[Twisted-web] sendLine and connectionLost question

DAVID JIMENEZ CARRASCO djimenez at unipost.es
Thu May 27 02:42:02 EDT 2010

Hi Jean Paul,

A lot of thanks for your quick answer. It's really appreciated. Regarding your answer, I understand that when the remote hosts stop responding, after a timer, the connection is considered lost. But the main problem is that the remaining client (the one that have not been disconnected) should continue working without problems and the fact is that the server closes connection to that client too in a "non clean fashion".

Regards and a lot of thanks for your help,


De: twisted-web-bounces at twistedmatrix.com [twisted-web-bounces at twistedmatrix.com] En nombre de exarkun at twistedmatrix.com [exarkun at twistedmatrix.com]
Enviado el: jueves, 27 de mayo de 2010 3:38
Para: Twisted Web World
Asunto: Re: [Twisted-web] sendLine and connectionLost question

On 26 May, 10:46 pm, djimenez at unipost.es wrote:
>Hi all,
>I'm trying to write a typical chat server application with twisted. At
>this moment, all is working fine except for some strange behaviour with
>sendLine and connectionLost funcs. Let me explain the problem:
>- I have a server on the internet.
>- I connect two PCs (2 clients) from the same LAN through a router to
>that server
>- All is working fine until I disconnect the LAN of one of those PC
>(The client is disconnected but the server doesn't know about it). Just
>to test a typical wireless disconnection without closing sockets,
>- After disconnecting I try to send some messages through the remaining
>clients to all clients through this function:
>    def sendMessageToAllClients(self, mesg,reqClient):
>        for client in self.clientProtocols:
>            dataLength = str(len(mesg))
>            if (len(dataLength) < 8):
>                dif = 8 - len(dataLength)
>                dataLength = "0"*dif + dataLength
>            print "Enviando a:",str(client)
>            client.sendLine(dataLength+mesg)
>            client.clearLineBuffer()

You shouldn't be calling `client.clearLineBuffer()` here.
>As you can see, I send a message to all clients, including the one
>disconnected because the server doesn't
>know at this moment that the client is "out". I'm able to send 6 or 7
>messages to the remaining client but
>after that, the connection get lost. I would expect to have a
>connectionLost with the client offline but actually
>I got a connectionLost in both clients and I don't know why. The server
>disconnect both clients with "non clean fashion".
>Any help or advice would be highly appreciated.

This is how TCP works.  If the remote host stops responding to packets,
then there's a period of time where the connection still appears to be
up anyway.  After a TCP-level timer expires, the connection is
considered lost.


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