Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/
Expires: November 30, 2020                                  May 29, 2020

       Registration Data Access Protocol (RDAP) Partial Response


   The Registration Data Access Protocol (RDAP) does not include
   capabilities to request partial responses.  Servers will only return
   full responses that includes all of the information that a client is
   authorized to receive.  A partial response capability that limits the
   amount of information returned, especially in the case of search
   queries, could bring benefits to both clients and servers.  This
   document describes an RDAP query extension that allows clients to
   specify their preference for obtaining a partial response.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 30, 2020.

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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
   2.  RDAP Path Segment Specification . . . . . . . . . . . . . . .   3
     2.1.  Subsetting Metadata . . . . . . . . . . . . . . . . . . .   3
       2.1.1.  RDAP Conformance  . . . . . . . . . . . . . . . . . .   4
       2.1.2.  Representing Subsetting Links . . . . . . . . . . . .   4
   3.  Dealing with Relationships  . . . . . . . . . . . . . . . . .   5
   4.  Basic Field Sets  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Negative Answers  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     6.1.  IIT-CNR/ . . . . . . . . . . . . . . . . . . .   8
     6.2.  APNIC . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Approaches to Partial Response Implementation  . . .  11
     A.1.  Specific Issues Raised by RDAP  . . . . . . . . . . . . .  12
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The use of partial responses in RESTful API ([REST]) design is very
   common.  The rationale is quite simple: instead of returning objects
   in API responses with all data fields, only a subset of the fields in
   each result object is returned.  The benefit is obvious: less data
   transferred over the network means less bandwidth usage, faster
   server responses, less CPU time spent both on the server and the
   client, and less memory usage on the client.

   Several leading API providers (e.g.  LinkedIn [LINKEDIN], Facebook
   [FACEBOOK], Google [GOOGLE]) implement partial response features by
   providing an optional query parameter by which clients identify the
   fields they wish to receive.  Support for partial responses is also
   considered a leading principle by many best practice guidelines in
   REST API implementation ([REST-API1], [REST-API2]) in order to
   improve performance, save on bandwidth and possibly accelerate the
   overall interaction.  In other contexts, for example in digital
   libraries and bibliographic catalogues, servers can provide responses

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   according to different element sets (i.e. "brief" to get back a short
   response and "full" to get back the complete response).

   Currently, RDAP does not provide a client with any way to request a
   partial response.  Servers can only provide the client with a full
   response ([RFC7483]).  Servers cannot limit the amount of information
   returned in a response based on a client's preferences, and this
   creates inefficiencies.

   The protocol described in this specification extends RDAP search
   capabilities to enable partial responses through the provisioning of
   pre-defined sets of fields that clients can submit to an RDAP service
   by adding a new query parameter.  The service is implemented using
   the Hypertext Transfer Protocol (HTTP) ([RFC7230]) and the
   conventions described in RFC 7480 ([RFC7480]).

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown

2.  RDAP Path Segment Specification

   The path segment defined in this section is an OPTIONAL extension of
   search path segments defined in RFC 7482 ([RFC7482]).  This document
   defines an RDAP query parameter, "fieldSet", whose value is a string
   identifying a server-defined set of supported fields (Figure 1).*.com&fieldSet=afieldset

      Figure 1: Example of RDAP search query reporting the "fieldSet"

   This solution can be implemented by RDAP providers with less effort
   than field selection and is easily requested by clients.  The
   considerations that have led to this solution are described in more
   detail in Appendix A.

2.1.  Subsetting Metadata

   According to most advanced principles in REST design, collectively
   known as HATEOAS (Hypermedia as the Engine of Application State)
   ([HATEOAS]), a client entering a REST application through an initial
   URI should use server-provided links to dynamically discover

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   available actions and access the resources it needs.  In this way,
   the client is not required to have prior knowledge of the service
   and, consequently, to hard code the URIs of different resources.
   This allows the server to make URI changes as the API evolves without
   breaking clients.  Definitively, a REST service should be as self-
   descriptive as possible.

