CODEWITHSUNDEEP
pythonqtsocketspyqtpyside
LBarret
LBarret

Reputation: 1123

Why is there no content when calling readAll in a Qtcpsocket's readyRead callback?

I am building a minimal socket server that display a window when it receives a message.

The server uses the newConnection signal to get the client connections and connect the proper signals (connected, disconnected and readyRead) for each socket.

When running the server program, and sending some data to the proper address, for each datum sent, a QTCPSocket is connected, then readyRead, then immediately disconnected. And within the readyRead callback, the readAll return nothing. (I suppose this is the cause of the disconnected signal).

Still, the client gets no "broken pipe error" and can continue to send data.

How that can happen ?

here's the code :

class Client(QObject):
    def connects(self):
        self.connect(self.socket, SIGNAL("connected()"), SLOT(self.connected()))
        self.connect(self.socket, SIGNAL("disconnected()"), SLOT(self.disconnected()))
        self.connect(self.socket, SIGNAL("readyRead()"), SLOT(self.readyRead()))
        self.socket.error.connect(self.error)
        print "Client Connected from IP %s" % self.socket.peerAddress().toString()

    def error(self):
        print "error somewhere"

    def connected(self):
        print "Client Connected Event"

    def disconnected(self):
        self.readyRead()
        print "Client Disconnected"

    def readyRead(self):
        print "reading"
        msg = self.socket.readAll()
        print QString(msg), len(msg)
        n = Notification(QString(msg))
        n.show()

class Server(QObject):
    def __init__(self, parent=None):
        QObject.__init__(self)
        self.clients = []

    def setup_client_socket(self):
        print "incoming"
        client = Client(self)
        client.socket = self.server.nextPendingConnection()
        #self.client.socket.nextBlockSize = 0
        client.connects()
        self.clients.append(client)

    def StartServer(self):
        self.server = QTcpServer()
        self.server.listen(QHostAddress.LocalHost, 8888)
        print self.server.isListening(), self.server.serverAddress().toString(), self.server.serverPort()
        self.server.newConnection.connect(self.setup_client_socket)

update : I tested directly with the socket module from python standard lib and it works. So the general setup of my machine and the network are not the guilty parties there. This is likely some QT issue.

Upvotes: 0

Views: 841

Answers (2)

alexisdm
alexisdm

Reputation: 29896

The SLOT function expects a string representing the name of a slot, and it should be preceded by the target of the slot:

self.connect(self.socket, SIGNAL("connected()"), self, SLOT("connected()"))

but without quotes, you are making an immediate call to the function where the connect line is. As you didn't even declare these functions as slots using the QtCore.Slot/pyqtSlot decorator, they wouldn't be called anyway when the signals are emitted, if you use the SLOT function.

For undecorated python functions, you should use one of these syntaxes:

self.connect(self.socket, SIGNAL("connected()"), self.connected)

Or

self.socket.connected.connect(self.connected)

Notice the lack of () at the end of the last parameter.

Additionally you shouldn't call readyRead in disconnected, if there was data to read before the disconnection, the readyRead function was most likely already called.

Upvotes: 1

synthesizerpatel
synthesizerpatel

Reputation: 28036

Probably a half-open socket - you can't trust clients to always open or terminate sessions correctly. Client might be disconnecting without doing a proper hangup on the server? I haven't looked at the QTcpServer code, but it might be caused by someone port scanning your box?

Either way, the server should always be able to handle bad or no data gracefully. The internet is a crazy place with all sorts of weird packets floating around.

Upvotes: 1

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