seaweedfs/weed/storage/volume_vacuum_test.go

package storage

import (
	"bytes"
	"errors"
	"fmt"
	"math/rand"
	"os"
	"path/filepath"
	"reflect"
	"testing"
	"time"

	"github.com/seaweedfs/seaweedfs/weed/stats"
	"github.com/seaweedfs/seaweedfs/weed/storage/idx"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
	"github.com/seaweedfs/seaweedfs/weed/storage/types"
	"github.com/seaweedfs/seaweedfs/weed/util"
)

/*
makediff test steps
1. launch weed server at your local/dev environment, (option
"garbageThreshold" for master and option "max" for volume should be set with specific value which would let
preparing test prerequisite easier )
   a) ./weed master -garbageThreshold=0.99 -mdir=./m
   b) ./weed volume -dir=./data -max=1 -master=localhost:9333 -port=8080
2. upload 4 different files, you could call dir/assign to get 4 different fids
   a)  upload file A with fid a
   b)  upload file B with fid b
   c)  upload file C with fid c
   d)  upload file D with fid d
3. update file A and C
   a)  modify file A and upload file A with fid a
   b)  modify file C and upload file C with fid c
   c)  record the current 1.idx's file size(lastCompactIndexOffset value)
4. Compacting the data file
   a)  run curl http://localhost:8080/admin/vacuum/compact?volumeId=1
   b)  verify the 1.cpd and 1.cpx is created under volume directory
5. update file B and delete file D
   a)  modify file B and upload file B with fid b
   d)  delete file B with fid b
6. Now you could run the following UT case, the case should be run successfully
7. Compact commit manually
   a)  mv 1.cpd 1.dat
   b)  mv 1.cpx 1.idx
8. Restart Volume Server
9. Now you should get updated file A,B,C
*/

func TestMakeDiff(t *testing.T) {

	v := new(Volume)
	// lastCompactIndexOffset value is the index file size before step 4
	v.lastCompactIndexOffset = 96
	v.SuperBlock.Version = 0x2
	/*
		err := v.makeupDiff(
			"/yourpath/1.cpd",
			"/yourpath/1.cpx",
			"/yourpath/1.dat",
			"/yourpath/1.idx")
		if err != nil {
			t.Errorf("makeupDiff err is %v", err)
		} else {
			t.Log("makeupDiff Succeeded")
		}
	*/
}

func TestMemIndexCompaction(t *testing.T) {
	testCompactionByIndex(t, NeedleMapInMemory)
}

func TestLDBIndexCompaction(t *testing.T) {
	testCompactionByIndex(t, NeedleMapLevelDb)
}

func testCompactionByIndex(t *testing.T, needleMapKind NeedleMapKind) {
	dir := t.TempDir()

	v, err := NewVolume(dir, dir, "", 1, needleMapKind, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}

	beforeCommitFileCount := 10000
	afterCommitFileCount := 10000

	infos := make([]*needleInfo, beforeCommitFileCount+afterCommitFileCount)

	for i := 1; i <= beforeCommitFileCount; i++ {
		doSomeWritesDeletes(i, v, t, infos)
	}

	startTime := time.Now()
	v.CompactByIndex(nil)
	speed := float64(v.ContentSize()) / time.Now().Sub(startTime).Seconds()
	t.Logf("compaction speed: %.2f bytes/s", speed)

