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

Hugh Secker-Walker hugh@merl.com
Mon Jul 23 18:02:00 GMT 2007

Eric Blake <ebb9 <at> byu.net> writes:

 > 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.
 > As a workaround, you can force gzip to see stdout in binary mode by 
using an
 > intermediary pipe, as in popen("gzip | cat > outputfile", "wb").

Thank you.  That simple workaround appears to work.

Interestingly, I had tried popen("gzip | dd of=outputfile", "wb") as a
lower-level way to avoid what I guessed was a problem with gzip using
the stdout.  The dd attempt didn't work.  This failure suggests to me
that dd and gzip experience a similar problem in this popen() context,
a problem that cat somehow avoids.


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