Python线程WebSocket服务器中的Ping和Pong

Question

我用Python写了一个支持多线程的websocket服务器，遵循了最新的websocket规范。现在我想让它每隔一段时间给每个客户端发送一个ping请求。我想到的唯一方法是重写BaseServer.server_forever()，代码如下：

# override BaseServer's serve_forever to send a ping request every now and then
class ModTCPServer(SocketServer.TCPServer):
    def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
        SocketServer.TCPServer.__init__(self, server_address, RequestHandlerClass, bind_and_activate)
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False
        
    def serve_forever(self, poll_interval=0.5):
        ###
        global PING_EVERY_SEC
        self.lastPing = int(time())
        ###
        self.__is_shut_down.clear()
        try:
            while not self.__shutdown_request:
                r, w, e = select.select([self], [], [], poll_interval)
                if self in r:
                    self._handle_request_noblock()
                ###
                now = int(time())
                if (now - self.lastPing) >= PING_EVERY_SEC:
                    self.socket.send(WebSocketPing(['0x89','0x21','0xa7','0x4b'], now)) # arbitrary key
                    self.lastPing = now
                ###
        finally:
            self.__shutdown_request = False
            self.__is_shut_down.set()

class LoginServer(SocketServer.ThreadingMixIn, ModTCPServer):
    pass

server = LoginServer(("", PORT), ApplicationHandler)
print "serving at port", PORT

server_thread = threading.Thread(target=server.serve_forever)
server_thread.daemon = True
server_thread.start()

while server_thread.isAlive():
    pass

server.shutdown()

这是构建Ping帧的函数，它只是把时间戳放在内容里：

def WebSocketPing(key, timestamp=False):
    data = ['0x89','0x8a'] # 0x89 = fin,ping 0x8a = masked,len=10
    data.extend(key)
    if timestamp:
        t = str(timestamp)
    else:
        t = str(int(time()))
    for i in range(10):
        masking_byte = int(key[i%4],16)
        masked = ord(t[i])
        data.append(hex(masked ^ masking_byte))
    frame = ''
    for i in range(len(data)):
        frame += chr(int(data[i],16))
    return frame

当我运行这个代码时，出现了一些问题。

Traceback (most recent call last):
  File "LoginServer.py", line 91, in <module>
    server = LoginServer(("", PORT), ApplicationHandler)
  File "LoginServer.py", line 63, in __init__
    SocketServer.TCPServer.__init__(self, server_address, RequestHandlerClass, bind_and_activate)
  File "/usr/lib/python2.6/SocketServer.py", line 400, in __init__
    self.server_bind()
  File "/usr/lib/python2.6/SocketServer.py", line 411, in server_bind
    self.socket.bind(self.server_address)
  File "<string>", line 1, in bind
socket.error: [Errno 112] Address already in use

我猜这可能是因为我对Python中重写的理解不够，或者是我处理这个问题的方法根本就不对。有没有更好的方法或者能让这个代码正常工作的办法呢？

Answer 1

这段代码没有在任何地方设置属性 __is_shut_down 和 __shutdown_request。所以，试图访问它们的时候会失败。你可以在构造函数里创建它们，像这样：

class ModTCPServer(SocketServer.TCPServer):
    def __init__(self, *args, **kwargs):
        SocketServer.TCPServer.__init__(self, *args, **kwargs)
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = threading.Event()

关于更新的内容：

socket.error: [Errno 112] Address already in use

这意味着另一个进程已经占用了指定的端口。在Unix系统上，你可以用 sudo netstat -ltpn 来找到那个进程。或者，你也可以选择一个不同的端口。