[bug #27983] Windows text mode mis-interpreted

[Ilguiz Latypov]

URL:
  <http://savannah.gnu.org/bugs/?27983>

                 Summary: Windows text mode mis-interpreted
                 Project: findutils
            Submitted by: ilgiz
            Submitted on: Mon 09 Nov 2009 11:04:14 PM EST
                Category: xargs
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: None
           Fixed Release: None

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Details:

When xargs receives its input from a pipe or redirect, it uses the stdin file
descriptor prepared for it by the OS environment.

Emulation of Unix on Windows introduces an extra entity into file operations,
text vs. binary mode processing.  One has to explicitly set it with the "r"
vs. "rb" (O_BINARY) open mode.

The Unix-on-Windows OS environment has to rely on heuristic such as the mount
flag "binmode" and CYGWIN variable's "binmode" element to decide on the
default mode for stdin and stdout file descriptors.  

I am not sure if the implementation of "r" and "w" modes in fopen() calls
also relies on this heuristic, but this could be verified by running my script
before and after the change.

It appears that there is not such thing as "rt" and "wt" modes in the Open
Group standard.  These would be nice to turn the text mode processing
explicitly.

  http://www.opengroup.org/onlinepubs/000095399/functions/fopen.html

I believe text processing utilities that care about the Unix-on-Windows
emulations need an option to specify input/output modes explicitly or, at
least, to declare a certain mode of operation explicitly.  The "sed" utility
has a "--binary" option and other utilities such as "wc" and "tr" have
switched to the certain binary mode.

With xargs, the heuristic rules of choosing the text processing mode for the
input stream work in synchronization with other tools producing such streams.

There is a corner case where a text stream is obtained from a pipe.  I
believe pipes are always opened in binary mode by the Unix-on-Windows
environment as it is difficult to predict the kind of processing that will
consume the pipe.

I am attaching a test script that shows how xargs fails to set the text
processing mode on standard input obtained from a pipe.  I believe this could
be done in a way similar to the "tr" implementation but with the opposite
intention,

  stdin = freopen( NULL, "r", stdin );

 
http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=blob;f=gl/lib/xfreopen.c;h=32e68fa35c8f8cc5c95641a0fc3b761d23d6bf8d;hb=HEAD

 
http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=blob;f=src/tr.c;h=c5f18f98384e10ff871a4e4daac42270e96743d6;hb=HEAD

  http://www.opengroup.org/onlinepubs/000095399/functions/freopen.html

(The xfreopen wrapper ignores the possibility that freopen may return a
different pointer, so I would not recommend using this wrapper).




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File Attachments:


-------------------------------------------------------
Date: Mon 09 Nov 2009 11:04:14 PM EST  Name: text-mode.sh  Size: 3kB   By:
ilgiz
A script showing how xargs 4.4.0 accepts the existing text processing mode of
stdin
<http://savannah.gnu.org/bugs/download.php?file_id=19022>

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