1 Internet Engineering Task Force (IETF) M. Loffredo
2 Request for Comments: 8982 M. Martinelli
3 Category: Standards Track IIT-CNR/Registro.it
4 ISSN: 2070-1721 February 2021
5
6
7 Registration Data Access Protocol (RDAP) Partial Response
8
9 Abstract
10
11 The Registration Data Access Protocol (RDAP) does not include
12 capabilities to request partial responses. Servers will only return
13 full responses that include all of the information that a client is
14 authorized to receive. A partial response capability that limits the
15 amount of information returned, especially in the case of search
16 queries, could bring benefits to both clients and servers. This
17 document describes an RDAP query extension that allows clients to
18 specify their preference for obtaining a partial response.
19
20 Status of This Memo
21
22 This is an Internet Standards Track document.
23
24 This document is a product of the Internet Engineering Task Force
25 (IETF). It represents the consensus of the IETF community. It has
26 received public review and has been approved for publication by the
27 Internet Engineering Steering Group (IESG). Further information on
28 Internet Standards is available in Section 2 of RFC 7841.
29
30 Information about the current status of this document, any errata,
31 and how to provide feedback on it may be obtained at
32 https://www.rfc-editor.org/info/rfc8982.
33
34 Copyright Notice
35
36 Copyright (c) 2021 IETF Trust and the persons identified as the
37 document authors. All rights reserved.
38
39 This document is subject to BCP 78 and the IETF Trust's Legal
40 Provisions Relating to IETF Documents
41 (https://trustee.ietf.org/license-info) in effect on the date of
42 publication of this document. Please review these documents
43 carefully, as they describe your rights and restrictions with respect
44 to this document. Code Components extracted from this document must
45 include Simplified BSD License text as described in Section 4.e of
46 the Trust Legal Provisions and are provided without warranty as
47 described in the Simplified BSD License.
48
49 Table of Contents
50
51 1. Introduction
52 1.1. Conventions Used in This Document
53 2. RDAP Path Segment Specification
54 2.1. Subsetting Metadata
55 2.1.1. RDAP Conformance
56 2.1.2. Representing Subsetting Links
57 3. Dealing with Relationships
58 4. Basic Field Sets
59 5. Negative Answers
60 6. IANA Considerations
61 7. Security Considerations
62 8. References
63 8.1. Normative References
64 8.2. Informative References
65 Appendix A. Approaches to Partial Response Implementation
66 A.1. Specific Issues Raised by RDAP
67 Acknowledgements
68 Authors' Addresses
69
70 1. Introduction
71
72 The use of partial responses in RESTful API [REST] design is very
73 common. The rationale is quite simple: instead of returning objects
74 in API responses with all data fields, only a subset of the fields in
75 each result object is returned. The benefit is obvious: less data
76 transferred over the network means less bandwidth usage, faster
77 server responses, less CPU time spent both on the server and the
78 client, and less memory usage on the client.
79
80 Currently, RDAP does not provide a client with any way to request a
81 partial response. Servers can only provide the client with a full
82 response [RFC7483]. Servers cannot limit the amount of information
83 returned in a response based on a client's preferences, and this
84 creates inefficiencies.
85
86 The protocol described in this specification extends RDAP search
87 capabilities to enable partial responses through the provisioning of
88 predefined sets of fields that clients can submit to an RDAP service
89 by adding a new query parameter. The service is implemented using
90 the Hypertext Transfer Protocol (HTTP) [RFC7230] and the conventions
91 described in [RFC7480].
92
93 1.1. Conventions Used in This Document
94
95 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
96 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
97 "OPTIONAL" in this document are to be interpreted as described in
98 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
99 capitals, as shown here.
100
101 2. RDAP Path Segment Specification
102
103 The path segment defined in this section is an OPTIONAL extension of
104 search path segments defined in [RFC7482]. This document defines an
105 RDAP query parameter, "fieldSet", whose value is a non-empty string
106 identifying a server-defined set of fields returned in place of the
107 full response. The field sets supported by a server are usually
108 described in out-of-band documents (e.g., RDAP profile) together with
109 other features. Moreover, this document defines in Section 2.1 an
110 in-band mechanism by means of which servers can provide clients with
111 basic information about the supported field sets.
112
113 The following is an example of an RDAP query including the "fieldSet"
114 parameter:
115
116 https://example.com/rdap/domains?name=example*.com&fieldSet=afieldset
117
118 This solution can be implemented by RDAP providers with less effort
119 than field selection and is easily requested by clients. The
120 considerations that have led to this solution are described in more
121 detail in Appendix A.
