net/nanocoap: add function to iterate over options

sys/include/net/nanocoap.h

@@ -530,6 +530,38 @@ static inline ssize_t coap_get_uri_query(const coap_pkt_t *pkt, uint8_t *target)
     return coap_opt_get_string(pkt, COAP_OPT_URI_QUERY, target,
                                NANOCOAP_URI_MAX, '&');
 }
+
+/**
+ * @brief   Iterate over a packet's options
+ *
+ * To start iteration from the first option, set @p init_opt to true. To start
+ * iteration from a specific option, set @p init_opt to false, set
+ * @p opt->offset to the offset of the desired option from pkt->hdr, and
+ * @p opt->opt_num as required. See below for how @p opt->opt_num is modified.
+ *
+ * With each invocation, this function returns the length of the option value
+ * and sets @p value to point to the start of the value. The value for
+ * @p opt->opt_num is increased by the delta in the option number value over
+ * the preceding option in the packet. So, @p opt->opt_num is accurate if
+ * iteration started with the first option. Otherwise, it is useful for
+ * identification of repeated options. Finally, @p opt->offset is set to the
+ * offset for any following option, to prepare for the next iteration.
+ *
+ * The end of the options is indicated by a -ENOENT return value. In this case
+ * @p value and @p opt are unchanged from their input values.
+ *
+ * @param[in]     pkt         packet to read from
+ * @param[in,out] opt         option attributes; read on input if @p init_opt
+ *                            is false
+ * @param[out]    value       start of the option value
+ * @param[in]     init_opt    true to retrieve first option; false to retrieve
+ *                            option at opt->offset
+ *
+ * @return        length of option value
+ * @return        -ENOENT if option not found
+ */
+ssize_t coap_opt_get_next(const coap_pkt_t *pkt, coap_optpos_t *opt,
+                          uint8_t **value, bool init_opt);
 /**@}*/
 
 

sys/net/application_layer/nanocoap/nanocoap.c

@@ -269,6 +269,30 @@ unsigned coap_get_content_type(coap_pkt_t *pkt)
     return content_type;
 }
 
+ssize_t coap_opt_get_next(const coap_pkt_t *pkt, coap_optpos_t *opt,
+                          uint8_t **value, bool init_opt)
+{
+    if (init_opt) {
+        opt->opt_num = 0;
+        opt->offset = coap_get_total_hdr_len(pkt);
+    }
+    uint8_t *start = (uint8_t*)pkt->hdr + opt->offset;
+
+    /* Find start of option value and value length. */
+    uint16_t delta;
+    int len;
+
+    start = _parse_option(pkt, start, &delta, &len);
+    if (!start) {
+        return -ENOENT;
+    }
+
+    *value = start;
+    opt->opt_num += delta;
+    opt->offset = start + len - (uint8_t*)pkt->hdr;
+    return len;
+}
+
 ssize_t coap_opt_get_string(const coap_pkt_t *pkt, uint16_t optnum,
                             uint8_t *target, size_t max_len, char separator)
 {