Hi everybody, This advisory is for people who have installed darcs 2.1.2 via the Cabal build method. As you may have noticed, the cabalised darcs sometimes fails with errors like Codec.Compression.Zlib: incorrect data check Why this happens ---------------- Older versions of darcs can to produce gzipped files with broken CRCs. We never noticed this because our homegrown wrapper around the C libz library does not pick up these errors. Lately, we have been working on adopting the Haskell zlib wrapper, which is made available by default in darcs.cabal. This new wrapper is more stringent and fails when it encounters these files. Workaround 1 : use C libz instead of Haskell zlib ------------------------------------------------- So how can you work around these errors? If you are building darcs on any Unix-y operating system (e.g. Linux or MacOS X), you can cabal configure darcs to use the old C libz binding: cabal configure -f external-zlib This will restore our homegrown wrapper which ignores the broken CRCs (note that the darcs head no longer *produces* these broken files, thanks to debugging by Matthias Andree and to a bugfix by David Roundy; http://bugs.darcs.net/issue844 for details). In principle, the same advice applies for Windows users, with more details hopefully to follow on how the C libz in a GHC-accesible location. Details to follow. In the meantime, you can either build darcs using the old configure and make technique (assuming you have MSYS and related tools), or use a binary that does not use the Haskell zlib wrapper (for example, by downgrading to http://www.haskell.org/~simonmar/darcs-2.0.2+75.zip ) Workaround 2 : fix your broken gzipped files -------------------------------------------- If you have control over the repositories with broken gzipped files, it should be possible to repair these files by gunzipping them and then redo-ing the gzip. We think that the attached script should help. Please report back if this is not the case. How we will fix this problem in the long term --------------------------------------------- I'm very sorry for the grief this has caused. To begin with, we will ensure that the 2.2 release gets more testing before releasing it in January. It will also handle these broken CRCs more gracefully. Our plan is to - either extend darcs repair or provide a Haskell script to fix these broken files - detect the broken files and advise users to run darcs repair (or the script) as needed - somewhere in the future, disallow broken CRC files whilst still advising users on how to fix their files. Many thanks! -- Eric Kow http://www.nltg.brighton.ac.uk/home/Eric.Kow PGP Key ID: 08AC04F9