122
123 2.1. Subsetting Metadata
124
125 According to most advanced principles in REST design, collectively
126 known as "Hypermedia as the Engine of Application State" (HATEOAS)
127 [HATEOAS], a client entering a REST application through an initial
128 URI should use server-provided links to dynamically discover
129 available actions and access the resources it needs. In this way,
130 the client is not required to have prior knowledge of the service
131 nor, consequently, to hard-code the URIs of different resources.
132 This allows the server to make URI changes as the API evolves without
133 breaking clients. Definitively, a REST service should be as self-
134 descriptive as possible.
135
136 Therefore, servers implementing the query parameter described in this
137 specification SHOULD provide additional information in their
138 responses about the available field sets. Such information is
139 collected in a new JSON data structure named "subsetting_metadata"
140 containing the following properties:
141
142 "currentFieldSet": "String" (REQUIRED)
143 either the value of the "fieldSet" parameter as specified in the
144 query string, or the field set applied by default.
145
146 "availableFieldSets": "AvailableFieldSet[]" (OPTIONAL)
147 an array of objects, with each element describing an available
148 field set. The AvailableFieldSet object includes the following
149 members:
150
151 "name": "String" (REQUIRED)
152 the field set name.
153
154 "default": "Boolean" (REQUIRED)
155 indicator of whether the field set is applied by default. An
156 RDAP server MUST define only one default field set.
157
158 "description": "String" (OPTIONAL)
159 a human-readable description of the field set.
160
161 "links": "Link[]" (OPTIONAL)
162 an array of links as described in [RFC8288] containing the
163 query string that applies the field set (see Section 2.1.2).
164
165 2.1.1. RDAP Conformance
166
167 Servers returning the "subsetting_metadata" section in their
168 responses MUST include "subsetting" in the rdapConformance array.
169
170 2.1.2. Representing Subsetting Links
171
172 An RDAP server MAY use the "links" array of the "subsetting_metadata"
173 element to provide ready-made references [RFC8288] to the available
174 field sets (Figure 1). The target URI in each link is the reference
175 to an alternative to the current view of results identified by the
176 context URI.
177
178 The "value", "rel", and "href" JSON values MUST be specified. All
179 other JSON values are OPTIONAL.
180
181 {
182 "rdapConformance": [
183 "rdap_level_0",
184 "subsetting"
185 ],
186 ...
187 "subsetting_metadata": {
188 "currentFieldSet": "afieldset",
189 "availableFieldSets": [
190 {
191 "name": "anotherfieldset",
192 "description": "Contains some fields",
193 "default": false,
194 "links": [
195 {
196 "value": "https://example.com/rdap/domains?name=example*.com
197 &fieldSet=afieldset",
198 "rel": "alternate",
199 "href": "https://example.com/rdap/domains?name=example*.com
200 &fieldSet=anotherfieldset",
201 "title": "Result Subset Link",
202 "type": "application/rdap+json"
203 }
204 ]
205 },
206 ...
207 ]
208 },
209 ...
210 "domainSearchResults": [
211 ...
212 ]
213 }
214
215 Figure 1: Example of a "subsetting_metadata" Instance
216
217 3. Dealing with Relationships
218
219 Representation of second-level objects within a field set produces
220 additional considerations. Since the representation of the topmost
221 returned objects will vary according to the field set in use, the
222 response may contain no relationships (e.g., for an abbreviated field
223 set) or may contain associated objects as in a normal RDAP query
224 response. Each field set can indicate the format of the additional
225 objects to be returned, in the same manner that the format of the
226 topmost objects is controlled by the field set.
227
228 4. Basic Field Sets
229
230 This section defines three basic field sets that servers MAY
231 implement to facilitate their interaction with clients:
232
233 "id": The server provides only the key field; "handle" for entities,
234 and "ldhName" for domains and nameservers. If a returned domain
235 or nameserver is an Internationalized Domain Name (IDN) [RFC5890],
236 then the "unicodeName" field MUST additionally be included in the
237 response. This field set could be used when the client wants to
238 obtain a collection of object identifiers (Figure 2).
239
240 "brief": The field set contains the fields that can be included in a
241 "short" response. This field set could be used when the client is
242 asking for a subset of the full response that provides only basic
243 knowledge of each object.
244
245 "full": The field set contains all of the information the server can
246 provide for a particular object.
247
248 The "objectClassName" field is implicitly included in each of the
249 above field sets. RDAP providers SHOULD include a "links" field
250 indicating the "self" link relationship. RDAP providers MAY also add
251 any property providing service information.
252
253 Fields included in the "brief" and "full" field set responses MUST
254 take into account the user's access and authorization levels.
255
256 {
257 "rdapConformance": [
258 "rdap_level_0",
259 "subsetting"
260 ],
261 ...
