Set a stable signature for .patch endpoints to create reproducible patches

This commit adds the `--signature` flag set to `GitLab` to the format-patch git
subcommand used in RawPatch of the Diff service.
This will result in the default signature of resulting .patch-files
to be replaced with `GitLab`, resulting in more stable patches, that will not change
file content based on the git version of the host (which is the default
signature appended to the patch). This is relevant to be able to
generate checksums or signatures for patches referenced via a GitLab
URL.

Implements #2842

3 files changed, 39 insertions, 1 deletions

diff --git a/changelogs/unreleased/t4cc0re-format-patch-no-sig.yml b/changelogs/unreleased/t4cc0re-format-patch-no-sig.yml
new file mode 100644
index 000000000..1f0c7a663
--- /dev/null
+++ b/changelogs/unreleased/t4cc0re-format-patch-no-sig.yml
@@ -0,0 +1,5 @@
+---
+title: Set a stable signature for .patch endpoints to create reproducible patches
+merge_request: 2253
+author:
+type: changed
diff --git a/internal/service/diff/raw.go b/internal/service/diff/raw.go
index a65ac53cc..fb9540813 100644
--- a/internal/service/diff/raw.go
+++ b/internal/service/diff/raw.go
@@ -36,7 +36,7 @@ func (s *server) RawPatch(in *gitalypb.RawPatchRequest, stream gitalypb.DiffServ
 
 	subCmd := git.SubCmd{
 		Name:  "format-patch",
-		Flags: []git.Option{git.Flag{"--stdout"}},
+		Flags: []git.Option{git.Flag{"--stdout"}, git.ValueFlag{"--signature", "GitLab"}},
 		Args:  []string{in.LeftCommitId + ".." + in.RightCommitId},
 	}
 
diff --git a/internal/service/diff/raw_test.go b/internal/service/diff/raw_test.go
index 4e3ce322a..02dbfc976 100644
--- a/internal/service/diff/raw_test.go
+++ b/internal/service/diff/raw_test.go
@@ -2,6 +2,8 @@ package diff
 
 import (
 	"fmt"
+	"io/ioutil"
+	"regexp"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -202,6 +204,37 @@ func TestFailedRawPatchRequestDueToValidations(t *testing.T) {
 	}
 }
 
+func TestRawPatchContainsGitLabSignature(t *testing.T) {
+	server, serverSocketPath := runDiffServer(t)
+	defer server.Stop()
+
+	client, conn := newDiffClient(t, serverSocketPath)
+	defer conn.Close()
+
+	ctx, cancel := testhelper.Context()
+	defer cancel()
+
+	testRepo, _, cleanupFn := testhelper.NewTestRepo(t)
+	defer cleanupFn()
+
+	rightCommit := "e395f646b1499e8e0279445fc99a0596a65fab7e"
+	leftCommit := "8a0f2ee90d940bfb0ba1e14e8214b0649056e4ab"
+	rpcRequest := &gitalypb.RawPatchRequest{Repository: testRepo, RightCommitId: rightCommit, LeftCommitId: leftCommit}
+
+	c, err := client.RawPatch(ctx, rpcRequest)
+	require.NoError(t, err)
+
+	reader := streamio.NewReader(func() ([]byte, error) {
+		response, err := c.Recv()
+		return response.GetData(), err
+	})
+
+	patch, err := ioutil.ReadAll(reader)
+	require.NoError(t, err)
+
+	require.Regexp(t, regexp.MustCompile(`\n-- \nGitLab\s+$`), string(patch))
+}
+
 func drainRawDiffResponse(c gitalypb.DiffService_RawDiffClient) error {
 	var err error
 	for err == nil {