coap_resource man page

coap_resource, coap_resource_init, coap_resource_unknown_init, coap_add_resource, coap_delete_resource, coap_delete_all_resources, coap_resource_set_mode — Work with CoAP resources

Synopsis

#include <coap2/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);

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_delete_all_resources(coap_context_t *context);

void coap_resource_set_mode(coap_resource_t *resource, int mode);

Link with -lcoap-2, -lcoap-2-gnutls, -lcoap-2-openssl or -lcoap-2-tinydtls depending on your (D)TLS library type.

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_NONSet the notification message type to non-confirmable for any trigggered "observe" responses.
COAP_RESOURCE_FLAGS_NOTIFY_CONSet the notification message type to confirmable for any trigggered "observe" responses.
COAP_RESOURCE_FLAGS_RELEASE_URIFree 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() 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_add_resource() function registers the given resource with the context. The resource must have been created by coap_resource_init(), or coap_resource_unknown_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_delete_all_resources() function deletes all resources from context and frees their storage.

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 or COAP_RESOURCE_FLAGS_NOTIFY_CON.

Return Values

The coap_resource_init() and coap_resource_unknown_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.

Examples

Fixed Resources Set Up

#include <coap2/coap.h>

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

void
hnd_get_index(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {
  unsigned char buf[3];

  response->code = COAP_RESPONSE_CODE(205);

  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);

}

void
hnd_delete_time(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  /* .. code .. */

}

void
hnd_get_time(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  /* .. code .. */

}

void
hnd_put_time(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  /* .. code .. */

}

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 .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("\"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 <coap2/coap.h>

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

void
hnd_delete(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  /* .. code .. */

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

}

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

void
hnd_get(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  coap_str_const_t *get_uri_path;
  coap_string_t *get_query;
  coap_opt_iterator_t opt_iter;
  coap_opt_filter_t filter;
  coap_opt_t *option;
  int len;

  /*
   * 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);
  get_query = query;

  /* .. code .. */

}

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

void
hnd_put(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  coap_string_t *put_uri_path;

  /* get the uri_path */
  put_uri_path = coap_get_uri_path(request);
  if (!put_uri_path) {
    response->code = COAP_RESPONSE_CODE(404);
    return;
  }

  /* .. code .. */

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

}

/* Unknown Resource PUT handler */

void
hnd_unknown_put(coap_context_t *ctx, coap_resource_t *resource,
coap_session_t *session, coap_pdu_t *request, coap_string_t *token,
coap_string_t *query, coap_pdu_t *response) {

  coap_resource_t *r;
  int len;
  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) {
    response->code = COAP_RESPONSE_CODE(404);
    return;
  }

  /* Check if new URI Path is valid */
  if (!check_url_fn (uri_path, request->code)) {
    response->code = COAP_RESPONSE_CODE(404);
    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(ctx, r);

  /* Do the PUT for this first call */
  hnd_put(ctx, r, session, request, token, 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

Authors

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

Referenced By

coap(7), coap_attribute(3), coap_context(3), coap_encryption(3), coap_handler(3), coap_observe(3), coap_pdu_setup(3), coap_session(3).

The man pages coap_add_resource(3), coap_delete_all_resources(3), coap_delete_resource(3), coap_resource_init(3), coap_resource_set_mode(3) and coap_resource_unknown_init(3) are aliases of coap_resource(3).

07/25/2019 coap_resource 4.2.0 libcoap Manual