262 "domainSearchResults": [
263 {
264 "objectClassName": "domain",
265 "ldhName": "example1.com",
266 "links": [
267 {
268 "value": "https://example.com/rdap/domain/example1.com",
269 "rel": "self",
270 "href": "https://example.com/rdap/domain/example1.com",
271 "type": "application/rdap+json"
272 }
273 ]
274 },
275 {
276 "objectClassName": "domain",
277 "ldhName": "example2.com",
278 "links": [
279 {
280 "value": "https://example.com/rdap/domain/example2.com",
281 "rel": "self",
282 "href": "https://example.com/rdap/domain/example2.com",
283 "type": "application/rdap+json"
284 }
285 ]
286 },
287 ...
288 ]
289 }
290
291 Figure 2: Example of RDAP Response According to the "id" Field Set
292
293 5. Negative Answers
294
295 Each request including an empty or unsupported "fieldSet" value MUST
296 produce an HTTP 400 (Bad Request) response code. Optionally, the
297 response MAY include additional information regarding the supported
298 field sets in the HTTP entity body (Figure 3).
299
300 {
301 "errorCode": 400,
302 "title": "Field set 'unknownfieldset' is not valid",
303 "description": [
304 "Supported field sets are: 'afieldset', 'anotherfieldset'."
305 ]
306
307 }
308
309 Figure 3: Example of RDAP Error Response Due to an Invalid Field
310 Set Included in the Request
311
312 6. IANA Considerations
313
314 IANA has registered the following value in the "RDAP Extensions"
315 registry:
316
317 Extension identifier: subsetting
318 Registry operator: Any
319 Published specification: RFC 8982
320 Contact: IETF <iesg@ietf.org>
321 Intended usage: This extension describes a best practice for partial
322 response provisioning.
323
324 7. Security Considerations
325
326 A search query typically requires more server resources (such as
327 memory, CPU cycles, and network bandwidth) when compared to a lookup
328 query. This increases the risk of server resource exhaustion and
329 subsequent denial of service. This risk can be mitigated by
330 supporting the return of partial responses combined with other
331 strategies (e.g., restricting search functionality, limiting the rate
332 of search requests, and truncating and paging results).
333
334 Support for partial responses gives RDAP operators the ability to
335 implement data access control policies based on the HTTP
336 authentication mechanisms described in [RFC7481]. RDAP operators can
337 vary the information returned in RDAP responses based on a client's
338 access and authorization levels. For example:
339
340 * the list of fields for each set can differ based on the client's
341 access and authorization levels;
342
343 * the set of available field sets could be restricted based on the
344 client's access and authorization levels.
345
346 Servers can also define different result limits according to the
347 available field sets, so a more flexible truncation strategy can be
348 implemented. The new query parameter presented in this document
349 provides RDAP operators with a way to implement a server that reduces
350 inefficiency risks.
351
352 8. References
353
354 8.1. Normative References
355
356 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
357 Requirement Levels", BCP 14, RFC 2119,
358 DOI 10.17487/RFC2119, March 1997,
359 <https://www.rfc-editor.org/info/rfc2119>.
360
361 [RFC5890] Klensin, J., "Internationalized Domain Names for
362 Applications (IDNA): Definitions and Document Framework",
363 RFC 5890, DOI 10.17487/RFC5890, August 2010,
364 <https://www.rfc-editor.org/info/rfc5890>.
365
366 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
367 Protocol (HTTP/1.1): Message Syntax and Routing",
368 RFC 7230, DOI 10.17487/RFC7230, June 2014,
369 <https://www.rfc-editor.org/info/rfc7230>.
370
371 [RFC7480] Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
372 Registration Data Access Protocol (RDAP)", RFC 7480,
373 DOI 10.17487/RFC7480, March 2015,
374 <https://www.rfc-editor.org/info/rfc7480>.
375
376 [RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the
377 Registration Data Access Protocol (RDAP)", RFC 7481,
378 DOI 10.17487/RFC7481, March 2015,
379 <https://www.rfc-editor.org/info/rfc7481>.
380
381 [RFC7482] Newton, A. and S. Hollenbeck, "Registration Data Access
382 Protocol (RDAP) Query Format", RFC 7482,
383 DOI 10.17487/RFC7482, March 2015,
384 <https://www.rfc-editor.org/info/rfc7482>.
385
386 [RFC7483] Newton, A. and S. Hollenbeck, "JSON Responses for the
387 Registration Data Access Protocol (RDAP)", RFC 7483,
388 DOI 10.17487/RFC7483, March 2015,
389 <https://www.rfc-editor.org/info/rfc7483>.
390
391 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
392 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
393 May 2017, <https://www.rfc-editor.org/info/rfc8174>.
394
395 [RFC8288] Nottingham, M., "Web Linking", RFC 8288,
396 DOI 10.17487/RFC8288, October 2017,
397 <https://www.rfc-editor.org/info/rfc8288>.
