Merge pull request #8882 from anttiylitokola/mbed-coap-4.7.3

Update mbed-coap to version 4.7.3

features/frameworks/mbed-coap/CHANGELOG.md

@@ -1,5 +1,14 @@
 # Change Log
 
+## [v4.7.3](https://github.com/ARMmbed/mbed-coap/releases/tag/v4.7.3) 
+
+- Do not store EMPTY response to blockwise list
+    An Empty message only contains the 4-byte header so it does not require any blockwise operations.
+    This will fix unneseccary message sending timeouts which leads mbed cloud client to do unnecessary
+    reconnections which increases the network traffic.
+
+-[Full Changelog](https://github.com/ARMmbed/mbed-coap/compare/v4.7.2...v4.7.3)
+
 ## [v4.7.2](https://github.com/ARMmbed/mbed-coap/releases/tag/v4.7.2) 
 
 - Fix handling of duplicate blockwise ACK's

features/frameworks/mbed-coap/module.json

@@ -1,6 +1,6 @@
 {
   "name": "mbed-coap",
-  "version": "4.7.2",
+  "version": "4.7.3",
   "description": "COAP library",
   "keywords": [
     "coap",

features/frameworks/mbed-coap/source/sn_coap_protocol.c

@@ -564,7 +564,8 @@ int16_t sn_coap_protocol_build(struct coap_s *handle, sn_nsdl_addr_s *dst_addr_p
         stored_blockwise_msg_ptr->param = param;
         stored_blockwise_msg_ptr->msg_id = stored_blockwise_msg_ptr->coap_msg_ptr->msg_id;
         ns_list_add_to_end(&handle->linked_list_blockwise_sent_msgs, stored_blockwise_msg_ptr);
-    } else if (src_coap_msg_ptr->msg_code <= COAP_MSG_CODE_REQUEST_DELETE) {
+    } else if (src_coap_msg_ptr->msg_code <= COAP_MSG_CODE_REQUEST_DELETE &&
+               src_coap_msg_ptr->msg_code != COAP_MSG_CODE_EMPTY) {
         /* Add message to linked list - response can be in blocks and we need header to build response.. */
         coap_blockwise_msg_s *stored_blockwise_msg_ptr;