filer: repack verifies the entry against the store at commit time

The entry lock is filer-local, so a writer on another filer could
commit between repack's read and its swap, and repack then restored the
old bytes over an acknowledged update. Re-read the entry and revalidate
the chunk fingerprint and WORM right before the swap, answering 409 on
any change, and build the new entry from the fresh read so concurrent
metadata-only updates are carried forward. This shrinks the unguarded
window from the whole repack to the commit itself; closing it entirely
needs owner routing.

weed/server/filer_server_format.go

@@ -307,6 +307,7 @@ func (fs *FilerServer) formatRepack(ctx context.Context, w http.ResponseWriter,
 		return
 	}
 	oldChunks := entry.GetChunks()
+	oldIdentity := formatChunkIdentity(oldChunks)
 	if len(oldChunks) == 0 {
 		writeJsonError(w, r, http.StatusBadRequest, errors.New("entry has no chunks to repack"))
 		return
@@ -406,10 +407,41 @@ func (fs *FilerServer) formatRepack(ctx context.Context, w http.ResponseWriter,
 		return
 	}
 
-	newEntry := *entry
+	// The entry lock is filer-local, so a writer on another filer is not
+	// blocked by it. Re-read from the store and revalidate right before the
+	// swap: the unguarded window shrinks from the whole repack to this
+	// commit. Full enforcement needs owner routing.
+	current, err := fs.filer.FindEntry(ctx, fullPath)
+	if err != nil {
+		cleanup()
+		if errors.Is(err, filer_pb.ErrNotFound) {
+			writeJsonError(w, r, http.StatusConflict, errors.New("entry was deleted during repack"))
+		} else {
+			writeJsonError(w, r, http.StatusInternalServerError, err)
+		}
+		return
+	}
+	if !bytes.Equal(formatChunkIdentity(current.GetChunks()), oldIdentity) {
+		cleanup()
+		writeJsonError(w, r, http.StatusConflict, errors.New("entry changed during repack"))
+		return
+	}
+	if enforced, wormErr := fs.wormEnforcedForEntry(ctx, r.URL.Path); wormErr != nil {
+		cleanup()
+		writeJsonError(w, r, http.StatusInternalServerError, wormErr)
+		return
+	} else if enforced {
+		cleanup()
+		writeJsonError(w, r, http.StatusForbidden, errors.New("cannot repack WORM-enforced entry"))
+		return
+	}
+
+	// build from the fresh read so a concurrent metadata-only update on
+	// another filer is carried forward, not clobbered
+	newEntry := *current
 	newEntry.Chunks = newChunks
 	newEntry.Extended = make(map[string][]byte)
-	for k, v := range entry.Extended {
+	for k, v := range current.Extended {
 		newEntry.Extended[k] = v
 	}
 	newEntry.Extended[format.LayoutKey] = encoded
@@ -417,15 +449,15 @@ func (fs *FilerServer) formatRepack(ctx context.Context, w http.ResponseWriter,
 	if len(newEntry.Md5) == 0 {
 		newEntry.Md5 = md5Hash.Sum(nil)
 	}
-	if err := fs.filer.UpdateEntry(context.WithoutCancel(ctx), entry, &newEntry); err != nil {
+	if err := fs.filer.UpdateEntry(context.WithoutCancel(ctx), current, &newEntry); err != nil {
 		cleanup()
 		writeJsonError(w, r, http.StatusInternalServerError, err)
 		return
 	}
-	fs.filer.DeleteChunks(context.WithoutCancel(ctx), fullPath, oldChunks)
+	fs.filer.DeleteChunks(context.WithoutCancel(ctx), fullPath, current.GetChunks())
 	// Filer.UpdateEntry only writes the store; notify subscribers (sync,
 	// backup, replication) of the new chunk ids like the gRPC path does.
-	fs.filer.NotifyUpdateEvent(ctx, entry, &newEntry, true, false, nil)
+	fs.filer.NotifyUpdateEvent(ctx, current, &newEntry, true, false, nil)
 	writeJsonQuiet(w, r, http.StatusOK, map[string]interface{}{
 		"name": entry.Name(), "size": size, "extents": len(layout.ExtentSizes),
 	})