1 files changed, 58 insertions, 3 deletions

diff --git a/plumbing/object/commit.go b/plumbing/object/commit.go
index 8a0f35c..ceed5d0 100644
--- a/plumbing/object/commit.go
+++ b/plumbing/object/commit.go
@@ -17,14 +17,25 @@ import (
 )
 
 const (
-	beginpgp  string = "-----BEGIN PGP SIGNATURE-----"
-	endpgp    string = "-----END PGP SIGNATURE-----"
-	headerpgp string = "gpgsig"
+	beginpgp       string = "-----BEGIN PGP SIGNATURE-----"
+	endpgp         string = "-----END PGP SIGNATURE-----"
+	headerpgp      string = "gpgsig"
+	headerencoding string = "encoding"
+
+	// https://github.com/git/git/blob/bcb6cae2966cc407ca1afc77413b3ef11103c175/Documentation/gitformat-signature.txt#L153
+	// When a merge commit is created from a signed tag, the tag is embedded in
+	// the commit with the "mergetag" header.
+	headermergetag string = "mergetag"
+
+	defaultUtf8CommitMesageEncoding MessageEncoding = "UTF-8"
 )
 
 // Hash represents the hash of an object
 type Hash plumbing.Hash
 
+// MessageEncoding represents the encoding of a commit
+type MessageEncoding string
+
 // Commit points to a single tree, marking it as what the project looked like
 // at a certain point in time. It contains meta-information about that point
 // in time, such as a timestamp, the author of the changes since the last
@@ -38,6 +49,9 @@ type Commit struct {
 	// Committer is the one performing the commit, might be different from
 	// Author.
 	Committer Signature
+	// MergeTag is the embedded tag object when a merge commit is created by
+	// merging a signed tag.
+	MergeTag string
 	// PGPSignature is the PGP signature of the commit.
 	PGPSignature string
 	// Message is the commit message, contains arbitrary text.
@@ -46,6 +60,8 @@ type Commit struct {
 	TreeHash plumbing.Hash
 	// ParentHashes are the hashes of the parent commits of the commit.
 	ParentHashes []plumbing.Hash
+	// Encoding is the encoding of the commit.
+	Encoding MessageEncoding
 
 	s storer.EncodedObjectStorer
 }
@@ -173,6 +189,7 @@ func (c *Commit) Decode(o plumbing.EncodedObject) (err error) {
 	}
 
 	c.Hash = o.Hash()
+	c.Encoding = defaultUtf8CommitMesageEncoding
 
 	reader, err := o.Reader()
 	if err != nil {
@@ -184,6 +201,7 @@ func (c *Commit) Decode(o plumbing.EncodedObject) (err error) {
 	defer sync.PutBufioReader(r)
 
 	var message bool
+	var mergetag bool
 	var pgpsig bool
 	var msgbuf bytes.Buffer
 	for {
@@ -192,6 +210,16 @@ func (c *Commit) Decode(o plumbing.EncodedObject) (err error) {
 			return err
 		}
 
+		if mergetag {
+			if len(line) > 0 && line[0] == ' ' {
+				line = bytes.TrimLeft(line, " ")
+				c.MergeTag += string(line)
+				continue
+			} else {
+				mergetag = false
+			}
+		}
+
 		if pgpsig {
 			if len(line) > 0 && line[0] == ' ' {
 				line = bytes.TrimLeft(line, " ")
@@ -225,6 +253,11 @@ func (c *Commit) Decode(o plumbing.EncodedObject) (err error) {
 				c.Author.Decode(data)
 			case "committer":
 				c.Committer.Decode(data)
+			case headermergetag:
+				c.MergeTag += string(data) + "\n"
+				mergetag = true
+			case headerencoding:
+				c.Encoding = MessageEncoding(data)
 			case headerpgp:
 				c.PGPSignature += string(data) + "\n"
 				pgpsig = true
@@ -286,6 +319,28 @@ func (c *Commit) encode(o plumbing.EncodedObject, includeSig bool) (err error) {
 		return err
 	}
 
+	if c.MergeTag != "" {
+		if _, err = fmt.Fprint(w, "\n"+headermergetag+" "); err != nil {
+			return err
+		}
+
+		// Split tag information lines and re-write with a left padding and
+		// newline. Use join for this so it's clear that a newline should not be
+		// added after this section. The newline will be added either as part of
+		// the PGP signature or the commit message.
+		mergetag := strings.TrimSuffix(c.MergeTag, "\n")
+		lines := strings.Split(mergetag, "\n")
+		if _, err = fmt.Fprint(w, strings.Join(lines, "\n ")); err != nil {
+			return err
+		}
+	}
+
+	if string(c.Encoding) != "" && c.Encoding != defaultUtf8CommitMesageEncoding {
+		if _, err = fmt.Fprintf(w, "\n%s %s", headerencoding, c.Encoding); err != nil {
+			return err
+		}
+	}
+
 	if c.PGPSignature != "" && includeSig {
 		if _, err = fmt.Fprint(w, "\n"+headerpgp+" "); err != nil {
 			return err