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COAP_PDU_ACCESS(3) libcoap Manual COAP_PDU_ACCESS(3) NAME coap_pdu_access, coap_check_option, coap_decode_var_bytes, coap_de- code_var_bytes8, coap_get_data, coap_opt_length, coap_opt_value, coap_op- tion_filter_clear, coap_option_filter_get, coap_option_filter_set, coap_op- tion_filter_unset, coap_option_iterator_init, coap_option_next, coap_pdu_get_code, coap_pdu_get_mid, coap_pdu_get_token, coap_pdu_get_type, coap_get_uri_path - Accessing CoAP PDUs SYNOPSIS #include <coap3/coap.h> coap_opt_t *coap_check_option(const coap_pdu_t *pdu, coap_option_num_t num- ber, coap_opt_iterator_t *oi); unsigned int coap_decode_var_bytes(const uint8_t *buf, size_t length); uint64_t coap_decode_var_bytes8(const uint8_t *buf, size_t length); int coap_get_data(const coap_pdu_t *pdu, size_t *length, const uint8_t **_data); uint32_t coap_opt_length(const coap_opt_t *opt); const uint8_t *coap_opt_value(const coap_opt_t *opt); void coap_option_filter_clear(coap_opt_filter_t *filter); int coap_option_filter_get(coap_opt_filter_t *filter, coap_option_num_t number); int coap_option_filter_set(coap_opt_filter_t *filter, coap_option_num_t number); int coap_option_filter_unset(coap_opt_filter_t *filter, coap_option_num_t number); coap_opt_iterator_t *coap_option_iterator_init(const coap_pdu_t *pdu, coap_opt_iterator_t *oi, const coap_opt_filter_t *filter); coap_opt_t *coap_option_next(coap_opt_iterator_t *oi); coap_pdu_code_t coap_pdu_get_code(const coap_pdu_t *pdu); coap_mid_t coap_pdu_get_mid(const coap_pdu_t *pdu); coap_bin_const_t coap_pdu_get_token(const coap_pdu_t *pdu); coap_pdu_type_t coap_pdu_get_type(const coap_pdu_t *pdu); coap_string_t *coap_get_uri_path(const coap_pdu_t *pdu); For specific (D)TLS library support, link with -lcoap-3-notls, -lcoap-3-gnutls, -lcoap-3-openssl, -lcoap-3-mbedtls, -lcoap-3-wolfssl or -lcoap-3-tinydtls. Otherwise, link with -lcoap-3 to get the default (D)TLS library support. DESCRIPTION The CoAP PDU is of the form --header--|--optional token--|--optional options--|--optional payload-- The terminology used is taken mainly from "RFC7252 1.2. Terminology". The following functions provide access to the information held within dif- ferent parts of a PDU. PDU HEADER FUNCTIONS Function: coap_pdu_get_type() The coap_pdu_get_type() function returns one of the messages types below from the PDU pdu header. COAP_MESSAGE_CON Type confirmable. COAP_MESSAGE_NON Type non-confirmable. COAP_MESSAGE_ACK Type acknowledge COAP_MESSAGE_RST Type reset. NOTE: For reliable messages RFC8323, this will always return COAP_MES- SAGE_CON. Function: coap_pdu_get_code() The coap_pdu_get_code() function returns one of the codes below from the PDU pdu header. It is possible that new codes are added in over time. COAP_EMPTY_CODE 0.00 COAP_REQUEST_CODE_GET 0.01 COAP_REQUEST_CODE_POST 0.02 COAP_REQUEST_CODE_PUT 0.03 COAP_REQUEST_CODE_DELETE 0.04 COAP_REQUEST_CODE_FETCH 0.05 COAP_REQUEST_CODE_PATCH 0.06 COAP_REQUEST_CODE_IPATCH 0.07 COAP_RESPONSE_CODE_OK 2.00 COAP_RESPONSE_CODE_CREATED 2.01 COAP_RESPONSE_CODE_DELETED 2.02 COAP_RESPONSE_CODE_VALID 2.03 COAP_RESPONSE_CODE_CHANGED 2.04 COAP_RESPONSE_CODE_CONTENT 2.05 COAP_RESPONSE_CODE_CONTINUE 2.31 COAP_RESPONSE_CODE_BAD_REQUEST 4.00 COAP_RESPONSE_CODE_UNAUTHORIZED 4.01 