func Fuzz(data []byte) int {
	n, err := snappy.DecodedLen(data)
	if err != nil || n > 1e6 {
		return 0
	}
	if n < 0 {
		panic("negative decoded len")
	}
	dec, err := snappy.Decode(nil, data)
	if err != nil {
		if dec != nil {
			panic("dec is not nil")
		}
		return 0
	}
	if len(dec) != n {
		println(len(dec), n)
		panic("bad decoded len")
	}
	n = snappy.MaxEncodedLen(len(dec))
	enc := snappy.Encode(nil, dec)
	if len(enc) > n {
		panic("bad encoded len")
	}

	dec1, err := snappy.Decode(nil, enc)
	if err != nil {
		panic(err)
	}
	if bytes.Compare(dec, dec1) != 0 {
		panic("not equal")
	}
	return 1
}

func (snappyMessageCompressor) decompressData(dst, src []byte) (n int, err error) {
	n, err = snappy.DecodedLen(src)
	if err != nil {
		return
	}
	if n < 0 || n > len(dst) {
		err = io.ErrShortBuffer
		return
	}
	_, err = snappy.Decode(dst, src)
	return
}

func (r *Reader) readRawBlock(bh blockHandle, verifyChecksum bool) ([]byte, error) {
	data := r.bpool.Get(int(bh.length + blockTrailerLen))
	if _, err := r.reader.ReadAt(data, int64(bh.offset)); err != nil && err != io.EOF {
		return nil, err
	}

	if verifyChecksum {
		n := bh.length + 1
		checksum0 := binary.LittleEndian.Uint32(data[n:])
		checksum1 := util.NewCRC(data[:n]).Value()
		if checksum0 != checksum1 {
			r.bpool.Put(data)
			return nil, r.newErrCorruptedBH(bh, fmt.Sprintf("checksum mismatch, want=%#x got=%#x", checksum0, checksum1))
		}
	}

	switch data[bh.length] {
	case blockTypeNoCompression:
		data = data[:bh.length]
	case blockTypeSnappyCompression:
		decLen, err := snappy.DecodedLen(data[:bh.length])
		if err != nil {
			return nil, r.newErrCorruptedBH(bh, err.Error())
		}
		decData := r.bpool.Get(decLen)
		decData, err = snappy.Decode(decData, data[:bh.length])
		r.bpool.Put(data)
		if err != nil {
			r.bpool.Put(decData)
			return nil, r.newErrCorruptedBH(bh, err.Error())
		}
		data = decData
	default:
		r.bpool.Put(data)
		return nil, r.newErrCorruptedBH(bh, fmt.Sprintf("unknown compression type %#x", data[bh.length]))
	}
	return data, nil
}

// Next indicates if there is a value to read
func (r *WALSegmentReader) Next() bool {
	b := getBuf(defaultBufLen)
	defer putBuf(b)
	var nReadOK int

	// read the type and the length of the entry
	n, err := io.ReadFull(r.r, b[:5])
	if err == io.EOF {
		return false
	}

	if err != nil {
		r.err = err
		// We return true here because we want the client code to call read which
		// will return the this error to be handled.
		return true
	}
	nReadOK += n

	entryType := b[0]
	length := binary.BigEndian.Uint32(b[1:5])

	// read the compressed block and decompress it
	if int(length) > len(b) {
		b = make([]byte, length)
	}

	n, err = io.ReadFull(r.r, b[:length])
	if err != nil {
		r.err = err
		return true
	}
	nReadOK += n

	decLen, err := snappy.DecodedLen(b[:length])
	if err != nil {
		r.err = err
		return true
	}
	decBuf := getBuf(decLen)
	defer putBuf(decBuf)

	data, err := snappy.Decode(decBuf, b[:length])
	if err != nil {
		r.err = err
		return true
	}

