go-mailpatch

go-mailpatch is a small Go library that reads git format-patch emails back into structured data — author, date, series position, commit message, and a fully parsed diff — using only the standard library and without ever shelling out to git.

It grew out of matcha's developer-mail features (inline patch review and git-mail), pulled into a standalone, git-free, dependency-free package.

The format-patch lifecycle

go-mailpatch sits on the read side: it parses what format-patch and send-email produced, so your program can review, display, thread, or index a patch. Applying it (git am) stays your responsibility — the library never touches a repository.

What it parses

• The envelope. From (split into name + email), Date, Subject, Message-ID, In-Reply-To, References — decoded from RFC 2047 encoded-words, with quoted-printable / base64 / multipart bodies handled.
• The subject prefix. [PATCH 2/3], [RFC PATCH v3 1/4] → index, total, version, and a cover-letter flag, with a clean subject left over.
• The diff. Each file as a FileChange (change type, paths, modes, binary flag, hunks, add/delete counts), plus a DiffStat over the whole patch.
• Whole threads. ParseMbox for every message in an mbox; ParseSeries to group them into a cover letter plus ordered patches.

What it is not

• Not a patch applier. No git am, no working-tree writes. Parse here, apply and validate yourself.
• Not a diff renderer. You get structure; coloring and printing are yours.
• Not a full email stack. It handles the headers and encodings format-patch mail uses in practice, not every RFC 5322 corner.

Sister projects