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Michiel De WitteandClaude Fable 5
091f189e7a
Server sessions are keyed on (remote address, local port) only, and
session->addr_info.local is overwritten by the destination of every
received packet. When a unicast CON request is parked in a coap_async_t
for a separate response and a multicast packet from the same peer
arrives before the async fires, the re-invoked handle_request() sees a
multicast local address, drops the CON per RFC7252 8.1 ("Invalid
multicast packet received"), and coap_check_async() frees the async:
the response is silently never sent.
Snapshot the local address in coap_register_async() and restore it on
the session before the async fires, so the deferred request is handled
(and its response source selected) against the address it actually
arrived on.
Seen in the field with a CoAP remote control whose GET /endpoint was
answered via the async path while it also multicast periodic
announcements from the same source port: the device received the empty
ACK and then never got the response.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>