DESCRIPTION

CoAP Resources on a CoAP Server need to be created, updated and deleted as appropriate. The URI in the request packet defines the resource to work with, with possibly the Query or data in the request 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. See coap_register_request_handler(3) for further information.

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. See coap_add_attr(3) for further information.

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 should then update a suitable response packet for returning back to the requester.

There is support for handling incoming packets where the URI is unknown (no specific resource has been created). 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 (RFC7641) 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.

There is support for handling incoming proxy based requests using the Proxy-Uri or Proxy-Scheme options.

FUNCTIONS

Function: coap_resource_init()

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. Normally there is no need for the leading / - e.g. just "full/path/for/resource". flags can be zero or more of the following definitions or’ed together.

NOTE: The following flags are only tested against if coap_mcast_per_resource() has been called. If coap_mcast_per_resource() has not been called, then all resources have multicast support, libcoap adds in random delays to the responses, and 4.xx / 5.xx responses are dropped.

NOTE: The pseudo resource for ".well-known/core" always has multicast support enabled and is not configurable. It is possible for a server to create a resource for ".well-known/core" that can then control the multicast support and the provided GET request handler can call coap_print_wellknown() to produce the same information as the pseudo resource.

NOTE: uri_path, if not 7 bit readable ASCII, binary bytes must be hex encoded according to the rules defined in "RFC3986 2.1. Percent-Encoding".

Function: coap_resource_unknown_init()

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.

Function: coap_resource_unknown_init2()

The coap_resource_unknown_init2() 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. flags can be zero or more of the COAP_RESOURCE_FLAGS MCAST definitions.

NOTE: There can only be one reverse-proxy or unknown resource handler per context - attaching a new one overrides the previous definition.

Function: coap_resource_proxy_uri_init()

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, or the request has to be passed on to an upstream server.

Function: coap_resource_proxy_uri_init2()

The coap_resource_proxy_uri_init2() 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, or the request has to be passed on to an upstream server. flags can be zero or more COAP_RESOURCE_FLAGS MCAST definitions.

NOTE: There can only be one proxy resource handler per context - attaching a new one overrides the previous definition.

Function: coap_resource_reverse_proxy_init()

The coap_resource_reverse_proxy_init() function returns a newly created resource of type coap_resource_t *. rev_proxy_handler is automatically added to the resource to handle all the PUT/POST/GET etc. requests including .well-known/core. There is no need to add explicit request type handlers. flags can be zero or more COAP_RESOURCE_FLAGS MCAST definitions.

NOTE: There can only be one reverse-proxy or unknown resource handler per context - attaching a new one overrides the previous definition.

Function: coap_add_resource()

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(), coap_resource_unknown_init2(), coap_resource_proxy_uri_init() or coap_resource_proxy_uri_init2(). 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() will delete any previous resource with the same uri_path before adding in the new resource.

Function: coap_delete_resource()

The coap_delete_resource() function deletes the resource identified by resource. The context parameter is ignored. The storage allocated for that resource is freed, along with any attributes associated with the resource.

Function: coap_resource_set_mode()

The coap_resource_set_mode() changes the unsolicited 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.

Function: coap_resource_set_userdata()

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.

Function: coap_resource_get_userdata()

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().

Function: coap_resource_release_userdata_handler()

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.

Function: coap_resource_get_uri_path()

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

Function: coap_get_resource_from_uri_path()

The coap_get_resource_from_uri_path() function is used to return the resource identified by the unique string uri_path associated with context.

Function: coap_print_wellknown()

The coap_print_wellknown() function prints the names of all known resources of the given context into buf which has a maximum size of buflen. The first offset bytes are skipped from the output to handle block transfers. Setting offset to 0 means the entire (matching) information is output. Setting offset to UINT_MAX skips, but calculates the size of, the (matching) output. The query_filter is usually defined by the CoAP Uri-Query options as a query.

RETURN VALUES

coap_resource_init(), coap_resource_unknown_init(), coap_resource_unknown_init2(), coap_resource_proxy_uri_init(), coap_resource_proxy_uri_init2() and coap_resource_reverse_proxy_init() return a newly created resource or NULL if there is a malloc failure.

coap_delete_resource() returns 0 on failure (resource not found), 1 on success.

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

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

coap_get_resource_from_uri_path() returns the resource or NULL if not found.

coap_print_wellknown() returns COAP_PRINT_STATUS_ERROR on error. Otherwise, the lower 28 bits are set to the number of bytes that have actually been written. COAP_PRINT_STATUS_TRUNC is set when the output has been truncated.

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_request_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_request_handler(r, COAP_REQUEST_GET, hnd_get_time);
  coap_register_request_handler(r, COAP_REQUEST_PUT, hnd_put_time);
  coap_register_request_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(NULL, 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;

  /*
   * Get the specific resource being requested to determine what the response is
   * 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_put_unknown(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_request_handler(r, COAP_REQUEST_PUT, hnd_put);
  coap_register_request_handler(r, COAP_REQUEST_DELETE, hnd_delete);
  /* We possibly want to Observe the GETs */
  coap_resource_set_get_observable(r, 1);
  coap_register_request_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_init2(hnd_put_unknown, 0);
  /*
   * Additional handlers can be added - for example
   *  coap_register_request_handler(r, COAP_REQUEST_POST, hnd_post_unknown);
   *  coap_register_request_handler(r, COAP_REQUEST_GET, hnd_get_unknown);
   *  coap_register_request_handler(r, COAP_REQUEST_DELETE, hnd_delete_unknown);
   */
  coap_add_resource(ctx, r);

}

SEE ALSO

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

FURTHER INFORMATION

See

"RFC7252: The Constrained Application Protocol (CoAP)"

"RFC3986: Uniform Resource Identifier (URI): Generic Syntax"

for further information.

BUGS

Please raise an issue on GitHub at https://github.com/obgm/libcoap/issues to report any bugs.

Please raise a Pull Request at https://github.com/obgm/libcoap/pulls for any fixes.

AUTHORS

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