	// and marshal it and send it to the cache
	switch WalEntryType(entryType) {
	case WriteWALEntryType:
		r.entry = &WriteWALEntry{
			Values: map[string][]Value{},
		}
	case DeleteWALEntryType:
		r.entry = &DeleteWALEntry{}
	case DeleteRangeWALEntryType:
		r.entry = &DeleteRangeWALEntry{}
	default:
		r.err = fmt.Errorf("unknown wal entry type: %v", entryType)
		return true
	}
	r.err = r.entry.UnmarshalBinary(data)
	if r.err == nil {
		// Read and decode of this entry was successful.
		r.n += int64(nReadOK)
	}

	return true
}

// writeIndex writes a set of points for a single key.
func (e *Engine) writeIndex(tx *bolt.Tx, key string, a [][]byte) error {
	// Ignore if there are no points.
	if len(a) == 0 {
		return nil
	}
	e.statMap.Add(statPointsWrite, int64(len(a)))

	// Create or retrieve series bucket.
	bkt, err := tx.Bucket([]byte("points")).CreateBucketIfNotExists([]byte(key))
	if err != nil {
		return fmt.Errorf("create series bucket: %s", err)
	}
	c := bkt.Cursor()

	// Ensure the slice is sorted before retrieving the time range.
	a = tsdb.DedupeEntries(a)
	e.statMap.Add(statPointsWriteDedupe, int64(len(a)))

	// Convert the raw time and byte slices to entries with lengths
	for i, p := range a {
		timestamp := int64(btou64(p[0:8]))
		a[i] = MarshalEntry(timestamp, p[8:])
	}

	// Determine time range of new data.
	tmin, tmax := int64(btou64(a[0][0:8])), int64(btou64(a[len(a)-1][0:8]))

	// If tmin is after the last block then append new blocks.
	//
	// This is the optimized fast path. Otherwise we need to merge the points
	// with existing blocks on disk and rewrite all the blocks for that range.
	if k, v := c.Last(); k == nil {
		bkt.FillPercent = 1.0
		if err := e.writeBlocks(bkt, a); err != nil {
			return fmt.Errorf("new blocks: %s", err)
		}
		return nil
	} else {
		// Determine uncompressed block size.
		sz, err := snappy.DecodedLen(v[8:])
		if err != nil {
			return fmt.Errorf("snappy decoded len: %s", err)
		}

		// Append new blocks if our time range is past the last on-disk time
		// and if our previous block was at least the minimum block size.
		if int64(btou64(v[0:8])) < tmin && sz >= e.BlockSize {
			bkt.FillPercent = 1.0
			if err := e.writeBlocks(bkt, a); err != nil {
				return fmt.Errorf("append blocks: %s", err)
			}
			return nil
		}

		// Otherwise fallthrough to slower insert mode.
		e.statMap.Add(statSlowInsert, 1)
	}

	// Generate map of inserted keys.
	m := make(map[int64]struct{})
	for _, b := range a {
		m[int64(btou64(b[0:8]))] = struct{}{}
	}

	// If time range overlaps existing blocks then unpack full range and reinsert.
	var existing [][]byte
	for k, v := c.First(); k != nil; k, v = c.Next() {
		// Determine block range.
		bmin, bmax := int64(btou64(k)), int64(btou64(v[0:8]))

		// Skip over all blocks before the time range.
		// Exit once we reach a block that is beyond our time range.
		if bmax < tmin {
			continue
		} else if bmin > tmax {
			break
		}

		// Decode block.
		buf, err := snappy.Decode(nil, v[8:])
		if err != nil {
			return fmt.Errorf("decode block: %s", err)
		}

		// Copy out any entries that aren't being overwritten.
		for _, entry := range SplitEntries(buf) {
			if _, ok := m[int64(btou64(entry[0:8]))]; !ok {
				existing = append(existing, entry)
			}
		}

		// Delete block in database.
		c.Delete()
	}

	// Merge entries before rewriting.
	a = append(existing, a...)
	sort.Sort(tsdb.ByteSlices(a))

//.........这里部分代码省略.........