	// update & delete original objects, upload & delete new objects
	for i := 1; i <= afterCommitFileCount+beforeCommitFileCount; i++ {
		doSomeWritesDeletes(i, v, t, infos)
	}
	v.CommitCompact()
	realRecordCount := v.nm.IndexFileSize() / types.NeedleMapEntrySize
	if needleMapKind == NeedleMapLevelDb {
		nm := reflect.ValueOf(v.nm).Interface().(*LevelDbNeedleMap)
		mm := nm.mapMetric
		watermark := getWatermark(nm.db)
		realWatermark := (nm.recordCount / watermarkBatchSize) * watermarkBatchSize
		t.Logf("watermark from levelDB: %d, realWatermark: %d, nm.recordCount: %d, realRecordCount:%d, fileCount=%d, deletedcount:%d", watermark, realWatermark, nm.recordCount, realRecordCount, mm.FileCount(), v.DeletedCount())
		if realWatermark != watermark {
			t.Fatalf("testing watermark failed")
		}
	} else {
		t.Logf("realRecordCount:%d, v.FileCount():%d mm.DeletedCount():%d", realRecordCount, v.FileCount(), v.DeletedCount())
	}
	if realRecordCount != v.FileCount() {
		t.Fatalf("testing file count failed")
	}

	v.Close()

	v, err = NewVolume(dir, dir, "", 1, needleMapKind, nil, nil, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume reloading: %v", err)
	}
	defer v.Close()

	for i := 1; i <= beforeCommitFileCount+afterCommitFileCount; i++ {

		if infos[i-1] == nil {
			t.Fatal("not found file", i)
		}

		if infos[i-1].size == 0 {
			continue
		}

		n := newEmptyNeedle(uint64(i))
		size, err := v.readNeedle(n, nil, nil)
		if err != nil {
			t.Fatalf("read file %d: %v", i, err)
		}
		if infos[i-1].size != types.Size(size) {
			t.Fatalf("read file %d size mismatch expected %d found %d", i, infos[i-1].size, size)
		}
		if infos[i-1].crc != n.Checksum {
			t.Fatalf("read file %d checksum mismatch expected %d found %d", i, infos[i-1].crc, n.Checksum)
		}

	}

}

// A deletion replayed by makeupDiff appends a tombstone to the compacted .dat.
// When that tombstone is the .dat tail, its .idx entry must carry the real
// offset, not 0, or the post-commit integrity check can't see the trailing
// tombstone and wrongly flips the volume read-only — loading a
// SortedFileNeedleMap instead of the writable LevelDb map.
func TestCommitCompactDeletionTailKeepsWritable(t *testing.T) {
	dir := t.TempDir()

	v, err := NewVolume(dir, dir, "", 1, NeedleMapLevelDb, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}

	for i := uint64(1); i <= 5; i++ {
		if _, _, _, err := v.writeNeedle2(newRandomNeedle(i), true, false, false); err != nil {
			t.Fatalf("write %d: %v", i, err)
		}
	}

	v.CompactByIndex(nil)

	// The sole change in the commit window is a deletion, so makeupDiff appends
	// its tombstone last, putting it at the .dat tail.
	if _, err := v.deleteNeedle2(newEmptyNeedle(3)); err != nil {
		t.Fatalf("delete: %v", err)
	}

	if err := v.CommitCompact(); err != nil {
		t.Fatalf("commit compact: %v", err)
	}

	if _, ok := v.nm.(*LevelDbNeedleMap); !ok {
		t.Fatalf("after compaction v.nm is %T, want *LevelDbNeedleMap (volume wrongly marked read-only)", v.nm)
	}
	v.Close()

	// Reload from disk to confirm the integrity check passes and the volume
	// stays writable.
	v, err = NewVolume(dir, dir, "", 1, NeedleMapLevelDb, nil, nil, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("reload: %v", err)
	}
	defer v.Close()
	if v.noWriteOrDelete {
		t.Fatal("volume reloaded read-only after a deletion-tail compaction")
	}
}

func TestCompactVolumeFilesOffline(t *testing.T) {
	dir := t.TempDir()
	location := NewDiskLocation(dir, 10, util.MinFreeSpace{}, dir, "", nil, stats.DefaultDiskIOProbeConfig())
	defer location.Close()

	v, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}

	infos := make([]*needleInfo, 32)
	for i := 1; i <= 32; i++ {
		doSomeWritesDeletes(i, v, t, infos)
	}
	v.Close()

