Campaign patches with binaries don't apply

[eseliger]

• Sourcegraph version: master
• Platform information: macOS 10.15.4, Chrome 81

Steps to reproduce:

1. Create an action that touches a binary file (ie. compress images in docs/ folder)
2. Create campaign

Expected behavior:

It

• works
• or warned me that it can't work
• or skips binaries so it doesn't fail

Actual behavior:

It fails with errors like

creating commit from patch for repository "X": gitserver: applying patch: exit status 1

$ git apply --cached -p0 --unidiff-zero
error: cannot apply binary patch to 'binary.ttf' without full index line
error: binary.ttf: patch does not apply

Corresponding diff (see that binary content is not inlined):

diff --git binary.ttf binary.ttf
index 563872c..3d12770 100644
Binary files binary.ttf and binary.ttf differ

[eseliger]

Findings:

• adding --binary to git diff in src-cli inlines the file, which should make it applicable.

• our go-diff parser doesn't understand that and skips that file. It should also account for a GIT binary patch header. In that case, the whole binary content needs to be decoded and set on the diff, so we can use it in the newFileContent function in patch_sets.go, making it correctly return binary: true in the resolver.

Seems to be git encodes the binary file contents using base85: https://github.com/git/git/blob/master/base85.c
Seems like the ascii85 package in Go could decode it (?)