   Therefore, servers implementing the query parameter described in this
   specification SHOULD provide additional information in their
   responses about the available field sets.  Such information is
   collected in a new data structure named "subsetting_metadata"
   containing the following properties:

   o  "currentFieldSet": "String" (REQUIRED) either the value of the
      "fieldSet" parameter as specified in the query string, or the
      field set applied by default;

   o  "availableFieldSets": "AvailableFieldSet[]" (OPTIONAL) an array of
      objects, with each element describing an available field set.
      Members are:

      *  "name": "String" (REQUIRED) the field set name;
      *  "default": "Boolean" (REQUIRED) whether the field set is
         applied by default;
      *  "description": "String" (OPTIONAL) a human-readable description
         of the field set;
      *  "links": "Link[]" (OPTIONAL) an array of links as described in
         RFC 8288 ([RFC8288]) containing the query string that applies
         the field set.

2.1.1.  RDAP Conformance

   Servers returning the "subsetting_metadata" section in their
   responses MUST include "subsetting" in the rdapConformance array.

2.1.2.  Representing Subsetting Links

   An RDAP server MAY use the "links" array of the "subsetting_metadata"
   element to provide ready-made references ([RFC8288]) to the available
   field sets (Figure 2).  The target URI in each link is the reference
   to an alternate view of the results with respect to the current view
   of the results identified by the context URI.

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     "rdapConformance": [
     "subsetting_metadata": {
       "currentFieldSet": "afieldset",
       "availableFieldSets": [
         "name": "anotherfieldset",
         "description": "Contains some fields",
         "default": false,
         "links": [
           "value": "*
           "rel": "alternate",
           "href": "*
           "title": "Result Subset Link",
           "type": "application/rdap+json"
     "domainSearchResults": [

           Figure 2: Example of a "subsetting_metadata" instance

3.  Dealing with Relationships

   Representation of second level objects within a field set produces
   additional considerations.  Since the topmost objects could be
   returned according to different field sets, the same field sets could
   be applied to their related objects.  As a consequence, the response
   could contain either no relationship or associated objects which are
   in turn provided according to a field set.

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4.  Basic Field Sets

   This section defines three basic field sets which servers MAY
   implement to facilitate their interaction with clients:

   o  "id": the server provides only the key field, respectively:
      "handle" for entities, "ldhName" for domains and nameservers.  If
      a returned domain or nameserver is an Internationalized Domain
      Name (IDN, [RFC5890]), then the "unicodeName" field MUST be
      included in the response.  This field set could be used when the
      client wants to obtain a collection of object identifiers
      (Figure 3);

   o  "brief": the field set contains the fields that can be included in
      a "short" response.  This field set could be used when the client
      is asking for a subset of the full response which provides only
      basic knowledge of each object;

   o  "full": the field set contains all of the information the server
      can provide for a particular object.

   The "objectClassName" field is implicitly included in each of the
   above field sets.  RDAP providers are RECOMMENDED to include a "self"
   link in each field set.  RDAP providers MAY also add any property
   providing service information.

   Fields included in the "brief" and "full" field sets MUST be returned
   according to the user's access and authorization levels.

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     "rdapConformance": [
     "domainSearchResults": [
         "objectClassName": "domain",
         "ldhName": "",
         "links": [
           "value": "",
           "rel": "self",
           "href": "",
           "type": "application/rdap+json"
         "objectClassName": "domain",
         "ldhName": "",
         "links": [
           "value": "",
           "rel": "self",
           "href": "",
           "type": "application/rdap+json"

    Figure 3: Example of RDAP response according to the "id" field set

5.  Negative Answers

   Each request including an unsupported field set SHOULD produce an
   HTTP 400 (Bad Request) response code.  Optionally, the response MAY
   include additional information regarding the negative answer in the
   HTTP entity body.