	store := &Store{}
	if err := store.CompactVolumeFiles(needle.VolumeId(1), "", location, NeedleMapInMemory, 0, 0, 0); err != nil {
		t.Fatalf("CompactVolumeFiles: %v", err)
	}

	reloaded, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, nil, nil, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume reload: %v", err)
	}
	defer reloaded.Close()

	if _, err := os.Stat(filepath.Join(dir, "1.cpd")); !os.IsNotExist(err) {
		t.Fatalf("expected no .cpd after successful offline compaction, got err=%v", err)
	}
	if _, err := os.Stat(filepath.Join(dir, "1.cpx")); !os.IsNotExist(err) {
		t.Fatalf("expected no .cpx after successful offline compaction, got err=%v", err)
	}
}

func TestCleanupCompactRemovesTempFiles(t *testing.T) {
	dir := t.TempDir()
	location := NewDiskLocation(dir, 10, util.MinFreeSpace{}, dir, "", nil, stats.DefaultDiskIOProbeConfig())
	defer location.Close()

	v, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}

	infos := make([]*needleInfo, 16)
	for i := 1; i <= 16; i++ {
		doSomeWritesDeletes(i, v, t, infos)
	}
	v.Close()

	if err := os.WriteFile(filepath.Join(dir, "1.cpx"), []byte("broken"), 0o644); err != nil {
		t.Fatalf("write broken cpx: %v", err)
	}
	if err := os.WriteFile(filepath.Join(dir, "1.cpd"), []byte("temp"), 0o644); err != nil {
		t.Fatalf("write cpd: %v", err)
	}
	if err := os.Mkdir(filepath.Join(dir, "1.cpldb"), 0o755); err != nil {
		t.Fatalf("mkdir cpldb: %v", err)
	}

	tempVolume, err := loadVolumeWithoutWorker(dir, dir, "", needle.VolumeId(1), NeedleMapInMemory, 0)
	if err != nil {
		t.Fatalf("loadVolumeWithoutWorker: %v", err)
	}
	tempVolume.location = location
	defer tempVolume.doClose()

	if err := tempVolume.cleanupCompact(); err != nil {
		t.Fatalf("cleanupCompact: %v", err)
	}

	if _, err := os.Stat(filepath.Join(dir, "1.cpd")); !os.IsNotExist(err) {
		t.Fatalf("expected cleanup to remove .cpd, got err=%v", err)
	}
	if _, err := os.Stat(filepath.Join(dir, "1.cpx")); !os.IsNotExist(err) {
		t.Fatalf("expected cleanup to remove .cpx, got err=%v", err)
	}
	if _, err := os.Stat(filepath.Join(dir, "1.cpldb")); !os.IsNotExist(err) {
		t.Fatalf("expected cleanup to remove .cpldb, got err=%v", err)
	}
}

// TestCompactByIndex_DropsDanglingNeedle verifies that vacuum compaction
// tolerates an .idx entry whose offset points past the end of the .dat file
// (the failure mode reported in issue #8928). The bad entry should be silently
// dropped from the resulting .cpx, while every healthy needle is preserved.
func TestCompactByIndex_DropsDanglingNeedle(t *testing.T) {
	dir := t.TempDir()

	v, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}

	const goodNeedleCount = 8
	infos := make([]*needleInfo, goodNeedleCount)
	for i := 1; i <= goodNeedleCount; i++ {
		n := newRandomNeedle(uint64(i))
		_, size, _, err := v.writeNeedle2(n, true, false, false)
		if err != nil {
			t.Fatalf("write needle %d: %v", i, err)
		}
		infos[i-1] = &needleInfo{size: size, crc: n.Checksum}
	}

	if err := v.DataBackend.Sync(); err != nil {
		t.Fatalf("sync .dat: %v", err)
	}
	if err := v.nm.Sync(); err != nil {
		t.Fatalf("sync .idx: %v", err)
	}

	datSize, _, err := v.DataBackend.GetStat()
	if err != nil {
		t.Fatalf("stat .dat: %v", err)
	}

