Provided by: libcoap3t64_4.3.4-1.1build4_amd64 bug

NAME

       coap_block, coap_context_set_block_mode, coap_add_data_large_request,
       coap_add_data_large_response, coap_get_data_large, coap_block_build_body,
       coap_q_block_is_supported - Work with CoAP Blocks

SYNOPSIS

       #include <coap3/coap.h>

       void coap_context_set_block_mode(coap_context_t *context, uint8_t block_mode);

       int coap_add_data_large_request(coap_session_t *session, coap_pdu_t *pdu, size_t length,
       const uint8_t *data, coap_release_large_data_t release_func, void *app_ptr);

       int coap_add_data_large_response(coap_resource_t *resource, coap_session_t *session, const
       coap_pdu_t *request, coap_pdu_t *response, const coap_string_t *query, uint16_t
       media_type, int maxage, uint64_t etag, size_t length, const uint8_t *data,
       coap_release_large_data_t release_func, void *app_ptr);

       int coap_get_data_large(const coap_pdu_t *pdu, size_t *length, const uint8_t **_data,
       size_t *offset, size_t *total);

       coap_binary_t *coap_block_build_body(coap_binary_t *body_data, size_t length, const
       uint8_t *data, size_t offset, size_t total);

       int coap_q_block_is_supported(void);

       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

       Regular setting up of a PDU and transmission is covered in coap_pdu_setup(3) where all the
       payload data can fit in a single packet. This man page covers how to work with PDUs where
       the overall body of information may need to be split across several packets by using CoAP
       Block-Wise Transfers (RFC7959 and RFC9177).

       The block-wise transfers can be controlled by the application, or libcoap is instructed to
       do all the requests for the next blocks and only present the final body of the result to
       the application. In summary, the following three ways handle processing a body of data
       that has to be split across multiple payloads (blocks).

        1. Application does all the work

           It is the responsibility of the application to analyze each block transmission at
           receipt and then generate the next request as per RFC7959. In this case,
           coap_context_set_block_mode() function must not be called to maintain backward
           compatibility with applications that did the block handling within the application.

        2. Application sees individual blocks

           By calling coap_context_set_block_mode(context, COAP_BLOCK_USE_LIBCOAP) and using the
           appropriate functions, the requests for the next block of data is handled
           automatically by the libcoap layer. Each individual block of data is presented to the
           application for processing.

           By calling coap_get_data_large(), the application can determine if this is the first
           block or not (using offset value), whether the first block is all the data (offset =
           0, length = total) and whether this is the last block (offset + length = total). It is
           the responsibility of the application to re-assemble the individual blocks into a
           single body of data.

           NOTE: total is only an approximation (it will be > offset + length) until the final
           block is received.

           If this is the request handler in a server, the server still needs to return a
           COAP_RESPONSE_CODE_CONTINUE 2.31 (Continue) response code if the received data is not
           for the final block, otherwise a COAP_RESPONSE_CODE_CREATED 2.01 (Created) or
           COAP_RESPONSE_CODE_CHANGED 2.04 (Changed) should be returned.

        3. Application only sees all of the body

           By calling coap_context_set_block_mode(context,
           COAP_BLOCK_USE_LIBCOAP|COAP_BLOCK_SINGLE_BODY) and using the appropriate functions,
           the requests for all the blocks of data is handled automatically by the libcoap layer.
           Only the complete body of the data is presented to the application, unless there is an
           error.

           coap_get_data_large() will only return the entire body of data (offset always 0,
           length = total) and there is no need to re-assemble individual blocks into a large
           body of data.

           In RAM constrained environments, option 2 may be the preferred method.

       This man page focuses on getting libcoap to do all the work, not how to do it all in the
       application.

       However, if the client supplies a Block1 or Block2 Option in the PDU where the block
       number is not 0, this is assumed to be a random access request and any other blocks will
       not be requested by libcoap even if instructed otherwise.

       The functions that are named _large are intended as replacements for the equivalent
       functions as described in coap_pdu_setup(3).

CALLBACK HANDLER

       Callback Type: coap_release_large_data_t

           /**
            * Callback handler for de-allocating the data based on @p app_ptr provided to
            * coap_add_data_large_*() functions following transmission of the supplied
            * data.
            *
            * @param session The session that this data is associated with
            * @param app_ptr The application provided pointer to the
            *                coap_add_data_large_*() functions
            */
           typedef void (*coap_release_large_data_t)(coap_session_t *session,
                                                     void *app_ptr);

FUNCTIONS

       Function: coap_context_set_block_mode()

       The coap_context_set_block_mode() function is used to set up the context level block_mode
       block handling bits for supporting RFC7959 block_mode flows down to a session when a
       session is created and if the peer does not support the respective block mode, an
       appropriate bit may get disabled in the session block_mode.

