COAP_RESOURCE(3)

NAME
coap_resource, coap_resource_init, coap_resource_unknown_init, coap_resource_proxy_uri_init, coap_add_resource, coap_delete_resource, coap_resource_set_mode, coap_resource_set_userdata, coap_resource_get_userdata - Work with CoAP resources

SYNOPSIS

#include <coap3/coap.h>

coap_resource_t *coap_resource_init(coap_str_const_t *uri_path, int flags);

coap_resource_t *coap_resource_unknown_init(coap_method_handler_t put_handler);

coap_resource_t *coap_resource_proxy_uri_init(coap_method_handler_t proxy_handler, size_t host_name_count, const char *host_name_list[]);

void coap_add_resource(coap_context_t *context, coap_resource_t *resource);

int coap_delete_resource(coap_context_t *context, coap_resource_t *resource);

void coap_resource_set_mode(coap_resource_t *resource, int mode);

void coap_resource_set_userdata(coap_resource_t *resource, void *data);

void *coap_resource_get_userdata(coap_resource_t *resource);

void coap_resource_release_userdata_handler(coap_context_t *context, coap_resource_release_userdata_handler_t callback);

coap_str_const_t *coap_resource_get_uri_path(coap_resource_t *resource);

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

CoAP Resources on a CoAP Server need to be created and updated etc. The URI in the request packet defines the resource to work with, with possibly the Query referring to a sub-resource.

When resources are configured on the CoAP server, the URI to match against in the request packet is specified.

Callback Handlers are then added to the resource to handle the different request methods.

Adding Attributes allows textual information to be added to the resource which can then be reported back to any client doing a "GET .well-known/core" request.

If an incoming packet request matches a resource’s URI and Method, then the appropriate callback resource handler is invoked to process the packet which then should update a suitable response packet for sending back to the requester.

There is support for handling incoming packets where the URI is unknown. This could, for example, happen when a PUT request is trying to create a new resource. It is the responsibility of the unknown resource callback handler to either create a new resource for the URI or just manage things separately.

CoAP Observe (RFC 7641) is not supported for unknown resources, so a new resource with GET handler must be created by the unknown resource callback handle matching the URI which then can be Observable.

The coap_resource_init() function returns a newly created resource of type coap_resource_t * . uri_path specifies the uri string path to match against. flags is used to define whether the resource is of type Confirmable Message or Non-Confirmable Message for any "observe" responses. See coap_observe(3). flags can be one of the following definitions or’ed together.
COAP_RESOURCE_FLAGS_NOTIFY_NON | Set the notification message type to non-confirmable for any trigggered "observe" responses with type set to confirmable every 5 packets as required by RFC7641 section-4.5.
COAP_RESOURCE_FLAGS_NOTIFY_NON_ALWAYS | Set the notification message type to always non-confirmable for any trigggered "observe" responses. This should only be used if a upper layer protocol requires it.
COAP_RESOURCE_FLAGS_NOTIFY_CON | Set the notification message type to confirmable for any trigggered "observe" responses.
COAP_RESOURCE_FLAGS_RELEASE_URI | Free off the coap_str_const_t for uri_path when the resource is deleted.

NOTE: uri_path, if not 7 bit readable ASCII, binary bytes must be hex encoded according to the rules defined in RFC3968 Section 2.1.

The coap_resource_unknown_init() function returns a newly created resource of type coap_resource_t *. put_handler is automatically added to the resource to handle PUT requests to resources that are unknown. Additional handlers can be added to this resource if required.

The coap_resource_proxy_uri_init() function returns a newly created resource of type coap_resource_t *. proxy_handler is automatically added to the resource to handle PUT/POST/GET etc. requests that use the Proxy-Uri: option. There is no need to add explicit request type handlers. One or more names by which the proxy is known by (IP address, DNS name etc.) must be supplied in the array defined by host_name_list[] which has a count of host_name_count. This is used to check whether the current endpoint is the proxy target address.

The coap_add_resource() function registers the given resource with the context. The resource must have been created by coap_resource_init(), coap_resource_unknown_init() or coap_resource_proxy_uri_init(). The storage allocated for the resource will be released by coap_delete_resource().

As the uri_path of the resource has to be unique across all of the resources associated with a context, coap_add_resource() (or coap_add_resource_release()) will delete any previous resource with the same uri_path before adding in the new resource.

The coap_delete_resource() function deletes a resource identified by resource from context. The storage allocated for that resource is freed, along with any attrigutes associated with the resource.

