On Thu, 15 Jan 2009 11:44:44 +0100, Alessio Pace <alessio.p...@gmail.com> wrote:
Hi,
I would like to have a client connect via TCP to a server (say, server "A"),
then the client close the connection and connect via TCP to another server
(say, server "B") using the same TCP port that was bound locally while
connecting to "A". And then this done over and over again switching from B
to A to B etc..
The fact is that it all works if both the client and the server do
transport.loseConnection() before the client tries to connect to the other
server from the same local port, instead if *only* the client does
transport.loseConnection(), I obtain:
[Failure instance: Traceback (failure with no frames): <class
'twisted.internet.error.ConnectBindError'>: Couldn't bind: 98: Address
already in use.
which it is strange to me as the next connectTCP() attempt is called in the
connectionLost() method of the client, so the socket should be closed
already.
This is because the client connection goes into the CLOSE_WAIT state instead
of really closing all the way right away. Google for "tcp state diagram"
and take a look at how a socket can close - notice that of the two paths
there are to get to CLOSED, only one of them goes through CLOSE_WAIT.
There are ways to change this (on most platforms, you can reduce the amount
of time a socket spends in CLOSE_WAIT before going to CLOSED), but it may not
be a good idea to use them. The CLOSE_WAIT state helps make sure that all
data is delivered to the right TCP connection and not a different, unrelated
TCP connection by accident.
Jean-Paul
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