[Nix-dev] Handling unavailable NARs in Hydra

[Ludovic Courtès]

Hello!

I stumbled upon the following problem:

  $ wget \
    http://hydra.nixos.org/project/nixpkgs/channel/all/nar/nix/store/pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6
  $ file pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6 
  pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6: XML

Indeed, the file is an HTML page that reads this:

  <h1>Error</h1>

  <p>I'm very sorry, but the following error(s) occurred:</p>

  <ul>

  <li><div class="error-msg">Path /nix/store/pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6 is no longer available.</div></li>

Shouldn't it instead return 404 so that `nix-build' et al. can actually
notice that the NAR is not available?  Currently, they just bail out
like this:

  *** Step 1/1: downloading `http://hydra.nixos.org/project/nixpkgs/channel/all/nar/nix/store/pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6' into `/nix/store/pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6'
  bunzip2: (stdin) is not a bzip2 file.
  error: unexpected end-of-file
  cannot unpack `/nix/store/maih07ail14jp5hd8d70r0kvvj1gx035-pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6' into `/nix/store/pra59fbsjvmw16fpasj7hn3jcbadwivl-guile-1.8.6' at /nix/store/k266y7lmai2y61ni79743m91zrjb0clv-nix-0.13pre14722/libexec/nix/substituters/download

Thanks,
Ludo'.