fix(storage): surface stat error on zero-size idx scrub, mirror to rust (#9612)

fix(storage): harden zero-size idx scrub and mirror to rust

When a zero-size .idx is found, openIndex stats the backing .dat through
v.DataBackend: wrap that GetStat failure with %w, fix the indices typo, and
guard both openIndex and scrubVolumeData against a nil DataBackend (closed or
remote-only volumes) instead of panicking.

Add rust scrub tests for empty (superblock-only .dat, zero-size .idx) and
healthy volumes, keeping the volume server in parity with the go zero-size
scrub handling.

seaweed-volume/src/storage/volume.rs

@@ -3643,6 +3643,67 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_scrub_empty_volume() {
+        // Mirror of Go's TestScrubVolumeData "zero-size volume without index"
+        // case (weed/storage/volume_checking_test.go): a freshly created /
+        // pre-allocated volume has a superblock-only .dat and a zero-size .idx,
+        // and must scrub clean instead of being flagged as corrupt.
+        let tmp = TempDir::new().unwrap();
+        let dir = tmp.path().to_str().unwrap();
+        let v = make_test_volume(dir);
+
+        // .dat holds only the superblock; .idx is empty.
+        assert_eq!(v.dat_file_size().unwrap(), SUPER_BLOCK_SIZE as u64);
+
+        let (files_checked, broken) = v.scrub().unwrap();
+        assert_eq!(files_checked, 0);
+        assert!(
+            broken.is_empty(),
+            "empty volume should scrub clean, got {:?}",
+            broken
+        );
+
+        // The index-only mode must agree.
+        let (idx_checked, idx_broken) = v.scrub_index().unwrap();
+        assert_eq!(idx_checked, 0);
+        assert!(
+            idx_broken.is_empty(),
+            "empty volume should scrub_index clean, got {:?}",
+            idx_broken
+        );
+    }
+
+    #[test]
+    fn test_scrub_healthy_volume() {
+        // Mirror of Go's TestScrubVolumeData "healthy volume" case: a volume
+        // with live needles scrubs clean and the .dat size accounting matches.
+        let tmp = TempDir::new().unwrap();
+        let dir = tmp.path().to_str().unwrap();
+        let mut v = make_test_volume(dir);
+
+        for i in 1..=5 {
+            let data = format!("needle data {}", i);
+            let mut n = Needle {
+                id: NeedleId(i),
+                cookie: Cookie(i as u32),
+                data: data.as_bytes().to_vec(),
+                data_size: data.len() as u32,
+                ..Needle::default()
+            };
+            v.write_needle(&mut n, true).unwrap();
+        }
+        v.sync_to_disk().unwrap();
+
+        let (files_checked, broken) = v.scrub().unwrap();
+        assert_eq!(files_checked, 5);
+        assert!(
+            broken.is_empty(),
+            "healthy volume should scrub clean, got {:?}",
+            broken
+        );
+    }
+
     #[test]
     fn test_volume_multiple_needles() {
         let tmp = TempDir::new().unwrap();

weed/storage/volume_checking.go

@@ -29,14 +29,18 @@ func (v *Volume) openIndex() (*os.File, int64, error) {
 	}
 
 	if idxStat.Size() == 0 {
+		if v.DataBackend == nil {
+			idxFile.Close()
+			return nil, 0, fmt.Errorf("volume %v has no data backend", v.Id)
+		}
 		volumeFileSize, _, err := v.DataBackend.GetStat()
 		if err != nil {
 			idxFile.Close()
-			return nil, 0, fmt.Errorf("failed to stat storage for zero-size IDX volume %v", v.Id)
+			return nil, 0, fmt.Errorf("failed to stat storage for zero-size IDX volume %v: %w", v.Id, err)
 		}
 
 		// account for pre-allocated volumes (f.ex. after running "volume.grow") without data, as these
-		// are allowed to have zero-size indeces.
+		// are allowed to have zero-size indices.
 		if volumeFileSize > int64(super_block.SuperBlockSize) {
 			idxFile.Close()
 			return nil, 0, fmt.Errorf("zero-size IDX file for volume %v with store size %d", v.Id, volumeFileSize)
@@ -62,6 +66,10 @@ func (v *Volume) ScrubIndex() (int64, []error) {
 
 // scrubVolumeData checks a volume content + index for issues.
 func (v *Volume) scrubVolumeData(idxFile *os.File, idxFileSize int64) (int64, []error) {
+	if v.DataBackend == nil {
+		return 0, []error{fmt.Errorf("volume %d has no data backend", v.Id)}
+	}
+
 	// full scrubbing means also scrubbing the index
 	var count int64
 	_, errs := idx.CheckIndexFile(idxFile, idxFileSize, v.Version())