122 lines
3.5 KiB
Go
122 lines
3.5 KiB
Go
// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package codec
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import (
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"bytes"
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"github.com/juju/errors"
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)
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const (
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encGroupSize = 8
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avgEncGroupCount = 20
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encMarker = byte(0xFF)
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encPad = byte(0x0)
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)
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// Refer: https://github.com/facebook/mysql-5.6/wiki/MyRocks-record-format#memcomparable-format
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// EncodeBytes guarantees the encoded value is in ascending order for comparison,
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// encoding with the following rule:
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// [group1][marker1]...[groupN][markerN]
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// group is 8 bytes sclice which maybe padding with 0.
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// marker is 0xFF - appending 0 number
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// For example:
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// [] -> [1 0 0 0 0 0 0 0 0 247]
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// [1, 2, 3] -> [1 1 2 3 0 0 0 0 0 250]
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// [1, 2, 3, 0] -> [1 1 2 3 0 0 0 0 0 251]
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// [1, 2, 3, 4, 5, 6, 7, 8] -> [1 1 2 3 4 5 6 7 8 255 0 0 0 0 0 0 0 0 247]
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func EncodeBytes(b []byte, data []byte) []byte {
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// Allocate more space to avoid unnecessary slice growing.
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// Assume that the byte slice size is about 20*8 = 160 bytes.
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dl := len(data)
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bs := reallocBytes(b, dl+avgEncGroupCount)
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for idx := 0; idx <= dl; idx += encGroupSize {
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remain := dl - idx
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padCount := 0
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if remain >= encGroupSize {
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bs = append(bs, data[idx:idx+encGroupSize]...)
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} else {
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padCount = encGroupSize - remain
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bs = append(bs, data[idx:]...)
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bs = append(bs, make([]byte, padCount)...)
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}
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marker := encMarker - byte(padCount)
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bs = append(bs, marker)
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}
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return bs
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}
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func decodeBytes(b []byte, reverse bool) ([]byte, []byte, error) {
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if len(b) < encGroupSize+1 {
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return nil, nil, errors.Errorf("insufficient bytes to decode value")
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}
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data := []byte{}
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for {
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groupBytes := b[:encGroupSize+1]
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if reverse {
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reverseBytes(groupBytes)
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}
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group := groupBytes[:encGroupSize]
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marker := groupBytes[encGroupSize]
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// Check validity of marker.
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padCount := encMarker - marker
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realGroupSize := encGroupSize - padCount
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if realGroupSize < 0 {
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return nil, nil, errors.Errorf("invalid marker byte, group %v", group)
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}
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data = append(data, group[:realGroupSize]...)
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b = b[encGroupSize+1:]
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if marker != encMarker {
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// Check validity of padding bytes.
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if bytes.Count(group[realGroupSize:], []byte{encPad}) != int(padCount) {
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return nil, nil, errors.Errorf("invalid padding byte, group %v", group)
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}
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break
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}
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}
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return b, data, nil
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}
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// DecodeBytes decodes bytes which is encoded by EncodeBytes before,
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// returns the leftover bytes and decoded value if no error.
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func DecodeBytes(b []byte) ([]byte, []byte, error) {
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return decodeBytes(b, false)
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}
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// EncodeBytesDesc first encodes bytes using EncodeBytes, then bitwise reverses
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// encoded value to guarentee the encoded value is in descending order for comparison,
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// The encoded value is >= SmallestNoneNilValue and < InfiniteValue.
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func EncodeBytesDesc(b []byte, data []byte) []byte {
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n := len(b)
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b = EncodeBytes(b, data)
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reverseBytes(b[n:])
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return b
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}
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// DecodeBytesDesc decodes bytes which is encoded by EncodeBytesDesc before,
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// returns the leftover bytes and decoded value if no error.
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func DecodeBytesDesc(b []byte) ([]byte, []byte, error) {
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return decodeBytes(b, true)
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}
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