           #define COAP_BLOCK_USE_LIBCOAP   0x01 /* Use libcoap to do block requests */
           #define COAP_BLOCK_SINGLE_BODY   0x02 /* Deliver the data as a single body */
           #define COAP_BLOCK_TRY_Q_BLOCK   0x04 /* Try Q-Block method */
           #define COAP_BLOCK_USE_M_Q_BLOCK 0x08 /* Use M bit when recovering Q-Block2 */
           #define COAP_BLOCK_NO_PREEMPTIVE_RTAG 0x10 /* Don't use pre-emptive Request-Tags */

       block_mode is an or’d set of zero or more COAP_BLOCK_* definitions.

       If COAP_BLOCK_USE_LIBCOAP is not set, then everything works as per Option 1 above.

       If COAP_BLOCK_SINGLE_BODY is set, then the entire body of data is presented to the
       receiving handler, otherwise each individual block is presented on arrival. To obtain the
       data, length and current offset, coap_get_data_large() must be used instead of
       coap_get_data(). It may be appropriate not to set COAP_BLOCK_SINGLE_BODY if there are RAM
       limitations.

       NOTE: It is the responsibility of the receiving application to re-assemble the data as
       appropriate (e.g., using coap_block_build_body()) if COAP_BLOCK_SINGLE_BODY is not set.

       NOTE: If COAP_BLOCK_SINGLE_BODY is not set, then the CoAP server on receiving request data
       that is split over multiple data blocks must respond with COAP_RESPONSE_CODE_CONTINUE 2.31
       (Continue) response code if the received data is not for the final block, otherwise a
       COAP_RESPONSE_CODE_CREATED 2.01 (Created) or COAP_RESPONSE_CODE_CHANGED 2.04 (Changed)
       should be returned.

       To indicate support for Q-Block-1 and Q-Block2, COAP_BLOCK_TRY_Q_BLOCK needs to be set on
       both the client and server. COAP_BLOCK_SINGLE_BODY is assumed to be set if using Q-Block
       as the data will always be presented as a single body. If COAP_BLOCK_USE_M_Q_BLOCK is
       defined, then the M bit version of recovery will be used if possible.

       If COAP_BLOCK_USE_LIBCOAP is set, then any PDUs presented to the application handlers will
       get the tokens set back to the initiating token so that requests can be matched with
       responses even if different tokens had to be used for the series of packet interchanges.
       Furthermore, if COAP_BLOCK_SINGLE_BODY is set, then the PDU that presents the entire body
       will have any BlockX or Q-BlockX option removed.

       NOTE: COAP_BLOCK_USE_LIBCOAP must be set if libcoap is to do all the block tracking and
       requesting, otherwise the application will have to do all of this work (the default if
       coap_context_set_block_mode() is not called).

       If COAP_BLOCK_NO_PREEMPTIVE_RTAG is set, then Request-Tag options are only sent when a
       large amount of data is being sent to the server using the Block1 option. Otherwise, a
       Request-Tag option is sent with any request (apart from DELETE) on the off chance that
       there may be multiple Block2 based responses for multiple requests to the same resource
       that need to be differentiated between.

       Function: coap_add_data_large_request()

       The coap_add_data_large_request() function is similar to coap_add_data(), but supports the
       transmission of data that has a body size that is potentially larger than can be fitted
       into a single client request PDU. The specified payload data of length length is
       associated with the session with the first block of data added to the PDU pdu along with
       the appropriate CoAP options such as (Q-)Block1, Size1 and Request-Tag if the data does
       not fit in a single PDU.

       When the block receipt has been acknowledged by the peer, the library will then send the
       next block of data until all the data has been transmitted.

       The data passed to the function coap_add_data_large_request() must exist until all blocks
       have been transmitted. The callback function release_func can be used to release storage
       that has been dynamically allocated to hold the transmit data. If not NULL, the callback
       function is called once the final block of data has been transmitted. The user-defined
       parameter app_ptr is the same value that was passed to coap_add_data_large_request().

       NOTE: This function must only be called once per pdu.

       NOTE: Options cannot be added to the pdu after coap_add_data_large_request() is called.

