132 lines
3.1 KiB
Go
132 lines
3.1 KiB
Go
package snappy
|
|
|
|
import (
|
|
"bytes"
|
|
"encoding/binary"
|
|
"errors"
|
|
|
|
master "github.com/golang/snappy"
|
|
)
|
|
|
|
const (
|
|
sizeOffset = 16
|
|
sizeBytes = 4
|
|
)
|
|
|
|
var (
|
|
xerialHeader = []byte{130, 83, 78, 65, 80, 80, 89, 0}
|
|
|
|
// This is xerial version 1 and minimally compatible with version 1
|
|
xerialVersionInfo = []byte{0, 0, 0, 1, 0, 0, 0, 1}
|
|
|
|
// ErrMalformed is returned by the decoder when the xerial framing
|
|
// is malformed
|
|
ErrMalformed = errors.New("malformed xerial framing")
|
|
)
|
|
|
|
func min(x, y int) int {
|
|
if x < y {
|
|
return x
|
|
}
|
|
return y
|
|
}
|
|
|
|
// Encode encodes data as snappy with no framing header.
|
|
func Encode(src []byte) []byte {
|
|
return master.Encode(nil, src)
|
|
}
|
|
|
|
// EncodeStream *appends* to the specified 'dst' the compressed
|
|
// 'src' in xerial framing format. If 'dst' does not have enough
|
|
// capacity, then a new slice will be allocated. If 'dst' has
|
|
// non-zero length, then if *must* have been built using this function.
|
|
func EncodeStream(dst, src []byte) []byte {
|
|
if len(dst) == 0 {
|
|
dst = append(dst, xerialHeader...)
|
|
dst = append(dst, xerialVersionInfo...)
|
|
}
|
|
|
|
// Snappy encode in blocks of maximum 32KB
|
|
var (
|
|
max = len(src)
|
|
blockSize = 32 * 1024
|
|
pos = 0
|
|
chunk []byte
|
|
)
|
|
|
|
for pos < max {
|
|
newPos := min(pos + blockSize, max)
|
|
chunk = master.Encode(chunk[:cap(chunk)], src[pos:newPos])
|
|
|
|
// First encode the compressed size (big-endian)
|
|
// Put* panics if the buffer is too small, so pad 4 bytes first
|
|
origLen := len(dst)
|
|
dst = append(dst, dst[0:4]...)
|
|
binary.BigEndian.PutUint32(dst[origLen:], uint32(len(chunk)))
|
|
|
|
// And now the compressed data
|
|
dst = append(dst, chunk...)
|
|
pos = newPos
|
|
}
|
|
return dst
|
|
}
|
|
|
|
// Decode decodes snappy data whether it is traditional unframed
|
|
// or includes the xerial framing format.
|
|
func Decode(src []byte) ([]byte, error) {
|
|
return DecodeInto(nil, src)
|
|
}
|
|
|
|
// DecodeInto decodes snappy data whether it is traditional unframed
|
|
// or includes the xerial framing format into the specified `dst`.
|
|
// It is assumed that the entirety of `dst` including all capacity is available
|
|
// for use by this function. If `dst` is nil *or* insufficiently large to hold
|
|
// the decoded `src`, new space will be allocated.
|
|
func DecodeInto(dst, src []byte) ([]byte, error) {
|
|
var max = len(src)
|
|
if max < len(xerialHeader) {
|
|
return nil, ErrMalformed
|
|
}
|
|
|
|
if !bytes.Equal(src[:8], xerialHeader) {
|
|
return master.Decode(dst[:cap(dst)], src)
|
|
}
|
|
|
|
if max < sizeOffset+sizeBytes {
|
|
return nil, ErrMalformed
|
|
}
|
|
|
|
if dst == nil {
|
|
dst = make([]byte, 0, len(src))
|
|
}
|
|
|
|
dst = dst[:0]
|
|
var (
|
|
pos = sizeOffset
|
|
chunk []byte
|
|
err error
|
|
)
|
|
|
|
for pos+sizeBytes <= max {
|
|
size := int(binary.BigEndian.Uint32(src[pos : pos+sizeBytes]))
|
|
pos += sizeBytes
|
|
|
|
nextPos := pos + size
|
|
// On architectures where int is 32-bytes wide size + pos could
|
|
// overflow so we need to check the low bound as well as the
|
|
// high
|
|
if nextPos < pos || nextPos > max {
|
|
return nil, ErrMalformed
|
|
}
|
|
|
|
chunk, err = master.Decode(chunk[:cap(chunk)], src[pos:nextPos])
|
|
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
pos = nextPos
|
|
dst = append(dst, chunk...)
|
|
}
|
|
return dst, nil
|
|
}
|