398
399 8.2. Informative References
400
401 [CQL] Whitaker, G., "Catnap Query Language Reference", commit
402 d4f402c, September 2017,
403 <https://github.com/gregwhitaker/catnap/wiki/Catnap-Query-
404 Language-Reference>.
405
406 [HATEOAS] Jedrzejewski, B., "HATEOAS - a simple explanation",
407 February 2018, <https://www.e4developer.com/2018/02/16/
408 hateoas-simple-explanation/>.
409
410 [REST] Fielding, R., "Architectural Styles and the Design of
411 Network-based Software Architectures", Ph.D. Dissertation,
412 University of California, Irvine, 2000,
413 <https://www.ics.uci.edu/~fielding/pubs/dissertation/
414 fielding_dissertation.pdf>.
415
416 Appendix A. Approaches to Partial Response Implementation
417
418 Looking at the implementation experiences of partial responses
419 offered by data providers on the web, two approaches are observed:
420
421 * the client explicitly describes the data fields to be returned;
422
423 * the client describes a name identifying a server-defined set of
424 data fields.
425
426 The former is more flexible than the latter because clients can
427 specify all the data fields they need. However, it has some
428 drawbacks:
429
430 * Fields have to be declared according to a given syntax. This is a
431 simple task when the data structure of the object is flat, but it
432 is much more difficult when the object has a tree structure like
433 that of a JSON object. The presence of arrays and deep nested
434 objects complicate both the syntax definition of the query and,
435 consequently, the processing required on the server side.
436
437 * Clients need to recognize the returned data structure to avoid
438 cases when the requested fields are invalid.
439
440 * The request of some fields might not match the client's access and
441 authorization levels. Clients might request unauthorized fields,
442 and servers have to define a strategy for responding such as
443 always returning an error response or returning a response that
444 ignores the unauthorized fields.
445
446 A.1. Specific Issues Raised by RDAP
447
448 In addition to those listed above, RDAP responses raise some specific
449 issues:
450
451 * Relevant entity object information is included in a jCard, but
452 such information cannot be easily selected because it is split
453 into the items of a jagged array.
454
455 * RDAP responses contain some properties providing service
456 information (e.g., rdapConformance, links, notices, remarks,
457 etc.), which are not normally selected but are just as important.
458 They could be returned anyway but, in this case, the server would
459 provide unrequested data.
460
461 It is possible to address these issues. For example, the Catnap
462 Query Language [CQL] is a comprehensive expression language that can
463 be used to customize the JSON response of a RESTful web service.
464 Application of CQL to RDAP responses would explicitly identify the
465 output fields that would be acceptable when a few fields are
466 requested but it would become very complicated when processing a
467 larger number of fields. In the following, two CQL expressions for a
468 domain search query are shown (Figure 4). In the first, only
469 objectClassName and ldhName are requested. In the second, the fields
470 of a possible WHOIS-like response are listed.
471
472 https://example.com/rdap/domains?name=example*.com
473 &fields=domainSearchResults(objectClassName,ldhName)
474
475 https://example.com/rdap/domains?name=example*.com
476 &fields=domainSearchResults(objectClassName,ldhName,
477 unicodeName,
478 status,
479 events(eventAction,eventDate),
480 entities(objectClassName,handle,roles),
481 nameservers(objectClassName,ldhName))
482
483 Figure 4: Examples of CQL Expressions for a Domain Search Query
484
485 The field set approach seems to facilitate RDAP interoperability.
486 Servers can define basic field sets that, if known to clients, can
487 increase the probability of obtaining a valid response. The usage of
488 field sets makes the query string less complex. Moreover, the
489 definition of predefined sets of fields makes it easier to establish
490 result limits.
491
492 Finally, considering that there is no real need for RDAP users to
493 have the maximum flexibility in defining all the possible sets of
494 logically connected fields (e.g., users interested in domains usually
495 need to know the status, the creation date, and the expiry date of
496 each domain), the field set approach is preferred.
497
498 Acknowledgements
499
500 The authors would like to acknowledge Scott Hollenbeck, Tom Harrison,
501 Karl Heinz Wolf, Jasdip Singh, Patrick Mevzek, Benjamin Kaduk, Roman
502 Danyliw, Murray Kucherawy, Erik Kline, and Robert Wilton for their
503 contribution to this document.
504
505 Authors' Addresses
506
507 Mario Loffredo
508 IIT-CNR/Registro.it
509 Via Moruzzi,1
510 56124 Pisa
511 Italy
512
513 Email: mario.loffredo@iit.cnr.it
514 URI: https://www.iit.cnr.it
515
516
517 Maurizio Martinelli
518 IIT-CNR/Registro.it
519 Via Moruzzi,1
520 56124 Pisa
521 Italy
522
523 Email: maurizio.martinelli@iit.cnr.it
524 URI: https://www.iit.cnr.it
525
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