Internet-Draft rdap-x May 2023
Newton & Singh Expires 22 November 2023 [Page]
Registration Protocols Extensions (regext)
7480 (if approved)
Intended Status:
Standards Track
A. Newton
J. Singh

An RDAP With Extensions Media Type


This document defines a media type for RDAP that can be used to describe RDAP content with RDAP extensions. Additionally, this document describes the usage of this media type with RDAP.

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 22 November 2023.

Table of Contents

1. Background

[RFC7480] defines the 'application/rdap+json' media type to be used with RDAP. This document defines a new media type to be used in conjuction with the current media type when an RDAP extension needs to be described during HTTP content negotiation.

2. RDAP-X: The RDAP With Extensions Media Type

The media type defined by this document is 'application/rdap-x+json'. This media type has a parameter of "extensions" which is a whitespace-separated list of RDAP extensions as defined in the IANA RDAP Extensions registry.

Here is an example:

application/rdap-x+json;extensions="rdap_level_0 fred"

For readability, this document will refer to this media type, RDAP With Extensions, as RDAP-X.

3. Using The RDAP-X Media Type

[RFC7480] specifies the usage of 'application/json', 'application/rdap+json' or both with HTTP Accept header. When using the media type defined by this document, the 'application/rdap+json' media type MUST also be used in the Accept header.

An example:

accept: application/rdap+json, application/rdap-x+json;extensions="rdap_level_0 fred"

When a server is programmed to understand the RDAP-X media type, it SHOULD respond with this media type in the Content-Type header. By doing so, clients will be able to detect if the server recognizes the media type. Otherwise, the server will use the 'application/rdap+json' media type signalling to the client that the RDAP-X media type is not recognized by the server. This updates the usage of the Content-Type header with RDAP defined in RFC 7480, but this usage is backward compatible.

If both a client and server support the RDAP-X media type, and the client requests an extension that is unimplemented by the server, the server SHOULD respond with the RDAP-X media type using only extensions implemented by the server. This behavior is backward compatible as RDAP clients must ignore unknown extensions as specified by [RFC9083]. Responding with an HTTP 406 Not Acceptable status code is NOT RECOMMENDED.

When the RDAP-X media type is used in the Content-Type header, the values in the media type's extension parameter SHOULD match the values in the rdapConformance array in the return JSON. When there is a mismatch between extension parameters and the rdapConformance array, clients SHOULD give preference to the rdapConformance array.

5. IANA Considerations

Type name: application

Subtype name: rdap-x+json

Required parameters: This media type has a parameter of "extensions" which is a whitespace-separated list of RDAP extensions as defined in the IANA RDAP Extensions registry.

Optional parameters: N/A

Encoding considerations: See Section 3.1 of [RFC6839].

Security considerations: The media represented by this identifier does not have security considerations beyond that found in Section 12 of [RFC8259].

Interoperability considerations: There are no known interoperability problems regarding this media format.

Published specification: This document.

Applications that use this media type: Implementations of the Registration Data Access Protocol (RDAP) with Extensions.

Additional information: This media type is a product of the IETF REGEXT Working Group. The REGEXT charter, information on the REGEXT mailing list, and other documents produced by the REGEXT Working Group can be found at

Person & email address to contact for further information: IESG <iesg&>

Intended usage: COMMON

Restrictions on usage: none

Author: Andy Newton

Change controller: IETF

Provisional Registration: No

6. Normative References

Hansen, T. and A. Melnikov, "Additional Media Type Structured Syntax Suffixes", RFC 6839, DOI 10.17487/RFC6839, , <>.
Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the Registration Data Access Protocol (RDAP)", STD 95, RFC 7480, DOI 10.17487/RFC7480, , <>.
Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, , <>.
Hollenbeck, S. and A. Newton, "JSON Responses for the Registration Data Access Protocol (RDAP)", STD 95, RFC 9083, DOI 10.17487/RFC9083, , <>.

7. Informative References

Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <>.
Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, , <>.
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <>.

Appendix A. Design Considerations

A.1. Not Reusing the Existing Media Type

Section 4.3 of [RFC6838] strongly discourages the creation of new parameters on existing media types to enable new features. As RDAP has always had extensions, it could be argued that adding an "extensions" parameter to the existing application/rdap+json media type is not adding a new feature to RDAP. However, the opposite could be argued that adding the capability for clients to signal desired RDAP extensions is a new feature.

