NAME

       coap_attribute, coap_add_attr, coap_find_attr, coap_attr_get_value - Work with CoAP
       attributes

SYNOPSIS

       #include <coap3/coap.h>

       coap_attr_t *coap_add_attr(coap_resource_t *resource, coap_str_const_t *name,
       coap_str_const_t *value, int flags);

       coap_attr_t *coap_find_attr(coap_resource_t *resource, coap_str_const_t *name);

       coap_str_const_t *coap_attr_get_value(coap_attr_t *attribute);

       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, 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 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 Resource Discovery using a "GET /.well-known/core"
       request with an optional query. See https://tools.ietf.org/html/rfc6690#section-5 for some
       examples of resource discovery usage. Common attribute names are rt, if, sz, ct, obs, rel,
       anchor, rev, hreflang, media, title and type. href cannot be an attribute name.

       Attributes are automatically deleted when a Resource is deleted.

       The coap_add_attr() function registers a new attribute called name for the resource. The
       value of the attribute is value which can be NULL.

       flags can be one or more of the following, which, if set, defines what is to be internally
       freed off when the attribute is deleted with coap_delete_resource().

       COAP_ATTR_FLAGS_RELEASE_NAME    Free off name when attribute is
                                       deleted with
                                       coap_delete_resource().

       COAP_ATTR_FLAGS_RELEASE_VALUE   Free off value when attribute is
                                       deleted with
                                       coap_delete_resource().

       The coap_find_attr() function returns the attribute with the name, if found, associated
       with resource.

       The coap_attr_get_value() function returns the value associated with the specified
       attribute.

RETURN VALUES

       coap_add_attr() function returns a pointer to the attribute that was created or NULL if
       there is a malloc failure.

       coap_find_attr() function returns a pointer to the first matching attribute or NULL if the
       name was not found.

       coap_attr_get_value() function returns a pointer to the value held within the attribute.
       The pointer can be NULL if the value id NULL, or NULL if attribute does not exist.

EXAMPLE

       Initialize Resources

           #include <coap3/coap.h>

           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);

           }

SEE ALSO

       coap_resource(3) and coap_handler(3)

FURTHER INFORMATION

       See

       "RFC7252: The Constrained Application Protocol (CoAP)"

       "RFC6690: Constrained RESTful Environments (CoRE) Link Format"

       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>