diff --git a/src/Engine/Engine.php b/src/Engine/Engine.php
index 68ba7d9..14903f2 100644
--- a/src/Engine/Engine.php
+++ b/src/Engine/Engine.php
@@ -30,13 +30,13 @@ class Engine extends Emitter
         'Bad request'
     ];
 
-    const ERROR_UNKNOWN_TRANSPORT = 0;
+    private const ERROR_UNKNOWN_TRANSPORT = 0;
 
-    const ERROR_UNKNOWN_SID = 1;
+    private const ERROR_UNKNOWN_SID = 1;
 
-    const ERROR_BAD_HANDSHAKE_METHOD = 2;
+    private const ERROR_BAD_HANDSHAKE_METHOD = 2;
 
-    const ERROR_BAD_REQUEST = 3;
+    private const ERROR_BAD_REQUEST = 3;
 
     public function __construct($opts = [])
     {
@@ -48,6 +48,7 @@ public function __construct($opts = [])
             'allowUpgrades',
             'allowRequest'
         ];
+
         foreach ($ops_map as $key) {
             if (isset($opts[$key])) {
                 $this->$key = $opts[$key];
@@ -61,7 +62,7 @@ public function __destruct()
         Debug::debug('Engine __destruct');
     }
 
-    public function handleRequest($req, $res)
+    public function handleRequest(object $req, object $res)
     {
         $this->prepare($req);
         $req->res = $res;
@@ -71,7 +72,7 @@ public function handleRequest($req, $res)
     /**
      * @throws Exception
      */
-    public function dealRequest($err, $success, $req)
+    public function dealRequest($err, bool $success, object $req)
     {
         if (! $success) {
             self::sendErrorMessage($req, $req->res, $err);
@@ -85,7 +86,7 @@ public function dealRequest($err, $success, $req)
         }
     }
 
-    protected function sendErrorMessage($req, $res, $code)
+    protected function sendErrorMessage(object $req, object $res, string $code): void
     {
         $headers = ['Content-Type' => 'application/json'];
         if (isset($req->headers['origin'])) {
@@ -106,7 +107,7 @@ protected function sendErrorMessage($req, $res, $code)
         );
     }
 
-    protected function verify($req, $res, $upgrade, $fn)
+    protected function verify(object $req, object $res, bool $upgrade, callable $fn)
     {
         if (! isset($req->_query['transport']) || ! isset(self::$allowTransports[$req->_query['transport']])) {
             return call_user_func($fn, self::ERROR_UNKNOWN_TRANSPORT, false, $req, $res);
@@ -129,7 +130,7 @@ protected function verify($req, $res, $upgrade, $fn)
         call_user_func($fn, null, true, $req, $res);
     }
 
-    public function checkRequest($req, $res, $fn)
+    public function checkRequest(object $req, object $res, callable $fn)
     {
         if ($this->origins === "*:*" || empty($this->origins)) {
             return call_user_func($fn, null, true, $req, $res);
@@ -158,7 +159,6 @@ public function checkRequest($req, $res, $fn)
                     $allow_origin === $parts['scheme'] . '://' . $parts['host'] . ':*' ||
                     $allow_origin === '*:' . $parts['port'];
                 if ($ok) {
-                    // 只需要有一个白名单通过，则都通过
                     return call_user_func($fn, null, true, $req, $res);
                 }
             }
@@ -166,7 +166,7 @@ public function checkRequest($req, $res, $fn)
         call_user_func($fn, null, false, $req, $res);
     }
 
-    protected function prepare($req)
+    protected function prepare(object $req)
     {
         if (! isset($req->_query)) {
             $info = parse_url($req->url);
@@ -179,7 +179,7 @@ protected function prepare($req)
     /**
      * @throws Exception
      */
-    public function handshake($transport, $req)
+    public function handshake(string $transport, object $req)
     {
         $id = bin2hex(pack('d', microtime(true)) . pack('N', function_exists('random_int') ? random_int(1, 100000000) : rand(1, 100000000)));
         if ($transport == 'websocket') {
@@ -203,18 +203,18 @@ public function handshake($transport, $req)
         $this->emit('connection', $socket);
     }
 
