Deduplication on server

[magdalenaszumny]

Hi,

Does server supports coap message deduplication (https://datatracker.ietf.org/doc/html/rfc7252#section-4.5)?

[mrdeep1]

Yes, deduplication is supported. See the first 25 lines in the handle_response() function in src/coap_net.c.

Are you having an issue here?

[magdalenaszumny]

Thank you for quick answer!

Isn't handle_response function enabled only for the client? I am mainly interested in server behavior in context of deduplication. I tried to find some related implementation, but couldn't find it.

[mrdeep1]

handle_response() is server side as well - for handling the ACK responses to unsolicited responses (Observe) and separate responses (Async). You are right that this does not handle server request deduplication.

In the function coap_dispatch() (which later calls handle_request() and handle_response()), if COAP_BLOCK_CACHE_RESPONSE is set by coap_context_set_block_mode(), if the exact same request is repeated (but there is no MID checking), the previous response is returned. without any further processing. Note that any Observe update will update the previous response, so any response is current.

I think that the coap_dispatch() logic should include a MID alternative test for a cached response, but need to check into that for potential unintended consequences.

[mrdeep1]

#1733 is now in the develop branch. COAP_BLOCK_CACHE_RESPONSE needs to be set to enable the server to cache the previous response should a duplicate request come in.

Please confirm that this works for you.