[Tutor] Network programming
Kent Johnson
kent_johnson at skillsoft.com
Mon Sep 13 12:03:59 CEST 2004
At 09:48 AM 9/13/2004 +0200, Johan Geldenhuys wrote:
>Thanks Kent,
>
>I will look at my loop and at the links you gave. My links stays up, but
>as you noticed, I must get away of sending the data received from either
>connections. Will I be able to use the select.select for this.
Yes, you can use select, or either of the modules built on top of select -
asyncore and asynchat.
>There are three file desriptors in this. One for incoming, one for
>outgoing and the other for errors. Can I use the outgoing one to send the
>data the incoming list received?
Yes, that is the right approach.
Kent
>Thanks
>
>Johan
>
>On Fri, 2004-09-10 at 03:44, Kent Johnson wrote:
>>
>>Johan,
>>
>>It looks to me like your program will get stuck in the inner while loop.
>>There is no way inside this loop to get a new value for indata or outdata.
>>
>>There are two approaches you could use to solve your problem - either put
>>the two sides of the transfer into separate threads, or use some kind of
>>polling to look for data available on either socket.
>>
>>The thread approach usually uses three threads:
>>- a master thread that listens to the server socket and accepts the
>>incoming connection. It then opens the forwarding socket and spawns two
>>forwarding threads.
>>- the forwarding threads read from one socket and write to another. They
>>are symmetric - one thread reads from socket A and writes to socket B; the
>>other thread reads from socket B and writes to socket A.
>>
>>Each thread uses blocking I/O - the master thread blocks on
>>socket.accept(); the forwarding threads block on socket.recv().
>>
>>A simple example that uses the treaded approach to do something similar to
>>what you want to do is here:
>><http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/114642>http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/114642
>>In this case the Pinhole class is the master thread; when it gets a
>>connection it creates two PipeThreads to do the reading and writing.
>>
>>
>>The polling approach uses non-blocking I/O. In it's crudest form its loop
>>looks like this:
>>forever:
>> if data available on socket A:
>> read from socket A
>> write to socket B
>> if data available on socket B:
>> read from socket B
>> write to socket A
>> sleep for a bit
>>
>>This is crude because it is either unresponsive (if the sleep is long) or
>>wasteful of CPU (if the sleep is short and there is not much to do). It
>>might be fine for a simple use with just one connection, though.
>>
>>The Python asyncore and asynchat modules use a more sophisticated version
>>of this; instead of sleeping, they use a system call that blocks until
>>there is activity on any of the sockets it is watching. This is very
>>efficient, as the polling loop only wakes up when there is something for it
>>to do. Medusa
>><<http://www.nightmare.com/medusa/index.html>http://www.nightmare.com/medusa/index.html>
>>and Twisted
>><<http://www.twistedmatrix.com/>http://www.twistedmatrix.com/> are two
>>servers that are based on this
>>approach. It can be more efficient for large numbers of connections because
>>it doesn't have to create a thread for each one.
>>
>>asyncore and asynchat hide the actual polling loop from you. You interact
>>with them by defining callback methods that get called when data is
>>available or when a channel is available for writing. This tutorial is a
>>good introduction to this approach. The proxy server at the end is similar
>>to what you are trying to do.
>><http://www.nightmare.com/medusa/programming.html>http://www.nightmare.com/medusa/programming.html
>>
>>Medusa includes a chat server which is also similar to your application.
>>
>>I hope this helps get you on the right track!
>>Kent
>>
>>At 10:14 AM 9/9/2004 +0200, Johan Geldenhuys wrote:
>> >I still have trouble when I want to send data out as soon as it comes in
>> >from one side.
>> >My server listens and accepts the calls and then builds the client
>> >connection to the destination. Please see if you can assist.
