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snappy.go
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snappy.go
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// Copyright 2019+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.
// Based on work by Yann Collet, released under BSD License.
package zstd
import (
"encoding/binary"
"errors"
"hash/crc32"
"io"
"github.com/golang/snappy"
"github.com/klauspost/compress/huff0"
)
const (
snappyTagLiteral = 0x00
snappyTagCopy1 = 0x01
snappyTagCopy2 = 0x02
snappyTagCopy4 = 0x03
)
const (
snappyChecksumSize = 4
snappyMagicBody = "sNaPpY"
// snappyMaxBlockSize is the maximum size of the input to encodeBlock. It is not
// part of the wire format per se, but some parts of the encoder assume
// that an offset fits into a uint16.
//
// Also, for the framing format (Writer type instead of Encode function),
// https://github.com/google/snappy/blob/master/framing_format.txt says
// that "the uncompressed data in a chunk must be no longer than 65536
// bytes".
snappyMaxBlockSize = 65536
// snappyMaxEncodedLenOfMaxBlockSize equals MaxEncodedLen(snappyMaxBlockSize), but is
// hard coded to be a const instead of a variable, so that obufLen can also
// be a const. Their equivalence is confirmed by
// TestMaxEncodedLenOfMaxBlockSize.
snappyMaxEncodedLenOfMaxBlockSize = 76490
)
const (
chunkTypeCompressedData = 0x00
chunkTypeUncompressedData = 0x01
chunkTypePadding = 0xfe
chunkTypeStreamIdentifier = 0xff
)
var (
// ErrSnappyCorrupt reports that the input is invalid.
ErrSnappyCorrupt = errors.New("snappy: corrupt input")
// ErrSnappyTooLarge reports that the uncompressed length is too large.
ErrSnappyTooLarge = errors.New("snappy: decoded block is too large")
// ErrSnappyUnsupported reports that the input isn't supported.
ErrSnappyUnsupported = errors.New("snappy: unsupported input")
errUnsupportedLiteralLength = errors.New("snappy: unsupported literal length")
)
// SnappyConverter can read SnappyConverter-compressed streams and convert them to zstd.
// Conversion is done by converting the stream directly from Snappy without intermediate
// full decoding.
// Therefore the compression ratio is much less than what can be done by a full decompression
// and compression, and a faulty Snappy stream may lead to a faulty Zstandard stream without
// any errors being generated.
// No CRC value is being generated and not all CRC values of the Snappy stream are checked.
// However, it provides really fast recompression of Snappy streams.
// The converter can be reused to avoid allocations, even after errors.
type SnappyConverter struct {
r io.Reader
err error
buf []byte
block *blockEnc
}
// Convert the Snappy stream supplied in 'in' and write the zStandard stream to 'w'.
// If any error is detected on the Snappy stream it is returned.
// The number of bytes written is returned.
func (r *SnappyConverter) Convert(in io.Reader, w io.Writer) (int64, error) {
initPredefined()
r.err = nil
r.r = in
if r.block == nil {
r.block = &blockEnc{}
r.block.init()
}
r.block.initNewEncode()
if len(r.buf) != snappyMaxEncodedLenOfMaxBlockSize+snappyChecksumSize {
r.buf = make([]byte, snappyMaxEncodedLenOfMaxBlockSize+snappyChecksumSize)
}
r.block.litEnc.Reuse = huff0.ReusePolicyNone
var written int64
var readHeader bool
{
var header []byte
var n int
header, r.err = frameHeader{WindowSize: snappyMaxBlockSize}.appendTo(r.buf[:0])
n, r.err = w.Write(header)
if r.err != nil {
return written, r.err
}
written += int64(n)
}
for {
if !r.readFull(r.buf[:4], true) {
// Add empty last block
r.block.reset(nil)
r.block.last = true
err := r.block.encodeLits(r.block.literals, false)
if err != nil {
return written, err
}
n, err := w.Write(r.block.output)
if err != nil {
return written, err
}
written += int64(n)
return written, r.err
