I tried to upload a simple app to a local cf build, and it failed because the go-buildpack download failed.
It turns out that the buildpack /var/vcap/store/shared/cc-buildpacks/75/21/ \ 75210aea-160c-4438-a9f9-3710734f35cd_a25a466217b64d5e4d47a6796be8ab23e7b7eeaf
had lost its pkzip header (but the end of the file looked like it was part of a zip file).
When I moved it out of the way ('mv 75 hide-75') I got a stranger error message, which unfortunately scrolled off my window before I thought to report it.
What's the best way to push a faulty buildpack out of the cache?
