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