-    public function onSocketClose($id)
+    public function onSocketClose($id): void
     {
         unset($this->clients[$id]);
     }
 
-    public function attach($worker)
+    public function attach($worker): void
     {
         $this->server = $worker;
         $worker->onConnect = [$this, 'onConnect'];
     }
 
-    public function onConnect($connection)
+    public function onConnect(object $connection): void
     {
         $connection->onRequest = [$this, 'handleRequest'];
         $connection->onWebSocketConnect = [$this, 'onWebSocketConnect'];
@@ -237,7 +237,7 @@ public function onConnect($connection)
         };
     }
 
-    public function onWebSocketConnect($connection, $req, $res)
+    public function onWebSocketConnect($connection, object $req, object $res): void
     {
         $this->prepare($req);
         $this->verify($req, $res, true, [$this, 'dealWebSocketConnect']);
@@ -246,7 +246,7 @@ public function onWebSocketConnect($connection, $req, $res)
     /**
      * @throws Exception
      */
-    public function dealWebSocketConnect($err, $success, $req, $res)
+    public function dealWebSocketConnect($err, bool $success, object $req, object $res): void
     {
         if (! $success) {
             self::sendErrorMessage($req, $res, $err);
diff --git a/src/Engine/Parser.php b/src/Engine/Parser.php
index 503813b..3023eb7 100644
--- a/src/Engine/Parser.php
+++ b/src/Engine/Parser.php
@@ -43,32 +43,15 @@ public static function encodePacket($packet): string
         return self::$packets[$packet['type']] . $data;
     }
 
-
-    /**
-     * Encodes a packet with binary data in a base64 string
-     *
-     * @param  {Object} packet, has `type` and `data`
-     * @return string {String} base64 encoded message
-     */
-    public static function encodeBase64Packet($packet): string
-    {
-        return 'b' . self::$packets[$packet['type']] . base64_encode($packet['data']);
-    }
-
     /**
      * Decodes a packet. Data also available as an ArrayBuffer if requested.
      *
-     * @param $data
-     * @param null $binaryType
-     * @param bool $utf8decode
      * @return array|string[] {Object} with `type` and `data` (if any)
-     * @api    private
      */
-    public static function decodePacket($data, $binaryType = null, $utf8decode = true)
+    public static function decodePacket(string $data): array
     {
-        // String data todo check if (typeof data == 'string' || data === undefined)
         if ($data[0] === 'b') {
-            return self::decodeBase64Packet(substr($data, 1), $binaryType);
+            return self::decodeBase64Packet(substr($data, 1));
         }
 
         $type = $data[0];
@@ -87,13 +70,12 @@ public static function decodePacket($data, $binaryType = null, $utf8decode = tru
      * Decodes a packet encoded in a base64 string.
      *
      * @param $msg
-     * @param $binaryType
      * @return array {Object} with `type` and `data` (if any)
      */
-    public static function decodeBase64Packet($msg, $binaryType)
+    public static function decodeBase64Packet($msg): array
     {
         $type = self::$packetsList[$msg[0]];
-        $data = base64_decode(substr($data, 1));
+        $data = base64_decode(substr($msg, 1));
         return ['type' => $type, 'data' => $data];
     }
 
@@ -124,12 +106,12 @@ public static function encodePayload($packets, $supportsBinary = null): string
 
         $results = '';
         foreach ($packets as $msg) {
-            $results .= self::encodeOne($msg, $supportsBinary);
+            $results .= self::encodeOne($msg);
         }
         return $results;
     }
 
-    public static function encodeOne($packet, $supportsBinary = null, $result = null): string
+    public static function encodeOne($packet): string
     {
         $message = self::encodePacket($packet);
         return strlen($message) . ':' . $message;
@@ -165,10 +147,10 @@ public static function decodePayload($data, $binaryType = null)
                     return self::$err;
                 }
 