       Function: coap_add_data_large_response()

       The coap_add_data_large_response() function is responsible for handling the server’s large
       responses to requests. coap_add_data_large_response() should be used as a direct
       replacement for coap_add_data() if it is possible that the length of data will not fit in
       a single server’s response pdu. This function adds in the initial part of the payload data
       of length length to the PDU pdu.

       The data passed to the function coap_add_data_large_response() must exist until all blocks
       have been transmitted. The callback function release_func can be used to release storage
       that has been dynamically allocated to hold the transmit data. If not NULL, the callback
       function is called once the final block of data has been transmitted. The user-defined
       parameter app_ptr is the same value that was passed to coap_add_data_large_response().

       It also adds in the appropriate CoAP options such as Block2, Size2 and ETag to handle
       block-wise transfer if the data does not fit in a single PDU.

       resource, query, session, request, and response are the same parameters as in the called
       resource handler that invokes coap_add_data_large_response(). If etag is 0, then a unique
       ETag value will be generated, else is the ETag value to use. The media_type is for the
       format of the data and maxage defines the lifetime of the response. If maxage is set to
       -1, then the Max-Age option does not get included (which indicates the default value of 60
       seconds according to "RFC7252 5.6.1. Freshness Model").

       The application request handler for the resource is only called once instead of
       potentially multiple times.

       NOTE: This function must only be called once per pdu.

       NOTE: Options cannot be added to the pdu after coap_add_data_large_request() is called.

       Function: coap_get_data_large()

       The coap_get_data_large() function is used abstract from the pdu information about the
       received data by updating length with the length of data available, data with a pointer to
       where the data is located, offset with where this block of data starts and total with the
       total amount of data. offset will always be zero if block_mode includes
       COAP_BLOCK_SINGLE_BODY. All of the body’s data has been received if "offset + length ==
       total".

       NOTE: total is potentially only an indication of the total size of the body and is only
       exact when all of the data has been received.

       Function: coap_block_build_body()

       The coap_block_build_body() function is used to re-assemble the received data as returned
       by coap_get_data_large() into a single blob of data. Data from data of length length
       starting from offset offset is added to body_data. The resultant state of body_data is
       returned. If body_data is NULL, or total is larger than the current size of body_data,
       then body_data is re-allocated and returned. If there is an error, body_data gets
       de-allocated.

       If block_mode (as set by coap_context_set_block_mode()) includes COAP_BLOCK_SINGLE_BODY,
       then the request/response handler will only get called once with the entire body
       containing the data from all of the individual blocks. If there is a change of data during
       the blocks receipt (e.g., ETag value changes), then the entire set of data is re-requested
       and the partial body dropped.

       Function: coap_q_block_is_supported()

       The coap_q_block_is_supported() function is used to determine whether libcoap has been
       build with Q-Block support or not.

RETURN VALUES

       coap_add_data_large_request(), coap_add_data_large_response(), and coap_get_data_large()
       return 0 on failure, 1 on success.

       coap_block_build_body() returns the current state of the body’s data (which may have some
       missing gaps) or NULL on error.

       coap_q_block_is_supported() returns 0 on failure, 1 on success.

EXAMPLES

       Setup PDU and Transmit

           #include <coap3/coap.h>

           static int
           build_send_pdu(coap_context_t *context, coap_session_t *session,
           uint8_t msgtype, uint8_t request_code, const char *uri, const char *query,
           unsigned char *data, size_t length, int observe) {

             coap_pdu_t *pdu;
             uint8_t buf[1024];
             size_t buflen;
             uint8_t *sbuf = buf;
             int res;
             coap_optlist_t *optlist_chain = NULL;
             /* Remove (void) definition if variable is used */
             (void)context;

             /* Create the pdu with the appropriate options */
             pdu = coap_pdu_init(msgtype, request_code, coap_new_message_id(session),
                                 coap_session_max_pdu_size(session));
             if (!pdu)
               return 0;

