DESCRIPTION

This man page focuses on the CoAP Context and how to update or get information from the opaque coap_context_t structure.

The CoAP stack’s global state is stored in a coap_context_t Context object. Resources, Endpoints and Sessions are associated with this context object. There can be more than one coap_context_t object per application, it is up to the application to manage each one accordingly.

FUNCTIONS

Function: coap_new_context()

The coap_new_context() function creates a new Context that is then used to keep all the CoAP Resources, Endpoints and Sessions information. The optional listen_addr parameter, if set for a CoAP server, creates an Endpoint that is added to the context that is listening for un-encrypted traffic on the IP address and port number defined by listen_addr.

Function: coap_free_context()

The coap_free_context() function must be used to release the CoAP stack context. It clears all entries from the receive queue and send queue and deletes the Resources that have been registered with context, and frees the attached Sessions and Endpoints.

WARNING: It is unsafe to call coap_free_context() in an atexit() handler as other libraries may also call atexit() and clear down some CoAP required functionality.

WARNING: It is unsafe to call coap_free_context() in any libcoap callback handlers as set up in coap_handler(3).

WARNING: In a multi-thread, libcoap thread-safe environment, if other threads are using context, it is not recommended to call coap_free_context() as various libcoap APIs will unexpectedly fail. It is best to clear down those other threads first before calling coap_free_context().

Function: coap_context_set_max_idle_sessions()

The coap_context_set_max_idle_sessions() function sets the maximum number of idle server sessions to max_idle_sessions for context. If this number is exceeded, the least recently used server session is completely removed. 0 (the initial default) means that the number of idle sessions is not monitored.

Function: coap_context_get_max_idle_sessions()

The coap_context_get_max_idle_sessions() function returns the maximum number of idle server sessions for context.

Function: coap_context_set_max_handshake_sessions()

The coap_context_set_max_handshake_sessions() function sets the maximum number of outstanding server sessions in (D)TLS handshake to max_handshake_sessions for context. If this number is exceeded, the least recently used server session in handshake is completely removed. 0 (the default) means that the number of handshakes is not monitored.

Function: coap_context_get_max_handshake_sessions()

The coap_context_get_max_handshake_sessions() function returns the maximum number of outstanding server sessions in (D)TLS handshake for context.

Function: coap_context_set_session_timeout()

The coap_context_set_session_timeout() function sets the number of seconds of inactivity to session_timeout for context before an idle server session is removed. 0 (the default) means wait for the default of 300 seconds.

Function: coap_context_get_session_timeout()

The coap_context_get_session_timeout() function returns the seconds to wait before timing out an idle server session for context.

Function: coap_context_set_csm_timeout_ms()

The coap_context_set_csm_timeout_ms() function sets the number of milliseconds to wait for a (TCP) CSM negotiation response from the peer to csm_timeout_ms for context before timing out and assuming CoAP server is broken. The default is 1000 milliseconds. The minimum value for csm_timeout_ms is set to 10 milliseconds and the maximum value for csm_timeout_ms is set to 10000 milliseconds.

Function: coap_context_get_csm_timeout_ms()

The coap_context_get_csm_timeout_ms() function returns the milliseconds to wait for a (TCP) CSM negotiation response from the peer for context,

Function: coap_context_set_max_token_size()

The coap_context_set_max_token_size() function sets the max_token_size for context. max_token_size must be greater than 8 to indicate support for RFC8974 up to max_token_size bytes, else 8 to disable RFC8974 (if previously set).

NOTE: For the client, it will send an initial PDU to test the server supports the requested extended token size as per "RFC8794 Section 2.2.2"

Function: coap_context_set_app_data()

The coap_context_set_app_data() function is used to define a app_data pointer for the context which can then be retrieved at a later date.

Function: coap_context_get_app_data()

The coap_context_get_app_data() function is used to retrieve the app_data pointer previously defined by coap_context_set_app_data().

Function: coap_context_set_cid_tuple_change()

The coap_context_set_cid_tuple_change() function is used to define to a client to force the client’s port to change every packets sent, providing the ability to test a CID (RFC9146) enabled server. Only supported by DTLS libraries that support CID.

RETURN VALUES

coap_new_context() returns a newly created context or NULL if there is a creation failure.

coap_context_get_max_idle_sessions() returns the maximum number of idle server sessions.

coap_context_get_max_handshake_sessions() returns the maximum number of outstanding server sessions in (D)TLS handshake.

coap_context_get_session_timeout() returns the seconds to wait before timing out an idle server session.

coap_context_get_csm_timeout_ms() returns the milliseconds to wait for a (TCP) CSM negotiation response from the peer.

coap_context_get_app_data() returns a previously defined pointer.

coap_context_set_cid_tuple_change() returns 1 on success, else 0;

SEE ALSO

coap_session(3)

FURTHER INFORMATION

See

"RFC7252: The Constrained Application Protocol (CoAP)"

"RFC8974: Extended Tokens and Stateless Clients in the Constrained Application Protocol (CoAP)"

for further information.

BUGS

Please raise an issue on GitHub at https://github.com/obgm/libcoap/issues to report any bugs.

Please raise a Pull Request at https://github.com/obgm/libcoap/pulls for any fixes.

AUTHORS

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