COAP_RESPONSE_CODE_BAD_OPTION 4.02 COAP_RESPONSE_CODE_FORBIDDEN 4.03 COAP_RESPONSE_CODE_NOT_FOUND 4.04 COAP_RESPONSE_CODE_NOT_ALLOWED 4.05 COAP_RESPONSE_CODE_NOT_ACCEPTABLE 4.06 COAP_RESPONSE_CODE_INCOMPLETE 4.08 COAP_RESPONSE_CODE_CONFLICT 4.09 COAP_RESPONSE_CODE_PRECONDITION_FAILED 4.12 COAP_RESPONSE_CODE_REQUEST_TOO_LARGE 4.13 COAP_RESPONSE_CODE_UNSUPPORTED_CONTENT_FORMAT 4.15 COAP_RESPONSE_CODE_UNPROCESSABLE 4.22 COAP_RESPONSE_CODE_TOO_MANY_REQUESTS 4.29 COAP_RESPONSE_CODE_INTERNAL_ERROR 5.00 COAP_RESPONSE_CODE_NOT_IMPLEMENTED 5.01 COAP_RESPONSE_CODE_BAD_GATEWAY 5.02 COAP_RESPONSE_CODE_SERVICE_UNAVAILABLE 5.03 COAP_RESPONSE_CODE_GATEWAY_TIMEOUT 5.04 COAP_RESPONSE_CODE_PROXYING_NOT_SUPPORTED 5.05 COAP_RESPONSE_CODE_HOP_LIMIT_REACHED 5.08 COAP_SIGNALING_CODE_CSM 7.01 COAP_SIGNALING_CODE_PING 7.02 COAP_SIGNALING_CODE_PONG 7.03 COAP_SIGNALING_CODE_RELEASE 7.04 COAP_SIGNALING_CODE_ABORT 7.05 NOTE: For reliable messages "ttps://rfc-editor.org/rfc/rfc8323[RFC8323], this will always return COAP_EMPTY_CODE. Function: coap_pdu_get_mid() The coap_pdu_get_mid() returns the message id from the PDU pdu header. NOTE: For reliable messages RFC8323, this will always return 0. PDU TOKEN FUNCTIONS Function: coap_pdu_get_token() The coap_pdu_get_token() returns the token information held in the PDU pdu token which may be zero length. PDU OPTIONS FUNCTIONS The following is the current list of options with their numeric value /* * The C, U, and N flags indicate the properties * Critical, Unsafe, and NoCacheKey, respectively. * If U is set, then N has no meaning as per * https://rfc-editor.org/rfc/rfc7252#section-5.10 * and is set to a -. * Separately, R is for the options that can be repeated * * The least significant byte of the option is set as followed * as per https://rfc-editor.org/rfc/rfc7252#section-5.4.6 * * 0 1 2 3 4 5 6 7 * --+---+---+---+---+---+---+---+ * | NoCacheKey| U | C | * --+---+---+---+---+---+---+---+ * * https://rfc-editor.org/rfc/rfc8613#section-4 goes on to define E, I and U * properties Encrypted and Integrity Protected, Integrity Protected Only and * Unprotected respectively. Integrity Protected Only is not currently used. * * An Option is tagged with CUNREIU with any of the letters replaced with _ if * not set, or - for N if U is set (see above) for aiding understanding of the * Option. */ COAP_OPTION_IF_MATCH 1 /* C__RE__, opaque, 0-8 B, RFC7252 */ COAP_OPTION_URI_HOST 3 /* CU-___U, String, 1-255 B, RFC7252 */ COAP_OPTION_ETAG 4 /* ___RE__, opaque, 1-8 B, RFC7252 */ COAP_OPTION_IF_NONE_MATCH 5 /* C___E__, empty, 0 B, RFC7252 */ COAP_OPTION_OBSERVE 6 /* _U-_E_U, empty/uint, 0 B/0-3 B, RFC7641 */ COAP_OPTION_URI_PORT 7 /* CU-___U, uint, 0-2 B, RFC7252 */ COAP_OPTION_LOCATION_PATH 8 /* ___RE__, String, 0-255 B, RFC7252 */ COAP_OPTION_OSCORE 9 /* C_____U, *, 0-255 B, RFC8613 */ COAP_OPTION_URI_PATH 11 /* CU-RE__, String, 0-255 B, RFC7252 */ COAP_OPTION_CONTENT_FORMAT 12 /* ____E__, uint, 0-2 B, RFC7252 */ /* COAP_OPTION_MAXAGE default 60 seconds if not set */ COAP_OPTION_MAXAGE 14 /* _U-_E_U, uint, 0-4 B, RFC7252 */ COAP_OPTION_URI_QUERY 15 /* CU-RE__, String, 1-255 B, RFC7252 */ COAP_OPTION_HOP_LIMIT 16 /* ______U, uint, 1 B, RFC8768 */ COAP_OPTION_ACCEPT 17 /* C___E__, uint, 0-2 B, RFC7252 */ COAP_OPTION_LOCATION_QUERY 20 /* ___RE__, String, 0-255 B, RFC7252 */ COAP_OPTION_BLOCK2 23 /* CU-_E_U, uint, 0-3 B, RFC7959 */ COAP_OPTION_BLOCK1 27 /* CU-_E_U, uint, 0-3 B, RFC7959 */ COAP_OPTION_SIZE2 28 /* __N_E_U, uint, 0-4 B, RFC7959 */ COAP_OPTION_PROXY_URI 35 /* CU-___U, String, 1-1034 B, RFC7252 */ COAP_OPTION_PROXY_SCHEME 39 /* CU-___U, String, 1-255 B, RFC7252 */ COAP_OPTION_SIZE1 60 /* __N_E_U, uint, 0-4 B, RFC7252 */ COAP_OPTION_NORESPONSE 258 /* _U-_E_U, uint, 0-1 B, RFC7967 */ See FURTHER INFORMATION as to how to get the latest list. Function: coap_check_option() The coap_check_option() function is used to check whether the specified op- tion number is in the PDU pdu options. The option iterator oi is used as a scratch (does not need to be initialized) internal storage location while iterating through the options looking for the specific number. If the num- ber is repeated in the pdu, only the first occurrence will be returned. If the option is not found, NULL is returned. Function: coap_option_iterator_init() The coap_option_iterator_init() function can be used to initialize option iterator oi, applying a filter filter to indicate which options are to be ignored when iterating through the options. The filter can be NULL (or COAP_OPT_ALL) if all of the options are required. To set up the filter oth- erwise, the following 4 functions are available. Function: coap_option_filter_clear() The coap_option_filter_clear() function initializes filter to have no op- tions set. Function: coap_option_filter_get() The coap_option_filter_get() function is used to check whether option num- ber is set in filter. Function: coap_option_filter_set() The coap_option_filter_set() function is used to set option number in fil- ter. Function: coap_option_filter_unset() The coap_option_filter_unset() function is used to remove option number in filter. Function: coap_option_next() The coap_option_next() function is then used following coap_option_itera- tor_init() in a loop to return all the appropriate options until NULL is returned - indicating the end of the available options. See EXAMPLES below for further information. Function: coap_opt_length() The coap_opt_length() function returns the length of the option opt (as re- turned by coap_check_option() or coap_option_next()). Function: coap_opt_value() The coap_opt_value() function returns a pointer to the start of the data for the option opt (as returned by coap_check_option() or coap_op- tion_next()). Function: coap_decode_var_bytes() The coap_decode_var_bytes() function will decode an option value up to 4 bytes long from buf and length into an unsigned 32bit number. Function: coap_decode_var_bytes8() The coap_decode_var_bytes8() function will decode an option value up to 8 bytes long from buf and length into an unsigned 64bit number. Function: coap_get_uri_path() The coap_get_uri_path() function will abstract the uri path from the speci- fied pdu options. The returned uri path will need to be freed off when no longer required. PDU PAYLOAD FUNCTIONS Function: coap_get_data() The coap_get_data() function is used abstract from the pdu payload informa- tion about the received data by updating length with the length of data available, and data with a pointer to where the data is located. NOTE: This function has been updated by coap_get_data_large() when large transfers may take place. See