COAP_HANDLER(3)

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>