}
chunkType := r.buf[0]
if !readHeader {
if chunkType != chunkTypeStreamIdentifier {
println("chunkType != chunkTypeStreamIdentifier", chunkType)
r.err = ErrSnappyCorrupt
return written, r.err
}
readHeader = true
}
chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
if chunkLen > len(r.buf) {
println("chunkLen > len(r.buf)", chunkType)
r.err = ErrSnappyUnsupported
return written, 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 < snappyChecksumSize {
println("chunkLen < snappyChecksumSize", chunkLen, snappyChecksumSize)
r.err = ErrSnappyCorrupt
return written, r.err
}
buf := r.buf[:chunkLen]
if !r.readFull(buf, false) {
return written, r.err
}
//checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
buf = buf[snappyChecksumSize:]
n, hdr, err := snappyDecodedLen(buf)
if err != nil {
r.err = err
return written, r.err
}
buf = buf[hdr:]
if n > snappyMaxBlockSize {
println("n > snappyMaxBlockSize", n, snappyMaxBlockSize)
r.err = ErrSnappyCorrupt
return written, r.err
}
r.block.reset(nil)
r.block.pushOffsets()
if err := decodeSnappy(r.block, buf); err != nil {
r.err = err
return written, r.err
}
if r.block.size+r.block.extraLits != n {
printf("invalid size, want %d, got %d\n", n, r.block.size+r.block.extraLits)
r.err = ErrSnappyCorrupt
return written, r.err
}
err = r.block.encode(nil, false, false)
switch err {
case errIncompressible:
r.block.popOffsets()
r.block.reset(nil)
r.block.literals, err = snappy.Decode(r.block.literals[:n], r.buf[snappyChecksumSize:chunkLen])
if err != nil {
return written, err
}
err = r.block.encodeLits(r.block.literals, false)
if err != nil {
return written, err
}
case nil:
default:
return written, err
}
n, r.err = w.Write(r.block.output)
if r.err != nil {
return written, err
}
written += int64(n)
continue
case chunkTypeUncompressedData:
if debug {
println("Uncompressed, chunklen", chunkLen)
}
// Section 4.3. Uncompressed data (chunk type 0x01).
if chunkLen < snappyChecksumSize {
println("chunkLen < snappyChecksumSize", chunkLen, snappyChecksumSize)
r.err = ErrSnappyCorrupt
return written, r.err
}
r.block.reset(nil)
buf := r.buf[:snappyChecksumSize]
if !r.readFull(buf, false) {
return written, 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 - snappyChecksumSize
if n > snappyMaxBlockSize {
println("n > snappyMaxBlockSize", n, snappyMaxBlockSize)
r.err = ErrSnappyCorrupt
return written, r.err
}
r.block.literals = r.block.literals[:n]
if !r.readFull(r.block.literals, false) {
return written, r.err
}
if snappyCRC(r.block.literals) != checksum {
println("literals crc mismatch")
r.err = ErrSnappyCorrupt
return written, r.err
}
err := r.block.encodeLits(r.block.literals, false)
if err != nil {
return written, err
}
n, r.err = w.Write(r.block.output)
if r.err != nil {
return written, err
}
written += int64(n)
continue
case chunkTypeStreamIdentifier:
if debug {
println("stream id", chunkLen, len(snappyMagicBody))
}
// Section 4.1. Stream identifier (chunk type 0xff).
if chunkLen != len(snappyMagicBody) {
println("chunkLen != len(snappyMagicBody)", chunkLen, len(snappyMagicBody))
r.err = ErrSnappyCorrupt
return written, r.err
}
if !r.readFull(r.buf[:len(snappyMagicBody)], false) {
return written, r.err
}
for i := 0; i < len(snappyMagicBody); i++ {
if r.buf[i] != snappyMagicBody[i] {
println("r.buf[i] != snappyMagicBody[i]", r.buf[i], snappyMagicBody[i], i)
r.err = ErrSnappyCorrupt
return written, r.err
}
}
continue
}
if chunkType <= 0x7f {
// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
println("chunkType <= 0x7f")
r.err = ErrSnappyUnsupported
return written, 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], false) {
return written, r.err
}
}
}
// decodeSnappy writes the decoding of src to dst. It assumes that the varint-encoded
// length of the decompressed bytes has already been read.