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6.  Implementation Status

   NOTE: Please remove this section and the reference to RFC 7942 prior
   to publication as an RFC.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 7942
   ([RFC7942]).  The description of implementations in this section is
   intended to assist the IETF in its decision processes in progressing
   drafts to RFCs.  Please note that the listing of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify the information
   presented here that was supplied by IETF contributors.  This is not
   intended as, and must not be construed to be, a catalog of available
   implementations or their features.  Readers are advised to note that
   other implementations may exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

6.1.  IIT-CNR/

      Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/
      Description: This implementation includes support for RDAP queries
      using data from .it public test environment.
      Level of Maturity: This is an "alpha" test implementation.
      Coverage: This implementation includes all of the features
      described in this specification.
      Contact Information: Mario Loffredo,

6.2.  APNIC

      Responsible Organization: Asia-Pacific Network Information Centre
      Description: A proof-of-concept for RDAP mirroring.
      Level of Maturity: This is a proof-of-concept implementation.
      Coverage: This implementation includes all of the features
      described in this specification.
      Contact Information: Tom Harrison,

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7.  IANA Considerations

   IANA is requested to register the following value in the RDAP
   Extensions Registry:

      Extension identifier: subsetting
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <>
      Intended usage: This extension describes a best practice for
      partial response provisioning.

8.  Security Considerations

   A search query typically requires more server resources (such as
   memory, CPU cycles, and network bandwidth) when compared to a lookup
   query.  This increases the risk of server resource exhaustion and
   subsequent denial of service due to abuse.  Thiss risk can be
   mitigated by supporting return of partial responses combined with
   other strategies (e.g. restricting search functionality, limiting the
   rate of search requests, and truncating and paging results).

   Support for partial responses gives RDAP operators the ability to
   implement data access control policies based on the HTTP
   authentication mechanisms described in RFC 7481 ([RFC7481]).  RDAP
   operators can vary the information returned in RDAP responses based
   on a client's access and authorization levels.  For example:

   o  The list of fields for each set can differ based on the client's
      access and authorization levels;

   o  The set of available field sets could be restricted based on the
      client's access and authorization levels.

   Servers can also define different result limits according to the
   available field sets, so a more flexible truncation strategy can be
   implemented.  The new query parameter presented in this document
   provides RDAP operators with a way to implement a server that reduces
   inefficiency risks.

9.  Acknowledgements

   The authors would like to acknowledge Scott Hollenbeck, Tom Harrison,
   Karl Heinz Wolf, Jasdip Singh and Patrick Mevzek for their
   contribution to this document.

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10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,

   [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
              Registration Data Access Protocol (RDAP)", RFC 7480,
              DOI 10.17487/RFC7480, March 2015,

   [RFC7481]  Hollenbeck, S. and N. Kong, "Security Services for the
              Registration Data Access Protocol (RDAP)", RFC 7481,
              DOI 10.17487/RFC7481, March 2015,

   [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access
              Protocol (RDAP) Query Format", RFC 7482,
              DOI 10.17487/RFC7482, March 2015,

   [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the
              Registration Data Access Protocol (RDAP)", RFC 7483,
              DOI 10.17487/RFC7483, March 2015,

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

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   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,

10.2.  Informative References

   [CQL]      Whitaker, G., "Catnap Query Language Reference", September
              2017, <

    , "facebook for developers - Using the Graph
              API", July 2017, <

   [GOOGLE], "Making APIs Faster: Introducing Partial
              Response and Partial Update", March 2010,

   [HATEOAS]  Jedrzejewski, B., "HATEOAS - a simple explanation", 2018,

    , "Java One 2009: Building Consistent RESTful
              APIs in a High Performance Environment", July 2009,

   [REST]     Fielding, R., "Architectural Styles and the Design of
              Network-based Software Architectures", 2000,

              Jobinesh, P., "RESTful Java Web Services - Second
              Edition", September 2015.

              Masse, M., "REST API Design Rulebook", October 2011.

Appendix A.  Approaches to Partial Response Implementation

   Looking at the implementation experiences described in Section 1, two
   approaches to the implementation of partial response are observed:

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   o  The client explicitly describes the data fields to be returned;

   o  The client describeds a name identifying a server-defined set of
      data fields.

