How to properly close socket in both client and server (python)

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It looks like what you are looking for is an graceful shutdown. First your code does not work because you are closing socket immediately after calling shutdown.

The rule is that in a graceful shutdown, both sides must be aware of the shutting down and have acknowledged it before any actually closes the socket. I only found reference for that in this MSDN page, even if it is cited on this other SO answer.

Here is a simplified presentation of what is better explained if referenced page (I do not know how to properly format tables in SO 🙁 ) :

  • part 1 issues shutdown(socket.SHUT_WR) to notify it wants to terminate connexion, and continues to read from socket
  • part 2 receives end of file indication on socket (empty read), and can still send any remaining data – it then calls in turn shutdown(socket.SHUT_WR)
  • part 1 receives end of file on socket and knows that other part has terminated using connection
  • both parts can then close the socket

Remark : it does not matter if part 2 actually closes socket before part 1 received end of file, because part 1 was already only waiting for an indication of termination : no data can have been lost

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