mirror of https://github.com/siddontang/go.git
125 lines
2.8 KiB
Go
125 lines
2.8 KiB
Go
// Copyright 2011 The Snappy-Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package snappy
|
|
|
|
import (
|
|
"encoding/binary"
|
|
"errors"
|
|
)
|
|
|
|
// ErrCorrupt reports that the input is invalid.
|
|
var ErrCorrupt = errors.New("snappy: corrupt input")
|
|
|
|
// DecodedLen returns the length of the decoded block.
|
|
func DecodedLen(src []byte) (int, error) {
|
|
v, _, err := decodedLen(src)
|
|
return v, err
|
|
}
|
|
|
|
// decodedLen returns the length of the decoded block and the number of bytes
|
|
// that the length header occupied.
|
|
func decodedLen(src []byte) (blockLen, headerLen int, err error) {
|
|
v, n := binary.Uvarint(src)
|
|
if n == 0 {
|
|
return 0, 0, ErrCorrupt
|
|
}
|
|
if uint64(int(v)) != v {
|
|
return 0, 0, errors.New("snappy: decoded block is too large")
|
|
}
|
|
return int(v), n, nil
|
|
}
|
|
|
|
// Decode returns the decoded form of src. The returned slice may be a sub-
|
|
// slice of dst if dst was large enough to hold the entire decoded block.
|
|
// Otherwise, a newly allocated slice will be returned.
|
|
// It is valid to pass a nil dst.
|
|
func Decode(dst, src []byte) ([]byte, error) {
|
|
dLen, s, err := decodedLen(src)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
if len(dst) < dLen {
|
|
dst = make([]byte, dLen)
|
|
}
|
|
|
|
var d, offset, length int
|
|
for s < len(src) {
|
|
switch src[s] & 0x03 {
|
|
case tagLiteral:
|
|
x := uint(src[s] >> 2)
|
|
switch {
|
|
case x < 60:
|
|
s += 1
|
|
case x == 60:
|
|
s += 2
|
|
if s > len(src) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
x = uint(src[s-1])
|
|
case x == 61:
|
|
s += 3
|
|
if s > len(src) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
x = uint(src[s-2]) | uint(src[s-1])<<8
|
|
case x == 62:
|
|
s += 4
|
|
if s > len(src) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
x = uint(src[s-3]) | uint(src[s-2])<<8 | uint(src[s-1])<<16
|
|
case x == 63:
|
|
s += 5
|
|
if s > len(src) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
x = uint(src[s-4]) | uint(src[s-3])<<8 | uint(src[s-2])<<16 | uint(src[s-1])<<24
|
|
}
|
|
length = int(x + 1)
|
|
if length <= 0 {
|
|
return nil, errors.New("snappy: unsupported literal length")
|
|
}
|
|
if length > len(dst)-d || length > len(src)-s {
|
|
return nil, ErrCorrupt
|
|
}
|
|
copy(dst[d:], src[s:s+length])
|
|
d += length
|
|
s += length
|
|
continue
|
|
|
|
case tagCopy1:
|
|
s += 2
|
|
if s > len(src) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
length = 4 + int(src[s-2])>>2&0x7
|
|
offset = int(src[s-2])&0xe0<<3 | int(src[s-1])
|
|
|
|
case tagCopy2:
|
|
s += 3
|
|
if s > len(src) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
length = 1 + int(src[s-3])>>2
|
|
offset = int(src[s-2]) | int(src[s-1])<<8
|
|
|
|
case tagCopy4:
|
|
return nil, errors.New("snappy: unsupported COPY_4 tag")
|
|
}
|
|
|
|
end := d + length
|
|
if offset > d || end > len(dst) {
|
|
return nil, ErrCorrupt
|
|
}
|
|
for ; d < end; d++ {
|
|
dst[d] = dst[d-offset]
|
|
}
|
|
}
|
|
if d != dLen {
|
|
return nil, ErrCorrupt
|
|
}
|
|
return dst[:d], nil
|
|
}
|