The coap_resource_set_mode() changes the notification message type of resource to the given mode which must be one of COAP_RESOURCE_FLAGS_NOTIFY_NON, COAP_RESOURCE_FLAGS_NOTIFY_NON_ALWAYS or COAP_RESOURCE_FLAGS_NOTIFY_CON.

The coap_resource_set_userdata() function allows a pointer to user data to be associated with a resource that can accessed in any callback that includes resource as a parameter.

NOTE: data must point to a static, or allocated, block of memory.

The coap_resource_get_userdata() function obtains the user data pointer from the resource that had previously been set up by coap_resource_set_userdata().

The coap_resource_release_userdata_handler() function defines the context wide callback handler to call to release the allocated user data that has been added to the resource using coap_resource_set_userdata() when the resource is deleted. callback can be NULL (which is the default) if nothing needs to be freed off.

The coap_resource_get_uri_path() function is used to obtain the UriPath of the resource definion.

RETURN VALUES

The coap_resource_init(), coap_resource_unknown_init() and coap_resource_proxy_uri_init() functions return a newly created resource or NULL if there is a malloc failure.

The coap_delete_resource() function return 0 on failure (resource not found), 1 on success.

The coap_resource_get_userdata() function returns the value previously set by the coap_resource_set_userdata() function or NULL.

The coap_resource_get_uri_path() function returns the uri_path or NULL if there was a failure.

EXAMPLES

Fixed Resources Set Up

    #include <coap3/coap.h>

    #define INDEX "This is an example server using libcoap\n"

    static void
    hnd_get_index(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      unsigned char buf[3];
      /* Remove (void) definition if variable is used */
      (void)resource;
      (void)session;
      (void)request;
      (void)query;

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTENT);

      coap_add_option(response,
                      COAP_OPTION_CONTENT_TYPE,
                      coap_encode_var_safe(buf, sizeof(buf),
                                           COAP_MEDIATYPE_TEXT_PLAIN),
                      buf);

      coap_add_option(response,
                      COAP_OPTION_MAXAGE,
                      coap_encode_var_safe(buf, sizeof(buf), 0x2ffff), buf);

      coap_add_data(response, strlen(INDEX), (const uint8_t *)INDEX);

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTENT);
    }

    static void
    hnd_delete_time(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      /* Remove (void) definition if variable is used */
      (void)resource;
      (void)session;
      (void)request;
      (void)query;

      /* .. code .. */

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_DELETED);
    }

    static void
    hnd_get_time(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      /* Remove (void) definition if variable is used */
      (void)resource;
      (void)session;
      (void)request;
      (void)query;
      (void)response;

      /* .. code .. */

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTENT);
    }

    static void
    hnd_put_time(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      /* Remove (void) definition if variable is used */
      (void)resource;
      (void)session;
      (void)request;
      (void)query;
      (void)response;

      /* .. code .. */

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_CHANGED);
    }

    static void
    init_resources(coap_context_t *ctx) {

      coap_resource_t *r;

      /* Create a resource to return general information */
      r = coap_resource_init(NULL, 0);
      coap_register_handler(r, COAP_REQUEST_GET, hnd_get_index);

      /* Document resource for '.well-known/core' request */
      coap_add_attr(r, coap_make_str_const("ct"), coap_make_str_const("0"), 0);
      coap_add_attr(r, coap_make_str_const("title"),
                    coap_make_str_const("\"General Info\""), 0);

      coap_add_resource(ctx, r);

      /* Create a resource to return return or update time */
      r = coap_resource_init(coap_make_str_const("time"),
                             COAP_RESOURCE_FLAGS_NOTIFY_CON);
      coap_resource_set_get_observable(r, 1);
      coap_register_handler(r, COAP_REQUEST_GET, hnd_get_time);
      coap_register_handler(r, COAP_REQUEST_PUT, hnd_put_time);
      coap_register_handler(r, COAP_REQUEST_DELETE, hnd_delete_time);

      /* Document resource for 'time' request */
      coap_add_attr(r, coap_make_str_const("ct"), coap_make_str_const("0"), 0);
      coap_add_attr(r, coap_make_str_const("title"),
                    coap_make_str_const("\"Internal Clock\""), 0);
      coap_add_attr(r, coap_make_str_const("rt"), coap_make_str_const("\"secs\""),
                    0);
      coap_add_attr(r, coap_make_str_const("if"), coap_make_str_const("\"clock\""),
                    0);

      coap_add_resource(ctx, r);

    }

Dynamic Resources Set Up

    #include <coap3/coap.h>

    /* Regular DELETE handler - used by resources created by the
     * Unknown Resource PUT handler */

    static void
    hnd_delete(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      /* Remove (void) definition if variable is used */
      (void)session;
      (void)request;
      (void)query;
      (void)response;

