nanocoap: Allow accessing opaque and other written options

sys/include/net/nanocoap.h

@@ -748,6 +748,27 @@ size_t coap_opt_put_block2(uint8_t *buf, uint16_t lastonum, coap_block_slicer_t
  */
 unsigned coap_get_content_type(coap_pkt_t *pkt);
 
+/**
+ * @brief   Access an option by its struct offset
+ *
+ * This function is for accessing arbitrary options in a message that was
+ * received, or was built using the struct-based API. It is useful for reading
+ * opaque options, updating values after they have been added (e.g. putting a
+ * value into a pre-allocated ETag after the payload was calculate), and when
+ * iterating over a message's options.
+ *
+ * It is up to the caller to ensure that optnum is valid, i.e. that `0 <= optnum
+ * < pkt->options_len`.
+ *
+ * @param[in]   pkt         packet to read from
+ * @param[in]   index       absolute option number
+ * @param[out]  start       pointer to the start of the option value
+ *
+ * @return      number of bytes available at @p start
+ */
+size_t coap_opt_by_index(const coap_pkt_t *pkt, uint16_t index,
+                            uint8_t **start);
+
 /**
  * @brief   Read a full option as null terminated string into the target buffer
  *

sys/net/application_layer/nanocoap/nanocoap.c

@@ -256,6 +256,21 @@ unsigned coap_get_content_type(coap_pkt_t *pkt)
     return content_type;
 }
 
+size_t coap_opt_by_index(const coap_pkt_t *pkt, uint16_t index,
+                            uint8_t **start)
+{
+    assert(pkt && index < pkt->options_len);
+
+    const coap_optpos_t *optslot = &pkt->options[index];
+    uint8_t *opt_pos = (uint8_t*)pkt->hdr + optslot->offset;
+    int opt_len;
+    uint16_t delta;
+
+    *start = _parse_option(pkt, opt_pos, &delta, &opt_len);
+
+    return opt_len;
+}
+
 ssize_t coap_opt_get_string(const coap_pkt_t *pkt, uint16_t optnum,
                             uint8_t *target, size_t max_len, char separator)
 {

tests/nanocoap_cli/README.md

@@ -10,6 +10,9 @@ which to listen. Provides these resources:
 `/value`<br>
 Reads/Writes an unsigned 8-bit integer.
 
+`/req-opts`<br>
+Hex-dumps all options in the request message into a response.
+
 `/.well-known/core`<br>
 Reads the list of resources. Expects a block2 based request or else returns at
 most the first 16 bytes of the list.

tests/nanocoap_cli/request_handlers.c

@@ -71,9 +71,43 @@ static ssize_t _value_handler(coap_pkt_t *pkt, uint8_t *buf, size_t len, void *c
             COAP_FORMAT_TEXT, (uint8_t*)rsp, p);
 }
 
+static ssize_t _reqopts_handler(coap_pkt_t *pkt, uint8_t *buf, size_t len, void *context)
+{
+    (void) context;
+
+    ssize_t p = 0;
+    char rsp[128];
+
+    for (uint16_t i = 0; i < pkt->options_len; ++i) {
+        uint16_t optnum = pkt->options[i].opt_num;
+        p += snprintf(&rsp[p], sizeof(rsp) - p, "%d: ", optnum);
+        if ((size_t)p >= sizeof(rsp))
+            goto error;
+        uint8_t *optcursor;
+        size_t length = coap_opt_by_index(pkt, i, &optcursor);
+        for (size_t j = 0; j < length; ++j) {
+            p += snprintf(&rsp[p], sizeof(rsp) - p, "%02x", optcursor[j]);
+            if ((size_t)p >= sizeof(rsp))
+                goto error;
+        }
+        p += snprintf(&rsp[p], sizeof(rsp) - p, "\n");
+        if ((size_t)p >= sizeof(rsp))
+            goto error;
+    }
+
+    return coap_reply_simple(pkt, COAP_CODE_205, buf, len,
+            COAP_FORMAT_TEXT, (uint8_t*)rsp, p);
+
+error:
+    rsp[sizeof(rsp) - 1] = '_';
+    return coap_reply_simple(pkt, COAP_CODE_205, buf, len,
+            COAP_FORMAT_TEXT, (uint8_t*)rsp, sizeof(rsp));
+}
+
 /* must be sorted by path (ASCII order) */
 const coap_resource_t coap_resources[] = {
     COAP_WELL_KNOWN_CORE_DEFAULT_HANDLER,
+    { "/req-opts", COAP_GET, _reqopts_handler, NULL },
     { "/value", COAP_GET | COAP_PUT | COAP_POST, _value_handler, NULL },
 };