the server needs to recognize that the value supplied
% by a client could have been modified (maliciously), and implement
% appropriate bounds-checking and similar measures when parsing received
% values.

The current wording strongly suggests that base64-encoding a meaningful
value that the client could inspect or even construct is required, and I
do not think that is very maintainable or what was intended, given the
current second paragraph ("servers can change the method over time
without announcing anything to clients").

(side note) I'm also pretty partial to the way JMAP discusses returning
(paginated, but non-uniformly) changes to a given data stream, e.g., at
https://www.rfc-editor.org/rfc/rfc8620.html#section-5.2 -- any given
state is named, and you can get "stuff starting at <named state>" and
the name to use for the state as of the current reply.

Section 4

If the server doesn't have access to an efficient (e.g.) counting
operation on the backend, would we recommend that the server not support
sorting/pagination, since there's not much benefit from having the
server pull up all the results and count them just to be able to return
the total count value back to the client, and then go do the same work again
when the client asks for the next page of results?

Section 7

I suggest noting that (encoded) structured "cursor" values present a new
attack surface on the server that needs to be protected.

   results in a response.  However, this last security policy can result
   in a higher inefficiency if the RDAP server does not provide any
   functionality to return the truncated results.

I'm not sure I understand (or agree with) this last sentence -- it seems
that unlateral silent truncation of results by the server leads to not
just inefficiency but also potential security considerations in its own
right, with the client not knowing that it has incomplete results.
Also, if the server is truncating the results, by definition it "has
functionality to return the truncated results" -- that's what it's
doing!  So I assume the intent was to say something about negotiating or
indicating that the results are truncated, not actually doing the
truncation.

   The new parameters presented in this document provide RDAP operators
   with a way to implement a server that reduces inefficiency risks.

[same question about "inefficiency" being the right word]

Appendix B

   o  It does not allow direct navigation to arbitrary pages because the
      result set must be scrolled in sequential order starting from the
      initial page;

(side note) I didn't follow the references, so maybe this was covered
there, but I don't quite follow why direct navigation is impossible.  If
you use a key field for seeking, can't you just start in the middle from
some known value for that key field?

Appendix C.2

   total count.  Therefore, as "totalCount" is an optional response
   information, fetching always the total number of rows has been

I'm not entirely sure in what sense "optional response information" is
intended -- my reading of Section 2.1 is that it's mandatory to return
totalCount if the client included the 'count' query parameter.

---

From: Mario Loffredo <[email-masked]>
Date: Sat, 26 Sep 2020 15:56:03 +0200

Hi Benjamin,

thanks a lot for your extensive review. I apologize for the delay in 
replying but I have been very busy the last two days and your feedback 
is very detailed.

Please find my coments inline.

> https://datatracker.ietf.org/doc/draft-ietf-regext-rdap-sorting-and-paging/
[ML] The common interpretation is from left to right so I don't think we 
need to clarify this concept.
> is the list in Section 2.3.1 normative, or just an example?

[ML] I would say "normative" just to facilitate interoperability and 
avoid ambiguities. Maybe it could be enough to say that the sorting 
properties deifined in the document are considered reserved so an RDAP 
server MUST not map them onto other RDAP response values.

Does it work for you?

[ML] Could it be better to replace RFC7230 with RFC7231 and put a 
refernce to Section 8.3.1 
(https://tools.ietf.org/html/rfc7231#section-8.3.1) ?

> other context what type of object it refers to?)
[ML]  All the JSONPath expressions defined in the document are relative 
to the root of an RDAP response.  The sorting_metadata object is 
included in the same response so I think that the context is clear and 
no further clarification is needed.
> coming up with a great way to deduplicate the definitions, off the top
[ML] Yes. The sorting links have the same structure as the subsetting 
links (see Section 2.3.2.).
> for when the things that are supposed to be identical have different

[ML]  I think this situation is very unlinkely.  Anyway, in this case, 
the length of the results array really counts. Obviously, it is a bit 
more likely that the totalCount value might be different from the sum 
of  the number of results in each page. In fact, even if the 
registration data can't be considered real-time data, it might happen 
that the count parameter is present in the initial query and it might 
take time to scroll the result set, so there could be a small likelihood 
that the initial totalCount value is obsolete because the result set is 
changed in the meantime. Also in this case, the sum of each result array 
length really counts.

Should I write something about?

> a guarantee could be made, given that servers can define their own

[ML] The other primitive JSON type remaining is boolean but I don't 
think it makes sense to sort by a boolean property. Instead, I missed 
that those values denoting dates and times MUST be sorted in 
chronological order even if they are strings. I'll update the sentence 
as in the following:

Except for sorting IP addresses and values denoting dates and times, servers MUST implement sorting
    according to the JSON value type of the RDAP field the sorting
    property refers to.  That is, JSON strings MUST be sorted
    lexicographically and JSON numbers MUST be sorted numerically.
    Values denoting dates and times MUST be sorted in chronological order.  If IP
    addresses are represented as JSON strings, they MUST be sorted based
    on their numeric conversion.

