[Nix-dev] nix-channel can't process channel data from Hydra

[Peter Simons]

Hi Eelco,

 >> I use the channel from my own Hydra instance on several machines just fine,
 >> but on one of them I get this error during "nix-channel --update" for no
 >> apparent reason:
 >
 > Is this a reproducible problem on that machine?

yes, it is. One difference between that machine and those that work fine is
that it requires a proxy server to connect to the Internet. So, I guess, the
problem could be due to a caching proxy server responding with a broken file.

What is strange, though, is that a manually downloaded version of

  http://hydra.cryp.to:8080/jobset/nixpkgs/haskell-updates/channel/latest/nixexprs.tar.bz2

looks just fine -- it's an okay bz2-compressed tarball. Now, when
nix-channel downloads the same file

  downloading Nix expressions from `http://hydra.cryp.to:8080/jobset/nixpkgs/haskell-updates/channel/latest/nixexprs.tar.bz2'...
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                   Dload  Upload   Total   Spent    Left  Speed
  100 32672    0 32672    0     0  22659      0 --:--:--  0:00:01 --:--:-- 22673
  unpacking channels...
  bzip2: (stdin) is not a bzip2 file.
  /nix/store/cv12p8zpy0fp6spirw9ph78byz55r6n0-gnutar-1.26/bin/tar: This does not look like a tar archive
  /nix/store/cv12p8zpy0fp6spirw9ph78byz55r6n0-gnutar-1.26/bin/tar: Exiting with failure status due to previous errors
  builder for `/nix/store/n4hi4l4r5z7z5m20v9v5spwfb9xg728h-hydra-crypto.drv' failed with exit code 2
  error: build of `/nix/store/n4hi4l4r5z7z5m20v9v5spwfb9xg728h-hydra-crypto.drv' failed
  cannot unpack the channels at /run/current-system/sw/bin/nix-channel line 145.

..., then the tarball referred to by

  /nix/store/n4hi4l4r5z7z5m20v9v5spwfb9xg728h-hydra-crypto.drv

is broken, indeed, it's *not* a valid bz2-compressed tarball. Apparently,
nix-channel downloads this file somehow differntly than my manual invocation of
curl does.

Take care,
Peter