Provided by: libcoap3_4.3.0-2build1_amd64 
NAME
coap_handler, coap_register_handler, coap_register_response_handler, coap_register_nack_handler,
coap_register_ping_handler, coap_register_pong_handler, coap_register_event_handler - Work with CoAP
handlers
SYNOPSIS
#include <coap3/coap.h>
void coap_register_handler(coap_resource_t *resource, coap_request_t method, coap_method_handler_t
handler);
void coap_register_response_handler(coap_context_t *context, coap_response_handler_t handler);
void coap_register_nack_handler(coap_context_t *context, coap_nack_handler_t handler);
void coap_register_ping_handler(coap_context_t *context, coap_ping_handler_t handler);
void coap_register_pong_handler(coap_context_t *context, coap_pong_handler_t handler);
void coap_register_event_handler(coap_context_t *context, coap_event_handler_t handler);
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
The coap_register_handler() function registers a callback handler handler that is called when there is a
URI match against the resource and there is a method (e.g. PUT, POST etc.) match. method can be one of
the following.
COAP_REQUEST_GET
COAP_REQUEST_POST
COAP_REQUEST_PUT
COAP_REQUEST_DELETE
COAP_REQUEST_FETCH
COAP_REQUEST_PATCH
COAP_REQUEST_IPATCH
The method handler function prototype is defined as:
typedef void (*coap_method_handler_t)(coap_resource_t *resource,
coap_session_t *session,
const coap_pdu_t *incoming_pdu,
const coap_string_t *query,
coap_pdu_t *response_pdu);
NOTE: incoming_pdu will be NULL for the GET Handler if this is an internally generated Observe Response.
coap_resource_get_uri_path() can be used to determine the URI in this case.
NOTE: Any data associated with incoming_pdu is no longer be available after exiting this function as
incoming_pdu is deleted, unless coap_add_data() was used to update response_pdu where a copy of the data
is taken. In particular incoming_pdu's data must not be used if calling coap_add_data_large_response().
The coap_register_response_handler() function defines a request’s response handler for traffic associated
with the context. The application can use this for handling any response packets, including sending a RST
packet if this response was unexpected. If handler is NULL, then the handler is de-registered.
The response handler function prototype is defined as:
typedef enum coap_response_t {
COAP_RESPONSE_FAIL, /* Response not liked - send CoAP RST packet */
COAP_RESPONSE_OK /* Response is fine */
} coap_response_t;
typedef coap_response_t (*coap_response_handler_t)(coap_session_t *session,
const coap_pdu_t *sent,
const coap_pdu_t *received,
const coap_mid_t id);
NOTE: sent will only be non NULL when the request PDU is Confirmable and this is an ACK or RST response
to the request. In general, matching of Requests and Responses whould be done by generating unique Tokens
for each Request and then matching up based on the Token in received Response.
NOTE: If the returned value is COAP_RESPONSE_FAIL, then a CoAP RST packet will get sent to the server by
libcoap. The returned value of COAP_RESPONSE_OK indicates that all is OK.
The coap_register_nack_handler() function defines a request’s negative response handler for traffic
associated with the context. If handler is NULL, then the handler is de-registered.
The nack handler function prototype is defined as:
typedef void (*coap_nack_handler_t)(coap_session_t *session,
const coap_pdu_t *sent,
const coap_nack_reason_t reason,
const coap_mid_t mid);
NACKs can be one of the following
COAP_NACK_TOO_MANY_RETRIES
COAP_NACK_NOT_DELIVERABLE
COAP_NACK_RST
COAP_NACK_TLS_FAILED
COAP_NACK_ICMP_ISSUE
The coap_register_ping_handler() function defines a handler for tracking receipt of CoAP ping traffic
associated with the context. If handler is NULL, then the handler is de-registered.
The ping handler function prototype is defined as:
typedef void (*coap_ping_handler_t)(coap_session_t *session,
const coap_pdu_t *received,
const coap_mid_t mid);
The coap_register_pong_handler() function defines a handler for tracking receipt of CoAP ping response
traffic associated with the context. If handler is NULL, then the handler is de-registered.
The pong handler function prototype is defined as:
typedef void (*coap_pong_handler_t)(coap_session_t *session,
const coap_pdu_t *received,
const coap_mid_t mid);
The coap_register_event_handler() function defines a handler for tracking (D)TLS events associated with
the context. If handler is NULL, then the handler is de-registered.
