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Date: Sat, 25 Oct 2014 15:42:12 +0300
From: Martin <martin@libtec.org>
To: python-list@python.org
Subject: asyncio: setting file permissions of a Unix socket?
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Hi! :)

I'm using the asyncio.Protocol interface to build a server which binds
to a unix socket file.  I want other system users to connect to the
unix socket, so to communicate with the server.

Where should I set the permissions of the file?

The problem is that the socket file is created when the programs
starts listening for the connections.  Because of this, I can't change
the file permission before a connection is made.  At the same time, a
connection can't happen because of the file permissions.

Currently, I workaround this with os.umask(0o000).  But I also want to
make other files later with default permissions.  So I have to revert
the umask, but where?  I can only do this in the client connection
code, which is out of place.

Bellow is what I've done.  Can you suggest a better way?  I wish to
avoid permission fixing code like os.umask() for every connection.
Maybe I shouldn't use asyncio.Protocol in the first place?

Thank you! :)

Example code:

#! /usr/bin/env python3

import os
import asyncio

class ExampleServer(asyncio.Protocol):
    def __init__(self):
        os.umask(0o002)    # This is my workaround.  Can I avoid this?
        # if not umask_restored: # An alternative workaround.
        #     os.umask(0o002)

    def connection_made(self, transport):
        self.transport = transport

    def data_received(self, data):
        print("Data: ", data)
        self.transport.write(b"OK, bye!\n")
        self.transport.close()


def main():
    socket_filepath = "/tmp/example-server.socket"
    loop = asyncio.get_event_loop()
    server_coroutine = loop.create_unix_server(ExampleServer, socket_filepath)
    server = loop.run_until_complete(server_coroutine)

    os.umask(0o000)             # This is my workaround.

    try:
        loop.run_forever()
    except KeyboardInterrupt:
        print("exit")
    finally:
        server.close()
        loop.close()
        os.remove(socket_filepath)


if __name__ == "__main__":
    main()