      /* .. code .. */

      /* Dynamic resource no longer required - delete it */
      coap_delete_resource(coap_session_get_context(session), resource);

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_DELETED);
    }

    /* Regular GET handler - used by resources created by the
     * Unknown Resource PUT handler */

    static void
    hnd_get(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {

      coap_str_const_t *get_uri_path;
      /* Remove (void) definition if variable is used */
      (void)resource;
      (void)session;
      (void)request;
      (void)query;
      (void)response;

      /*
       * request will be NULL if an Observe triggered request, so the uri_path,
       * if needed, must be abstracted from the resource.
       * The uri_path string is a const pointer
       */

      get_uri_path = coap_resource_get_uri_path(resource);

      /* .. code .. */

      coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTENT);
    }

    /* Regular PUT handler - used by resources created by the
     * Unknown Resource PUT handler */

    static void
    hnd_put(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      /* Remove (void) definition if variable is used */
      (void)resource;
      (void)session;
      (void)query;

      coap_string_t *put_uri_path;
      size_t length;
      const uint8_t *data;
      size_t offset;
      size_t total;
      int new_resource = 0;

      /* get the uri_path */
      put_uri_path = coap_get_uri_path(request);
      if (!put_uri_path) {
        coap_pdu_set_code(response, COAP_RESPONSE_CODE_NOT_FOUND);
        return;
      }
      coap_get_data_large(request, &length, &data, &offset, &total);

      /* .. code .. */

      /* Need to do this as coap_get_uri_path() created it */
      coap_delete_string(put_uri_path);

      if (length + offset < total)
        coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTINUE);
      else if (new_resource)
        coap_pdu_set_code(response, COAP_RESPONSE_CODE_CREATED);
      else
        coap_pdu_set_code(response, COAP_RESPONSE_CODE_CHANGED);
    }

    static int
    check_url_fn(coap_string_t *uri_path, uint8_t code) {
      /* Remove (void) definition if variable is used */
      (void)uri_path;
      (void)code;

      /* Code to determine whether the uri is valid or not */

      return 1;
    }

    /* Unknown Resource PUT handler */

    static void
    hnd_unknown_put(coap_resource_t *resource, coap_session_t *session,
    const coap_pdu_t *request, const coap_string_t *query, coap_pdu_t *response) {
      /* Remove (void) definition if variable is used */
      (void)resource;
      coap_pdu_code_t req_code = coap_pdu_get_code(request);

      coap_resource_t *r;
      coap_string_t *uri_path;

      /* get the uri_path - which will get used by coap_resource_init() */
      uri_path = coap_get_uri_path(request);
      if (!uri_path) {
        coap_pdu_set_code(response, COAP_RESPONSE_CODE_NOT_FOUND);
        return;
      }

      /* Check if new URI Path is valid */
      if (!check_url_fn (uri_path, req_code)) {
        coap_pdu_set_code(response, COAP_RESPONSE_CODE_NOT_FOUND);
        coap_delete_string(uri_path);
        return;
      }

      /*
       * Create a resource to handle the new URI
       * uri_path will get deleted when the resource is removed
       */
      r = coap_resource_init((coap_str_const_t*)uri_path,
            COAP_RESOURCE_FLAGS_RELEASE_URI | COAP_RESOURCE_FLAGS_NOTIFY_NON);
      coap_register_handler(r, COAP_REQUEST_PUT, hnd_put);
      coap_register_handler(r, COAP_REQUEST_DELETE, hnd_delete);
      /* We possibly want to Observe the GETs */
      coap_resource_set_get_observable(r, 1);
      coap_register_handler(r, COAP_REQUEST_GET, hnd_get);
      coap_add_resource(coap_session_get_context(session), r);

      /* Do the PUT for this first call */
      hnd_put(r, session, request, query, response);

      return;

    }

    /* Initialize single Unknown Resource PUT handler */

    static void
    init_resources(coap_context_t *ctx) {

      coap_resource_t *r;

      /* Create a resource to handle PUTs to unknown URIs */
      r = coap_resource_unknown_init(hnd_unknown_put);
      /*
       * Additional handlers can be added - for example
       *  coap_register_handler(r, COAP_REQUEST_POST, hnd_post_unknown);
       *  coap_register_handler(r, COAP_REQUEST_GET, hnd_get_unknown);
       *  coap_register_handler(r, COAP_REQUEST_DELETE, hnd_delete_unknown);
       */
      coap_add_resource(ctx, r);

    }

SEE ALSO

coap_attribute(3), coap_context(3), coap_observe(3) and coap_handler(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>