More practically, there is concern that adding a new parameter to the existing media type would not be backward compatible with some server software. That is, servers examining media types as exact string matches may incorrectly conclude that the existing media type with an unknown, new parameter may not be the same as the existing media type without parameters. A similar, though less likely, concern exists for clients.

As servers are required to handle multiple media types according to [RFC7480] and [RFC9110], it therefore seems reasonable to conclude that defining a new media type for use with the existing media type is best to preserve backward compatibility.

A.2. Query Parameters Considered Harmful

Another design approach to communicating RDAP extensions from the client to the server would be the use of URI query parameters:


A.2.1. Copy and Paste

Consider two RDAP users, Alice and Bob. Alice has an RDAP client that supports the extensions "fizzbuzz", and Bob has an RDAP client that does not support this extension.

Now consider the scenario where Alice copies and pastes the RDAP URL from above into an email and sends it to Bob. When Bob uses that URL with his RDAP client, it will be communicating to the server that the extension "fizzbuzz" is understood by Bob's client when it is not.

In this scenario, Bob's client will be unable to render the RDAP extension regardless of the usage or not of the query parameter. However, if the server is using the query parameter for secondary purposes, such as gathering metrics and statistics, then the capabilities of Bob's client will have been incorrectly signalled to the server.

A.2.2. Redirects

The RDAP ecosystem uses redirects in many situations. [RFC7480] discusses "aggregators", which are RDAP servers used to help clients find authoritative RDAP servers using the RDAP bootstrap registries. Redirects are also heavily used by the RIRs when IP addresses or autonomous system numbers are transferred from one RIR to another.

Within HTTP, URI query parameters are not explicitly preserved during a redirect (probably due to architecture considerations, see the section below). Specific to RDAP, [RFC7480] instructs RDAP servers to ignore unknown query parameters and instructs clients not to transform a URL of a redirect.

Therefore, query parameters denoting RDAP extensions will not survive redirects. This can be readily observed in currently deployed RDAP servers:

curl -v

To further demonstrate that query parameters do not survive redirects but that media types do survive redirects, consider the code found here. This code consists of a simple client and a simple server. The client sets both a new media type and query parameters. The servers listens on two ports, redirecting the client from a URL on the first port to a URL on the second port.

Here is the output of the client. It shows that the query parameters are not automatically preserved but that the media type is automatically preserved.

2023-05-13T19:48:42.055902Z  INFO client: sending reqwest
2023-05-13T19:48:42.098605Z DEBUG reqwest::connect: starting new connection:
2023-05-13T19:48:42.098696Z DEBUG hyper::client::connect::http: connecting to
2023-05-13T19:48:42.098915Z DEBUG hyper::client::connect::http: connected to
2023-05-13T19:48:42.099407Z DEBUG hyper::proto::h1::io: flushed 147 bytes
2023-05-13T19:48:42.100343Z DEBUG hyper::proto::h1::io: parsed 3 headers
2023-05-13T19:48:42.100392Z DEBUG hyper::proto::h1::conn: incoming body is empty
2023-05-13T19:48:42.100537Z DEBUG hyper::client::pool: pooling idle connection for ("http",
2023-05-13T19:48:42.100730Z DEBUG reqwest::async_impl::client: redirecting '' to ''
2023-05-13T19:48:42.100873Z DEBUG reqwest::connect: starting new connection:
2023-05-13T19:48:42.100933Z DEBUG hyper::client::connect::http: connecting to
2023-05-13T19:48:42.101157Z DEBUG hyper::client::connect::http: connected to
2023-05-13T19:48:42.101667Z DEBUG hyper::proto::h1::io: flushed 202 bytes
2023-05-13T19:48:42.102419Z DEBUG hyper::proto::h1::io: parsed 3 headers
2023-05-13T19:48:42.102462Z DEBUG hyper::proto::h1::conn: incoming body is content-length (66 bytes)
2023-05-13T19:48:42.102533Z DEBUG hyper::proto::h1::conn: incoming body completed
2023-05-13T19:48:42.102634Z DEBUG hyper::client::pool: pooling idle connection for ("http",
2023-05-13T19:48:42.102642Z  INFO client: returned content type: "application/rdap-x;extensions=\"foo bar\""
2023-05-13T19:48:42.102664Z  INFO client: status code is 418 I'm a teapot
2023-05-13T19:48:42.102777Z  INFO client: response is {"errorCode":418,"title": "Your Beverage Choice is Not Available"}

Here is the output of the server. It show that the client, upon redirect, automatically sends the media type but does not automatically preserve the query parameters.

