GPG commit validation (#1150)

* GPG commit validation

* Add translation

+ some little fix

* Move hash calc after retrieving of potential key + missing translation

* Add some little test

vendor/code.gitea.io/git/commit.go

@@ -6,6 +6,7 @@ package git
 
 import (
 	"bufio"
+	"bytes"
 	"container/list"
 	"fmt"
 	"net/http"
@@ -22,11 +23,30 @@ type Commit struct {
 	Author        *Signature
 	Committer     *Signature
 	CommitMessage string
+	Signature     *CommitGPGSignature
 
 	parents        []SHA1 // SHA1 strings
 	submoduleCache *ObjectCache
 }
 
+// CommitGPGSignature represents a git commit signature part.
+type CommitGPGSignature struct {
+	Signature string
+	Payload   string //TODO check if can be reconstruct from the rest of commit information to not have duplicate data
+}
+
+// similar to https://github.com/git/git/blob/3bc53220cb2dcf709f7a027a3f526befd021d858/commit.c#L1128
+func newGPGSignatureFromCommitline(data []byte, signatureStart int) (*CommitGPGSignature, error) {
+	sig := new(CommitGPGSignature)
+	signatureEnd := bytes.LastIndex(data, []byte("-----END PGP SIGNATURE-----"))
+	if signatureEnd == -1 {
+		return nil, fmt.Errorf("end of commit signature not found")
+	}
+	sig.Signature = strings.Replace(string(data[signatureStart:signatureEnd+27]), "\n ", "\n", -1)
+	sig.Payload = string(data[:signatureStart-8]) + string(data[signatureEnd+27:])
+	return sig, nil
+}
+
 // Message returns the commit message. Same as retrieving CommitMessage directly.
 func (c *Commit) Message() string {
 	return c.CommitMessage