   The former is more flexible than the latter because clients can
   specify all the data fields they need.  However, it has some

   o  Fields have to be declared according to a given syntax.  This is a
      simple task when the data structure of the object is flat, but it
      is much more difficult when the object has a tree structure like
      the one of a JSON object.  The presence of arrays and deep nested
      objects complicate both the syntax definition of the query and,
      consequently, the processing required on the server side;

   o  Clients need to recognize the returned data structure to avoid
      cases when the requested fields are invalid;

   o  The request of some fields might not match the client's access and
      authorization levels.  Clients might request unauthorized fields
      and servers should define a strategy for providing a response,
      such as always returning an error response or returning a response
      that ignores the unauthorized fields.

A.1.  Specific Issues Raised by RDAP

   In addition to those listed above, RDAP responses raise some specific

   o  Relevant entity object information is included in a jCard, but
      such information cannot be easily selected because it is split
      into the items of a jagged array;

   o  RDAP responses contain some properties providing service
      information (e.g. rdapConformance, links, notices, remarks, etc.)
      which are not normally selected but they are just as important.
      They could be returned anyway but, in this case, the server would
      provide unrequested data.

   It's possible to address these issues.  For example, the Catnap Query
   Language ([CQL]) is a comprehensive expression language that can be
   used to customize the JSON response of a RESTful web service.
   Application of CQL to RDAP responses would explicitly identify the
   output fields that would be acceptable when a few fields are
   requested but it would become very complicated when processing some
   larger number of fields.  In the following, two CQL expressions for a
   domain search query are shown (Figure 4).  In the first, only

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   objectClassName and ldhName are requested.  In the second, the fields
   of a possible WHOIS-like response are listed.*.com

      Figure 4: Examples of CQL expressions for a domain search query

   The latter approach seems to facilitate RDAP interoperability.
   Servers can define basic field sets which, if known to clients, can
   increase the probability to get a valid response.  The usage of field
   sets lets the query string be less complex.  In addition, the
   definition of pre-defined sets of fields makes it easier to establish
   result limits.

   Finally, considering that there is no real need for RDAP users to
   have the maximum flexibility in defining all the possible sets of
   logically connected fields (e.g. users interested in domains usually
   need to know the status, the creation date, and the expiry date of
   each domain), the latter approach is preferred.

Appendix B.  Change Log

   00:  Initial working group version ported from draft-loffredo-regext-
   01:  Removed "FOR DISCUSSION" items.  Changed the basic field sets
      from REQUIRED to OPTIONAL.  Removed the definition of fields
      included in "brief" field set.  Provided a more detailed
      description of "subsetting_metadata" structure.  Removed some
   02:  Added the "Negative Answers" section.  Changed "IANA
      Considerations" section.
   03:  Added the "unicodeName" field in the id fieldSet when a returned
      domain or nameserver is an IDN.  Added RFC5890 to "Normative
      References" section.
   04:  Recommended the RDAP providers to include a "self" link in any
      field set other than "full".  Updated "Acknowledgements" section.
   05:  Moved "Approaches to Partial Response Implementation" section to
      the appendix.

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   06:  Clarified the use of self links in "Basic Field Sets" section.
      Added APNIC to the implementations of the "Implementation Status"
   07:  Changed "only a subset is returned" to "only a subset of fields
      in each result object is returned" in the "Introduction" section.
      Moved the "RDAP Conformance" section up in the document.  Updated
      the "Acknowledgements" section.
   08:  Changed the rdapConformance tag "subsetting_level_0" to
      "subsetting".  Moved [RFC7942] to the "Normative References".
   09:  Corrected the "rdapConformance" content in Figure 3.
   10:  Corrected the JSON content in Figure 2.  Clarified the meaning
      of both context and target URIs in a result subset link defined in
      Section 2.1.2.  Updated the "Acknowledgements" section.
   11:  Minor pre-AD review edits.

Authors' Addresses

   Mario Loffredo
   Via Moruzzi,1
   Pisa  56124


   Maurizio Martinelli
   Via Moruzzi,1
   Pisa  56124


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