python sockets: make sure that TCP packets are send before closing connection

Question

I am working with a relay that is controlled via TCP. As far as I understood the following code is supposed to work:

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('192.168.0.200', 17494))
s.send(chr(101))
s.close()

However, I noticed that the socket gets closed before the package is actually send, and the relay does not do anything. As dirty solution I now put a sleep statement before closing the connection and it works properly.

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('192.168.0.200', 17494))
s.send(chr(101))
time.sleep(0.01)
s.close()

Is there something more clever one can do to ensure that the package got actually send before closing the connection?

This is pretty awkward. Calling close(2) on a socket should still send the data that's queued. — cnicutar
– cnicutar, Commented Sep 18, 2013 at 11:55

Manoj Pandey · Accepted Answer · 2013-09-18 17:44:05Z

2

You could set the SO_LINGER option using s.setsockopt. The linger option makes the socket wait (internally) and close only after sending all the pending data upto the specified timeout value. Something like:

linger_enabled = 1
linger_time = 10 #This is in seconds.
linger_struct = struct.pack('ii', linger_enabled, linger_time)
s.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, linger_struct)

answered Sep 18, 2013 at 17:44

Manoj Pandey

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