	// Inject an .idx entry that points 1 MB past the end of the .dat. The
	// bad entry must go through nm.Put so it ends up in both the in-memory
	// map and the on-disk .idx — exactly the corruption pattern in #8928.
	badKey := types.Uint64ToNeedleId(uint64(goodNeedleCount + 100))
	badOffset := types.ToOffset(datSize + 1024*1024)
	badSize := types.Size(2048)
	if err := v.nm.Put(badKey, badOffset, badSize); err != nil {
		t.Fatalf("inject bad idx entry: %v", err)
	}
	if err := v.nm.Sync(); err != nil {
		t.Fatalf("sync .idx after inject: %v", err)
	}

	if err := v.CompactByIndex(nil); err != nil {
		t.Fatalf("CompactByIndex should tolerate dangling entries, got: %v", err)
	}

	// Walk the new index and confirm the dangling entry was dropped while
	// all of the original keys made it through.
	cpx, err := os.Open(filepath.Join(dir, "1.cpx"))
	if err != nil {
		t.Fatalf("open .cpx: %v", err)
	}
	defer cpx.Close()
	keptKeys := map[types.NeedleId]bool{}
	if err := idx.WalkIndexFile(cpx, 0, func(key types.NeedleId, _ types.Offset, size types.Size) error {
		if !size.IsDeleted() {
			keptKeys[key] = true
		}
		return nil
	}); err != nil {
		t.Fatalf("walk .cpx: %v", err)
	}
	if keptKeys[badKey] {
		t.Fatalf("dangling key %d should have been dropped from .cpx", badKey)
	}
	for i := 1; i <= goodNeedleCount; i++ {
		if infos[i-1].size == 0 {
			continue
		}
		k := types.Uint64ToNeedleId(uint64(i))
		if !keptKeys[k] {
			t.Fatalf("healthy key %d missing from compacted .cpx", k)
		}
	}

	v.Close()
}

// TestCompactByIndex_ConcurrentWriteDoesNotFailIntegrityCheck reproduces the
// vacuum-vs-live-traffic race: a needle written to the volume after
// CompactByIndex has already loaded its point-in-time index snapshot must not
// trip the post-copy integrity check. CommitCompact's makeupDiff is what
// reconciles a write landing mid-copy (see TestCommitCompactDeletionTailKeepsWritable);
// the copy-phase check must not treat that expected case as corruption.
func TestCompactByIndex_ConcurrentWriteDoesNotFailIntegrityCheck(t *testing.T) {
	dir := t.TempDir()

	v, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}
	defer v.Close()

	for i := 1; i <= 8; i++ {
		if _, _, _, err := v.writeNeedle2(newRandomNeedle(uint64(i)), true, false, false); err != nil {
			t.Fatalf("write needle %d: %v", i, err)
		}
	}

	wroteConcurrently := false
	opts := &CompactOptions{
		ProgressCallback: func(processed int64) bool {
			if !wroteConcurrently {
				wroteConcurrently = true
				// Simulate a client write landing on the live volume while
				// CompactByIndex is still copying the pre-write snapshot.
				if _, _, _, err := v.writeNeedle2(newRandomNeedle(uint64(100)), true, false, false); err != nil {
					t.Fatalf("concurrent write: %v", err)
				}
			}
			return true
		},
	}

	if err := v.CompactByIndex(opts); err != nil {
		t.Fatalf("CompactByIndex should tolerate a write that lands mid-copy, got: %v", err)
	}
}