2023-05-13T19:48:30.935786Z  INFO servers: starting server on port 3000
2023-05-13T19:48:30.935816Z  INFO servers: starting server on port 4000
2023-05-13T19:48:42.099642Z DEBUG hyper::proto::h1::io: parsed 2 headers
2023-05-13T19:48:42.099688Z DEBUG hyper::proto::h1::conn: incoming body is empty
2023-05-13T19:48:42.099847Z  INFO servers: Serving request from
2023-05-13T19:48:42.099877Z  INFO servers: accept values: "application/rdap+json, application/rdap-x+json;extensions=\"foo bar\""
2023-05-13T19:48:42.099902Z  INFO servers: redirecting to server on port 4000
2023-05-13T19:48:42.100047Z DEBUG hyper::proto::h1::io: flushed 147 bytes
2023-05-13T19:48:42.101783Z DEBUG hyper::proto::h1::io: parsed 3 headers
2023-05-13T19:48:42.101811Z DEBUG hyper::proto::h1::conn: incoming body is empty
2023-05-13T19:48:42.101921Z  INFO servers: Serving request from
2023-05-13T19:48:42.101940Z  INFO servers: accept values: "application/rdap+json, application/rdap-x+json;extensions=\"foo bar\""
2023-05-13T19:48:42.101953Z  INFO servers: responding with an unuseful error
2023-05-13T19:48:42.102096Z DEBUG hyper::proto::h1::io: flushed 207 bytes
2023-05-13T19:48:42.103705Z DEBUG hyper::proto::h1::conn: read eof
2023-05-13T19:48:42.103697Z DEBUG hyper::proto::h1::conn: read eof

Preservation of query parameters is not a common feature of HTTP client and server libraries, whereas preservation of media types is common.

A.2.3. Architectual Violations

As noted in [RFC3986], URI query parameters are meant to be part of the identity of the resource being identified by a URI and pointed to by the location of a URL. RDAP extensions change the portions of JSON returned by the server but are not intended to change the resource being identified. That is, a domain registration is the same domain registration regardless of whether the postal address in that domain registration is communicated via JCard or a new RDAP extension for JSContact.

Changing how the content of a resource is conveyed is called content negotiation and is discussed in detail in [RFC9110] using media types.

Readers should note that protocol design is not a "priestly affair" in which architectural violations are strictly forbidden. Every design decision is a trade-off. However, following the architecture of an ecosystem generally makes re-use of software and systems easier, and often eases the adoption of newer features in the future. When given the choice between two designs, the design that does not violate architecture should be preferred.

A.3. RDAP Extension Versioning

It is beyond the scope of this document to define the versioning of RDAP extensions. However, there is design intent to allow the use of explicitly versioned RDAP extension identifiers where they are also compatible with the identifiers used in the rdapConformance array of RDAP.

Consider the scenario in which the IETF decides that RDAP extension identifiers suffixed with the character string __V denotes RDAP extensions versioned using a semantic versioning scheme. In this scenario, the RDAP extension identifier fizzbuzz__V is registered with IANA. The __V suffix indicates that when the identifier is used in the rdapConformance array, it must appear appended with a character string denoting the semantic version of the extension.

For example, fizzbuzz__V_2_1 denotes version 2.1 of the fizzbuzz extension. In RDAP JSON, the conformance would appear as:

"rdapConformance" : [

The usage with the rdap-x media type would be:

application/rdap-x+json;extensions="rdap_level_0 fizzbuzz__V_2_1"

Readers should note that this scenario is provided to show design intent and is not a full-fledged extension versioning design. Additionally, the new media type defined in this document has utility with existing, opaquely versioned RDAP extensions and does not depend on the definition of a new versioning scheme for RDAP extensions.

Authors' Addresses

Andy Newton
Jasdip Singh