-                $msg = substr($data, $i + 1/*, $n*/);
+                $msg = substr($data, $i + 1);
 
                 if (isset($msg[0])) {
-                    $packet = self::decodePacket($msg, $binaryType);
+                    $packet = self::decodePacket($msg);
 
                     if (self::$err['type'] == $packet['type'] && self::$err['data'] == $packet['data']) {
                         // parser error in individual packet - ignoring payload
@@ -215,7 +197,6 @@ public static function encodePayloadAsBinary($packets): string
 
     public static function encodeOneAsBinary($p): string
     {
-        // todo is string or arraybuf
         $packet = self::encodePacket($p);
         $encodingLength = '' . strlen($packet);
         $sizeBuffer = chr(0);
@@ -257,7 +238,7 @@ public static function decodePayloadAsBinary($data, $binaryType = null): array
             }
             $bufferTail = substr($bufferTail, strlen($strLen) + 1);
 
-            $msgLength = intval($strLen, 10);
+            $msgLength = intval($strLen);
 
             $msg = substr($bufferTail, 1, $msgLength + 1);
             $buffers[] = $msg;
@@ -265,7 +246,7 @@ public static function decodePayloadAsBinary($data, $binaryType = null): array
         }
         $packets = [];
         foreach ($buffers as $i => $buffer) {
-            $packets[] = self::decodePacket($buffer, $binaryType);
+            $packets[] = self::decodePacket($buffer);
         }
         return $packets;
     }
diff --git a/src/Engine/Socket.php b/src/Engine/Socket.php
index 3e7c08b..760d8b1 100644
--- a/src/Engine/Socket.php
+++ b/src/Engine/Socket.php
@@ -40,7 +40,7 @@ public function __destruct()
         Debug::debug('Engine/Socket __destruct');
     }
 
-    public function maybeUpgrade($transport)
+    public function maybeUpgrade(object $transport): void
     {
         $this->upgrading = true;
         $this->upgradeTimeoutTimer = Timer::add(
@@ -56,7 +56,7 @@ public function maybeUpgrade($transport)
         $this->once('close', [$this, 'onUpgradeTransportClose']);
     }
 
-    public function onUpgradePacket($packet)
+    public function onUpgradePacket(array $packet): void
     {
         if (empty($this->upgradeTransport)) {
             $this->onError('upgradeTransport empty');
@@ -82,15 +82,13 @@ public function onUpgradePacket($packet)
                 $this->transport->close([$this, 'onClose']);
             }
         } else {
-            if (! empty($this->upgradeTransport)) {
-                $this->upgradeCleanup();
-                $this->upgradeTransport->close();
-                $this->upgradeTransport = null;
-            }
+            $this->upgradeCleanup();
+            $this->upgradeTransport->close();
+            $this->upgradeTransport = null;
         }
     }
 
-    public function upgradeCleanup()
+    public function upgradeCleanup(): void
     {
         $this->upgrading = false;
         Timer::del($this->checkIntervalTimer);
@@ -103,12 +101,12 @@ public function upgradeCleanup()
         $this->removeListener('close', [$this, 'onUpgradeTransportClose']);
     }
 
-    public function onUpgradeTransportClose()
+    public function onUpgradeTransportClose(): void
     {
         $this->onUpgradeTransportError('transport closed');
     }
 
-    public function onUpgradeTransportError($err)
+    public function onUpgradeTransportError($err): void
     {
         $this->upgradeCleanup();
         if ($this->upgradeTransport) {
@@ -117,7 +115,7 @@ public function onUpgradeTransportError($err)
         }
     }
 
-    public function upgradeTimeoutCallback($transport)
+    public function upgradeTimeoutCallback(object $transport): void
     {
         $this->upgradeCleanup();
         if ('open' === $transport->readyState) {
@@ -125,7 +123,7 @@ public function upgradeTimeoutCallback($transport)
         }
     }
 
-    public function setTransport($transport)
+    public function setTransport(object $transport)
     {
         $this->transport = $transport;
         $this->transport->once('error', [$this, 'onError']);
@@ -136,11 +134,10 @@ public function setTransport($transport)
         $this->setupSendCallback();
     }
 