coap_block(3). RETURN VALUES coap_check_option() and coap_option_next() returns a coap_opt_t* or NULL if not found. coap_decode_var_bytes() and coap_decode_var_bytes8() return the decoded value. coap_pdu_get_code(), coap_pdu_get_mid(), coap_pdu_get_type() return the ap- propriate value. coap_option_filter_get(), coap_option_filter_set() and coap_option_fil- ter_unset() return 1 on success or 0 on failure. coap_get_data() returns 1 if data, else 0. coap_opt_length() returns the option length. coap_opt_value() returns a pointer to the start of the option value or NULL if error. coap_option_iterator_init() returns ap pointer to the provided iterator or NULL on error. coap_pdu_get_token() returns a pointer to the token in the pdu. coap_get_uri_path() returns an allocated pointer to the uri path in the pdu or NULL on error. This pointer will need to be freed off. EXAMPLES Abstract information from PDU #include <coap3/coap.h> static void get_pdu_information(coap_pdu_t *pdu) { int ret; /* Header variables */ coap_pdu_type_t pdu_type; coap_pdu_code_t pdu_code; coap_mid_t pdu_mid; /* Token variables */ coap_bin_const_t pdu_token; /* Option variables */ coap_opt_iterator_t opt_iter; coap_opt_t *option; coap_opt_filter_t ignore_options; /* Data payload variables */ size_t pdu_data_length; const uint8_t *pdu_data; size_t pdu_data_offset; size_t pdu_data_total_length; /* Pull in the header information */ pdu_type = coap_pdu_get_type(pdu); pdu_code = coap_pdu_get_code(pdu); pdu_mid = coap_pdu_get_mid(pdu); /* Pull in the token information */ pdu_token = coap_pdu_get_token(pdu); /* Pull in the option information */ /* Specific option check */ option = coap_check_option(pdu, COAP_OPTION_OBSERVE, &opt_iter); if (option) { uint32_t value = coap_decode_var_bytes(coap_opt_value(option), coap_opt_length(option)); coap_log_info("Option OBSERVE, value %u\n", value); } /* Iterate through all options */ coap_option_iterator_init(pdu, &opt_iter, COAP_OPT_ALL); while ((option = coap_option_next(&opt_iter))) { coap_log_info("A: Option %d, Length %u\n", opt_iter.number, coap_opt_length(option)); } /* Iterate through options, some ignored */ coap_option_filter_clear(&ignore_options); coap_option_filter_set(&ignore_options, COAP_OPTION_OBSERVE); coap_option_iterator_init(pdu, &opt_iter, &ignore_options); while ((option = coap_option_next(&opt_iter))) { coap_log_info("I: Option %d, Length %u\n", opt_iter.number, coap_opt_length(option)); } /* Pull in the payload information */ ret = coap_get_data_large(pdu, &pdu_data_length, &pdu_data, &pdu_data_offset, &pdu_data_total_length); } SEE ALSO coap_block(3) and coap_pdu_setup(3) FURTHER INFORMATION See "RFC7252: The Constrained Application Protocol (CoAP)" "RFC8613: Object Security for Constrained RESTful Environments (OSCORE)" for further information. See https://www.iana.org/assignments/core-parameters/core-parame- ters.xhtml#option-numbers for the current set of defined CoAP Options. 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> coap_pdu_access 4.3.5 08/02/2026 COAP_PDU_ACCESS(3)
NAME | SYNOPSIS | DESCRIPTION | PDU HEADER FUNCTIONS | PDU TOKEN FUNCTIONS | PDU OPTIONS FUNCTIONS | PDU PAYLOAD FUNCTIONS | RETURN VALUES | EXAMPLES | SEE ALSO | FURTHER INFORMATION | BUGS | AUTHORS
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