modules/git: Recognize SSH signed tags too

Just like commits, tags can be signed with either an OpenPGP, or with an
SSH key. While the latter is supported already, SSH-signed tags have not
been. This patch teaches the git module to recognize and handle
SSH-signed tags too.

This will stop the signatures appearing in release notes, but are
currently unused otherwise.

Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>

modules/git/repo_tag.go

@@ -185,10 +185,15 @@ func parseTagRef(ref map[string]string) (tag *Tag, err error) {
 
 	tag.Tagger = parseSignatureFromCommitLine(ref["creator"])
 	tag.Message = ref["contents"]
-	// strip PGP signature if present in contents field
+	// strip the signature if present in contents field
 	pgpStart := strings.Index(tag.Message, beginpgp)
 	if pgpStart >= 0 {
 		tag.Message = tag.Message[0:pgpStart]
+	} else {
+		sshStart := strings.Index(tag.Message, beginssh)
+		if sshStart >= 0 {
+			tag.Message = tag.Message[0:sshStart]
+		}
 	}
 
 	// annotated tag with GPG signature

modules/git/tag.go

@@ -14,6 +14,8 @@ import (
 const (
 	beginpgp = "\n-----BEGIN PGP SIGNATURE-----\n"
 	endpgp   = "\n-----END PGP SIGNATURE-----"
+	beginssh = "\n-----BEGIN SSH SIGNATURE-----\n"
+	endssh   = "\n-----END SSH SIGNATURE-----"
 )
 
 // Tag represents a Git tag.
@@ -71,17 +73,36 @@ l:
 			break l
 		}
 	}
-	idx := strings.LastIndex(tag.Message, beginpgp)
-	if idx > 0 {
-		endSigIdx := strings.Index(tag.Message[idx:], endpgp)
-		if endSigIdx > 0 {
-			tag.Signature = &CommitGPGSignature{
-				Signature: tag.Message[idx+1 : idx+endSigIdx+len(endpgp)],
-				Payload:   string(data[:bytes.LastIndex(data, []byte(beginpgp))+1]),
+
+	extractTagSignature := func(signatureBeginMark, signatureEndMark string) (bool, *CommitGPGSignature, string) {
+		idx := strings.LastIndex(tag.Message, signatureBeginMark)
+		if idx == -1 {
+			return false, nil, ""
 		}
-			tag.Message = tag.Message[:idx+1]
+
+		endSigIdx := strings.Index(tag.Message[idx:], signatureEndMark)
+		if endSigIdx == -1 {
+			return false, nil, ""
 		}
+
+		return true, &CommitGPGSignature{
+			Signature: tag.Message[idx+1 : idx+endSigIdx+len(signatureEndMark)],
+			Payload:   string(data[:bytes.LastIndex(data, []byte(signatureBeginMark))+1]),
+		}, tag.Message[:idx+1]
 	}
+
+	// Try to find an OpenPGP signature
+	found, sig, message := extractTagSignature(beginpgp, endpgp)
+	if !found {
+		// If not found, try an SSH one
+		found, sig, message = extractTagSignature(beginssh, endssh)
+	}
+	// If either is found, update the tag Signature and Message
+	if found {
+		tag.Signature = sig
+		tag.Message = message
+	}
+
 	return tag, nil
 }
 

modules/git/tag_test.go

@@ -46,6 +46,41 @@ ono`), tag: Tag{
 			Message:   "test message\no\n\nono",
 			Signature: nil,
 		}},
+		{data: []byte(`object d8d1fdb5b20eaca882e34ee510eb55941a242b24
+type commit
+tag v0
+tagger Jane Doe <jane.doe@example.com> 1709146405 +0100
+
+v0
+-----BEGIN SSH SIGNATURE-----
+U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgvD4pK7baygXxoWoVoKjVEc/xZh
+6w+1FUn5hypFqJXNAAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5
+AAAAQKFeTnxi9ssRqSg+sJcmjAgpgoPq1k5SXm306+mJmkPwvhim8f9Gz6uy1AddPmXaD7
+5LVB3fV2GmmFDKGB+wCAo=
+-----END SSH SIGNATURE-----
+`), tag: Tag{
+			Name:    "",
+			ID:      Sha1ObjectFormat.EmptyObjectID(),
+			Object:  &Sha1Hash{0xd8, 0xd1, 0xfd, 0xb5, 0xb2, 0x0e, 0xac, 0xa8, 0x82, 0xe3, 0x4e, 0xe5, 0x10, 0xeb, 0x55, 0x94, 0x1a, 0x24, 0x2b, 0x24},
+			Type:    "commit",
+			Tagger:  &Signature{Name: "Jane Doe", Email: "jane.doe@example.com", When: time.Unix(1709146405, 0)},
+			Message: "v0\n",
+			Signature: &CommitGPGSignature{
+				Signature: `-----BEGIN SSH SIGNATURE-----
+U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgvD4pK7baygXxoWoVoKjVEc/xZh
+6w+1FUn5hypFqJXNAAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5
+AAAAQKFeTnxi9ssRqSg+sJcmjAgpgoPq1k5SXm306+mJmkPwvhim8f9Gz6uy1AddPmXaD7
+5LVB3fV2GmmFDKGB+wCAo=
+-----END SSH SIGNATURE-----`,
+				Payload: `object d8d1fdb5b20eaca882e34ee510eb55941a242b24
+type commit
+tag v0
+tagger Jane Doe <jane.doe@example.com> 1709146405 +0100
+
+v0
+`,
+			},
+		}},
 	}
 
 	for _, test := range testData {