-    public function onOpen()
+    public function onOpen(): void
     {
         $this->readyState = 'open';
 
-        // sends an `open` packet
         $this->transport->sid = $this->id;
         $this->sendPacket(
             'open',
@@ -158,7 +155,7 @@ public function onOpen()
         $this->setPingTimeout();
     }
 
-    public function onPacket($packet)
+    public function onPacket(array $packet)
     {
         if ('open' === $this->readyState) {
             // export packet event
@@ -185,19 +182,19 @@ public function onPacket($packet)
         }
     }
 
-    public function check()
+    public function check(): void
     {
         if ('polling' == $this->transport->name && $this->transport->writable) {
             $this->transport->send([['type' => 'noop']]);
         }
     }
 
-    public function onError($err)
+    public function onError($err): void
     {
         $this->onClose('transport error', $err);
     }
 
-    public function setPingTimeout()
+    public function setPingTimeout(): void
     {
         if ($this->pingTimeoutTimer) {
             Timer::del($this->pingTimeoutTimer);
@@ -210,20 +207,19 @@ public function setPingTimeout()
         );
     }
 
-    public function pingTimeoutCallback()
+    public function pingTimeoutCallback(): void
     {
         $this->transport->close();
         $this->onClose('ping timeout');
     }
 
-
-    public function clearTransport()
+    public function clearTransport(): void
     {
         $this->transport->close();
         Timer::del($this->pingTimeoutTimer);
     }
 
-    public function onClose($reason = '', $description = null)
+    public function onClose(string $reason = '', ?string $description = null): void
     {
         if ('closed' !== $this->readyState) {
             Timer::del($this->pingTimeoutTimer);
@@ -257,18 +253,18 @@ public function onClose($reason = '', $description = null)
         }
     }
 
-    public function send($data, $options, $callback): Socket
+    public function send($data, $options, ?callable $callback): Socket
     {
         $this->sendPacket('message', $data, $callback);
         return $this;
     }
 
-    public function write($data, $options = [], $callback = null): Socket
+    public function write($data, ?array $options = [], ?callable $callback = null): Socket
     {
         return $this->send($data, $options, $callback);
     }
 
-    public function sendPacket($type, $data = null, $callback = null)
+    public function sendPacket(string $type, $data = null, $callback = null): void
     {
         if ('closing' !== $this->readyState) {
             $packet = [
@@ -288,7 +284,7 @@ public function sendPacket($type, $data = null, $callback = null)
         }
     }
 
-    public function flush()
+    public function flush(): void
     {
         if ('closed' !== $this->readyState && $this->transport->writable
             && $this->writeBuffer
@@ -319,7 +315,7 @@ public function getAvailableUpgrades(): array
         return ['websocket'];
     }
 
-    public function close()
+    public function close(): void
     {
         if ('open' !== $this->readyState) {
             return;
@@ -335,19 +331,18 @@ public function close()
         $this->closeTransport();
     }
 
-    public function closeTransport()
+    public function closeTransport(): void
     {
-        //todo onClose.bind(this, 'forced close'));
         $this->transport->close([$this, 'onClose']);
     }
 
-    public function setupSendCallback()
+    public function setupSendCallback(): void
     {
         //the message was sent successfully, execute the callback
         $this->transport->on('drain', [$this, 'onDrainCallback']);
     }
 
-    public function onDrainCallback()
+    public function onDrainCallback(): void
     {
         if ($this->sentCallbackFn) {
             $seqFn = array_shift($this->sentCallbackFn);
diff --git a/src/Engine/Transport.php b/src/Engine/Transport.php
index fb48e64..09f07a5 100644
--- a/src/Engine/Transport.php
+++ b/src/Engine/Transport.php
@@ -31,14 +31,14 @@ public function onRequest($req)
         $this->req = $req;
     }
 
-    public function close($fn = null)
+    public function close(?callable $fn = null): void
     {
         $this->readyState = 'closing';
-        $fn = $fn ? $fn : [$this, 'noop'];
+        $fn = $fn ?: [$this, 'noop'];
         $this->doClose($fn);
     }
 
