Build fails on snapcraft.io, works locally (during `cabal update`)

[Vidar]

I have a build that consistently fails on build.snapcraft.io, but I'm unable to reproduce it locally.

Here's the snapcraft log: https://build.snapcraft.io/user/koalaman/shellcheck/350552

It appears to fail during `cabal update` to fetch the list of available Haskell packages:

    Downloading the latest package list from hackage.haskell.org
    [11/Oct/2018:05:03:10 +0000] "GET http://hackage.haskell.org/packages/archive/00-index.tar.gz HTTP/1.1" 301 - "-" "cabal-install/1.22.6.0 (linux; x86_64)"
    cabal: <socket: 10>: resource vanished
    Failed to run 'build': Exit code was 1.

The same build fails with the same message for all architectures.

Meanwhile, `snapcraft cleanbuild --debug` on my local machine works fine:

    Downloading the latest package list from hackage.haskell.org
    Warning: ShellCheck.cabal: Ignoring unknown section type: custom-setup
    Resolving dependencies...
    Notice: installing into a sandbox located at
    /root/build_shellcheck/parts/shellcheck/build/.cabal-sandbox
    Downloading base-compat-0.10.4...
    Downloading dlist-0.8.0.5...
    Configuring dlist-0.8.0.5...
    [...]
    Retrieved 'shellcheck_git_amd64.snap'

Is this a proxy problem? Or a Hackage IP block? Or a cabal issue? I'm not sure how to troubleshoot it.

[Colin Watson (cjwatson)]

This is really a bug in the somewhat old version of the Haskell HTTP library present in xenial's version of cabal-install:

  https://github.com/haskell/HTTP/issues/14

We may be able to work around it by adding connection persistence support to launchpad-buildd's internal proxy.

[Colin Watson (cjwatson)]

Hmm, it doesn't actually seem to be just that, although the symptoms are extremely similar. xenial's haskell-cabal-install was built against libghc-http-dev 1:4000.2.20-3, and the bug above was fixed in HTTP 4000.2.11. The current issue is in fact:

  https://github.com/haskell/HTTP/issues/68

[Vidar (koalaman)]

I tried a number of workarounds:

* The Stack build fails, possibly because `haskell-stack` is too old to support custom-setup
* The Docker build fails because `docker.io` is too old to support intermediate images
* A new, custom Docker build fails because it doesn't appear to nest well in LXD
* I tried pre-downloading files for Cabal with wget, but I was not able to get deprecated local-repo going or to get it to build from tarballs

So... I added a squid proxy to proxy to the proxy ¯\_(ツ)_/¯

   https://github.com/koalaman/shellcheck/commit/359b1467a29

It's not exactly pretty, but it takes some of the pressure off.