NAME

       coap_keepalive, coap_context_set_keepalive - Work with CoAP keepalive

SYNOPSIS

       #include <coap3/coap.h>

       void coap_context_set_keepalive(coap_context_t *context, unsigned int seconds);

       For specific (D)TLS library support, link with -lcoap-3-notls, -lcoap-3-gnutls,
       -lcoap-3-openssl, -lcoap-3-mbedtls or -lcoap-3-tinydtls. Otherwise, link with -lcoap-3 to
       get the default (D)TLS library support.

DESCRIPTION

       There may be a requirement to send out keepalive traffic when the CoAP session is idle (no
       packets have been sent or received for a specified period) to keep, say, an interim NAT
       device "warm" with the NAT translation state, or to periodically check whether the device
       at the other end of the session has "gone away".

       For UDP/DTLS, this is done with the confirmable CoAP (0.00) Ping packet, which solicits a
       CoAP RST response. For TCP/TLS, this is done with CoAP (7.02) Ping packet, which solicits
       a CoAP (7.03) Pong response, all handled by libcoap.

FUNCTIONS

       Function: coap_context_set_keepalive()

       The coap_context_set_keepalive() function needs to be called to update the context with
       the keepalive for idle traffic timeout of seconds. If seconds is set to 0 (the default),
       then the sending of keepalives is disabled. Any sessions created from this context will
       use the same seconds value to determine whether a keepalive "ping" is to be sent out or
       not.

       Applications can track the usage of the receipt of "pings" and receipt of "responses" by
       defining the respective handlers to use by using coap_register_ping_handler() and
       coap_register_pong_handler().

       If the keepalive fails to solicit a response, then this can be tracked by defining the
       handler to use by using coap_register_event_handler() which will be called with a reason
       of COAP_EVENT_KEEPALIVE_FAILURE.

       NOTE: As this may be used to keep an interim NAT device "warm", the exponentially
       increasing retransmit times for CON requests is limited to seconds, but the retransmit
       counter is not affected. Unless needed, seconds shold not be set to less than 30.

SEE ALSO

       coap_handler(3)

FURTHER INFORMATION

       See

       "RFC7252: The Constrained Application Protocol (CoAP)"

       "RFC8323: CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets"

       for further information.

BUGS

       Please report bugs on the mailing list for libcoap:
       libcoap-developers@lists.sourceforge.net or raise an issue on GitHub at
       https://github.com/obgm/libcoap/issues

AUTHORS

       The libcoap project <libcoap-developers@lists.sourceforge.net>