Header "typ" syntax check

[sschulz-t]

I was wondering if the check for HeaderLabelType might be to strict.

go-cose/headers.go

Lines 514 to 517 in 92fbe95

	// We don't check the precise definition though (RFC 6838 Section 4.2).
	if strings.Count(v, "/") != 1 {
	return errors.New("header parameter: type: require text of form type/subtype")
	}

This line enforces having a / syntax. However I can not figure out if this is really required.

RFC9596 (https://www.rfc-editor.org/rfc/rfc9596) says it has the ContentType syntax, but refers to the names in https://www.iana.org/assignments/media-types which do not have that format.

My use case is implementing statuslists which requires the type label to be "statuslist+cwt"
https://datatracker.ietf.org/doc/html/draft-ietf-oauth-status-list-06#name-status-list-in-json-format

[shizhMSFT]

RFC 9596 Section 2 defines typ is either an uint CoAP Content-Format or a string content type value.

RFC 6838 Section 4.2 states that

All registered media types MUST be assigned top-level type and subtype names.

In other words, a string typ must be <type-name>/<subtype-name>. That is, a / is required.

The value statuslist+cwt does not meet name requirement and thus cannot be registered, and thus is not a valid value of typ as defined by RFC 9596.

[shizhMSFT]

Further reference can be found for the definition of the media type type "/" subtype *(";" parameter):

• RFC 2045 Section 5.1
• RFC 4855 Section 3

[sschulz-t]

Thanks for your detailed reply! You were right. I forwarded the feedback and the statuslist draft was updated to use application/statuslist+cwt 👍