// TestCompactByVolumeData_SkipsNegativeSizeHeader covers issue #6763: a .dat
// record whose header carries size -1 made compaction panic with "slice bounds
// out of range [:-1]". The corrupt record must be skipped and the needles on
// both sides of it kept.
func TestCompactByVolumeData_SkipsNegativeSizeHeader(t *testing.T) {
	dir := t.TempDir()

	v, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
	if err != nil {
		t.Fatalf("volume creation: %v", err)
	}
	defer v.Close()

	if _, _, _, err := v.writeNeedle2(newRandomNeedle(1), true, false, false); err != nil {
		t.Fatalf("write needle 1: %v", err)
	}

	// Size -1 still yields a positive body length, so the scan reads a body
	// for this record and parses it.
	datSize, _, err := v.DataBackend.GetStat()
	if err != nil {
		t.Fatalf("stat .dat: %v", err)
	}
	corrupt := make([]byte, needle.GetActualSize(-1, v.Version()))
	types.NeedleIdToBytes(corrupt[types.CookieSize:types.CookieSize+types.NeedleIdSize], types.Uint64ToNeedleId(99))
	types.SizeToBytes(corrupt[types.CookieSize+types.NeedleIdSize:types.NeedleHeaderSize], -1)
	if _, err := v.DataBackend.WriteAt(corrupt, datSize); err != nil {
		t.Fatalf("append corrupt record: %v", err)
	}

	if _, _, _, err := v.writeNeedle2(newRandomNeedle(2), true, false, false); err != nil {
		t.Fatalf("write needle 2: %v", err)
	}

	if err := v.CompactByVolumeData(nil); err != nil {
		t.Fatalf("CompactByVolumeData: %v", err)
	}

	cpx, err := os.Open(filepath.Join(dir, "1.cpx"))
	if err != nil {
		t.Fatalf("open .cpx: %v", err)
	}
	defer cpx.Close()
	kept := map[types.NeedleId]bool{}
	if err := idx.WalkIndexFile(cpx, 0, func(key types.NeedleId, _ types.Offset, size types.Size) error {
		if size.IsValid() {
			kept[key] = true
		}
		return nil
	}); err != nil {
		t.Fatalf("walk .cpx: %v", err)
	}
	for _, id := range []uint64{1, 2} {
		if !kept[types.Uint64ToNeedleId(id)] {
			t.Errorf("needle %d missing from the compacted index", id)
		}
	}
	if kept[types.Uint64ToNeedleId(99)] {
		t.Errorf("corrupt record 99 should not be in the compacted index")
	}
}

// A corrupt header the scan cannot advance past must fail compaction and
// leave the original volume untouched.
func TestCompactByVolumeData_FailsOnHeaderThatCannotAdvance(t *testing.T) {
	for _, size := range []types.Size{-36, -100} {
		t.Run(fmt.Sprintf("size%d", size), func(t *testing.T) {
			dir := t.TempDir()

			v, err := NewVolume(dir, dir, "", 1, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
			if err != nil {
				t.Fatalf("volume creation: %v", err)
			}
			stuck := false
			defer func() {
				if !stuck {
					v.Close() // blocks until a running compaction ends
				}
			}()

			if _, _, _, err := v.writeNeedle2(newRandomNeedle(1), true, false, false); err != nil {
				t.Fatalf("write needle 1: %v", err)
			}
			datSize, _, err := v.DataBackend.GetStat()
			if err != nil {
				t.Fatalf("stat .dat: %v", err)
			}
			corrupt := make([]byte, types.NeedleHeaderSize)
			types.NeedleIdToBytes(corrupt[types.CookieSize:types.CookieSize+types.NeedleIdSize], types.Uint64ToNeedleId(99))
			types.SizeToBytes(corrupt[types.CookieSize+types.NeedleIdSize:], size)
			if _, err := v.DataBackend.WriteAt(corrupt, datSize); err != nil {
				t.Fatalf("append corrupt header: %v", err)
			}
			if _, _, _, err := v.writeNeedle2(newRandomNeedle(2), true, false, false); err != nil {
				t.Fatalf("write needle 2: %v", err)
			}
			datBefore, err := os.ReadFile(v.FileName(".dat"))
			if err != nil {
				t.Fatalf("read .dat: %v", err)
			}

