nanocoap: Allow accessing opaque and other written options

sys/include/net/nanocoap.h

@@ -748,6 +748,32 @@ 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   Iterate over a packet's options
+ *
+ * This function is for accessing arbitrary options in a message in sequence.
+ * 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.
+ *
+ * The caller must provide a zeroed-out *opt to start iterating, and pass the
+ * same opt to subsequent calls. The function will, on each invocation, set
+ * *start to point to the beginning of the next option, and return the
+ * to-be-read length. The caller can read that option's number from
+ * opt.opt_num, and must ignore opt.offset.
+ *
+ * The end of the options is indicated by *start having a value of NULL; the
+ * return value is unspecified in that case.
+ *
+ * @param[in]     pkt         packet to read from
+ * @param[in,out] opt         iteration counter
+ * @param[out]    start       pointer to the start of the option value
+ *
+ * @return      number of bytes available at @p start
+ */
+size_t coap_opt_get_next(const coap_pkt_t *pkt, coap_optpos_t *opt,
+                            uint8_t **start);
+
 /**
  * @brief   Read a full option as null terminated string into the target buffer
  *
@@ -975,7 +1001,7 @@ static inline unsigned coap_get_type(coap_pkt_t *pkt)
  *
  * @returns     length of token in the given message (0-8 byte)
  */
-static inline unsigned coap_get_token_len(coap_pkt_t *pkt)
+static inline unsigned coap_get_token_len(const coap_pkt_t *pkt)
 {
     return (pkt->hdr->ver_t_tkl & 0xf);
 }

sys/net/application_layer/nanocoap/nanocoap.c

@@ -256,6 +256,28 @@ unsigned coap_get_content_type(coap_pkt_t *pkt)
     return content_type;
 }
 
+size_t coap_opt_get_next(const coap_pkt_t *pkt, coap_optpos_t *opt,
+                            uint8_t **start)
+{
+    uint8_t *opt_pos = (uint8_t*)pkt->hdr + (opt->offset == 0 ? sizeof(coap_hdr_t) + coap_get_token_len(pkt) : opt->offset);
+    int opt_len = -1;
+    uint16_t delta;
+
+    *start = _parse_option(pkt, opt_pos, &delta, &opt_len);
+
+    if (opt_len >= 0) {
+        opt->opt_num += delta;
+        opt->offset = *start + opt_len - (uint8_t*)pkt->hdr;
+        return opt_len;
+    } else {
+        // Terminal condition that can either be caused by reaching the end of
+        // the options (if there is no payload marker), or by reaching the
+        // payload marker
+        *start = 0;
+        return 0;
+    }
+}
+
 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 +71,49 @@ 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];
+
+    uint8_t *start;
+    size_t length;
+    coap_optpos_t cursor = {0};
+    while (1) {
+        length = coap_opt_get_next(pkt, &cursor, &start);
+        if (start == NULL) {
+            break;
+        }
+
+        p += snprintf(&rsp[p], sizeof(rsp) - p, "%d: ", cursor.opt_num);
+        if ((size_t)p >= sizeof(rsp))
+            goto error;
+
+        for (size_t j = 0; j < length; ++j) {
+            p += snprintf(&rsp[p], sizeof(rsp) - p, "%02x", start[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 | COAP_POST, _reqopts_handler, NULL },
     { "/value", COAP_GET | COAP_PUT | COAP_POST, _value_handler, NULL },
 };