>> >
>> >Thanks
>> >
>> >Johan
>> >####################################################
>> >
>> ># we have an incoming socket connect
>> > newConn, addr = self._serverSocket.accept()
>> > self.log('Connection received from: %s:%s' % addr)
>> >
>> > #while connection is active on server:
>> > while 1:
>> > #self._ne1_id = '1234'
>> > #self._ne2_id = '1111'
>> >
>> > indata = newConn.recv(8192)
>> > self.log('First Data received from LCT:' +
>> > `indata`)
>> >
>> > if '\xff' in indata:
>> > continue
>> >
>> > if '\x01' in indata:
>> > continue
>> >
>> > #Look for string of 1234 in indata:
>> > if indata[0:4] == self._ne1_id:
>> > self.log('indata 0:4 is:' + `indata[0:4]`)
>> > self.sock = socket(AF_INET, SOCK_STREAM)
>> >
>> > #connect to this destination if the string is
>> > 1234
>> > self.sock.connect((self._ne1_ip,
>> > self._ne1_port)) # This is previously defined
>> > self.log('Connection established to NE1:
>> > %s:%i' % (self._ne1_ip, self._ne1_port))
>> > outdata = self.sock.recv(8192)
>> > #when connection to destination is up:
>> > while 1:
>> > if indata:
>> > self.sock.send(indata)
>> > self.log('indata send to NE, line
>> > 106: ' + `indata`)
>> >
>> > # If break sequence is received from
>> > server side, close the client connection
>> > if '\x11' in indata:
>> > self.log('Break character received')
>> > break
>> > self.sock.close()
>> > self.log('connection to NE1 now
>> closed')
>> >
>> > if oudata:
>> > newConn.send(outdata)
>> > self.log('Data from NE:' +
>> `outdata`)
>> >###########################################################
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >On Tue, 2004-09-07 at 14:58, Kent Johnson wrote:
>> >>
>> >>
>> >>We might be better able to help if you post your code.
>> >>
>> >>Here is a list of HTTP proxy servers written in Python, you might find
>> >>something helpful there:
>> >><<http://xhaus.com/alan/python/proxies.html>http://xhaus.com/alan/pytho
>> n/proxies.html>http://xhaus.com/alan/python/proxies.html
>> >>
>> >>Kent
>> >>
>> >>At 02:19 PM 9/6/2004 +0200, Johan Geldenhuys wrote:
>> >> >Hi,
>> >> >
>> >> >I am new to Python and would like to know more about network programming
>> >> >in particilar.
>> >> >
>> >> >I have a script that sets up a socket server and must wait for incoming
>> >> >connections. Once a call has been accepted, it must make another socket
>> >> >connection to a destination.
>> >> >
>> >> >Now, I want to let these two "talk" to each other. Once the server
>> >> >receives data it must be send out to the destination and when the
>> >> >destination has data, it must be send out to the connection that
>> made the
>> >> >first call to the server.
>> >> >
>> >> >Does anybody have any examples or tips on how I can let this happen. My
>> >> >calls work for the first batch of data and then when new data is
>> received,
>> >> >the calls break.
>> >> >
>> >> >Thanks
>> >> >
>> >> >--
>> >> > Johan Geldenhuys
>> >> >Access Telecommunication Systems
>> >> > Mail to: johan at accesstel.co.za
>> >> >--
>> >> >This message has been scanned for viruses and
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>> >>
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>> and is
>> >> >believed to be clean.
>> >> >_______________________________________________
>> >> >Tutor maillist - Tutor at python.org
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>> >
>> >
>> >
>> >
>> >
>> >--
>> > Johan Geldenhuys
>> >Access Telecommunication Systems
>> > Mail to: johan at accesstel.co.za
>> >
>> >--
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>> >dangerous content by
>> <<http://www.azitech.co.za>http://www.azitech.co.za>Azitech, and is
>> >believed to be clean.
>>
>>_______________________________________________
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>
>
>
>
>
>--
> Johan Geldenhuys
>Access Telecommunication Systems
> Mail to: johan at accesstel.co.za
>
>--
>This message has been scanned for viruses and
>dangerous content by <http://www.azitech.co.za>Azitech, and is
>believed to be clean.
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