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Status: Reported (7)

RFC 7252, "The Constrained Application Protocol (CoAP)", June 2014

Source of RFC: core (app)

Errata ID: 4946

Status: Reported
Type: Technical

Reported By: Klaus Hartke
Date Reported: 2017-02-22

Section 6.1 says:

coap-URI = "coap:" "//" host [ ":" port ] path-abempty [ "?" query ]

It should say:

coap-URI = "coap:" "//" host [ ":" port ] path-abempty [ "?" query ]
               [ "#" fragment ]

Notes:

The optional fragment component allows for indirect identification of a secondary resource, as defined in Section 3.5 of RFC 3986. The fragment identifier is separated from the rest of the URI prior to a dereference; fragment identifiers are processed client-side and are not included in CoAP requests. The original text shows the syntax of coap:// URIs _after_ separating the fragment identifier, which leaves ambiguity as to whether fragment identifiers are supported or not. The corrected text shows the syntax of CoAP URIs _before_ separating the fragment identifier, which makes clear that fragment identifiers are supported.

Errata ID: 4947

Status: Reported
Type: Technical

Reported By: Klaus Hartke
Date Reported: 2017-02-22

Section 6.2 says:

coaps-URI = "coaps:" "//" host [ ":" port ] path-abempty
               [ "?" query ]

It should say:

coaps-URI = "coaps:" "//" host [ ":" port ] path-abempty
               [ "?" query ] [ "#" fragment ]

Notes:

The optional fragment component allows for indirect identification of a secondary resource, as defined in Section 3.5 of RFC 3986. The fragment identifier is separated from the rest of the URI prior to a dereference; fragment identifiers are processed client-side and are not included in CoAP requests. The original text shows the syntax of coaps:// URIs _after_ separating the fragment identifier, which leaves ambiguity as to whether fragment identifiers are supported or not. The corrected text shows the syntax of CoAP URIs _before_ separating the fragment identifier, which makes clear that fragment identifiers are supported.

Errata ID: 4948

Status: Reported
Type: Technical

Reported By: Klaus Hartke
Date Reported: 2017-02-22

Section 5.6 says:

For a presented request, a CoAP endpoint MUST NOT use a stored
response, unless:

o  the presented request method and that used to obtain the stored
   response match,

o  all options match between those in the presented request and those
   of the request used to obtain the stored response (which includes
   the request URI), except that there is no need for a match of any
   request options marked as NoCacheKey (Section 5.4) or recognized
   by the Cache and fully interpreted with respect to its specified
   cache behavior (such as the ETag request option described in
   Section 5.10.6; see also Section 5.4.2), and

o  the stored response is either fresh or successfully validated as
   defined below.

The set of request options that is used for matching the cache entry
is also collectively referred to as the "Cache-Key".

It should say:

For a presented request, a CoAP endpoint MUST NOT use a stored
response, unless:

o  [...]

o  [...]

o  the payload of the presented request and the payload of the
   request used to obtain the stored response match, and

o  [...]

The set of request options that is used for matching the cache entry
plus (if applicable) the request payload are also collectively referred
to as the "Cache-Key".

Notes:

CoAP servers may return error responses in reply to requests that are invalid at the CoAP level (e.g., 4.02 Bad Option if the client includes an unrecognized option) or at the application level above (e.g., 4.00 Bad Request if the client includes a malformed payload according to application semantics).

If the error response does not depend on the request payload, then it is desirable that repeated requests that differ only in the payload can be satisfied with the same cached response. E.g., repeated requests for a non-existing resource should result in a cached 4.04 Not Found response as often as possible, regardless of the payload, rather than hit the server every time.

If the error response depends on the request payload, then it is not desirable that cached responses are reused for repeated requests that differ only in the payload. E.g., a client should not receive an error response for a valid request payload because another client sent an identical request but with a malformed request payload. In this case, including the request payload in the Cache-Key would give the expected result.

The original text does not include the request in the Cache-Key, which may lead to unexpected results. The corrected text changes that.

Since CoAP does not provide any indication in responses to distinguish between the two cases, caches generally cannot determine whether the response depends on the request payload or not and thus must always include the request payload in the Cache-Key to give the expected result. (As an exception, a cache at an origin server may be able to determine whether a cached response depends on the request payload or not, and thus can reuse responses accordingly. This already applies to responses that do not depend on the request method.)

Errata ID: 4949

Status: Reported
Type: Technical

Reported By: Klaus Hartke
Date Reported: 2017-02-22

Section 5.10.7 says:

If any
of these reserved option numbers occurs in addition to Location-Path
and/or Location-Query and are not supported, then a 4.02 (Bad Option)
error MUST be returned.

