coaps_server.h File Reference

CoAP-over-DTLS server front-end - binds a UDP port to a pool of DtlsConn + the CoAPs bridge. More...

#include "ServerConfig.h"

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Detailed Description

CoAP-over-DTLS server front-end - binds a UDP port to a pool of DtlsConn + the CoAPs bridge.

The socket / per-peer glue on top of coaps_process(): it owns a fixed pool of DtlsConn handshake engines, binds the CoAPs UDP port (5684, coaps://) through the transport layer (det_udp), routes each inbound datagram to the connection for its peer address (a new peer opens a pool slot), drives the DTLS 1.3 handshake and its retransmission timer, and hands established application records to coap_server_process() through coaps_process(). CoAP resources are registered with the existing coap_server_add_resource() API; this module only carries them over DTLS, so a plaintext CoAP server (coap_server_begin_udp on :5683) and this secured one can run side by side over the same resources.

Threading (ESP32): det_udp delivers datagrams on the lwIP thread, but the handshake engines must run on the server loop, so the UDP handler only copies each datagram into a lock-free ingest ring; coaps_server_poll() (called from the loop) drains the ring, runs coaps_process(), fires the PTO retransmission timer, and reaps idle or failed connections. The engines therefore only ever run in one context. On host builds there is no UDP; datagrams are injected with coaps_server_ingest() and replies captured through an output sink, so the whole server is host-testable by shuttling byte buffers to an in-test DTLS client, exactly like dtls_conn and coaps_process themselves.

Constrained-friendly: unlike the HTTP/3 pool this is not PSRAM-gated - a small DtlsConn pool fits internal DRAM, which is the whole point of CoAP. Raise DETWS_COAPS_MAX_CONNS for more simultaneous peers (each slot is one DtlsConn handshake engine plus its per-connection key material).

Author

Douglas Quigg (dstroy0)

Date

2026

Definition in file coaps_server.h.