Problem Details For CoAP APIs

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Table of Contents

1. Introduction

CoAP [RFC7252] response codes are sometimes not sufficient to convey enough information about an error to be helpful. This specification defines a simple and extensible CoRAL [I-D.ietf-core-coral] vocabulary to suit this purpose. It is designed to be reused by CoAP APIs, which can identify distinct "problem types" specific to their needs. Thus, API clients can be informed of both the high-level error class (using the response code) and the finer-grained details of the problem (using this vocabulary), as shown in Figure 1.¶

+--------+          +--------+
|  CoAP  |          |  CoAP  |
| Client |          | Server |
+--------+          +--------+
     |                  |
     | Request          |
     |----------------->|
     |                  |
     |<-----------------|
     |   Error Response |
     |     with a CoRAL |
     |  Document giving |
     |  Problem Details |
     |                  |

The vocabulary presented is largely inspired by the Problem Details for HTTP APIs defined in [RFC7807].¶

2. Basic Problem Details

A CoAP Problem Details is a CoRAL document with the following elements:¶

• "type" (id) - The problem type. This is a mandatory element.¶
• "title" (text) - A short, human-readable summary of the problem type. It SHOULD NOT change from occurrence to occurrence of the problem.¶
• "detail" (text) - A human-readable explanation specific to this occurrence of the problem.¶
• "instance" (uri) - A URI reference that identifies the specific occurrence of the problem. It may or may not yield further information if dereferenced.¶

Consumers MUST use "type" as primary identifiers for the problem type; the "title" string is advisory and included only for consumers who are not aware of the semantics of the "type" value.¶

The "detail" member, if present, ought to focus on helping the client correct the problem, rather than giving debugging information. Consumers SHOULD NOT parse the "detail" member for information; extensions (see Section 3) are more suitable and less error-prone ways to obtain such information.¶

Note that the "instance" URI reference may be relative; this means that it must be resolved relative to the document's base URI, as per [I-D.ietf-core-coral].¶

#using pd = <http://example.org/vocabulary/problem-details#>
#using ex = <http://vocabulary.private-api.example/#>

pd:type         ex:unknown-key-id

#using pd = <http://example.org/vocabulary/problem-details#>
#using ex = <http://vocabulary.private-api.example/#>

pd:type         ex:unknown-key-id
pd:title        "unknown key id"
pd:detail       "Key with id 0x01020304 not registered"
pd:instance     <https://private-api.example/errors/5>

3. Additional Problem Details

Problem type definitions MAY extend the Problem Details document with additional elements to convey additional, problem-specific information.¶

Clients consuming problem details MUST ignore any such elements that they do not recognize; this allows problem types to evolve and include additional information in the future.¶

#using pd = <http://example.org/vocabulary/problem-details#>
#using ex = <http://vocabulary.private-api.example/#>

pd:type         ex:unknown-key-id
pd:title        "unknown key id"
pd:detail       "Key with id 0x01020304 not registered"
pd:instance     <https://private-api.example/errors/5>
ex:key-id       0x01020304

4. Security Considerations

Problem Details for CoAP APIs are serialized in the CoRAL binary format. See Section 11 of [RFC7252] for security considerations relating to CoAP. See Section 7 of [I-D.ietf-core-coral] for security considerations relating to CoRAL.¶

The security and privacy considerations outlined in Section 5 of [RFC7807] apply in full.¶

5. IANA Considerations

TODO.¶

Acknowledgments

Mark Nottingham and Erik Wilde, authors of RFC 7807. Carsten Bormann, Jim Schaad, Christian Amsuess for review and comments on this document.¶

Authors' Addresses