func decodeSnappy(blk *blockEnc, src []byte) error {
//decodeRef(make([]byte, snappyMaxBlockSize), src)
var s, length int
lits := blk.extraLits
var offset uint32
for s < len(src) {
switch src[s] & 0x03 {
case snappyTagLiteral:
x := uint32(src[s] >> 2)
switch {
case x < 60:
s++
case x == 60:
s += 2
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, src)
return ErrSnappyCorrupt
}
x = uint32(src[s-1])
case x == 61:
s += 3
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, src)
return ErrSnappyCorrupt
}
x = uint32(src[s-2]) | uint32(src[s-1])<<8
case x == 62:
s += 4
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, src)
return ErrSnappyCorrupt
}
x = uint32(src[s-3]) | uint32(src[s-2])<<8 | uint32(src[s-1])<<16
case x == 63:
s += 5
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, src)
return ErrSnappyCorrupt
}
x = uint32(src[s-4]) | uint32(src[s-3])<<8 | uint32(src[s-2])<<16 | uint32(src[s-1])<<24
}
if x > snappyMaxBlockSize {
println("x > snappyMaxBlockSize", x, snappyMaxBlockSize)
return ErrSnappyCorrupt
}
length = int(x) + 1
if length <= 0 {
println("length <= 0 ", length)
return errUnsupportedLiteralLength
}
//if length > snappyMaxBlockSize-d || uint32(length) > len(src)-s {
// return ErrSnappyCorrupt
//}
blk.literals = append(blk.literals, src[s:s+length]...)
//println(length, "litLen")
lits += length
s += length
continue
case snappyTagCopy1:
s += 2
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, len(src))
return ErrSnappyCorrupt
}
length = 4 + int(src[s-2])>>2&0x7
offset = uint32(src[s-2])&0xe0<<3 | uint32(src[s-1])
case snappyTagCopy2:
s += 3
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, len(src))
return ErrSnappyCorrupt
}
length = 1 + int(src[s-3])>>2
offset = uint32(src[s-2]) | uint32(src[s-1])<<8
case snappyTagCopy4:
s += 5
if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
println("uint(s) > uint(len(src)", s, len(src))
return ErrSnappyCorrupt
}
length = 1 + int(src[s-5])>>2
offset = uint32(src[s-4]) | uint32(src[s-3])<<8 | uint32(src[s-2])<<16 | uint32(src[s-1])<<24
}
if offset <= 0 || blk.size+lits < int(offset) /*|| length > len(blk)-d */ {
println("offset <= 0 || blk.size+lits < int(offset)", offset, blk.size+lits, int(offset), blk.size, lits)
return ErrSnappyCorrupt
}
// Check if offset is one of the recent offsets.
// Adjusts the output offset accordingly.
// Gives a tiny bit of compression, typically around 1%.
if false {
offset = blk.matchOffset(offset, uint32(lits))
} else {
offset += 3
}
blk.sequences = append(blk.sequences, seq{
litLen: uint32(lits),
offset: offset,
matchLen: uint32(length) - zstdMinMatch,
})
blk.size += length + lits
lits = 0
}
blk.extraLits = lits
return nil
}
func (r *SnappyConverter) readFull(p []byte, allowEOF bool) (ok bool) {
if _, r.err = io.ReadFull(r.r, p); r.err != nil {
if r.err == io.ErrUnexpectedEOF || (r.err == io.EOF && !allowEOF) {
r.err = ErrSnappyCorrupt
}
return false
}
return true
}
var crcTable = crc32.MakeTable(crc32.Castagnoli)
// crc implements the checksum specified in section 3 of
// https://github.com/google/snappy/blob/master/framing_format.txt
func snappyCRC(b []byte) uint32 {
c := crc32.Update(0, crcTable, b)
return c>>15 | c<<17 + 0xa282ead8
}
// snappyDecodedLen returns the length of the decoded block and the number of bytes
// that the length header occupied.
func snappyDecodedLen(src []byte) (blockLen, headerLen int, err error) {
v, n := binary.Uvarint(src)
if n <= 0 || v > 0xffffffff {
return 0, 0, ErrSnappyCorrupt
}
const wordSize = 32 << (^uint(0) >> 32 & 1)
if wordSize == 32 && v > 0x7fffffff {
return 0, 0, ErrSnappyTooLarge
}
return int(v), n, nil
}