It should say:

If any
of these reserved option numbers occurs in addition to Location-Path
and/or Location-Query and are not supported, then the response MUST
be rejected (Sections 4.2 and 4.3).

Notes:

The Location-* options are used in responses. A client cannot return a 4.02 (Bad Option) response in reply to a response. The correct behavior is to reject the response.

Errata ID: 5078

Status: Reported
Type: Technical

Reported By: Jim Schaad
Date Reported: 2017-08-07

Section 7.2.1 says:

The Content-Format code
attribute MAY include a space-separated sequence of Content-Format
codes, indicating that multiple content-formats are available.  The
syntax of the attribute value is summarized in the production "ct-
value" in Figure 12, where "cardinal", "SP", and "DQUOTE" are defined
as in [RFC6690].

It should say:

The Content-Format code
attribute MAY include a space-separated sequence of Content-Format
codes, indicating that multiple content-formats are available.
The Content-Format code attribute MUST NOT appear more than once in a 
link.  The syntax of the attribute value is summarized in the 
production "ct-value" in Figure 12, where "cardinal", "SP", and 
"DQUOTE" are defined as in [RFC6690].

Notes:

Insert a sentence that says that the code MUST NOT appear more than once. This appears to be what was intended, but not stated, by the authors since it supports the space separated values to appear in a single attribute value.

Errata ID: 4895

Status: Reported
Type: Editorial

Reported By: Esko Dijk
Date Reported: 2016-12-23

Section 6.4 says:

Note that these rules completely resolve any percent-encoding.

It should say:

Note that these rules completely resolve any percent-encoding. Also 
note that a trailing slash character in the <path> component represents
a separate, zero-character path segment (see [RFC3986] Section 3.3 
ABNF) and therefore it is encoded using a Uri-Path Option of zero
length.

Notes:

The current specification for decomposing a URI into CoAP Options (Section 6.4) is correct; however the text may still be unclear to implementers who may think that the phrase "not including the delimiting slash characters" means simply omitting a trailing slash character in the URI path. This is incorrect. See the discussion outcome in email thread https://www.ietf.org/mail-archive/web/core/current/msg08223.html . Therefore, a minor clarification is proposed in the notes after the parsing steps.

Errata ID: 4954

Status: Reported
Type: Editorial

Reported By: Klaus Hartke
Date Reported: 2017-02-28

Section 12.3 says:

CoAP does not include a separate way to convey content-encoding
information with a request or response, and for that reason the
content-encoding is also specified for each identifier (if any).  If
multiple content-encodings will be used with a media type, then a
separate Content-Format identifier for each is to be registered.
Similarly, other parameters related to an Internet media type, such
as level, can be defined for a CoAP Content-Format entry.

+--------------------------+----------+----+------------------------+
| Media type               | Encoding | ID | Reference              |
+--------------------------+----------+----+------------------------+

It should say:

CoAP does not include a separate way to convey content-coding
information with a request or response, and for that reason the
content-coding is also specified for each identifier (if any).  If
multiple content-codings will be used with a media type, then a
separate Content-Format identifier for each is to be registered.
Similarly, other parameters related to an Internet media type, such
as level, can be defined for a CoAP Content-Format entry.

+--------------------------+----------------+----+------------------+
| Media type               | Content coding | ID | Reference        |
+--------------------------+----------------+----+------------------+

Notes:

A CoAP Content-Format is the combination of an Internet Media Type with an HTTP Content Coding, as correctly explained in the first paragraphs of Section 12.3. However, the next paragraph (the original text above) incorrectly uses the term "content-encoding". The correct term is "content-coding", as shown in the corrected text.

Examples for _valid_ CoAP Content-Format registrations:

- media type "text/plain; charset=iso-8859-1" with content-coding "deflate"

- media type "image/png" with content-coding "" (no content-coding)

- media type "image/png" with content-coding "identity" (same as previous, no content-coding)

- media type "application/example+xml" with content-coding "exi"

Examples for _invalid_ CoAP Content-Format registrations:

- media type "application/coap-group+json" with content-coding "UTF-8" (UTF-8 is a character encoding, not a content-coding; should be media type "application/coap-group+json; charset=utf-8" with content-coding "identity")

- media type "audio/opus" with content-coding "identity" ("audio/opus" has a required parameter "rate"; should be media type "audio/opus; rate=48000" with content-coding "identity")

- media type "application/example+xml" with content-coding "identity, exi" (too many content-codings; should be media type "application/example+xml" with content-coding "identity" and, separately, media type "application/example+xml" with content-coding "exi")

- media type "application/example+exi" with content-coding "identity" ("+exi" is not a registered structured syntax suffix at the time of writing of this erratum)

- media type "video/ogg" with content-coding "exi" (EXI is a content-coding for XML information)

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