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[Python-Dev] socket timeouts fail w/ makefile()

Guido van Rossum guido@python.org
Fri, 21 Mar 2003 06:17:29 -0500 
>     >> I discovered much to my chagrin today that the socket
>     >> module's new timeout capability doesn't play well with file
>     >> objects as returned by a socket's makefile method.
> 
>     Guido> Can you explain better how it doesn't work?
> 
> When the socket is in non-blocking mode, reads on the file returned by
> .makefile() will fail with an IOError if there is nothing to return.

Isn't that exactly what a timeout is supposed to do?  What would you
have expected?

>     >> I would think the greatest use of timeouts would be using
>     >> higher-level line-oriented modules like urllib and ftplib.  In
>     >> addition, since makefile() isn't always available, it seems
>     >> worthwhile to implement something in socket.py, thus making
>     >> makefile() universally available.
> 
>     Guido> Um, when is makefile() not available?  
> 
> I don't know.  I was going by the doc string in socketmodule.c which
> says, in part:
> 
>     ...
>     makefile([mode, [bufsize]]) -- return a file object for the socket [*]\n\
>     ...
>      [*] not available on all platforms!");
> 
> Maybe the docs are just wrong.  According to the #ifdef in the code, if
> NO_DUP is defined (OS/2, Windows, BeOS), makefile() isn't.

That's the docs for the _socket module, which is (nowadays) an
implementation detail.  Read socket.py instead.

>     Guido> There's code for Windows that emulates it, returning a
>     Guido> file-like object.  Maybe that code should be enabled
>     Guido> universally rather than only on Windows...
> 
> That sounds similar to what is in timeoutsocket.py.  It would have the
> advantage of providing identical semantics across all platforms.

Again, I won't have time to do this until after I'm back from Python
UK, so I'd appreciate it if someone helped with this, e.g. by filing a
patch.

--Guido van Rossum (home page: http://www.python.org/~guido/)