-    public function onError($msg, $desc = '')
+    public function onError(string $msg, string $desc = '')
     {
         if ($this->listeners('error')) {
             $err = [
@@ -51,7 +51,7 @@ public function onError($msg, $desc = '')
         }
     }
 
-    public function onPacket($packet)
+    public function onPacket($packet): void
     {
         $this->emit('packet', $packet);
     }
@@ -69,9 +69,10 @@ public function onClose()
         $this->removeAllListeners();
     }
 
-    public function destroy()
+    public function destroy(): void
     {
-        $this->req = $this->res = null;
+        $this->req = null;
+        $this->res = null;
         $this->readyState = 'closed';
         $this->removeAllListeners();
         $this->shouldClose = null;
diff --git a/src/Engine/Transports/Polling.php b/src/Engine/Transports/Polling.php
index 028165f..bb8a50b 100644
--- a/src/Engine/Transports/Polling.php
+++ b/src/Engine/Transports/Polling.php
@@ -11,6 +11,9 @@ class Polling extends Transport
     public $chunks = '';
     public $shouldClose = null;
     public $writable = false;
+    public $supportsBinary = null;
+    public $dataRes = null;
+    public $dataReq = null;
 
     public function onRequest($req)
     {
@@ -26,11 +29,9 @@ public function onRequest($req)
         }
     }
 
-    public function onPollRequest($req, $res)
+    public function onPollRequest(object $req, object $res): void
     {
         if ($this->req) {
-            echo('request overlap');
-            // assert: this.res, '.req and .res should be (un)set together'
             $this->onError('overlap from client');
             $res->writeHead(500);
             return;
@@ -45,32 +46,29 @@ public function onPollRequest($req, $res)
         $this->writable = true;
         $this->emit('drain');
 
-        // if we're still writable but had a pending close, trigger an empty send
         if ($this->writable && $this->shouldClose) {
             echo('triggering empty send to append close packet');
             $this->send([['type' => 'noop']]);
         }
     }
 
-    public function pollRequestOnClose()
+    public function pollRequestOnClose(): void
     {
         $this->onError('poll connection closed prematurely');
         $this->pollRequestClean();
     }
 
-    public function pollRequestClean()
+    public function pollRequestClean(): void
     {
         if (isset($this->req)) {
-            $this->req->res = null;
-            $this->req->onClose = $this->req->cleanup = null;
-            $this->req = $this->res = null;
+            $this->req = null;
+            $this->res = null;
         }
     }
 
-    public function onDataRequest($req, $res)
+    public function onDataRequest($req, $res): void
     {
         if (isset($this->dataReq)) {
-            // assert: this.dataRes, '.dataReq and .dataRes should be (un)set together'
             $this->onError('data request overlap from client');
             $res->writeHead(500);
             return;
@@ -83,26 +81,25 @@ public function onDataRequest($req, $res)
         $req->onEnd = [$this, 'dataRequestOnEnd'];
     }
 
-    public function dataRequestCleanup()
+    public function dataRequestCleanup(): void
     {
         $this->chunks = '';
-        $this->dataReq->res = null;
-        $this->dataReq->onClose = $this->dataReq->onData = $this->dataReq->onEnd = null;
-        $this->dataReq = $this->dataRes = null;
+        $this->dataReq = null;
+        $this->dataRes = null;
     }
 
-    public function dataRequestOnClose()
+    public function dataRequestOnClose(): void
     {
         $this->dataRequestCleanup();
         $this->onError('data request connection closed prematurely');
     }
 
-    public function dataRequestOnData($req, $data)
+    public function dataRequestOnData($req, $data): void
     {
         $this->chunks .= $data;
     }
 
-    public function dataRequestOnEnd()
+    public function dataRequestOnEnd(): void
     {
         $this->onData($this->chunks);
 
@@ -137,13 +134,12 @@ public function onData($data)
     public function onClose()
     {
         if ($this->writable) {
-            // close pending poll request
             $this->send([['type' => 'noop']]);
         }
         parent::onClose();
     }
 
