fix(filer.backup): local sink readonly permission (#8907)

weed/replication/sink/localsink/local_sink.go

@@ -93,7 +93,11 @@ func (localsink *LocalSink) CreateEntry(key string, entry *filer_pb.Entry, signa
 	}
 
 	mode := os.FileMode(entry.Attributes.FileMode)
-	dstFile, err := os.OpenFile(util.ToShortFileName(key), os.O_RDWR|os.O_CREATE|os.O_TRUNC, mode)
+	shortFileName := util.ToShortFileName(key)
+	if err := os.Remove(shortFileName); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	dstFile, err := os.OpenFile(shortFileName, os.O_RDWR|os.O_CREATE|os.O_TRUNC, mode)
 	if err != nil {
 		return err
 	}

weed/replication/sink/localsink/local_sink_test.go

@@ -0,0 +1,74 @@
+package localsink
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"github.com/seaweedfs/seaweedfs/weed/replication/source"
+)
+
+// TestCreateEntry_OverwriteReadOnlyFile reproduces a bug where
+// filer.backup receives a create event (0-byte, mode 0400) followed by
+// an update event (with chunks) for the same file. The update event
+// calls CreateEntry again, which fails with "permission denied" because
+// OpenFile with O_RDWR cannot open the 0400 file created by the first
+// event.
+func TestCreateEntry_OverwriteReadOnlyFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	sink := &LocalSink{}
+	sink.initialize(tmpDir, false)
+	sink.SetSourceFiler(&source.FilerSource{})
+
+	key := filepath.Join(tmpDir, "objects", "5c", "9fb207")
+
+	// Create event: 0-byte file with mode 0400 (metadata only, no chunks)
+	createEntry := &filer_pb.Entry{
+		Attributes: &filer_pb.FuseAttributes{
+			FileMode: uint32(0400),
+		},
+	}
+	if err := os.MkdirAll(filepath.Dir(key), 0755); err != nil {
+		t.Fatalf("mkdir: %v", err)
+	}
+	if err := sink.CreateEntry(key, createEntry, nil); err != nil {
+		t.Fatalf("CreateEntry (create event) failed: %v", err)
+	}
+
+	// Verify: 0-byte, 0400 file exists
+	fi, err := os.Stat(key)
+	if err != nil {
+		t.Fatalf("stat after create event: %v", err)
+	}
+	if fi.Size() != 0 {
+		t.Errorf("expected 0 bytes after create event, got %d", fi.Size())
+	}
+	if fi.Mode().Perm() != 0400 {
+		t.Fatalf("expected 0400 after create event, got %o", fi.Mode().Perm())
+	}
+
+	// Update event: same file, now with content (simulated by entry.Content)
+	updateEntry := &filer_pb.Entry{
+		Attributes: &filer_pb.FuseAttributes{
+			FileMode: uint32(0400),
+			FileSize: 552,
+		},
+		Content: []byte("git object data placeholder"),
+	}
+	if err := sink.CreateEntry(key, updateEntry, nil); err != nil {
+		t.Fatalf("CreateEntry (update event) failed on read-only file: %v", err)
+	}
+
+	// Verify: file has content and correct permissions
+	fi, err = os.Stat(key)
+	if err != nil {
+		t.Fatalf("stat after update event: %v", err)
+	}
+	if fi.Size() == 0 {
+		t.Errorf("expected non-zero size after update event, got 0")
+	}
+	if fi.Mode().Perm() != 0400 {
+		t.Errorf("expected 0400 after update event, got %o", fi.Mode().Perm())
+	}
+}