repository: Fix intermingled stdout/stderr output for git-fsck(1)

We use two different buffers when spawning git-fsck(1) for its stdout
and stderr. This is inefficient as we now need to handle the overhead
for two buffers and need to spawn two Goroutines for them. Furthermore,
if git-fsck(1) was to print alternately to stdout and stderr, the order
of these messages gets lost as we used to just concatenate stdout and
stderr.

Fix this by using a single buffer for both standard streams. While at
it, convert the code to use a `strings.Builder` instead of a
`bytes.Buffer`, which is more efficient.

2 files changed, 8 insertions, 8 deletions

diff --git a/internal/gitaly/service/repository/fsck.go b/internal/gitaly/service/repository/fsck.go
index 9b5f0a9e9..6ccd7499b 100644
--- a/internal/gitaly/service/repository/fsck.go
+++ b/internal/gitaly/service/repository/fsck.go
@@ -1,8 +1,8 @@
 package repository
 
 import (
-	"bytes"
 	"context"
+	"strings"
 
 	"gitlab.com/gitlab-org/gitaly/v15/internal/git"
 	"gitlab.com/gitlab-org/gitaly/v15/internal/gitaly/service"
@@ -16,18 +16,18 @@ func (s *server) Fsck(ctx context.Context, req *gitalypb.FsckRequest) (*gitalypb
 		return nil, structerr.NewInvalidArgument("%w", err)
 	}
 
-	var stdout, stderr bytes.Buffer
+	var output strings.Builder
 	cmd, err := s.gitCmdFactory.New(ctx, repository,
 		git.Command{Name: "fsck"},
-		git.WithStdout(&stdout),
-		git.WithStderr(&stderr),
+		git.WithStdout(&output),
+		git.WithStderr(&output),
 	)
 	if err != nil {
 		return nil, err
 	}
 
 	if err = cmd.Wait(); err != nil {
-		return &gitalypb.FsckResponse{Error: append(stdout.Bytes(), stderr.Bytes()...)}, nil
+		return &gitalypb.FsckResponse{Error: []byte(output.String())}, nil
 	}
 
 	return &gitalypb.FsckResponse{}, nil
diff --git a/internal/gitaly/service/repository/fsck_test.go b/internal/gitaly/service/repository/fsck_test.go
index 932bac845..303ad8934 100644
--- a/internal/gitaly/service/repository/fsck_test.go
+++ b/internal/gitaly/service/repository/fsck_test.go
@@ -151,10 +151,10 @@ func TestFsck(t *testing.T) {
 				})
 
 				expectedErr := strings.Join([]string{
-					// This first error is a bug: we shouldn't complain about
-					// the dangling tree.
-					"dangling tree " + treeID.String(),
 					"error in tree " + treeID.String() + ": duplicateEntries: contains duplicate file entries",
+					// This error is a bug: we shouldn't complain about the
+					// dangling tree.
+					"dangling tree " + treeID.String(),
 				}, "\n") + "\n"
 
 				return setupData{