Add Diff.ToBuf wrapping git_diff_to_buf

diff.go

@@ -405,6 +405,36 @@ func (diff *Diff) Patch(deltaIndex int) (*Patch, error) {
 	return newPatchFromC(patchPtr), nil
 }
 
+type DiffFormat int
+
+const (
+	DiffFormatPatch       DiffFormat = C.GIT_DIFF_FORMAT_PATCH
+	DiffFormatPatchHeader DiffFormat = C.GIT_DIFF_FORMAT_PATCH_HEADER
+	DiffFormatRaw         DiffFormat = C.GIT_DIFF_FORMAT_RAW
+	DiffFormatNameOnly    DiffFormat = C.GIT_DIFF_FORMAT_NAME_ONLY
+	DiffFormatNameStatus  DiffFormat = C.GIT_DIFF_FORMAT_NAME_STATUS
+)
+
+func (diff *Diff) ToBuf(format DiffFormat) ([]byte, error) {
+	if diff.ptr == nil {
+		return nil, ErrInvalid
+	}
+
+	diffBuf := C.git_buf{}
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	ecode := C.git_diff_to_buf(&diffBuf, diff.ptr, C.git_diff_format_t(format))
+	runtime.KeepAlive(diff)
+	if ecode < 0 {
+		return nil, MakeGitError(ecode)
+	}
+	defer C.git_buf_free(&diffBuf)
+
+	return C.GoBytes(unsafe.Pointer(diffBuf.ptr), C.int(diffBuf.size)), nil
+}
+
 type DiffOptionsFlag int
 
 const (