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Mads Kiilerich <mads at kiilerich.com> added the comment:

I was scared by the note in the documentation and wondered if the socket Python API was completely incapable of handling half-closed connections cross platform. pitrou helped me on IRC to track the note down to this issue.


IMO the bug report should have been rejected and the documentation patch should be removed. It shouldn't be that surprising that shutting something down that already has been shutdown (by the peer) will fail.

I don't see any indication that a "shutdown call closes the connection on the other half". It makes it half-closed as it should - and if it did anything else (which the note indicates) then it would be a big violation of BSD TCP API.

Ok, it might be slightly surprising that the next shutdown on the other end fails, but that is fully covered by "Note Some behavior may be platform dependent, since calls are made to the operating system socket APIs." It is not specific to Python in any way, AFAICT.

If anything it could just say something like "Note that shutdown of a socket that already has been shut down by the peer is platform dependent and might fail."

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nosy: +kiilerix, pitrou
title: socket.shudown documentation: on some platforms, closing one half closes the other half -> socket.shutdown documentation: on some platforms, closing one half closes the other half

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<http://bugs.python.org/issue6774>
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  • Antoine Pitrou at Jan 12, 2012 at 1:24 pm
    Changes by Antoine Pitrou <pitrou at free.fr>:


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    nosy: +neologix

    _______________________________________
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  • Charles-François Natali at Jan 12, 2012 at 7:48 pm

    Charles-Fran?ois Natali <neologix at free.fr> added the comment:

    I was scared by the note in the documentation and wondered if the
    socket Python API was completely incapable of handling half-closed
    connections cross platform. [...]
    It makes it half-closed as it should
    Indeed. Calling shutdown(SHUT_WR) doesn't close the other end (which doesn't make much sense), it just sends a FIN (or RST depending on the context). It's the other end which decides to return ENOTCONN upon shutdown(SHUT_RD) on OS X, which is questionable (not sure it's against the BSD socket API, since shutdown(SHUT_RD) doesn't have any counterpart in the TCP layer).

    I also find this note confusing and scary for no good reason, and since I don't think we should document every OS idiosyncrasies, it would probably be better to revert it.

    I'll leave this open for a couple days to see if anyone objects, otherwise I'll revert it.

    ----------
    resolution: accepted ->
    status: closed -> open

    _______________________________________
    Python tracker <report at bugs.python.org>
    <http://bugs.python.org/issue6774>
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  • Nicolas Dumazet at Jan 12, 2012 at 9:16 pm

    Nicolas Dumazet <nicdumz at gmail.com> added the comment:

    It's the other end which decides to return ENOTCONN upon shutdown(SHUT_RD) on OS X, which is questionable
    (not sure it's against the BSD socket API, since shutdown(SHUT_RD) doesn't have any counterpart in the TCP layer).
    Exactly. The same code raises a socket.error in one platform (mac os) and not on another (linux). Why not document this questionable behavior?

    I'm sorry, I realize that my original patch was imprecise. I'm not an expert here, and I simply read http://svn.python.org/view/python/trunk/Lib/test/test_socket.py?r1d125&r2h611&pathrevh611 . Ok, fine -- it doesn't close the other end per se, but shutdown(SH_RD) after a FIN on MacOS raises a socket.error . This is questionable, unexpected, and should be documented.


    If possible, I'd like to push for a rewording instead of a revert.

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    Python tracker <report at bugs.python.org>
    <http://bugs.python.org/issue6774>
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  • Charles-François Natali at Jan 14, 2012 at 10:29 am

    Charles-Fran?ois Natali <neologix at free.fr> added the comment:

    This is questionable, unexpected, and should be documented.
    There's already this note at the top of the socket module documentation:
    """
    Note

    Some behavior may be platform dependent, since calls are made to the
    operating system socket APIs.
    """

    There are other such subtleties with the socket API, e.g. SO_REUSEADDR
    which doesn't have the same semantics on Windows. As I said earlier, I
    don't think we should document every platform quirks: it will make
    users worry for no reason, and as time passes, there's a chance that
    the documentation doesn't match the actual behavior.
    For example, this specific behavior might very well be a bug, and it's
    not our responsibility to document this.

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    _______________________________________
    Python tracker <report at bugs.python.org>
    <http://bugs.python.org/issue6774>
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  • Roundup Robot at Jan 29, 2012 at 3:43 pm
    Roundup Robot <devnull at psf.upfronthosting.co.za> added the comment:

    New changeset 9be82f458b79 by Charles-Fran?ois Natali in branch 'default':
    Issue #6774: Back out c8b77efe8b56, which only brings confusion.
    http://hg.python.org/cpython/rev/9be82f458b79

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    nosy: +python-dev

    _______________________________________
    Python tracker <report at bugs.python.org>
    <http://bugs.python.org/issue6774>
    _______________________________________
  • Charles-François Natali at Jan 29, 2012 at 3:46 pm
    Charles-Fran?ois Natali <neologix at free.fr> added the comment:

    I've reverted the commit.

    ----------
    resolution: -> rejected
    stage: -> committed/rejected
    status: open -> closed
    versions: +Python 3.3

    _______________________________________
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postedJan 12, '12 at 1:19p
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