filer_pb: walk the whole tree when the BFS start path ends in a slash (#11099)

* filer_pb: build BFS child paths with FullPath.Child

A start path with a trailing slash produced "/dir//sub" for every
subdirectory, and the filer only trims a trailing slash, so those
listings came back empty and the walk stopped after the first level.

Claude-Session: https://claude.ai/code/session_01Jp9tXRpBv9gvh8fkaVFqxQ

* filer_pb: normalize the BFS start path

Entries directly under the start path were reported with the caller's
trailing slash, so filer.meta.backup wrote them under a directory the
incremental stream never names again.

Claude-Session: https://claude.ai/code/session_01Jp9tXRpBv9gvh8fkaVFqxQ

weed/pb/filer_pb/filer_client_bfs.go

@@ -15,6 +15,10 @@ import (
 func TraverseBfs(ctx context.Context, filerClient FilerClient, parentPath util.FullPath, fn func(parentPath util.FullPath, entry *Entry) error) (err error) {
 	K := 5
 
+	// callers hand in user-typed paths, and every entry is reported relative
+	// to this one, so a trailing slash must not reach the callback
+	parentPath = util.NormalizePath(string(parentPath))
+
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
@@ -102,11 +106,7 @@ func processOneDirectory(ctx context.Context, filerClient FilerClient, parentPat
 		}
 
 		if entry.IsDirectory {
-			subDir := fmt.Sprintf("%s/%s", parentPath, entry.Name)
-			if parentPath == "/" {
-				subDir = "/" + entry.Name
-			}
-			if !enqueue(util.FullPath(subDir)) {
+			if !enqueue(parentPath.Child(entry.Name)) {
 				return ctx.Err()
 			}
 		}

weed/pb/filer_pb/filer_client_bfs_test.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"reflect"
+	"sort"
 	"strings"
 	"sync"
 	"testing"
@@ -150,3 +152,40 @@ func TestReadDirAllEntriesStuckPagination(t *testing.T) {
 		t.Fatal("listing loops forever on a non-advancing store")
 	}
 }
+
+// A start path with a trailing slash must still descend into subdirectories.
+func TestTraverseBfsTrailingSlashRoot(t *testing.T) {
+	server := &stubFiler{}
+	server.listings = func(req *ListEntriesRequest, send func(*Entry) error) error {
+		if req.StartFromFileName != "" {
+			return nil
+		}
+		// the filer trims a single trailing slash, nothing more
+		switch strings.TrimSuffix(req.Directory, "/") {
+		case "/buckets/data":
+			return send(&Entry{Name: "sub", IsDirectory: true})
+		case "/buckets/data/sub":
+			return send(&Entry{Name: "a.txt"})
+		}
+		return nil
+	}
+	filerClient := startStubFiler(t, server)
+
+	var mu sync.Mutex
+	var seen []string
+	err := TraverseBfs(context.Background(), filerClient, "/buckets/data/", func(parentPath util.FullPath, entry *Entry) error {
+		mu.Lock()
+		seen = append(seen, fmt.Sprintf("%s -> %s", parentPath, entry.Name))
+		mu.Unlock()
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	sort.Strings(seen)
+	want := []string{"/buckets/data -> sub", "/buckets/data/sub -> a.txt"}
+	if !reflect.DeepEqual(seen, want) {
+		t.Fatalf("visited %v, want %v", seen, want)
+	}
+}