How to empty a socket in python?

Question

I need to empty the data on a socket (making sure that there is nothing to receive). Unfortunately, there is no function for this in the python socket module.

I've implemented something this way:

def empty_socket(sock):
    """remove the data present on the socket"""
    input = [sock]
    while 1:
        inputready, o, e = select.select(input,[],[], 0.0)
        if len(inputready)==0: break
        for s in inputready: s.recv(1)

What do you think? Is there a better way to do that?

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Update: I don't want to change the socket timeout. What's why i prefer a select to a read.

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Update: The original question was using the 'flush' term. It seems that 'empty' is a better term.

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Update - 2010-02-27 : I've noticed a bug when the pair has closed. The inputready is always filled with the sockets. I fixed that by adding a maximum number of loops. Is there a better fix?

Answer 1

Not sure if this will work, but you could attach a file object to the socket's file descriptor and call the flush() method on that file object:

import os

file_obj = os.fdopen(your_socket.fileno())
file_obj.flush()

This won't work in Windows because the descriptor returned by fileno() can't be passed to os.fdopen() in Windows

Answer 2

Using select.select is good practice, as indicated in the Socket Programming HOWTO. You'll need to set the socket as non-blocking, using sock.setblocking(0).

Just a comment about nomenclature: flush is normally associated with output operations.

Answer 3

If by "flush" you mean throw away any pending incoming data then you can either use select() like you do, or set the socket to nonblocking and read in a loop until you're out of data.

Also note that (from the Linux manpage):

 Under Linux, select() may report a socket file descriptor as "ready for
 reading", while nevertheless a subsequent read blocks.  This could  for
 example  happen  when  data  has arrived but upon examination has wrong
 checksum and is discarded.  There may be other circumstances in which a
 file  descriptor is spuriously reported as ready.  Thus it may be safer
 to use O_NONBLOCK on sockets that should not block.

http://stackoverflow.com/questions/858282/spurious-readiness-notification-for-select-system-call

And as has been noted by others, "flush" usually refers to output.