Does it work for you?
> is "present in the query component of the request URL"?
[ML] Sounds better.
> nit: is there a missing word here ("a JSONPath expression")?

[ML] Just for coinciseness, may I use "jsonpath" to mean "JSONPath 
expression" and keep "JSONPath" to refer to the specification?

I could write something like: "JSONPath expression (named "jsonpath" in 
the following)"

> structure of the first item.

[ML] OK. I'll change the sentence as in the following:

Object specific properties.  Note that some of these properties

> value of the ldhName is used instead"?
[ML] No, it wouldn't. I'll change the sentence as you suggest.
> It's a little bit of a juxtaposition to refer to jCard here in the prose

[ML] I would keep it as is. Instead, I would replace all the "vcard" 
occurrences with "jCard". Being jCard a transliteration of vCard in 
JSON, it seems appropriate to me to keep the references to RFC6350 
sections and  to use the corresponding jCard elements for the mapping 
between the sorting properties and the RDAP response elements. Besides, 
I would write a sentence about the fact that jCard is the JSON format of 
vCard, add a link to RFC7095 and insert RFC7095 among the Normative 
References.

Do you agree?

> describe the exception-handling procedure when the assumption is

[ML] May I udpate that sentence as in the following?

OLD

Therefore, the assumption of having a single IPv4 and/or
       IPv6 value for a nameserver cannot be considered too stringent.

NEW

Therefore, this specification makes the assumption that nameservers have a single IPv4 and/or
       IPv6 value.

> sorting on (say) the oldest event instead.
[ML] Well, I wrote that sentence because some RDAP events can appear 
multiple times. For example, a domain might be locked-unlocked 
repeatedly. The purpose of that sentence is just to avoid ambiguities 
and implicitly suggest RDAP providers to arrange events with the same 
type in descending chronological order.
> there a way it could be expressed in JSONPath?

[ML] If unicodeName and ldhName were alternative, the JSONPath union 
operator would fit (i.e. 
$.domainSearchResults[*].[unicodeName,ldhName]). Currently, RFC7483 
contains no assumption about when they should/must be present but 
examples seem to recommend to present unicodeName only for IDNs. When 
both the properties are present, the union operator doesn't fit exactly 
and I haven't still found the right JSONPath expression based only on 
the basic operators. However, since the "jsonPath" member is only for 
documentation, the aforesaid JSONPath expression could be the most 
suitable for conveying that sorting is applied on a kind of  
<unicodeName, ldhName> combination.

> Presumably this is supposed to be nameserverSearchResults?
[ML] Absolutely. It's a cut-and-paste typo :-)
> the name to use for the state as of the current reply.

[ML] Maybe I didn't make myself clear.

The Base64 encoding is a simple (unrecommended) trasformation to make 
the cursor value opaque to the client. It just seemed suitable to me for 
being used in some examples.But if you take a loook at the example of 
Figure 6, you may note that you can't obtain a meaningful result by 
simply Base64-decoding the cursor value. Definitively, the method to 
encrypt the cursor value must be more complex than a mere Base64 encoding.

Regarding the sentence between brackets, it means that servers can 
change the underlying pagination strategy without having an impact on 
clients. A server can initially implement the offset pagination and then 
turns to the keyset pagination but this has no effect on clients' features.

The same concepts about the checks that servers should make in order to 
check the cursor value are reported both in the "Negative Answer" 
section and in Appedix C.3. "Paging"

Anyway, I'll try to integrate your text in the current document and add 
a sentence with the purpose of discouraging the use of the 
Base64-encoding in the cursor implementations.

> when the client asks for the next page of results?
[ML] In my implementation the RDAP server doesn't present the count 
operator in the sorting and paging links. The number of results doesn't 
change at all if the result set is sorted by a property rather than 
another. The same generally occurs (as I wrote above) if the client is 
scrolling the result set pages. So why to repeat the count parameter in 
the links? The totalCount value is returned in the response to the 
initial query and, as It is no more repeated in the links,  the counting 
operation is not executed. Therefore, we don't need to make particular 
assumptions about the performance of counting operation.
> attack surface on the server that needs to be protected.
[ML] Sorry, could you futherly explain this concept? AFAIK, it is 
possible to protect REST API endpoints but not query parameters.
> indicating that the results are truncated, not actually doing the
[ML] I think that servers legitimately truncate the result sets to 
mitigate the risk of resource exhaustion and consequent denial of 
service. The implementation of the capablities described in this 
document makes servers to keep on managing sustainable result sets and, 
at the same time, increases clients'possibility to avoid truncation and 
find relevant results.
> [same question about "inefficiency" being the right word]

[ML] Maybe I can replace the phrase "that reduces inefficiency risks." 
with the phrase "that reduces the risk of resource exhaustion and 
consequent denial of service".

