[Python-Dev] 2.4 asyncore headache

[Nick Coghlan]

Tim Peters wrote:
> [Tim]
> 
>>>Now somebody, for some reason, added this to 2.4's asyncore.py:
>>>            if sys.platform == 'win32':
>>>                reuse_constant = socket.SO_EXCLUSIVEADDRUSE
> 
> 
> [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 SO_EXCLUSIVEADDRUSE 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 SO_EXCLUSIVEADDRUSE
> was a plausible Windowsy way to spell the Unixy SO_REUSEADDR ...

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