-    public function send($packets)
+    public function send($packets): void
     {
         $this->writable = false;
         if ($this->shouldClose) {
@@ -156,7 +152,7 @@ public function send($packets)
         $this->write($data);
     }
 
-    public function write($data)
+    public function write($data): void
     {
         $this->doWrite($data);
         if (! empty($this->req->cleanup)) {
@@ -164,7 +160,7 @@ public function write($data)
         }
     }
 
-    public function doClose($fn)
+    public function doClose(callable $fn): void
     {
         if (! empty($this->dataReq)) {
             $this->dataReq->destroy();
diff --git a/src/Engine/Transports/PollingJsonp.php b/src/Engine/Transports/PollingJsonp.php
index 5329c1a..0db5e2a 100644
--- a/src/Engine/Transports/PollingJsonp.php
+++ b/src/Engine/Transports/PollingJsonp.php
@@ -12,8 +12,7 @@ class PollingJsonp extends Polling
 
     public function __construct($req)
     {
-        $j = isset($req->_query['j']) ? preg_replace('/[^0-9]/', '', $req->_query['j']) : '';
-        $this->head = "___eio[ $j ](";
+        $this->head = '___eio[' . (isset($req['_query']['j']) ? preg_replace('/[^0-9]/', '', $req['_query']['j']) : '') . '](';
         Debug::debug('PollingJsonp __construct');
     }
 
@@ -30,11 +29,10 @@ public function onData($data)
         call_user_func([$this, 'parent::onData'], preg_replace('/\\\\n/', '\\n', $data));
     }
 
-    public function doWrite($data)
+    public function doWrite($data): void
     {
         $js = json_encode($data);
 
-        // prepare response
         $data = $this->head . $js . $this->foot;
 
         // explicit UTF-8 is required for pages not served under utf
@@ -47,11 +45,11 @@ public function doWrite($data)
             echo new Exception('empty $this->res');
             return;
         }
-        $this->res->writeHead(200, '', $this->headers($this->req, $headers));
+        $this->res->writeHead(200, '', $this->headers($headers));
         $this->res->end($data);
     }
 
-    public function headers($req, $headers = [])
+    public function headers(array $headers = []): array
     {
         $listeners = $this->listeners('headers');
         foreach ($listeners as $listener) {
diff --git a/src/Engine/Transports/PollingXHR.php b/src/Engine/Transports/PollingXHR.php
index 73f9140..7ce3ecc 100644
--- a/src/Engine/Transports/PollingXHR.php
+++ b/src/Engine/Transports/PollingXHR.php
@@ -47,7 +47,7 @@ public function doWrite($data)
         $this->res->end($data);
     }
 
-    public function headers($req, $headers = [])
+    public function headers(object $req, array $headers = []): array
     {
         if (isset($req->headers['origin'])) {
             $headers['Access-Control-Allow-Credentials'] = 'true';
diff --git a/src/Engine/Transports/WebSocket.php b/src/Engine/Transports/WebSocket.php
index b118e05..fbaeaac 100644
--- a/src/Engine/Transports/WebSocket.php
+++ b/src/Engine/Transports/WebSocket.php
@@ -28,17 +28,17 @@ public function __destruct()
         Debug::debug('WebSocket __destruct');
     }
 
-    public function onData2($connection, $data)
+    public function onData2($connection, $data): void
     {
         call_user_func([$this, 'parent::onData'], $data);
     }
 
-    public function onError2($conection, $code, $msg)
+    public function onError2($conection, $code, $msg): void
     {
         call_user_func([$this, 'parent::onClose'], $code, $msg);
     }
 
-    public function send($packets)
+    public function send(array $packets): void
     {
         foreach ($packets as $packet) {
             $data = Parser::encodePacket($packet);
@@ -49,7 +49,7 @@ public function send($packets)
         }
     }
 
-    public function doClose($fn = null)
+    public function doClose(callable $fn = null): void
     {
         if ($this->socket) {
             $this->socket->close();