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To: python-list@python.org
From: Malte Forkel <malte.forkel@berlin.de>
Subject: Re: How to determine whether client and server are on the same host
Date: Tue, 26 Nov 2013 12:23:49 +0100
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Am 26.11.2013 00:07, schrieb Chris Angelico:
> 
> Two easy ways you could do this. I would be inclined to do what
> PostgreSQL and others do, and have an explicit indication that you
> want to use a local method: for instance, the name "localhost". Use of
> anything else (including "127.0.0.1") means you use TCP/IP as normal,
> but the strict word "localhost", which is normally equivalent to the
> address 127.0.0.1, would signal your app to use the direct method (for
> PostgreSQL, that's a Unix socket rather than a TCP one). This means
> you can still force telnet to be used even if you're working locally -
> good for debugging.
>
Unfortunately, I can't rely on the user to use a specific way to specify
the (local) host.

> Alternatively, you can simply query the current network interfaces for
> their IPs, and see if the IP you were given is in that list. I don't
> know of a way to do that in core Python, but the C function you need
> is getifaddrs(), and this claims to wrap all that up nicely:
> 
> https://pypi.python.org/pypi/netifaces
> 
> This method would detect, for instance, that calling up 192.168.0.19
> port 12345 is a local lookup, because eth0 has address 192.168.0.19,
> and that 192.168.2.2 port 54321 is local too, because wlan0 has
> address 192.168.2.2.
> 
That's a very nice module which I wasn't aware of. But if possible I
wouldn't want to force the user to install a (binary) extension module.
Finding the right module for his platform and version of Python might be
too difficult.

> If you aren't too concerned with running this on multiple platforms
> (which seems likely - working with the local filesystem implies you
> know a lot about what the server and client are doing), you could
> simply parse the output of 'ip addr', 'ipconfig', 'ifconfig', or some
> equivalent network utility for your platform. That might be easier
> than playing with the package, depending on environment.
>
The application is run under Windows as well. So I'd have to parse the
output of other network utilities as well, possibly in a variety of
languages.

Thanks for your suggestions! I'm sorry I'm so picky. May be there just
is no easy solution.

Malte