Python PyQt4: Using QTcpServer to handle data from client, but I can't receive the data

Question

I am confused that why the QTcpSocket instance could send text to client before connected in the official example. While a connection came in, the result is: New connection came 0 New connection ran into thread: 944

My code is at the bottom of the content, it base on the official example [threadedfortuneserver.py] .

# -*- coding: utf-8 -*-
__author__ = 'erliang'
# TODO:消息处理以及UI响应

from PyQt4.QtCore import QThread, pyqtSignal
from PyQt4.QtGui import QMessageBox, QApplication
from PyQt4.QtNetwork import QTcpSocket, QTcpServer, QHostAddress

from ui import ServerWindow


class Socket(QTcpSocket):
    def __init__(self, parent=None):
        super(Socket, self).__init__(parent)
        self.connected.connect(self.on_connected)
        self.disconnected.connect(self.on_disconnected)
        self.readyRead.connect(self.on_ready_read)
        self.error.connect(self.on_error)

    def on_connected(self):
        print "Socket connected!"

    def on_disconnected(self):
        print "Socket disconnected!"

    def on_ready_read(self):
        print "Received data:", self.readAll()

    def on_error(self):
        print "Error occurred:", self.errorString()


class ChatThread(QThread):
    error = pyqtSignal(QTcpSocket.SocketError)

    def __init__(self, socketDescriptor, parent):
        super(ChatThread, self).__init__(parent)

        self.socketDescriptor = socketDescriptor
        self.received_data = None

    def run(self):
        # 在此处新建线程处理客户端消息
        self.tcp = Socket()
        print self.tcp.state()
        print "New connection ran into thread:", self.socketDescriptor
        if not self.tcp.setSocketDescriptor(self.socketDescriptor):
            self.error.emit(self.tcp.error())
            return
        # self.tcp.disconnectFromHost()
        # self.tcp.waitForDisconnected()

class ChatServer(QTcpServer):
    def __init__(self, parent=None):
        super(ChatServer, self).__init__(parent)
        self.newConnection.connect(self.on_new_connection)

    def incomingConnection(self, socketDescriptor):
        # print "New connection came!", socketDescriptor
        self.thread = ChatThread(socketDescriptor, self)
        self.thread.finished.connect(self.thread.deleteLater)
        self.thread.start()

    def on_new_connection(self):
        print "New connection came"


class Server(ServerWindow):
    def __init__(self):
        super(Server, self).__init__()
        self.StartServerButton.clicked.connect(self.start_server)
        self.StopServerButton.clicked.connect(self.stop_server)

        self.chat_server = ChatServer()

        # self.ClientLogTable.setRowCount(2)
        # self.ClientLogTable.setItem(1, 1, QTableWidgetItem('123'))

    def start_server(self):
        # GUi与Socket操作不能在同一线程, 每次打开服务器便新建一个线程
        if not self.chat_server.isListening():
            addr = QHostAddress()
            addr.setAddress('127.0.0.1')
            if not self.chat_server.listen(addr, 8888):
                QMessageBox.critical(self, u"服务器", u"无法初始化服务器: %s." % self.server.errorString())
                self.close()
                return
            self.InfoLabel.setText(u'服务器IP:{0}   端口：{1}'.format(self.chat_server.serverAddress().toString(),
                                                                self.chat_server.serverPort()))

    def stop_server(self):
        if self.chat_server.isListening():
            self.chat_server.close()
            self.InfoLabel.setText(u'服务器尚未启动！')


if __name__ == '__main__':
    import sys

    app = QApplication(sys.argv)
    client = Server()
    client.show()
    sys.exit(app.exec_())