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socket issue with recv()

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Hello,

I am starting socket scripting with python.
I do understand from the doc that a socket is bmocking by default.
I wrote 2 basics script to verify this behaviour.

my "tcp_server.py":


import socket, sys
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

HOST = '192.168.0.103'
PORT = 1060

s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((HOST, PORT))
while True:
   s.listen(1)
   print 'Listening at', s.getsockname()
   sc, sockname = s.accept()
   print 'We have accepted a connection from', sockname
   print 'Socket connects', sc.getsockname(), 'and', sc.getpeername()
   while True:
      data = sc.recv(1024)
      if data:
         print 'Got from client:', repr(data)
         data = ''
      else:
         #raise EOFError('socket closed')
         print 'socket closed by remote client'
         sc.close()
         sys.exit()


and my "tcp_client.py"

import socket, sys, time
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

HOST = '192.168.0.103'
PORT = 1060

s.connect((HOST, PORT))
print 'Client has been assigned socket name', s.getsockname()
while True:
   data = raw_input('cmd:')
   if (data == '\x05'):
      print 'closing socket and exit'
      s.close()
      sys.exit()
   s.sendall(data)

When both are running everything what I type in the client is received by the server.
When nothing is sent from the client the server is waiting (socket is blocking)
for next datas.
If I close the client with Ctrl-E (or a kill) the socket on the server is getting a null value and the server exit.
So everything is fine. And everything is clear in my mind.

The problem I have now is the following.
I have a script to connect to some telecom service.
The script is forking (parent/child)
The child is only reading what comes from the remote server.
Here the problematic code:

total = ''
while True:
   data = s.recv(1024)
   total += data
   if (data == ''):
      print 'remote site is closed'
      s.close()
      sys.exit()

What is happening is that I got some datas from the remote site,
Something like 'Contacting BH: ...'
But directly followed by 'remote site is closed.
And if I remove the 2 lines (s.close;sys.exit) my script is looping
So it means data=='' 
This makes no sense at all.
Why is the socket not waiting for the next datas flow ??
Why is the socket not blocking ?


With Perl I just have to write:

  while (sysread($socket,$data,1024)){
     syswrite(STDOUT,$data)
  }

And it works perfectly.

Any hint about what I missed in Python ?

kr,
Arthur.

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Thread

socket issue with recv() Arthur Clarck <aclarck5@gmail.com> - 2014-08-23 01:23 -0700
  Re: socket issue with recv() Arthur Clarck <aclarck5@gmail.com> - 2014-08-23 01:39 -0700
  Re: socket issue with recv() Marko Rauhamaa <marko@pacujo.net> - 2014-08-23 11:46 +0300
  Re: socket issue with recv() dieter <dieter@handshake.de> - 2014-08-24 07:59 +0200

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