Refactor commit signature parser (#30228)

To make it more flexible and support SSH signature.

The existing tests are not changed, there are also tests covering
`parseTagRef` which also calls `parsePayloadSignature` now. Add some new
tests to `Test_parseTagData`

modules/git/tag.go

@@ -6,16 +6,10 @@ package git
 import (
 	"bytes"
 	"sort"
-	"strings"
 
 	"code.gitea.io/gitea/modules/util"
 )
 
-const (
-	beginpgp = "\n-----BEGIN PGP SIGNATURE-----\n"
-	endpgp   = "\n-----END PGP SIGNATURE-----"
-)
-
 // Tag represents a Git tag.
 type Tag struct {
 	Name      string
@@ -24,7 +18,7 @@ type Tag struct {
 	Type      string
 	Tagger    *Signature
 	Message   string
-	Signature *CommitGPGSignature
+	Signature *CommitSignature
 }
 
 // Commit return the commit of the tag reference
@@ -32,6 +26,36 @@ func (tag *Tag) Commit(gitRepo *Repository) (*Commit, error) {
 	return gitRepo.getCommit(tag.Object)
 }
 
+func parsePayloadSignature(data []byte, messageStart int) (payload, msg, sign string) {
+	pos := messageStart
+	signStart, signEnd := -1, -1
+	for {
+		eol := bytes.IndexByte(data[pos:], '\n')
+		if eol < 0 {
+			break
+		}
+		line := data[pos : pos+eol]
+		signType, hasPrefix := bytes.CutPrefix(line, []byte("-----BEGIN "))
+		signType, hasSuffix := bytes.CutSuffix(signType, []byte(" SIGNATURE-----"))
+		if hasPrefix && hasSuffix {
+			signEndBytes := append([]byte("\n-----END "), signType...)
+			signEndBytes = append(signEndBytes, []byte(" SIGNATURE-----")...)
+			signEnd = bytes.Index(data[pos:], signEndBytes)
+			if signEnd != -1 {
+				signStart = pos
+				signEnd = pos + signEnd + len(signEndBytes)
+			}
+		}
+		pos += eol + 1
+	}
+
+	if signStart != -1 && signEnd != -1 {
+		msgEnd := max(messageStart, signStart-1)
+		return string(data[:msgEnd]), string(data[messageStart:msgEnd]), string(data[signStart:signEnd])
+	}
+	return string(data), string(data[messageStart:]), ""
+}
+
 // Parse commit information from the (uncompressed) raw
 // data from the commit object.
 // \n\n separate headers from message
@@ -40,47 +64,37 @@ func parseTagData(objectFormat ObjectFormat, data []byte) (*Tag, error) {
 	tag.ID = objectFormat.EmptyObjectID()
 	tag.Object = objectFormat.EmptyObjectID()
 	tag.Tagger = &Signature{}
-	// we now have the contents of the commit object. Let's investigate...
-	nextline := 0
-l:
+
+	pos := 0
 	for {
-		eol := bytes.IndexByte(data[nextline:], '\n')
-		switch {
-		case eol > 0:
-			line := data[nextline : nextline+eol]
-			spacepos := bytes.IndexByte(line, ' ')
-			reftype := line[:spacepos]
-			switch string(reftype) {
-			case "object":
-				id, err := NewIDFromString(string(line[spacepos+1:]))
-				if err != nil {
-					return nil, err
-				}
-				tag.Object = id
-			case "type":
-				// A commit can have one or more parents
-				tag.Type = string(line[spacepos+1:])
-			case "tagger":
-				tag.Tagger = parseSignatureFromCommitLine(util.UnsafeBytesToString(line[spacepos+1:]))
-			}
-			nextline += eol + 1
-		case eol == 0:
-			tag.Message = string(data[nextline+1:])
-			break l
-		default:
-			break l
+		eol := bytes.IndexByte(data[pos:], '\n')
+		if eol == -1 {
+			break // shouldn't happen, but could just tolerate it
 		}
+		if eol == 0 {
+			pos++
+			break // end of headers
+		}
+		line := data[pos : pos+eol]
+		key, val, _ := bytes.Cut(line, []byte(" "))
+		switch string(key) {
+		case "object":
+			id, err := NewIDFromString(string(val))
+			if err != nil {
+				return nil, err
+			}
+			tag.Object = id
+		case "type":
+			tag.Type = string(val) // A commit can have one or more parents
+		case "tagger":
+			tag.Tagger = parseSignatureFromCommitLine(util.UnsafeBytesToString(val))
+		}
+		pos += eol + 1
 	}
-	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]),
-			}
-			tag.Message = tag.Message[:idx+1]
-		}
+	payload, msg, sign := parsePayloadSignature(data, pos)
+	tag.Message = msg
+	if len(sign) > 0 {
+		tag.Signature = &CommitSignature{Signature: sign, Payload: payload}
 	}
 	return tag, nil
 }