coap_pdu.c: Report options with invalid length

Malformed PDUs were responsed to with a RST.  Now request PDUs with invalid
lengths are also reported with a 4.02 response.

See RFC7252 5.4.3 and 5.4.1.

include/coap3/coap_pdu.h

@@ -134,6 +134,7 @@ typedef enum coap_request_t {
 #define COAP_OPTION_ACCEPT         17 /* C___E__, uint,      0-2 B, RFC7252 */
 #define COAP_OPTION_Q_BLOCK1       19 /* CU__E_U, uint,      0-3 B, RFC9177 */
 #define COAP_OPTION_LOCATION_QUERY 20 /* ___RE__, String,  0-255 B, RFC7252 */
+#define COAP_OPTION_EDHOC          21 /* C_____U, empty,       0 B, RFC9668 */
 #define COAP_OPTION_BLOCK2         23 /* CU-_E_U, uint,      0-3 B, RFC7959 */
 #define COAP_OPTION_BLOCK1         27 /* CU-_E_U, uint,      0-3 B, RFC7959 */
 #define COAP_OPTION_SIZE2          28 /* __N_E_U, uint,      0-4 B, RFC7959 */

include/coap3/coap_pdu_internal.h

@@ -177,6 +177,27 @@ struct coap_pdu_t {
   coap_binary_t *data_free; /**< Data to be freed off by coap_delete_pdu() */
 };
 
+/**
+ * Parses @p data into the CoAP PDU structure given in @p result.
+ * The target pdu must be large enough to hold the token, options and data.
+ * This function returns @c 0 on error or a number greater than zero on success.
+ *
+ * @param proto   Session's protocol
+ * @param data    The raw data to parse as CoAP PDU.
+ * @param length  The actual size of @p data.
+ * @param pdu     The PDU structure to fill. Note that the structure must
+ *                provide space to hold the token, optional options and
+ *                optional data.
+ * @param error_opts Filled in with any options that have an error in the parsing.
+ *
+ * @return       1 on success or @c 0 on error.
+ */
+int coap_pdu_parse2(coap_proto_t proto,
+                    const uint8_t *data,
+                    size_t length,
+                    coap_pdu_t *pdu,
+                    coap_opt_filter_t *error_opts);
+
 /**
  * Dynamically grows the size of @p pdu to @p new_size. The new size
  * must not exceed the PDU's configure maximum size. On success, this
@@ -243,10 +264,11 @@ int coap_pdu_parse_header(coap_pdu_t *pdu, coap_proto_t proto);
  * marker.
  *
  * @param pdu     The PDU structure to check.
+ * @param error_opts Updated with error option(s) on failure.
  *
  * @return       1 on success or @c 0 on error.
  */
-int coap_pdu_parse_opt(coap_pdu_t *pdu);
+int coap_pdu_parse_opt(coap_pdu_t *pdu, coap_opt_filter_t *error_opts);
 
 /**
  * Clears any contents from @p pdu and resets @c used_size,