Parse unknown options as opaque instead of failing the whole message

[zalenskivolt]

Currently it is not possible to see anything about a message that includes an unsupported option, except that option number.

For example, the UDP message 40020011c13cffd1e91a8401020304: "Unsupported option number 258"

(Option 258 is the No-Response option RFC-7967, listed in IANA CoAP Option Numbers)

Removing the unsupported option, 40020011c13cff8401020304, you get to see the full message details:

Message:
{
"type": "Confirmable",
"code": "POST",
"id": 17,
"token": 0,
"options": [
"Content-Format: application/cbor"
]
}

Payload (CBOR):
[1, 2, 3, 4]

It would be nice if unsupported options could be listed as opaque option number, value pairs in the options list, perhaps with a warning at the end.

[twyatt]

This sounds like a good request, but admittedly, I don't have a lot of time to work on KoAP these days.
PRs are welcome, otherwise I will try to get to it eventually.