PyQt4的UDP广播似乎不起作用

Question

我用PyQt4写的应用程序似乎没有接收到任何数据。readyRead事件甚至都没有被触发。应用程序的使用方式如下：

python server.py -s -p 50000 #(server on port 50000)
python server.py -c -p 50000 #(client sending data to port 50000)

//

import sys
import time

from PyQt4 import QtNetwork, QtCore
from optparse import OptionParser

class Server(object):

    def __init__(self, port):

        self.port = port

        try:
            self.socket = QtNetwork.QUdpSocket()
            self.socket.bind(QtNetwork.QHostAddress.Broadcast, int(self.port), QtNetwork.QUdpSocket.ShareAddress)

            self.socket.readyRead.connect(self.receiver)

        except QtNetwork.QUdpSocket.NetworkError:
            print "EXCEPTION DURING INITIALIZING SERVER'S SOCKET"
            sys.exit(1)

    def receiver(self):
        print "DEBUG: RECEIVE"
        while(self.socket.hasPendingDatagrams()):
            try:
                size = self.socket.pendingDatagramSize()
                msg, host, port = self.socket.readDatagram(size)
            except:
                print "EXCEPTION DURING RECEIVEING AND READING DATAGRAM"
            else:
                print "HOST %s:%s MSG: %s" % (str(host), str(port), str(msg))

    def __del__(self):
        print "DESTRUCTOR"
        self.socket.close()

class Client(object):

    def __init__(self, port):

        self.port = port

        try:
            self.socket = QtNetwork.QUdpSocket()
        except:
            print "EXCEPTION DURING INITIALIZING CLIENT'S SOCKET"

        self.main_loop()

    def main_loop(self):
        for i in range(20):
            self.debug_msg()
            time.sleep(0.5)
        print "EXITING"
        self.socket.close()


    def debug_msg(self):
        msg = "DEBUG"
        self.socket.writeDatagram(msg, QtNetwork.QHostAddress.Broadcast, int(self.port))


if __name__ == "__main__":

    parser = OptionParser()
    parser.add_option("-p", "", action="store", type="string", dest="port")
    parser.add_option("-c", "", action="store_true", dest="client")
    parser.add_option("-s", "", action="store_true", dest="server")

    options, args = parser.parse_args()

    if not (options.server or options.client):
        print "Client/Server not specified. Could not continue..."
        sys.exit(1)

    elif not options.port:
        print "Server's port not specified. Could not continue..."
        sys.exit(1)

    else:

        if options.server:
            serv = Server(options.port)

            App = QtCore.QCoreApplication(sys.argv)
            sys.exit(App.exec_())
        else:
            client = Client(options.port)

Answer 1

QtNetwork.QUdpSocket.NetworkError 其实不是一种错误类型，而只是一个常量。至于为什么要把这个套接字绑定到 QHostAddress.Broadcast，你是不是应该用 QHostAddress.Any 呢？

Answer 2

在你的客户端程序中，你没有启动Qt的事件循环。你应该创建一个应用程序对象，然后要么调用它的exec_方法，通过定时器来处理debug_msg的调用，要么使用QCoreApplication.processEvents()来手动处理事件循环。

还有一个选择是使用flush()方法：

http://doc.qt.nokia.com/latest/qabstractsocket.html#flush

bool QAbstractSocket::flush ()

这个函数会尽量将内部写入缓冲区的数据写入到底层的网络套接字中，而不会让程序停下来。如果有数据被写入，这个函数会返回true；如果没有数据被写入，则返回false。

如果你需要QAbstractSocket立即开始发送缓冲的数据，就调用这个函数。成功写入的字节数取决于操作系统。在大多数情况下，你不需要调用这个函数，因为QAbstractSocket会在控制权返回到事件循环后自动开始发送数据。如果没有事件循环，应该调用waitForBytesWritten()。