             /*
              * Create unique token for this request for handling unsolicited /
              * delayed responses
              */
             coap_session_new_token(session, &buflen, buf);
             if (!coap_add_token(pdu, buflen, buf)) {
               coap_log_debug("cannot add token to request\n");
               goto error;
             }

             if (uri) {
               /* Add in the URI options */
               buflen = sizeof(buf);
               res = coap_split_path((const uint8_t*)uri, strlen(uri), sbuf, &buflen);
               while (res--) {
                 if (!coap_insert_optlist(&optlist_chain,
                                          coap_new_optlist(COAP_OPTION_URI_PATH,
                                   coap_opt_length(sbuf), coap_opt_value(sbuf))))
                   goto error;
                 sbuf += coap_opt_size(sbuf);
               }
             }

             if (query) {
               /* Add in the QUERY options */
               buflen = sizeof(buf);
               res = coap_split_query((const uint8_t*)query, strlen(query), sbuf, &buflen);
               while (res--) {
                 if (!coap_insert_optlist(&optlist_chain,
                                          coap_new_optlist(COAP_OPTION_URI_QUERY,
                                   coap_opt_length(sbuf), coap_opt_value(sbuf))))
                   goto error;
                 sbuf += coap_opt_size(sbuf);
               }
             }

             if (request_code == COAP_REQUEST_GET && observe) {
               /* Indicate that we want to observe this resource */
               if (!coap_insert_optlist(&optlist_chain,
                                        coap_new_optlist(COAP_OPTION_OBSERVE,
                                          coap_encode_var_safe(buf, sizeof(buf),
                                          COAP_OBSERVE_ESTABLISH), buf)
                                        ))
                 goto error;
             }

             /* ... Other code / options etc. ... */

             /* Add in all the options (after internal sorting) to the pdu */
             if (!coap_add_optlist_pdu(pdu, &optlist_chain))
               goto error;

             if (data && length) {
               /* Add in the specified data */
               if (!coap_add_data_large_request(session, pdu, length, data, NULL, NULL))
                 goto error;
             }

             if (coap_send(session, pdu) == COAP_INVALID_MID)
               goto error;
             return 1;

           error:

             if (pdu)
               coap_delete_pdu(pdu);
             return 0;

           }

           int
           main(int argc, char *argv[]) {
             coap_context_t *context = NULL;
             coap_session_t *session = NULL;
             unsigned char *data = NULL;
             size_t data_length = 0;

             (void)argc;
             (void)argv;

             /* Initialize libcoap library */
             coap_startup();

             /* ... Set up context, session etc. ... */

             /* Set up using libcoap to do the block work */
             coap_context_set_block_mode(context,
                                         COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);

             /* ... Other code etc. ... */

             /* .. build data and define data_length ... */

             build_send_pdu(context, session, COAP_MESSAGE_CON, COAP_REQUEST_PUT,
                            "/example/uri", NULL, data, data_length, 0);

             /* ... Other code etc. ... */

             coap_cleanup();
             return 0;
           }

       Resource Request Handler Response PDU Update

           #include <coap3/coap.h>

           #include <stdio.h>

           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) {

             unsigned char buf[40];
             size_t len;
             time_t now;

             /* ... Additional analysis code for resource, request pdu etc.  ... */

             /* After analysis, generate a failure response and return if needed */

             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.
              * [A good practice, even though ins this case, the amount of data is small]
              *
              * 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
              * Size2 Option added internally
              * ETag Option added internally
              */
             coap_add_data_large_response(resource, session, request, response,
                                          query, COAP_MEDIATYPE_TEXT_PLAIN, 1, 0,
                                          len,
                                          buf,
                                          NULL, NULL);
             /*
              * When request handler returns, the response pdu will get automatically
              * sent, unless the pdu code is not updated and this is a NON or TCP based
              * request.
              */
           }

           int
           main(int argc, char *argv[]) {
             coap_context_t *context = NULL;
             coap_resource_t *r;
             coap_resource_t *time_resource;
             int not_exit = 1;

             /* Initialize libcoap library */
             coap_startup();

             (void)argc;
             (void)argv;

             /* ... Set up context etc. ... */

             /* Set up using libcoap to do the block work */
             coap_context_set_block_mode(context,
                                         COAP_BLOCK_USE_LIBCOAP | COAP_BLOCK_SINGLE_BODY);

             /* Create a resource to return 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);

             /* 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(context, r);
             time_resource = r;

             /* ... Loop waiting for incoming traffic ... */
             while (!not_exit) {
               coap_io_process(context, 1000);

               /* Cause a notification to anyone Observing 'time' */
               coap_resource_notify_observers(time_resource, NULL);
             }

             /* Clean up */

             coap_free_context(context);
             coap_cleanup();

           }

SEE ALSO

       coap_init(3) coap_pdu_setup(3), coap_observe(3), and coap_resource(3)

FURTHER INFORMATION

       See

       "RFC7252: The Constrained Application Protocol (CoAP)"

       "RFC7959: Block-Wise Transfers in 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>