fix(mem): Fix memory leak in _accept() functions when _accept is called with a null pcb

Fix inspired by PR #21 from @willmmiles

Author: mathieucarbou

src/AsyncTCP.cpp

@@ -1616,21 +1616,42 @@ void AsyncServer::end() {
 
 // runs on LwIP thread
 int8_t AsyncServer::_accept(tcp_pcb *pcb, int8_t err) {
-  // ets_printf("+A: 0x%08x\n", pcb);
-  if (_connect_cb) {
-    AsyncClient *c = new (std::nothrow) AsyncClient(pcb);
-    if (c) {
-      c->setNoDelay(_noDelay);
-      const int8_t err = _tcp_accept(this, c);
-      if (err != ERR_OK) {
+  if (pcb) {
+    if (_connect_cb) {
+      AsyncClient *c = new (std::nothrow) AsyncClient(pcb);
+      if (c && c->pcb()) {
+        c->setNoDelay(_noDelay);
+        if (_tcp_accept(this, c) == ERR_OK) {
+          return ERR_OK;  // success
+        }
+      }
+      if (c->pcb()) {
+        // Couldn't allocate accept event
+        // We can't let the client object call in to close, as we're on the LWIP thread; it could deadlock trying to RPC to itself
+        c->_pcb = nullptr;
         tcp_abort(pcb);
+        log_e("_accept failed: couldn't allocate client");
+        return ERR_ABRT;
+      }
+      if (c) {
+        // Couldn't complete setup
+        // pcb has already been aborted
         delete c;
+        pcb = nullptr;
+        log_e("_accept failed: couldn't complete setup");
+        return ERR_ABRT;
       }
-      return err;
     }
+    if (pcb) {
+      if (tcp_close(pcb) != ERR_OK) {
+        tcp_abort(pcb);
+      }
+    }
+  } else {
+    log_e("_accept failed: pcb is NULL");
+    return ERR_ABRT;
   }
-  tcp_abort(pcb);
-  log_d("_accept failed");
+  log_e("_accept failed");
   return ERR_OK;
 }
 

src/AsyncTCP.h

@@ -246,6 +246,8 @@ class AsyncClient {
   }
 
 protected:
+  friend class AsyncServer;
+
   bool _connect(ip_addr_t addr, uint16_t port);
 
   tcp_pcb *_pcb;