CoAP response 4.02 cannot be used for missing CoAP Option (Esko WGLC)

[EskoDijk]

Section 5.4: "In case a required COAP option (i.e Content-Format) is omitted, the server is expected to return a 4.02." This is not possible in CoAP, only malformed Options or well-formed but unrecognized Critical Options can cause a 4.02. Absence of an option must not cause 4.02.

One example of a missing option can be a missing Content-Format Option in a POST request. In this case, 4.15 Unsupported Content-Format seems a better choice. Other missing Options we don't have to specify I think, one can rely on the general CoAP RFC7252 rules for CoAP servers. A server would return 4.00 Bad Request if the request is unusable due to a missing Option.

[petervanderstok]

Hi Esko,

I prefer 4.00, 4.15 Unsupported Content-Format suggests the presence of a content-format option.

Peter Esko Dijk schreef op 2019-01-30 11:22:

Section 5.4: "In case a required COAP option (i.e Content-Format) is omitted, the server is expected to return a 4.02." This is not possible in CoAP, only malformed Options or well-formed but unrecognized Critical Options can cause a 4.02. Absence of an option must not cause 4.02.

One example of a missing option can be a missing Content-Format Option in a POST request. In this case, 4.15 Unsupported Content-Format seems a better choice. Other missing Options we don't have to specify I think, one can rely on the general CoAP RFC7252 rules for CoAP servers. A server would return 4.00 Bad Request if the request is unusable due to a missing Option.

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[csosto-pk]

This text was referring to a Content-Format that the client requested with an Accept. @csosto-pk to address this.

[csosto-pk]

Rephrased to

In case a COAP option is unrecognized or unsafe, the server is expected to return a 4.02 (Bad Option). If the Content_Format requested in the client Accept Option, is not supported the server MUST return a 4.06 (Not Acceptable), unless another error code takes precedence for the response.

[EskoDijk]

An Option being Unsafe (=Unsafe-to-forward) alone does not trigger a 4.02 response; only Options that are both unrecognized and Unsafe that are processed by a Proxy lead to 4.02. In a server endpoint (not proxy), an Option that is both unrecognized and critical leads to a 4.02. (Elective Options that are unrecognized never lead to a 4.02.

So the first sentence could be updated to e.g.: (assuming we describe a server not proxy) In case a COAP Option is unrecognized and critical, the server is expected to return a 4.02 (Bad Option).

[csosto-pk]

Good catch. Fixed. Text now reads

In case a CoAP Option is unrecognized and critical, the server is expected to return a 4.02 (Bad Option).