[Python-Dev] 2.4 asyncore headache (original) (raw)

Nick Coghlan ncoghlan at iinet.net.au
Sat Aug 14 01:30:47 CEST 2004

Tim Peters wrote:

[Tim]

Now somebody, for some reason, added this to 2.4's asyncore.py: if sys.platform == 'win32': reuseconstant = socket.SOEXCLUSIVEADDRUSE [Andrew] I'll back out this change. But only if that's the right thing to do <0.9 wink>. I gave up reading the Windows SOEXCLUSIVEADDRUSE docs after it got to the "This situation can be quite complicated; even though the socket has been closed, the underlying transport may not terminate its connection ..." part. But by that point, it sure didn't seem like SOEXCLUSIVEADDRUSE was a plausible Windowsy way to spell the Unixy SOREUSEADDR ...

Is test_socketserver currently passing for you?

A couple of days ago I ran the test suite with -unetwork, and that test failed, but I haven't got around to looking into it yet. Could this be related?

[rambling discussion of what I found out about this so far follows]

Anyway, after some hunting, the difference between Windows and Unix SO_REUSEADDR, is that on Unix, this only allows local address reuse when the existing socket is in a TIME_WAIT state. On Windows, it allows local address reuse anytime.

See http://hea-www.harvard.edu/~fine/Tech/addrinuse.html. Look for the phrase 'security stigma', then read the bit starting with 'On some operating systems. . .'

The issue is that if we don't set SO_REUSEADDR on Windows, then you get into problems with getting EADDRINUSE when you shutdown and restart a TCP/IP server on the same local address (generally if the socket has gone into TIME_WAIT while shutting down).

Looking at MSDN, SO_EXCLUSIVEADDRUSE is a way to say 'make my socket behave like a UNIX socket without SO_REUSEADDR specified'. That is, with no options specified, a Windows socket is vulnerable to having another process come along, specify SO_REUSEADDR for their socket options, and succeed in reusing the same local port.

(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/winsock/using_so_exclusiveaddruse.asp)

What I can't find is a way to get Unix-like SO_REUSEADDR behaviour on Windows.

Cheers, Nick.

-- Nick Coghlan | Eugene, Oregon Email: ncoghlan at email.com | USA

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