nanocoap: make separate tree handling function

This refactors nanocoap to seperate out the resource tree parsing. It
allows for calling the tree handler with custom resource trees. The
advantage is that a resource with COAP_MATCH_SUBTREE can parse a new
separate resource tree.

sys/include/net/nanocoap.h

@@ -1405,6 +1405,26 @@ ssize_t coap_build_reply(coap_pkt_t *pkt, unsigned code,
  */
 ssize_t coap_handle_req(coap_pkt_t *pkt, uint8_t *resp_buf, unsigned resp_buf_len);
 
+/**
+ * @brief   Pass a coap request to a matching handler
+ *
+ * This function will try to find a matching handler in @p resources and call
+ * the handler.
+ *
+ * @param[in]   pkt             pointer to (parsed) CoAP packet
+ * @param[out]  resp_buf        buffer for response
+ * @param[in]   resp_buf_len    size of response buffer
+ * @param[in]   resources       Array of coap endpoint resources
+ * @param[in]   resources_numof length of the coap endpoint resources
+ *
+ * @returns     size of the reply packet on success
+ * @returns     <0 on error
+ */
+ssize_t coap_tree_handler(coap_pkt_t *pkt, uint8_t *resp_buf,
+                          unsigned resp_buf_len,
+                          const coap_resource_t *resources,
+                          size_t resources_numof);
+
 /**
  * @brief   Convert message code (request method) into a corresponding bit field
  *

sys/net/application_layer/nanocoap/nanocoap.c

@@ -384,7 +384,15 @@ ssize_t coap_handle_req(coap_pkt_t *pkt, uint8_t *resp_buf, unsigned resp_buf_le
     if (pkt->hdr->code == 0) {
         return coap_build_reply(pkt, COAP_CODE_EMPTY, resp_buf, resp_buf_len, 0);
     }
+    return coap_tree_handler(pkt, resp_buf, resp_buf_len, coap_resources,
+                             coap_resources_numof);
+}
 
+ssize_t coap_tree_handler(coap_pkt_t *pkt, uint8_t *resp_buf,
+                          unsigned resp_buf_len,
+                          const coap_resource_t *resources,
+                          size_t resources_numof)
+{
     coap_method_flags_t method_flag = coap_method2flag(coap_get_code_detail(pkt));
 
     uint8_t uri[NANOCOAP_URI_MAX];
@@ -393,8 +401,8 @@ ssize_t coap_handle_req(coap_pkt_t *pkt, uint8_t *resp_buf, unsigned resp_buf_le
     }
     DEBUG("nanocoap: URI path: \"%s\"\n", uri);
 
-    for (unsigned i = 0; i < coap_resources_numof; i++) {
-        const coap_resource_t *resource = &coap_resources[i];
+    for (unsigned i = 0; i < resources_numof; i++) {
+        const coap_resource_t *resource = &resources[i];
         if (!(resource->methods & method_flag)) {
             continue;
         }