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