Are you ok with it?

> some known value for that key field?
[ML]  Especially when you know the total counf of a result set,  you can 
directly jump to a specific point in the result set through offset 
pagination but you can't do the same through keyset pagination because 
you don't know the key value at that point in advance. One can wonder: 
what jumping in the result set is use for? Well, for example, if you are 
looking for a specific item in a ordered collection of items, you could 
find it through the quicksort algorithm.
> totalCount if the client included the 'count' query parameter.

[ML] Exactly but it isn't returned always. For this reason, it is an 
optional member of the paging_metadata object.

Looking forward for your reply to my questions/comments.

Best,

Mario

-- 
Dr. Mario Loffredo
Systems and Technological Development Unit
Institute of Informatics and Telematics (IIT)
National Research Council (CNR)
via G. Moruzzi 1, I-56124 PISA, Italy
Phone: +39.0503153497
Mobile: +39.3462122240
Web: http://www.iit.cnr.it/mario.loffredo

---

From: Benjamin Kaduk <[email-masked]>
Date: Mon, 28 Sep 2020 17:14:25 -0700

Hi Mario,

Also inline.

> need to clarify this concept.

I think I can accept not saying more on this subject, but I am curious:
when you say left to right, that means that the leftmost parameter is
higher priority?  So that, to give a totally contrived example, if I had
pairs of (name, id), a query with &sort=name;&sort=id; would give:

("alpha", 10)
("alpha", 20)
("beta", 10)
("beta", 20)

> server MUST not map them onto other RDAP response values.

Yes, that would work for me.  Thanks!

> (https://tools.ietf.org/html/rfc7231#section-8.3.1) ?

It might be, but I think I still don't understand why using the HTTP header
field for sorting and paging information is not compliant with HTTP -- the
linked section says that header fields can be used to communicate
information about the target resource, which IIUC includes the resource as
qualified by the query string.  (But note that I am not an HTTP expert...)

> no further clarification is needed.

Now that you mention it, I do recall other discussion of paths being
relative to the root; my apologies for the noise.

> Should I write something about?

Thanks for the additional explanation.  I think that if we were to write
anything more, it would just be a few words in the description here to
indicate that it's just for convenience, e.g., "representing the number of
objects that should have been returned in the current page".  But it is
probably okay to leave it unchanged, too.

> think it makes sense to sort by a boolean property. Instead, I missed 

I think I also had JSON maps in mind, but I guess it is not exactly defined
to sort by a map itself, only a primitive type, so my question was a bit
silly.

>     on their numeric conversion.

I think so; thanks.

> I could write something like: "JSONPath expression (named "jsonpath" in 

That's fine from my perspective, sure.

> vCard, add a link to RFC7095 and insert RFC7095 among the Normative 

Yes, thanks.

> Therefore, this specification makes the assumption that nameservers have a single IPv4 and/or

Yes, please!

> <unicodeName, ldhName> combination.

I have to defer to your expertise here; thank you for thinking about it.

> Base64-encoding in the cursor implementations.

Thank you; I did not know that you wanted to discourage the use of plain
base64 encoding, but that is reassuring to know.
(I did notice that the example in Figure 6 did not decode to a meaningful
result, but did not make much of a conclusion from that.)

> possible to protect REST API endpoints but not query parameters.

I think this was assuming that the server was going to just base64-encode
something like "offset=100,limit=50" -- in that case a client could pass in
the base64'd version of "offset=1000000000,limit=50".  The server would
need to sanity-check the results of base64 decoding and reject the
too-large offset.  If the server is expecting to do a fancier
self-encrypted-token scheme for the cursor, the integrity check associated
with the encryption takes care of this protection inherently, and we may
not need to mention anything about sanitizing these valuess..

> at the same time, increases clients'possibility to avoid truncation and 

I agree with the paragraph you just wrote.  However, I think that the state
of affairs prior to this document, with unilateral truncation by the
server, can lead not just to "inefficiency" but also to security risks.  So
I was hoping to see something like "can result in higher inefficiency or
risk due to acting on incomplete information".

My second point ("Also, if the server [...]") was intending to suggest that
the last sentence say something like "if the RDAP Server does not provide
any functionality to return sorted results or iterate through the full
result set".

> consequent denial of service".

Denial of service is only one of the risks I have in mind; another is that
if a server silently truncates, a client will have incomplete data and
might derive a conclusion ("domain X does not satisfy property Y") that is
false.

> find it through the quicksort algorithm.

