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start refactoring
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fatedier
296
vendor/github.com/golang/snappy/decode.go
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vendored
Normal file
296
vendor/github.com/golang/snappy/decode.go
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vendored
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@ -0,0 +1,296 @@
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// 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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"io"
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)
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var (
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// ErrCorrupt reports that the input is invalid.
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ErrCorrupt = errors.New("snappy: corrupt input")
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// ErrTooLarge reports that the uncompressed length is too large.
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ErrTooLarge = errors.New("snappy: decoded block is too large")
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// ErrUnsupported reports that the input isn't supported.
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ErrUnsupported = errors.New("snappy: unsupported input")
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errUnsupportedCopy4Tag = errors.New("snappy: unsupported COPY_4 tag")
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errUnsupportedLiteralLength = errors.New("snappy: unsupported literal length")
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)
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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 || v > 0xffffffff {
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return 0, 0, ErrCorrupt
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}
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const wordSize = 32 << (^uint(0) >> 32 & 1)
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if wordSize == 32 && v > 0x7fffffff {
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return 0, 0, ErrTooLarge
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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++
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case x == 60:
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s += 2
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if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
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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 uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
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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 uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
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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 uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
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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, errUnsupportedLiteralLength
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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, errUnsupportedCopy4Tag
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}
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if offset > d || length > len(dst)-d {
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return nil, ErrCorrupt
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}
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for end := d + length; 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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// NewReader returns a new Reader that decompresses from r, using the framing
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// format described at
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// https://github.com/google/snappy/blob/master/framing_format.txt
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func NewReader(r io.Reader) *Reader {
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return &Reader{
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r: r,
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decoded: make([]byte, maxUncompressedChunkLen),
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buf: make([]byte, MaxEncodedLen(maxUncompressedChunkLen)+checksumSize),
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}
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}
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// Reader is an io.Reader that can read Snappy-compressed bytes.
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type Reader struct {
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r io.Reader
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err error
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decoded []byte
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buf []byte
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// decoded[i:j] contains decoded bytes that have not yet been passed on.
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i, j int
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readHeader bool
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}
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// Reset discards any buffered data, resets all state, and switches the Snappy
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// reader to read from r. This permits reusing a Reader rather than allocating
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// a new one.
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func (r *Reader) Reset(reader io.Reader) {
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r.r = reader
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r.err = nil
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r.i = 0
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r.j = 0
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r.readHeader = false
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}
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func (r *Reader) readFull(p []byte) (ok bool) {
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if _, r.err = io.ReadFull(r.r, p); r.err != nil {
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if r.err == io.ErrUnexpectedEOF {
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r.err = ErrCorrupt
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}
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return false
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}
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return true
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}
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// Read satisfies the io.Reader interface.
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func (r *Reader) Read(p []byte) (int, error) {
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if r.err != nil {
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return 0, r.err
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}
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for {
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if r.i < r.j {
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n := copy(p, r.decoded[r.i:r.j])
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r.i += n
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return n, nil
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}
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if !r.readFull(r.buf[:4]) {
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return 0, r.err
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}
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chunkType := r.buf[0]
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if !r.readHeader {
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if chunkType != chunkTypeStreamIdentifier {
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r.err = ErrCorrupt
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return 0, r.err
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}
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r.readHeader = true
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}
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chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
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if chunkLen > len(r.buf) {
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r.err = ErrUnsupported
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return 0, r.err
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}
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// The chunk types are specified at
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// https://github.com/google/snappy/blob/master/framing_format.txt
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switch chunkType {
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case chunkTypeCompressedData:
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// Section 4.2. Compressed data (chunk type 0x00).
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if chunkLen < checksumSize {
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r.err = ErrCorrupt
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return 0, r.err
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}
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buf := r.buf[:chunkLen]
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if !r.readFull(buf) {
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return 0, r.err
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}
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checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
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buf = buf[checksumSize:]
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n, err := DecodedLen(buf)
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if err != nil {
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r.err = err
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return 0, r.err
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}
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if n > len(r.decoded) {
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r.err = ErrCorrupt
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return 0, r.err
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}
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if _, err := Decode(r.decoded, buf); err != nil {
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r.err = err
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return 0, r.err
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}
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if crc(r.decoded[:n]) != checksum {
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r.err = ErrCorrupt
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return 0, r.err
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}
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r.i, r.j = 0, n
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continue
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case chunkTypeUncompressedData:
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// Section 4.3. Uncompressed data (chunk type 0x01).
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if chunkLen < checksumSize {
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r.err = ErrCorrupt
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return 0, r.err
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}
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buf := r.buf[:checksumSize]
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if !r.readFull(buf) {
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return 0, r.err
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}
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checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
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// Read directly into r.decoded instead of via r.buf.
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n := chunkLen - checksumSize
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if !r.readFull(r.decoded[:n]) {
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return 0, r.err
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}
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if crc(r.decoded[:n]) != checksum {
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r.err = ErrCorrupt
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return 0, r.err
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}
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r.i, r.j = 0, n
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continue
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case chunkTypeStreamIdentifier:
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// Section 4.1. Stream identifier (chunk type 0xff).
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if chunkLen != len(magicBody) {
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r.err = ErrCorrupt
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return 0, r.err
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}
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if !r.readFull(r.buf[:len(magicBody)]) {
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return 0, r.err
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}
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for i := 0; i < len(magicBody); i++ {
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if r.buf[i] != magicBody[i] {
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r.err = ErrCorrupt
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return 0, r.err
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}
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}
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continue
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}
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if chunkType <= 0x7f {
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// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
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r.err = ErrUnsupported
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return 0, r.err
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}
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// Section 4.4 Padding (chunk type 0xfe).
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// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
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if !r.readFull(r.buf[:chunkLen]) {
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return 0, r.err
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}
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}
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}
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