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decoder.go
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/
decoder.go
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package codec
import (
"encoding/binary"
"io"
"github.com/dgallion1/bitcask/internal"
"github.com/pkg/errors"
)
var (
errInvalidKeyOrValueSize = errors.New("key/value size is invalid")
errCantDecodeOnNilEntry = errors.New("can't decode on nil entry")
errTruncatedData = errors.New("data is truncated")
)
// NewDecoder creates a streaming Entry decoder.
func NewDecoder(r io.Reader, maxKeySize uint32, maxValueSize uint64) *Decoder {
return &Decoder{
r: r,
maxKeySize: maxKeySize,
maxValueSize: maxValueSize,
}
}
// Decoder wraps an underlying io.Reader and allows you to stream
// Entry decodings on it.
type Decoder struct {
r io.Reader
maxKeySize uint32
maxValueSize uint64
}
// Decode decodes the next Entry from the current stream
func (d *Decoder) Decode(v *internal.Entry) (int64, error) {
if v == nil {
return 0, errCantDecodeOnNilEntry
}
prefixBuf := make([]byte, keySize+valueSize)
_, err := io.ReadFull(d.r, prefixBuf)
if err != nil {
return 0, err
}
actualKeySize, actualValueSize, err := getKeyValueSizes(prefixBuf, d.maxKeySize, d.maxValueSize)
if err != nil {
return 0, err
}
buf := make([]byte, uint64(actualKeySize)+actualValueSize+checksumSize)
if _, err = io.ReadFull(d.r, buf); err != nil {
return 0, errTruncatedData
}
decodeWithoutPrefix(buf, actualKeySize, v)
return int64(keySize + valueSize + uint64(actualKeySize) + actualValueSize + checksumSize), nil
}
// DecodeEntry decodes a serialized entry
func DecodeEntry(b []byte, e *internal.Entry, maxKeySize uint32, maxValueSize uint64) error {
valueOffset, _, err := getKeyValueSizes(b, maxKeySize, maxValueSize)
if err != nil {
return errors.Wrap(err, "key/value sizes are invalid")
}
decodeWithoutPrefix(b[keySize+valueSize:], valueOffset, e)
return nil
}
func getKeyValueSizes(buf []byte, maxKeySize uint32, maxValueSize uint64) (uint32, uint64, error) {
actualKeySize := binary.BigEndian.Uint32(buf[:keySize])
actualValueSize := binary.BigEndian.Uint64(buf[keySize:])
if actualKeySize > maxKeySize || actualValueSize > maxValueSize || actualKeySize == 0 {
return 0, 0, errInvalidKeyOrValueSize
}
return actualKeySize, actualValueSize, nil
}
func decodeWithoutPrefix(buf []byte, valueOffset uint32, v *internal.Entry) {
v.Key = buf[:valueOffset]
v.Value = buf[valueOffset : len(buf)-checksumSize]
v.Checksum = binary.BigEndian.Uint32(buf[len(buf)-checksumSize:])
}
// IsCorruptedData indicates if the error correspondes to possible data corruption
func IsCorruptedData(err error) bool {
switch err {
case errCantDecodeOnNilEntry, errInvalidKeyOrValueSize, errTruncatedData:
return true
default:
return false
}
}