coap: When a client is observing a server, a block is always leaked

When a client starts to observe a server, a struct was allocated
to keep some context data. When client asks to be unobserved from the
server, or if the client is terminated, this block leaks.

With this pathc sol-coap will always call reply_cb when a client is
unobserved, as it is done when timeout is reached, so users can free
memory.

One way to check this bahaviour is running the light-server +
light-client sample located in src/samples/flow/oic/ and terminating the
client execution.

Valgrind tells us this:

==2586== 40 bytes in 1 blocks are definitely lost in loss record 20 of 31
==2586==    at 0x4C28C10: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2586==    by 0x54128E1: sol_util_memdup (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x53A133A: _resource_request (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x53A1D7C: sol_oic_client_resource_set_observable (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0xCBAD915: found_resource (in /home/otavio/local/soletta/lib/soletta/modules/flow/oic.so)
==2586==    by 0x53A05E1: _iterate_over_resource_reply_payload (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x53A08FE: _find_resource_reply_cb (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x5391032: respond_packet (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x5391413: on_can_read (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x53A41F2: on_socket_read (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x538391E: fd_process (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==    by 0x53839FE: sol_mainloop_impl_iter (in /home/otavio/local/soletta/lib/libsoletta.so.0.0.1)
==2586==

src/lib/comms/sol-coap.c

@@ -1284,6 +1284,7 @@ sol_coap_server_destroy(struct sol_coap_server *server)
 
     SOL_PTR_VECTOR_FOREACH_REVERSE_IDX (&server->pending, reply, i) {
         sol_ptr_vector_del(&server->pending, i);
+        reply->cb(server, NULL, NULL, (void *)reply->data);
         pending_reply_free(reply);
     }
 
@@ -1600,6 +1601,7 @@ sol_coap_unobserve_server(struct sol_coap_server *server, const struct sol_netwo
         if (!match_observe_reply(reply, token, tkl))
             continue;
 
+        reply->cb(server, NULL, NULL, (void *)reply->data);
         sol_ptr_vector_del(&server->pending, i);
 
         r = send_unobserve_packet(server, cliaddr, reply->path, token, tkl);

src/lib/comms/sol-oic-client.c

@@ -737,8 +737,10 @@ _resource_request_cb(struct sol_coap_server *server,
 
     if (!ctx->cb)
         return false;
-    if (!req || !cliaddr)
+    if (!req || !cliaddr) {
+        free(data);
         return false;
+    }
     if (!_pkt_has_same_token(req, ctx->token))
         return true;
     if (!sol_oic_pkt_has_cbor_content(req))
@@ -813,7 +815,9 @@ _one_shot_resource_request_cb(struct sol_coap_server *server,
     struct sol_coap_packet *req, const struct sol_network_link_addr *cliaddr,
     void *data)
 {
-    _resource_request_cb(server, req, cliaddr, data);
+
+    if (req && cliaddr)
+        _resource_request_cb(server, req, cliaddr, data);
 
     free(data);
     return false;