Merging encrypted files with conflicts produces encrypted content in the "merged" file

[jmurty]

When you merge branches containing transcrypt-encrypted files, if the files have conflicts the resulting "merged" file produced by Git for manual resolution ends up as a real mess, mostly or entirely full of the encrypted text which cannot be sensibly merged.

The root problem seems to be that git does not run the smudge/textconv filter on all the BASE, LOCAL, REMOTE conflicting versions of files before attempting a three-way merge, and instead attempts the merge using at least one – and maybe all – of the encrypted versions of these files. E.g. the encrypted content as available from git show :1:FILENAME and git show :2:FILENAME etc mid-merge.

I have not been able to find a workaround just within Git, and have instead added a custom "crypt" merge driver to handle this situation.

Here is a PR against our fork of Transcrypt as an example: ixc#1

This change isn't yet fully tested, and is written against a fairly old version of transcrypt.

Let me know if I should bring it up to date and submit a PR here directly to add the "crypt" merge driver to the latest version of transcrypt?

[jmurty]

In case it helps someone else, here is our latest merge driver script that fixes merging of transcrypt-encrypted files whether or not the merged changes result in conflicts.

You can see the transcrypt (1.1.0) changes necessary to fully support this on the branch https://github.com/ixc/transcrypt/commits/fix-merge-with-conflicts

You enable the driver by:

• adding this block to .git/config:

  [merge "crypt"]
      driver = \"$(git rev-parse --git-common-dir)\"/crypt/merge %O %A %B %L %P
      name = Merge transcrypt secret files
  

• for each transcrypt-ed file entry in .gitattributes add merge=crypt like so:

  *.secret* filter=crypt diff=crypt merge=crypt
  

• save the following merge driver script to .git/crypt/merge

#!/usr/bin/env bash
# Decrypt BASE, LOCAL, and REMOTE versions of file being merged
echo "$(cat $1 | ./.git/crypt/smudge)" > $1
echo "$(cat $2 | ./.git/crypt/smudge)" > $2
echo "$(cat $3 | ./.git/crypt/smudge)" > $3

# Merge the decrypted files to the working copy named by $5
# We must redirect stdout to $5 here instead of letting merge-file write to
# $2 as it would by default, because we need $5 to contain the final result
# content so a later crypt `clean` generates the correct hash salt value
git merge-file --stdout --marker-size=$4 -L local -L base -L remote $2 $1 $3 > $5

if [[ "$?" == "0" ]]; then
  # If the merge was successful (no conflicts) re-encrypt the merged working
  # copy file to the incoming "local" temp file $2 which git will then
  # update in the index during the "Auto-merging" step.
  # Git needs the cleaned copy to avoid triggering the error:
  #     error: add_cacheinfo failed to refresh for path 'FILE'; merge aborting.
  echo "$(cat $5 | ./.git/crypt/clean $5)" > $2
  exit 0
else
  # If the merge was not successful, copy the merged working copy file to the
  # "local" temp file $2 which git will then re-copy back to the working copy
  # so the user can fix it manually
  cp $5 $2
  exit 1
fi

[jmurty]

A fix for this issue is now on the https://github.com/elasticdog/transcrypt/tree/legacy-v1 branch pending possible inclusion in a future update to the legacy version 1 stream, and definite inclusion in the version 2 stream.

[jmurty]

Tickets that are probably related to this one: #8 #23 #67

[jmurty]

Fix merged to master branch, to be included in the next release