Fix WebSocket (#153)

* Fix WebSocket
- Handle client disconnection event properly even if cleanupClients is not called within the main loop.
- Avoid self-deadlock by using recursive mutex.

* ci(pre-commit): Apply automatic fixes

* Update example

* ci(pre-commit): Apply automatic fixes

---------

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>
Co-authored-by: Mathieu Carbou <mathieu.carbou@gmail.com>

Author: 3 people

examples/WebSocket/WebSocket.ino

@@ -102,8 +102,10 @@ void loop() {
   }
 
   if (now - lastHeap >= 2000) {
-    // cleanup disconnected clients or too many clients
-    ws.cleanupClients();
+    Serial.printf("Connected clients: %u / %u total\n", ws.count(), ws.getClients().size());
+
+    // this can be called to also set a soft limit on the number of connected clients
+    ws.cleanupClients(2);  // no more than 2 clients
 
 #ifdef ESP32
     Serial.printf("Free heap: %" PRIu32 "\n", ESP.getFreeHeap());

src/AsyncWebSocket.cpp

@@ -333,7 +333,7 @@ AsyncWebSocketClient::AsyncWebSocketClient(AsyncWebServerRequest *request, Async
 AsyncWebSocketClient::~AsyncWebSocketClient() {
   {
 #ifdef ESP32
-    std::lock_guard<std::mutex> lock(_lock);
+    std::lock_guard<std::recursive_mutex> lock(_lock);
 #endif
     _messageQueue.clear();
     _controlQueue.clear();
@@ -351,7 +351,7 @@ void AsyncWebSocketClient::_onAck(size_t len, uint32_t time) {
   _lastMessageTime = millis();
 
 #ifdef ESP32
-  std::lock_guard<std::mutex> lock(_lock);
+  std::unique_lock<std::recursive_mutex> lock(_lock);
 #endif
 
   if (!_controlQueue.empty()) {
@@ -362,6 +362,14 @@ void AsyncWebSocketClient::_onAck(size_t len, uint32_t time) {
         _controlQueue.pop_front();
         _status = WS_DISCONNECTED;
         if (_client) {
+#ifdef ESP32
+          /*
+            Unlocking has to be called before return execution otherwise std::unique_lock ::~unique_lock() will get an exception pthread_mutex_unlock.
+            Due to _client->close(true) shall call the callback function _onDisconnect()
+            The calling flow _onDisconnect() --> _handleDisconnect() --> ~AsyncWebSocketClient()
+          */
+          lock.unlock();
+#endif
           _client->close(true);
         }
         return;
@@ -385,7 +393,7 @@ void AsyncWebSocketClient::_onPoll() {
   }
 
 #ifdef ESP32
-  std::unique_lock<std::mutex> lock(_lock);
+  std::unique_lock<std::recursive_mutex> lock(_lock);
 #endif
   if (_client && _client->canSend() && (!_controlQueue.empty() || !_messageQueue.empty())) {
     _runQueue();
@@ -415,21 +423,21 @@ void AsyncWebSocketClient::_runQueue() {
 
 bool AsyncWebSocketClient::queueIsFull() const {
 #ifdef ESP32
-  std::lock_guard<std::mutex> lock(_lock);
+  std::lock_guard<std::recursive_mutex> lock(_lock);
 #endif
   return (_messageQueue.size() >= WS_MAX_QUEUED_MESSAGES) || (_status != WS_CONNECTED);
 }
 
 size_t AsyncWebSocketClient::queueLen() const {
 #ifdef ESP32
-  std::lock_guard<std::mutex> lock(_lock);
+  std::lock_guard<std::recursive_mutex> lock(_lock);
 #endif
   return _messageQueue.size();
 }
 
 bool AsyncWebSocketClient::canSend() const {
 #ifdef ESP32
-  std::lock_guard<std::mutex> lock(_lock);
+  std::lock_guard<std::recursive_mutex> lock(_lock);
 #endif
   return _messageQueue.size() < WS_MAX_QUEUED_MESSAGES;
 }
@@ -440,7 +448,7 @@ bool AsyncWebSocketClient::_queueControl(uint8_t opcode, const uint8_t *data, si
   }
 
 #ifdef ESP32
-  std::lock_guard<std::mutex> lock(_lock);
+  std::lock_guard<std::recursive_mutex> lock(_lock);
 #endif
 
   _controlQueue.emplace_back(opcode, data, len, mask);
@@ -458,14 +466,22 @@ bool AsyncWebSocketClient::_queueMessage(AsyncWebSocketSharedBuffer buffer, uint
   }
 
 #ifdef ESP32
-  std::lock_guard<std::mutex> lock(_lock);
+  std::unique_lock<std::recursive_mutex> lock(_lock);
 #endif
 
   if (_messageQueue.size() >= WS_MAX_QUEUED_MESSAGES) {
     if (closeWhenFull) {
       _status = WS_DISCONNECTED;
 
       if (_client) {
+#ifdef ESP32
+        /*
+          Unlocking has to be called before return execution otherwise std::unique_lock ::~unique_lock() will get an exception pthread_mutex_unlock.
+          Due to _client->close(true) shall call the callback function _onDisconnect()
+          The calling flow _onDisconnect() --> _handleDisconnect() --> ~AsyncWebSocketClient()
+        */
+        lock.unlock();
+#endif
         _client->close(true);
       }
 
@@ -551,6 +567,7 @@ void AsyncWebSocketClient::_onTimeout(uint32_t time) {
 void AsyncWebSocketClient::_onDisconnect() {
   // Serial.println("onDis");
   _client = nullptr;
+  _server->_handleDisconnect(this);
 }
 
 void AsyncWebSocketClient::_onData(void *pbuf, size_t plen) {
@@ -857,6 +874,16 @@ AsyncWebSocketClient *AsyncWebSocket::_newClient(AsyncWebServerRequest *request)
   return &_clients.back();
 }
 
+void AsyncWebSocket::_handleDisconnect(AsyncWebSocketClient *client) {
+  const auto client_id = client->id();
+  const auto iter = std::find_if(std::begin(_clients), std::end(_clients), [client_id](const AsyncWebSocketClient &c) {
+    return c.id() == client_id;
+  });
+  if (iter != std::end(_clients)) {
+    _clients.erase(iter);
+  }
+}
+
 bool AsyncWebSocket::availableForWriteAll() {
   return std::none_of(std::begin(_clients), std::end(_clients), [](const AsyncWebSocketClient &c) {
     return c.queueIsFull();

src/AsyncWebSocket.h

@@ -152,7 +152,7 @@ class AsyncWebSocketClient {
   uint32_t _clientId;
   AwsClientStatus _status;
 #ifdef ESP32
-  mutable std::mutex _lock;
+  mutable std::recursive_mutex _lock;
 #endif
   std::deque<AsyncWebSocketControl> _controlQueue;
   std::deque<AsyncWebSocketMessage> _messageQueue;
@@ -385,6 +385,7 @@ class AsyncWebSocket : public AsyncWebHandler {
     return _cNextId++;
   }
   AsyncWebSocketClient *_newClient(AsyncWebServerRequest *request);
+  void _handleDisconnect(AsyncWebSocketClient *client);
   void _handleEvent(AsyncWebSocketClient *client, AwsEventType type, void *arg, uint8_t *data, size_t len);
   bool canHandle(AsyncWebServerRequest *request) const override final;
   void handleRequest(AsyncWebServerRequest *request) override final;