socket client server... simple example... not working...

[SpreadTooThin]

client:

import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("192.168.1.101", 8080))
print 'Connected'
s.send('ABCD')
buffer = s.recv(4)
print buffer
s.send('exit')


server:

serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.bind(("192.168.1.101", 8080))
serversocket.listen(5)
print 'Listen'
(clientsocket, address) = serversocket.accept()
print 'Accepted'
flag = True
while flag:
chunk = serversocket.recv(4)
if chunk == '':
raise RuntimeError, "socket connection broken"
elif chunk == 'exit':
flag = False
else:
serversocket.send(chunk)
print 'Done'

Server says!

Listen
Accepted
Traceback (most recent call last):
File "server.py", line 11, in ?
chunk = serversocket.recv(4)
socket.error: (57, 'Socket is not connected')


Client says:
Connected

What have I done wrong now!

 

[SpreadTooThin]

client:

import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("192.168.1.101", 8080))
print 'Connected'
s.send('ABCD')

Here you didn't check the return value of send to determine if all of the string was copied to the kernel buffer to be sent, so you may have only succeeded in sending part of 'ABCD'.

buffer = s.recv(4)

in the above call, 4 is the maximum number of bytes recv will return. It looks as though you are expecting it to return exactly 4 bytes, but in order to get that, you will need to check the length of the return value and call recv again with a lower limit until the combination of the return values of each call gives a total length of 4.

print buffer
s.send('exit')

Again, you didn't check the return value of send.

server:

serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.bind(("192.168.1.101", 8080))
serversocket.listen(5)
print 'Listen'
(clientsocket, address) = serversocket.accept()
print 'Accepted'
flag = True
while flag:
chunk = serversocket.recv(4)

You're calling recv on serversocket instead of on clientsocket. You're also relying on recv to return exactly 4 bytes, which it may not do.

if chunk == '':
raise RuntimeError, "socket connection broken"
elif chunk == 'exit':
flag = False
else:
serversocket.send(chunk)

Another missing check of the return value of send.

print 'Done'

Server says!

Listen
Accepted
Traceback (most recent call last):
File "server.py", line 11, in ?
chunk = serversocket.recv(4)
socket.error: (57, 'Socket is not connected')


Client says:
Connected

What have I done wrong now!

I recommend switching to Twisted. The Twisted equivalent (I guess - the protocol defined above is strange and complex (probably unintentionally, due to the things you left out, like any form of delimiter) and I doubt I really understand the end goal you are working towards), minus bugs (untested):

# client.py
from twisted.internet import reactor, protocol

class Client(protocol.Protocol):
buf = ''
def connectionMade(self):
self.transport.write('ABCD')
def dataReceived(self, data):
self.buf += data
if len(self.buf) >= 4:
reactor.stop()

protocol.ClientCreator(reactor, Client).connectTCP('192.168.1.101', 8080)
reactor.run()

# server.py
from twisted.internet import reactor, protocol

class Server(protocol.Protocol):
buf = ''
def dataReceived(self, bytes):
self.buf += bytes
exit = self.buf.find('exit')
if exit != -1:
self.transport.write(self.buf[:exit])
self.buf = self.buf[exit + 4:]
reactor.stop()
else:
self.transport.write(self.buf)
self.buf = ''

f = protocol.ServerFactory()
f.protocol = Server
reactor.listenTCP('192.168.1.101', 8080, f)
reactor.run()

Hope this helps,

Jean-Paul

Jean-Paul many thanks for this and your effort.
but why is it every time I try to do something with 'stock' python I
need another package?
By the time I've finished my project there are like 5 3rd party add-ons
to be installed.
I know I'm a python newbie... but I'm far from a developer newbie and
that can be a recipe for
disaster. The stock socket should work and I think I've missed an
obvious bug in the code other
than checking the return status.

 

[SpreadTooThin]

[snip]

Jean-Paul many thanks for this and your effort.
but why is it every time I try to do something with 'stock' python I
need another package?

Maybe you are trying to do things that are too complex

No quite the contrary.. Which is why I want to keep it simple...

I don't generally find this to be problematic.

I have because it usually means makeing on many platforms...
Most of the time this is the nightmare.

Not every library can be part of the standard library, neither can the
standard library satisfy every possible use-case. Relying on 3rd party
modules isn't a bad thing.

No but the less number of lines of code I have to support the better.

It was indeed as you said I was trying to read/write on the server
socket
not the client socket. (of the server module)

Well, I did mention one bug other than failure to check return values.
Maybe you missed it, since it was in the middle. Go back and re-read
my response.

Thanks again.
B.

 

[Bryan Olson]

Jean-Paul many thanks for this and your effort.
but why is it every time I try to do something with 'stock' python I
need another package?

Twisted has it's fan, but you don't "need" it. Your code had a few
specific problems, and fixing them has little or nothing to do with
Twisted.

By the time I've finished my project there are like 5 3rd party add-ons
to be installed.
I know I'm a python newbie... but I'm far from a developer newbie and
that can be a recipe for
disaster. The stock socket should work and I think I've missed an
obvious bug in the code other
than checking the return status.

Obviously you wanted to recv() on your 'clientsocket' not your
'seversocket'. You can use sendall() to send all the given data;
it will raise an exception if it fails so there's no return code to
check. Since TCP is a stream protocol and does not have any concept
of message boundaries, you'll need to delimit messages within your
protocol, and call recv() until you have an entire message.

 

[Fredrik Lundh]

but why is it every time I try to do something with 'stock' python I
need another package?

it's well known that all problems known to man can be solved by down-
loading Twisted, PyParsing, the Stream Editor, or that other programming
language that cannot be named.

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