1.5.24: data corruption problem with popen and gzip on a text mounted filesystem

Christopher Faylor cgf-use-the-mailinglist-please@cygwin.com
Mon Jul 23 17:02:00 GMT 2007

On Mon, Jul 23, 2007 at 03:42:55PM +0000, Eric Blake wrote:
>Hugh Secker-Walker <hugh <at> merl.com> writes:
>> I'm having trouble getting correct behavior on a third-party OpenSource 
>> project that I'm building using Cygwin.  The problem involves the 
>> writing of corrupt data to a file.  The output file is created and 
>> written via popen("gzip > outputfile", "wb").  The data is fine if the 
>> filesystem is mounted in binary mode.  The data is corrupted if the 
>> filesystem is mounted in text mode.
>> My understanding of the documentation is that pipes and shells' stdin 
>> and stdout will be in binary mode if the CYGWIN env variable contains 
>> the 'binmode' setting, regardless of the binary/text mount flag of the 
>> filesystem the file is mounted on.
>Indeed - so you are handing the data to gzip in binary mode.

And that's irrelevant wrt what goes on the disk anyway.  gzip can
compress a '\r\n' as well as a '\n'.

>The problem, then, is likely not your program, but gzip - it seems to
>me that gzip should be forcing binary mode but does not.  cgf is the
>cygwin gzip maintainer, so hopefully he can do something about this.
>In the meantime, I'll probably fire off a mail to the bug-gzip list
>with a patch (since the upstream maintainer for gzip also maintains
>coreutils, so he is already familiar with text vs.  binary issues in
>other apps that he maintains).

gzip is linked with binmode.o, like most of the things that I maintain
(i.e., no upstream patch really necessary - isn't that my call?).  If
I use a really simple test case of just outputting directly to a text
mode mount, it works fine.


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