The event handler function prototype is defined as:
typedef void (*coap_event_handler_t)(coap_session_t *session,
const coap_event_t event);
Events can be one of the following
/**
* (D)TLS events for COAP_PROTO_DTLS and COAP_PROTO_TLS
*/
COAP_EVENT_DTLS_CLOSED 0x0000
COAP_EVENT_DTLS_CONNECTED 0x01DE
COAP_EVENT_DTLS_RENEGOTIATE 0x01DF
COAP_EVENT_DTLS_ERROR 0x0200
/**
* TCP events for COAP_PROTO_TCP and COAP_PROTO_TLS
*/
COAP_EVENT_TCP_CONNECTED 0x1001
COAP_EVENT_TCP_CLOSED 0x1002
COAP_EVENT_TCP_FAILED 0x1003
/**
* CSM exchange events for reliable protocols only
*/
COAP_EVENT_SESSION_CONNECTED 0x2001
COAP_EVENT_SESSION_CLOSED 0x2002
COAP_EVENT_SESSION_FAILED 0x2003
EXAMPLES
GET Resource Callback Handler
#include <coap3/coap.h>
#include <stdio.h>
static void
hnd_get_time(coap_resource_t *resource, coap_session_t *session,
coap_pdu_t *request, coap_string_t *query, coap_pdu_t *response) {
unsigned char buf[40];
size_t len;
time_t now;
/* ... Additional analysis code for resource, request pdu etc. ... */
/* After analysis, generate a suitable response */
now = time(NULL);
if (query != NULL && coap_string_equal(query, coap_make_str_const("secs"))) {
/* Output secs since Jan 1 1970 */
len = snprintf((char *)buf, sizeof(buf), "%lu", now);
}
else {
/* Output human-readable time */
struct tm *tmp;
tmp = gmtime(&now);
if (!tmp) {
/* If 'now' is not valid */
coap_pdu_set_code(response, COAP_RESPONSE_CODE_NOT_FOUND);
return;
}
len = strftime((char *)buf, sizeof(buf), "%b %d %H:%M:%S", tmp);
}
coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTENT);
/*
* Invoke coap_add_data_large_response() to do all the hard work.
*
* Define the format - COAP_MEDIATYPE_TEXT_PLAIN - to add in
* Define how long this response is valid for (secs) - 1 - to add in.
*
* OBSERVE Option added internally if needed within the function
* BLOCK2 Option added internally if output too large
* ETAG Option added internally
*/
coap_add_data_large_response(resource, session, request, response,
query, COAP_MEDIATYPE_TEXT_PLAIN, 1, 0,
len,
buf, NULL, 0);
}
Packet Response Handler
#include <coap3/coap.h>
static int check_token(coap_pdu_t *received) {
/* Remove (void) definition if variable is used */
(void)received;
/* Code to validate the token is what we expect */
return 1;
}
static coap_response_t
response_handler(coap_context_t *ctx, coap_session_t *session,
coap_pdu_t *sent, coap_pdu_t *received, const coap_mid_t mid) {
/* Remove (void) definition if variable is used */
(void)ctx;
(void)session;
(void)mid;
coap_pdu_type_t rcv_type = coap_pdu_get_type(received);
coap_pdu_code_t rcv_code = coap_pdu_get_code(received);
/* check if this is a response to our original request */
if (!check_token(received)) {
/* drop if this was just some message, or send RST in case of notification */
if (!sent && (rcv_type == COAP_MESSAGE_CON ||
rcv_type == COAP_MESSAGE_NON)) {
/* Cause a CoAP RST to be sent */
return COAP_RESPONSE_FAIL;
}
return COAP_RESPONSE_OK;
}
if (rcv_type == COAP_MESSAGE_RST) {
coap_log(LOG_INFO, "got RST\n");
return COAP_RESPONSE_OK;
}
/* Output the received data, if any */
if (COAP_RESPONSE_CLASS(rcv_code) == 2) {
/* Additional code to deal with the response */
}
return COAP_RESPONSE_OK;
}
SEE ALSO
coap_block(3), coap_observe(3) and coap_resource(3)
FURTHER INFORMATION
See "RFC7252: The Constrained Application Protocol (CoAP)" 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>