adds 'SignatureTypeEmpty' check and improves description of 'GetSignatureType'

Signed-off-by: Ricardo Bartels <ricardo.bartels@telekom.de>

Author: bb-Ricardo

git/git_test.go

@@ -550,7 +550,7 @@ func TestSignatureType(t *testing.T) {
 			name:   "unsigned",
 			commit: &Commit{},
 			tag:    &Tag{},
-			want:   "unknown",
+			want:   "empty",
 		},
 		{
 			name: "unknown signature type",

git/signatures/signature.go

@@ -32,6 +32,8 @@ const (
 	SignatureTypeX509 SignatureType = "x509"
 	// SignatureTypeUnknown represents an unknown signature type.
 	SignatureTypeUnknown SignatureType = "unknown"
+	// SignatureTypeEmpty represents an empty signature.
+	SignatureTypeEmpty SignatureType = "empty"
 )
 
 // IsX509Signature is the prefix used by Git to identify x509 signatures.
@@ -72,9 +74,16 @@ func IsX509Signature(signature string) bool {
 	return startsWithStrings(signature, X509SignaturePrefix)
 }
 
+// IsEmptySignature tests if the given signature string is empty.
+// It returns true if the signature string has a length of 0.
+func IsEmptySignature(signature string) bool {
+	return len(signature) == 0
+}
+
 // GetSignatureType returns the type of the signature as a string.
 // It returns "pgp" for PGP signatures, "ssh" for SSH signatures,
-// and "unknown" for unrecognized or empty signatures.
+// "x509" for S/MIME signatures, "empty" for an empty signature
+// and "unknown" for unrecognized signatures.
 func GetSignatureType(signature string) string {
 	if IsPGPSignature(signature) {
 		return string(SignatureTypePGP)
@@ -85,5 +94,8 @@ func GetSignatureType(signature string) string {
 	if IsX509Signature(signature) {
 		return string(SignatureTypeX509)
 	}
+	if IsEmptySignature(signature) {
+		return string(SignatureTypeEmpty)
+	}
 	return string(SignatureTypeUnknown)
 }

git/signatures/signature_test.go

@@ -217,7 +217,7 @@ func TestGetSignatureType(t *testing.T) {
 		{
 			name:      "empty signature",
 			signature: "",
-			want:      string(SignatureTypeUnknown),
+			want:      string(SignatureTypeEmpty),
 		},
 		{
 			name:      "unknown signature",

git/signatures/ssh_signature.go

@@ -27,6 +27,8 @@ import (
 	gossh "golang.org/x/crypto/ssh"
 )
 
+const SSHSignatureNamespace = "git"
+
 // SSHSignaturePrefix is the prefix used by Git to identify SSH signatures.
 // https://github.com/git/git/blob/7b2bccb0d58d4f24705bf985de1f4612e4cf06e5/gpg-interface.c#L71
 var SSHSignaturePrefix = []string{"-----BEGIN SSH SIGNATURE-----"}
@@ -56,7 +58,7 @@ func ParseAuthorizedKeys(authorizedKeys string) ([]gossh.PublicKey, error) {
 	return publicKeys, nil
 }
 
-// verifySSHSignature verifies the SSH signature against the payload using
+// VerifySSHSignature verifies the SSH signature against the payload using
 // the provided authorized keys. It returns the fingerprint of the key that
 // successfully verified the signature, or an error.
 func VerifySSHSignature(signature string, payload []byte, authorizedKeys ...string) (string, error) {
@@ -88,8 +90,7 @@ func VerifySSHSignature(signature string, payload []byte, authorizedKeys ...stri
 		// Try to verify with each public key
 		for _, pubKey := range publicKeys {
 			// Verify the signature using sshsig library
-			// The namespace for Git is "git"
-			err := sshsig.Verify(bytes.NewReader(payload), sig, pubKey, sig.HashAlgorithm, "git")
+			err := sshsig.Verify(bytes.NewReader(payload), sig, pubKey, sig.HashAlgorithm, SSHSignatureNamespace)
 			if err == nil {
 				// Signature verified successfully
 				return getPublicKeyFingerprint(pubKey), nil