go-gitdiff

A Go library for parsing and applying patches generated by git diff, git show, and git format-patch. It can also parse and apply unified diffs generated by the standard diff tool.

It supports both standard line-oriented text patches and Git binary patches.

patch, err := os.Open("changes.patch")
if err != nil {
    log.Fatalf(err)
}

files, preamble, err := gitdiff.Parse(patch)
if err != nil {
    log.Fatalf(err)
}

// files is a slice of *gitdiff.File describing the files changed in the patch
// preamble is a string of the content of the patch before the first file

Status

In development, expect API changes. Patch parsing works, but has not been tested extensively against real-world patches. Patch application has not been implemented yet.

Why another git/unified diff parser?

Several packages with similar functionality exist, so why did I write another?

1. No other packages I found support binary diffs, as generated with the --binary flag. This is the main reason for writing a new packages, as the format is pretty different from line-oriented diffs and is unique to Git.

2. Most other packages only parse patches, so you need another package to apply them (and if they do support applies, it is only for text files.)

3. This package aims to accept anything that git apply accepts, and closely follows the logic in apply.c.

4. It seemed like a fun thing to write and a good way to learn more about Git.

Differences From Git

1. Certain types of invalid input that are accepted by git apply generate errors. These include:

   • Numbers immediately followed by non-numeric characters
   • Trailing characters on a line after valid or expected content

2. Errors for invalid input are generally more verbose and specific than those from git apply.

3. The translation from C to Go may have introduced inconsistencies in the way Unicode file names are handled; these are bugs, so please report any issues of this type.

4. When reading headers, there is no validation that OIDs present on an index line are shorter than or equal to the maximum hash length, as this requires knowing if the repository used SHA1 or SHA256 hashes.

5. When reading "traditional" patches (those not produced by git), prefixes are not stripped from file names; git apply attempts to remove prefixes that match the current repository directory/prefix.