I don't want to press this topic very much, so let me just try a brief
example.  Suppose I have a sorted set of ASCII strings, and I want to see if the
string "koala" is present.  I could start at the beginning and look at each
one in turn until I get to something that sorts after "koala", or I could
ask the database "give me the first thing you have that is after "k", which
gets me some of the say there.  Is the problem that you need an actual
value in the dataset to start from, and since "k" isn't guaranteed to be in
the set you are forced to start from the beginning?

> optional member of the paging_metadata object.

Okay.  (I think your reply to another ballot comment also helped clarify
this for me.)

> Looking forward for your reply to my questions/comments.

Thanks a lot for the explanations and updates; hopefully I have clarified
anything that was unclear.

-Ben

---

From: Mario Loffredo <[email-masked]>
Date: Wed, 30 Sep 2020 13:28:53 +0200

Hi Ben,

thanks a loto for uor quick reply to my responses. My comments are inline.

> pairs of (name, id), a query with &sort=name;&sort=id; would give:

[ML]  Exactly.

One minor comments: the right notation would be &sort=name,id

> Yes, that would work for me.  Thanks!
[ML] Perfect.
> qualified by the query string.  (But note that I am not an HTTP expert...)

[ML]  Would it be more appropriate to update the sentence as in the 
following?

OLD

[RFC7230]

NEW

The second approach is therefore not compliant with the most common 
practices about the usage of the HTTP headers [RFC7231]
> relative to the root; my apologies for the noise.
[ML] You are welcome.
> probably okay to leave it unchanged, too.
[ML] Changed.
> to sort by a map itself, only a primitive type, so my question was a bit
[ML] Yes. Only values with primitive types.
>>      on their numeric conversion.
[ML] Good.
> That's fine from my perspective, sure.
[ML] Perfect.
>> vCard, add a link to RFC7095 and insert RFC7095 among the Normative
[ML] OK.
>> Therefore, this specification makes the assumption that nameservers have a single IPv4 and/or
[ML] Done.
> I have to defer to your expertise here; thank you for thinking about it.
[ML] Thanks. Maybe this is the only case where the JSONPath WG outcomes 
might be helpful :-)
> result, but did not make much of a conclusion from that.)
[ML] OK. I will add some text to clarify that a mere Base64 encoding is 
not recommended to encrypt the cursor value.
> not need to mention anything about sanitizing these valuess..
[ML] OK.
> risk due to acting on incomplete information".
[ML] OK. I will change the sentence as you suggest.
> any functionality to return sorted results or iterate through the full

[ML] You are right. I mispelled the sentence. Is it fine for you if I 
change the sentence as in the follwing?

OLD

if the RDAP server does not provide any
     functionality to return the truncated results

NEW

if the RDAP server does not provide any
     functionality to return results removed by truncation

> fal
[ML] OK. As I wrote above, I'll change the sentence to outline the risk 
due to acting on incomplete information.
> se.

[ML] Offset pagination is based on the positions of the results within 
the result set while keyset pagination is based on a unique combination 
of values of the results. You can always skip the first K results of a 
result set by specifying offset=K but you can't do the same through 
keyset pagination because you don't know what is the combination of 
values placed at position K.

Let me give you an example that can clarify.

Let's suppose that the query "k*" returns N=1000 results and the length 
of result page is 100. The fastest method to find if "koala" is present 
is to jump to the middle (i.e. offset=500) of the result set and look 
the first result. If it is lexicographically lower than "koala" then 
"koala" might be in second half, on the contrary, "koala" might be in 
the first half. Let's suppose that the first item is greater than 
"koala", then you can jump to the middle of the first half (offset=250) 
and apply the above dichotomy in turn until you can find if "koala" is 
present or not. This process takes log2(N)  steps maximum.

You can't do the same through keyset pagination because you don't know 
how the values are distributed in the result set. You can only scroll 
the result set from the first page to the last and this process takes N 
steps maximum.

However, in general, one is interested in all the results (or in a 
subset) returned by a query rather than a single result. In this case, 
provided that the results can always be sorted according to a unique 
index, keyset pagination is more efficient than offset pagination. Let's 
take the afore example. By offset pagination, the underlying DBMS 
selects always 1000 results and then returns the current page so this 
means that, in the worst case, the DBMS will select 1000 results for 10 
times (from offset=0 to offset=900). By keyset pagination the number of 
results the underlying DBMS selects decreases by 100 results each step. 
At the beginning, it selects 1000 results and returns the first page, 
then it selects 900 results and returns the second page.

Note also two facts:

- the time needed to scroll the result set could be significant when the 
result set is huge

- for all the RDAP searchable objects, it is always possible to build 
more or less easily a combination of properties acting as unique index 
and this is true regardless of whether the search includes the sort 
parameter or not. For example, for the entity object class "handle" is a 
unique property but if the search includes "sort=registrationDate", the 
combination <registrationDate, handle> is unique.

> Okay.  (I think your reply to another ballot comment also helped clarify
[ML] Good.
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