Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/
Expires: November 28, 2019                                  May 27, 2019

       Registration Data Access Protocol (RDAP) Partial Response


   The Registration Data Access Protocol (RDAP) does not include
   capabilities to request partial responses.  In fact, according to the
   user authorization, the server can only return full responses.
   Partial responses capability, 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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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on November 28, 2019.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
   2.  Approaches to Partial Response Implementation . . . . . . . .   3
   3.  RDAP Path Segment Specification . . . . . . . . . . . . . . .   5
     3.1.  Subsetting Metadata . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  Representing Subsetting Links . . . . . . . . . . . .   6
   4.  Dealing with Relationships  . . . . . . . . . . . . . . . . .   7
   5.  Basic Field Sets  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Negative Answers  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  RDAP Conformance  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     8.1.  IIT-CNR/ . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     12.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The use of partial response 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 is returned.
   The benefit is obvious: less data transferred over the network means
   less bandwidth usage, faster server response, less CPU time spent
   both on the server and the client, as well as less memory usage on
   the client.

   Several leading APIs providers (e.g.  LinkedIn [LINKEDIN], Facebook
   [FACEBOOK], Google [GOOGLE]) implement the partial response feature
   by providing an optional query parameter by which users require the
   fields they wish to receive.  Partial response is also considered a
   leading principle by many best practices guidelines in REST APIs
   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 according to
   different element sets (i.e. "brief" to get back a short response and
   "full" to get back the complete response)

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   Currently, RDAP does not provide a client with any way to request a
   partial response: the server can only provide the client with the
   full response ([RFC7483]).  Furthermore, servers cannot define the
   limits of the results according to partial responses and this causes
   strong inefficiencies.

   The protocol described in this specification extends RDAP search
   capabilities to enable partial responses, by adding a new query
   parameter and using a RESTful web service.  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 RFC 2119 ([RFC2119]).

2.  Approaches to Partial Response Implementation

   Looking at the implementation experiences described above, two
   approaches to the implementation of partial response can be detected:

   o  the client declares explicitly the data fields to get back;

   o  the client declares a name identifying a server pre-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 contributes to complicate both the syntax definition of
      the query and, consequently, the processing phase on the server

   o  clients should perfectly know the returned data structure to avoid
      cases when the requested fields are invalid;

   o  the request of some fields might not match the user access levels.
      Clients might put unauthorized fields in their requests and
      servers should define a strategy for providing a response:
      returning always an error response or returning a response that
      ignores the unauthorized fields.

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

   o  most of the relevant information of the entity object is included
      in the 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.

   As an example compliant to the first approach, the Catnap Query
   Language ([CQL]) is a comprehensive expression language that can be
   used to customize the JSON response of a RESTful web service.  The
   practical application of CQL to RDAP responses points out that
   declaring explicitly the output fields would still be acceptable when
   a few fields are requested but it would become very complicated if
   the fields should be more.  In the following, two CQL expressions for
   a search domain query are shown (Figure 1): in the first, only
   objectClassName and ldhName are requested, in the second, the fields
   of a possible WHOIS-like response are listed.*.com

      Figure 1: Examples of CQL expressions for a search domain query

   The latter approach seems to facilitate RDAP interoperability.  In
   fact, servers can define some basic field sets which, if known to the
   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 easier
   to establish the results limits.

   Finally, considering that there is not a 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

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   need to know the status, the creation date, the expire date of each
   domain), the latter approach is preferred.

3.  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 pre-defined set of fields (Figure 2).*.com&fieldSet=afieldset

      Figure 2: Example of RDAP search query reporting the "fieldSet"

3.1.  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 the server-provided links to dynamically discover
   available actions and access the resources it needs.  In this way,
   the client is not requested to have prior knowledge of the service
   and, consequently, to hard code the URIs of different resources.
   This would allow the server to make URI changes as the API evolves
   without breaking the 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
      "fieldSet" parameter as specified in the query string or the field
      set applied by default;

   o  "availableFieldSets": "AvailableFieldSet[]" (OPTIONAL) an array of
      objects each one describing an alternate 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;

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      *  "links": "Link[]" (OPTIONAL) an array of links as described in
         RFC 8288 ([RFC8288]) containing the query string that applies
         the field set.

3.1.1.  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 3).  Each link represents a reference to an
   alternate view of the results.

     "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 3: Example of a "subsetting_metadata" instance

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4.  Dealing with Relationships

   Some additional considerations can be made about how second level
   objects could be represented within a field set.  In fact, since the
   topmost objects could be returned according to different field sets,
   the same thing could go for 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.

5.  Basic Field Sets

   In order to improve interoperability between clients and servers, the
   name, as well as the list of fields for each field set, should be
   shared by most of RDAP providers.  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 ("handle" for
      entities, "ldhName" for domains and nameservers).  This field set
      could be used when the client wants to simply obtain a collection
      of object identifiers (Figure 4);

   o  "brief": it 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 gives a basic knowledge of
      each object;

   o  "full": it contains all 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 MAY add any property providing
   service information.

   Fields included in "brief" and "full" field sets could be returned
   according to users access levels.

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     "rdapConformance": [
     "domainSearchResults": [
         "objectClassName": "domain",
         "ldhName": ""
         "objectClassName": "domain",
         "ldhName": ""

    Figure 4: Example of RDAP response according to the "id" field set

6.  Negative Answers

   Each request including an unsupported field set SHOULD obtain an HTTP
   400 (Bad Request) response code.

   Optionally, the response MAY include additional information regarding
   the negative answer in the HTTP entity body.

7.  RDAP Conformance

   Servers returning the "subsetting_metadata" section in their
   responses MUST include "subsetting_level_0" in the rdapConformance

8.  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

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   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".

8.1.  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 a "proof of concept" research
      Coverage: This implementation includes all of the features
      described in this specification.
      Contact Information: Mario Loffredo,

9.  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.

10.  Security Considerations

   Search query typically requires more server resources (such as
   memory, CPU cycles, and network bandwidth) when compared to lookup
   query.  This increases the risk of server resource exhaustion and
   subsequent denial of service due to abuse.  Partial response can
   contribute together with other strategies (e.g. restricting search
   functionality, limiting the rate of search requests, truncating and
   paging results) to mitigate this risk.

   Furthermore, partial response can support RDAP operators to implement
   a versatile access control policy through the HTTP authentication

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   mechanisms as described in RFC 7481 ([RFC7481]).  In fact, RDAP
   operators can follow different, not alternative, approaches to the
   building of responses according to the user access levels:

   o  the list of fields for each set can be different according to the
      user access levels;

   o  some field sets could be available only to some users.

   Servers can also define different results limits according to the
   available field sets, so a more flexible truncation strategy can be

   Therefore, the new query parameter presented in this document
   provides the RDAP operators with a way to implement a secure server
   without penalizing its efficiency.

11.  Acknowledgements

   The authors would like to acknowledge Scott Hollenbeck for his
   contribution to this document.

12.  References

12.1.  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,

   [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,

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   [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,

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

12.2.  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,

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

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

   [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,

Appendix A.  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.

Authors' Addresses

   Mario Loffredo
   Via Moruzzi,1
   Pisa  56124


   Maurizio Martinelli
   Via Moruzzi,1
   Pisa  56124


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