			err = runWithTimeout(10*time.Second, func() error { return v.CompactByVolumeData(nil) })
			if errors.Is(err, errDidNotReturn) {
				stuck = true
				t.Fatalf("CompactByVolumeData: %v", err)
			}
			if !errors.Is(err, needle.ErrorCorrupted) {
				t.Fatalf("CompactByVolumeData error = %v, want one wrapping ErrorCorrupted", err)
			}

			if _, err := os.Stat(v.FileName(".cpx")); !os.IsNotExist(err) {
				t.Errorf("failed compaction left a compacted index: %v", err)
			}
			datAfter, err := os.ReadFile(v.FileName(".dat"))
			if err != nil {
				t.Fatalf("read .dat: %v", err)
			}
			if !bytes.Equal(datBefore, datAfter) {
				t.Errorf(".dat changed: %d bytes before, %d after", len(datBefore), len(datAfter))
			}
			for _, id := range []uint64{1, 2} {
				n := &needle.Needle{Id: types.Uint64ToNeedleId(id)}
				if _, err := v.readNeedle(n, &ReadOption{}, nil); err != nil {
					t.Errorf("read needle %d from the original volume: %v", id, err)
				}
			}
		})
	}
}

// TestExceedsExpectedCompactedSize guards the copy-phase integrity check
// against regressing into double-subtracting skipped bytes: expectedLiveBytes
// already excludes needles dropped as unreadable (they return before being
// added to the tally), so the check must compare it directly against the
// compacted .dat size, with no further adjustment for skipped bytes.
func TestExceedsExpectedCompactedSize(t *testing.T) {
	cases := []struct {
		name              string
		expectedLiveBytes uint64
		dstDatSize        int64
		wantExceeds       bool
	}{
		{"destination matches expected size exactly", 100, 100, false},
		{"destination larger than expected is fine", 100, 150, false},
		{"destination short of expected signals data loss", 100, 90, true},
	}
	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			if got := exceedsExpectedCompactedSize(c.expectedLiveBytes, c.dstDatSize); got != c.wantExceeds {
				t.Fatalf("exceedsExpectedCompactedSize(%d, %d) = %v, want %v", c.expectedLiveBytes, c.dstDatSize, got, c.wantExceeds)
			}
		})
	}
}

func doSomeWritesDeletes(i int, v *Volume, t *testing.T, infos []*needleInfo) {
	n := newRandomNeedle(uint64(i))
	_, size, _, err := v.writeNeedle2(n, true, false, false)
	if err != nil {
		t.Fatalf("write file %d: %v", i, err)
	}
	infos[i-1] = &needleInfo{
		size: size,
		crc:  n.Checksum,
	}
	// println("written file", i, "checksum", n.Checksum.Value(), "size", size)
	if rand.Float64() < 0.03 {
		toBeDeleted := rand.Intn(i) + 1
		oldNeedle := newEmptyNeedle(uint64(toBeDeleted))
		v.deleteNeedle2(oldNeedle)
		// println("deleted file", toBeDeleted)
		infos[toBeDeleted-1] = &needleInfo{
			size: 0,
			crc:  n.Checksum,
		}
	}
}

type needleInfo struct {
	size types.Size
	crc  needle.CRC
}

func newRandomNeedle(id uint64) *needle.Needle {
	n := new(needle.Needle)
	// never zero bytes: an empty needle writes a size-0 .dat record, indistinguishable from a delete marker
	n.Data = make([]byte, 1+rand.Intn(1023))
	rand.Read(n.Data)

	n.Checksum = needle.NewCRC(n.Data)
	n.Id = types.Uint64ToNeedleId(id)
	return n
}

func newEmptyNeedle(id uint64) *needle.Needle {
	n := new(needle.Needle)
	n.Id = types.Uint64ToNeedleId(id)
	return n
}