Provided by: libcoap3_4.3.1-2_amd64 
NAME
coap_handler, coap_register_request_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_request_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_request_handler() is a server side function that registers a callback
handler handler that is called when there is an incoming request PDU and 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);
In handler, data from incoming_pdu can be abstracted as described in coap_pdu_access(3)
for analysis and then updates response_pdu as appropriate as described in
coap_pdu_setup(3). response_pdu is already pre-populated with the incoming_pdu's token and
the PDU type. If this handler is called as a result of an unsolicited Observe trigger,
then the option OBSERVE (and potentially option BLOCK2) are also added in. The
response_pdu's response code should always be updated.
NOTE: Any data associated with incoming_pdu is no longer be available after exiting this
function as incoming_pdu is deleted. In particular incoming_pdu's data must not be used if
calling coap_add_data_large_response(). However, it is safe to use the data if
coap_add_data() is used to update response_pdu where a copy of the data is taken.
NOTE: A request callback handler can be called with a generic resource (i.e. set up using
coap_resource_unknown_init2(3)), so coap_resource_get_uri_path(3) can be used to determine
the URI in this case.
The coap_register_response_handler() is a client side function that registers a request’s
response callback 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);
In handler, data from received (and optionally sent if set) can be abstracted as described
in coap_pdu_access(3) for analysis.
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() is a client side function that registers a request’s
negative response callback 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);
NACK reason 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
sent can be NULL. mid can be used for determining which is the transmitting request.
The coap_register_ping_handler() function registers a callback handler for tracking
receipt of CoAP ping traffic associated with the context. If handler is NULL, then the
handler is de-registered. It can be used both client and server side.
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 registers a callback handler for tracking
receipt of CoAP ping response traffic associated with the context. If handler is NULL,
then the handler is de-registered. It can be used both client and server side.
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 registers a callback handler for tracking
network events associated with the context. If handler is NULL, then the handler is
de-registered. It can be used both client and server side.
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
/**
* (Q-)BLOCK errors
*/
COAP_EVENT_PARTIAL_BLOCK 0x3001
COAP_EVENT_XMIT_BLOCK_FAIL 0x3002
/**
* Server session state management events
*/
COAP_EVENT_SERVER_SESSION_NEW 0x4001
COAP_EVENT_SERVER_SESSION_DEL 0x4002
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), coap_pdu_access(3), coap_pdu_setup(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>