Registration Data Access Protocol (RDAP) Partial Response

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Table of Contents

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.¶

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 [RFC7480].¶

2. RDAP Path Segment Specification

The path segment defined in this section is an OPTIONAL extension of search path segments defined in [RFC7482]. This document defines an RDAP query parameter, "fieldSet", whose value is a non-empty string identifying a server-defined set of fields returned in place of the full response. The field sets supported by a server are usually described in out-of-band documents (e.g., RDAP profile) together with other features. Moreover, this document defines in Section 2.1 an in-band mechanism by means of which servers can provide clients with a basic information about the supported field sets.¶

The following is an example of an RDAP query including the "fieldSet" parameter:¶

https://example.com/rdap/domains?name=example*.com&fieldSet=afieldset¶

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.¶

{
  "rdapConformance": [
    "rdap_level_0",
    "subsetting"
  ],
  ...
  "subsetting_metadata": {
    "currentFieldSet": "afieldset",
    "availableFieldSets": [
      {
      "name": "anotherfieldset",
      "description": "Contains some fields",
      "default": false,
      "links": [
        {
        "value": "https://example.com/rdap/domains?name=example*.com
                  &fieldSet=afieldset",
        "rel": "alternate",
        "href": "https://example.com/rdap/domains?name=example*.com
                 &fieldSet=anotherfieldset",
        "title": "Result Subset Link",
        "type": "application/rdap+json"
        }
      ]
      },
    ...
    ]
  },
  ...
  "domainSearchResults": [
    ...
  ]
}

3. Dealing with Relationships

Representation of second level objects within a field set produces additional considerations. Since the representation of the topmost returned objects will vary according to the field set in use, the response may contain no relationships (e.g., for an abbreviated field set) or may contain associated objects as in a normal RDAP query response. Each field set can indicate the format of the additional objects to be returned, in the same manner that the format of the topmost objects is controlled by the field set.¶

4. Basic Field Sets

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

• "id": the server provides only the key field: "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 additionally be included in the response. This field set could be used when the client wants to obtain a collection of object identifiers (Figure 2);¶

• "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;¶

• "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 SHOULD include a "links" field indicating the "self" link relationship. RDAP providers MAY also add any property providing service information.¶

Fields included in the "brief" and "full" field set responses MUST take into account the user's access and authorization levels.¶

{
  "rdapConformance": [
    "rdap_level_0",
    "subsetting"
  ],
  ...
  "domainSearchResults": [
    {
      "objectClassName": "domain",
      "ldhName": "example1.com",
      "links": [
        {
        "value": "https://example.com/rdap/domain/example1.com",
        "rel": "self",
        "href": "https://example.com/rdap/domain/example1.com",
        "type": "application/rdap+json"
        }
      ]
    },
    {
      "objectClassName": "domain",
      "ldhName": "example2.com",
      "links": [
        {
        "value": "https://example.com/rdap/domain/example2.com",
        "rel": "self",
        "href": "https://example.com/rdap/domain/example2.com",
        "type": "application/rdap+json"
        }
      ]
    },
    ...
  ]
}

5. Negative Answers

Each request including an empty or unsupported "fieldSet" value MUST produce an HTTP 400 (Bad Request) response code. Optionally, the response MAY include additional information regarding the supported field sets in the HTTP entity body (Figure 3).¶

{
    "errorCode": 400,
    "title": "Field set 'unknownfieldset' is not valid",
    "description": [
        "Supported field sets are: 'afieldset', 'anotherfieldset'."
    ]

}

6. 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: IETF <iesg@ietf.org>¶
• Intended usage: This extension describes best practice for partial response provisioning.¶

7. 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 [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".¶

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. This risk can be mitigated by supporting the 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 [RFC7481]. RDAP operators can vary the information returned in RDAP responses based on a client's access and authorization levels. For example:¶

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

• 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.¶

Appendix A. Approaches to Partial Response Implementation

Looking at the implementation experiences of partial response offered by data providers on the web, two approaches are observed:¶

• the client explicitly describes the data fields to be returned;¶

• the client describes 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 drawbacks:¶

• 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 that 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;¶

• clients need to recognize the returned data structure to avoid cases when the requested fields are invalid;¶

• the request of some fields might not match the client's access and authorization levels. Clients might request unauthorized fields and servers have to define a strategy for responding, such as always returning an error response or returning a response that ignores the unauthorized fields.¶

https://example.com/rdap/domains?name=example*.com
        &fields=domainSearchResults(objectClassName,ldhName)

https://example.com/rdap/domains?name=example*.com
        &fields=domainSearchResults(objectClassName,ldhName,
                unicodeName,
                status,
                events(eventAction,eventDate),
                entities(objectClassName,handle,roles),
                nameservers(objectClassName,ldhName))

Authors' Addresses