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https://github.com/talent-plan/tinykv.git
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5e089a2cd1
Signed-off-by: Connor <zbk602423539@gmail.com> Co-authored-by: Nick Cameron <nrc@ncameron.org> Co-authored-by: linning <linningde25@gmail.com> Co-authored-by: YangKeao <keao.yang@yahoo.com> Co-authored-by: andylokandy <andylokandy@hotmail.com> Co-authored-by: Iosmanthus Teng <myosmanthustree@gmail.com>
85 lines
2.5 KiB
Go
85 lines
2.5 KiB
Go
package codec
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import (
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"fmt"
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"github.com/pingcap/errors"
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)
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const (
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encGroupSize = 8
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encMarker = byte(0xFF)
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encPad = byte(0x0)
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)
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var pads = make([]byte, encGroupSize)
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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 slice which is padding with 0.
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// marker is `0xFF - padding 0 count`
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// For example:
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// [] -> [0, 0, 0, 0, 0, 0, 0, 0, 247]
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// [1, 2, 3] -> [1, 2, 3, 0, 0, 0, 0, 0, 250]
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// [1, 2, 3, 0] -> [1, 2, 3, 0, 0, 0, 0, 0, 251]
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// [1, 2, 3, 4, 5, 6, 7, 8] -> [1, 2, 3, 4, 5, 6, 7, 8, 255, 0, 0, 0, 0, 0, 0, 0, 0, 247]
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// Refer: https://github.com/facebook/mysql-5.6/wiki/MyRocks-record-format#memcomparable-format
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func EncodeBytes(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 `(len(data) / encGroupSize + 1) * (encGroupSize + 1)` bytes,
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// that is `(len(data) / 8 + 1) * 9` in our implement.
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dLen := len(data)
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result := make([]byte, 0, (dLen/encGroupSize+1)*(encGroupSize+1)+8) // make extra room for appending ts
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for idx := 0; idx <= dLen; idx += encGroupSize {
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remain := dLen - idx
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padCount := 0
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if remain >= encGroupSize {
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result = append(result, data[idx:idx+encGroupSize]...)
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} else {
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padCount = encGroupSize - remain
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result = append(result, data[idx:]...)
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result = append(result, pads[:padCount]...)
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}
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marker := encMarker - byte(padCount)
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result = append(result, marker)
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}
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return result
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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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data := make([]byte, 0, len(b))
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for {
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if len(b) < encGroupSize+1 {
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return nil, nil, fmt.Errorf("insufficient bytes to decode value: %d", len(b))
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}
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groupBytes := b[:encGroupSize+1]
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group := groupBytes[:encGroupSize]
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marker := groupBytes[encGroupSize]
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padCount := encMarker - marker
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if padCount > encGroupSize {
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return nil, nil, errors.Errorf("invalid marker byte, group bytes %q", groupBytes)
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}
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realGroupSize := encGroupSize - padCount
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data = append(data, group[:realGroupSize]...)
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b = b[encGroupSize+1:]
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if padCount != 0 {
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// Check validity of padding bytes.
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for _, v := range group[realGroupSize:] {
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if v != encPad {
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return nil, nil, errors.Errorf("invalid padding byte, group bytes %q", groupBytes)
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}
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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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