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encode.go
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encode.go
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// Copyright 2011 The Snappy-Go Authors. All rights reserved.
// Copyright (c) 2019 Klaus Post. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package s2
import (
"crypto/rand"
"encoding/binary"
"errors"
"fmt"
"io"
"math"
"math/bits"
"runtime"
"sync"
)
// Encode returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func Encode(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if cap(dst) < n {
dst = make([]byte, n)
} else {
dst = dst[:n]
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlock(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// EncodeBetter returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// EncodeBetter compresses better than Encode but typically with a
// 10-40% speed decrease on both compression and decompression.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func EncodeBetter(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if len(dst) < n {
dst = make([]byte, n)
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlockBetter(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// EncodeBest returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// EncodeBest compresses as good as reasonably possible but with a
// big speed decrease.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func EncodeBest(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if len(dst) < n {
dst = make([]byte, n)
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlockBest(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// EncodeSnappy returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// The output is Snappy compatible and will likely decompress faster.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func EncodeSnappy(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if cap(dst) < n {
dst = make([]byte, n)
} else {
dst = dst[:n]
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlockSnappy(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// EncodeSnappyBetter returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// The output is Snappy compatible and will likely decompress faster.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func EncodeSnappyBetter(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if cap(dst) < n {
dst = make([]byte, n)
} else {
dst = dst[:n]
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlockBetterSnappy(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// EncodeSnappyBest returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// The output is Snappy compatible and will likely decompress faster.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func EncodeSnappyBest(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if cap(dst) < n {
dst = make([]byte, n)
} else {
dst = dst[:n]
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlockBestSnappy(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// ConcatBlocks will concatenate the supplied blocks and append them to the supplied destination.
// If the destination is nil or too small, a new will be allocated.
// The blocks are not validated, so garbage in = garbage out.
// dst may not overlap block data.
// Any data in dst is preserved as is, so it will not be considered a block.
func ConcatBlocks(dst []byte, blocks ...[]byte) ([]byte, error) {
totalSize := uint64(0)
compSize := 0
for _, b := range blocks {
l, hdr, err := decodedLen(b)
if err != nil {
return nil, err
}
totalSize += uint64(l)
compSize += len(b) - hdr
}
if totalSize == 0 {
dst = append(dst, 0)
return dst, nil
}
if totalSize > math.MaxUint32 {
return nil, ErrTooLarge
}
var tmp [binary.MaxVarintLen32]byte
hdrSize := binary.PutUvarint(tmp[:], totalSize)
wantSize := hdrSize + compSize
if cap(dst)-len(dst) < wantSize {
dst = append(make([]byte, 0, wantSize+len(dst)), dst...)
}
dst = append(dst, tmp[:hdrSize]...)
for _, b := range blocks {
_, hdr, err := decodedLen(b)
if err != nil {
return nil, err
}
dst = append(dst, b[hdr:]...)
}
return dst, nil
}
// inputMargin is the minimum number of extra input bytes to keep, inside
// encodeBlock's inner loop. On some architectures, this margin lets us
// implement a fast path for emitLiteral, where the copy of short (<= 16 byte)
// literals can be implemented as a single load to and store from a 16-byte
// register. That literal's actual length can be as short as 1 byte, so this
// can copy up to 15 bytes too much, but that's OK as subsequent iterations of
// the encoding loop will fix up the copy overrun, and this inputMargin ensures
// that we don't overrun the dst and src buffers.
const inputMargin = 8
// minNonLiteralBlockSize is the minimum size of the input to encodeBlock that
// will be accepted by the encoder.
const minNonLiteralBlockSize = 32
// MaxBlockSize is the maximum value where MaxEncodedLen will return a valid block size.
// Blocks this big are highly discouraged, though.
const MaxBlockSize = math.MaxUint32 - binary.MaxVarintLen32 - 5
// MaxEncodedLen returns the maximum length of a snappy block, given its
// uncompressed length.
//
// It will return a negative value if srcLen is too large to encode.
// 32 bit platforms will have lower thresholds for rejecting big content.
func MaxEncodedLen(srcLen int) int {
n := uint64(srcLen)
if n > 0xffffffff {
// Also includes negative.
return -1
}
// Size of the varint encoded block size.
n = n + uint64((bits.Len64(n)+7)/7)
// Add maximum size of encoding block as literals.
n += uint64(literalExtraSize(int64(srcLen)))
if n > 0xffffffff {
return -1
}
return int(n)
}
var errClosed = errors.New("s2: Writer is closed")
// NewWriter returns a new Writer that compresses to w, using the
// framing format described at
// https://github.com/google/snappy/blob/master/framing_format.txt
//
// Users must call Close to guarantee all data has been forwarded to
// the underlying io.Writer and that resources are released.
// They may also call Flush zero or more times before calling Close.
func NewWriter(w io.Writer, opts ...WriterOption) *Writer {
w2 := Writer{
blockSize: defaultBlockSize,
concurrency: runtime.GOMAXPROCS(0),
randSrc: rand.Reader,
level: levelFast,
}
for _, opt := range opts {
if err := opt(&w2); err != nil {
w2.errState = err
return &w2
}
}
w2.obufLen = obufHeaderLen + MaxEncodedLen(w2.blockSize)
w2.paramsOK = true
w2.ibuf = make([]byte, 0, w2.blockSize)
w2.buffers.New = func() interface{} {
return make([]byte, w2.obufLen)
}
w2.Reset(w)
return &w2
}
// Writer is an io.Writer that can write Snappy-compressed bytes.
type Writer struct {
errMu sync.Mutex
errState error
// ibuf is a buffer for the incoming (uncompressed) bytes.
ibuf []byte
blockSize int
obufLen int
concurrency int
written int64
uncompWritten int64 // Bytes sent to compression
output chan chan result
buffers sync.Pool
pad int
writer io.Writer
randSrc io.Reader
writerWg sync.WaitGroup
index Index
// wroteStreamHeader is whether we have written the stream header.
wroteStreamHeader bool
paramsOK bool
snappy bool
flushOnWrite bool
appendIndex bool
level uint8
}
const (
levelUncompressed = iota + 1
levelFast
levelBetter
levelBest
)
type result struct {
b []byte
// Uncompressed start offset
startOffset int64
}
// err returns the previously set error.
// If no error has been set it is set to err if not nil.
func (w *Writer) err(err error) error {
w.errMu.Lock()
errSet := w.errState
if errSet == nil && err != nil {
w.errState = err
errSet = err
}
w.errMu.Unlock()
return errSet
}
// Reset discards the writer's state and switches the Snappy writer to write to w.
// This permits reusing a Writer rather than allocating a new one.
func (w *Writer) Reset(writer io.Writer) {
if !w.paramsOK {
return
}
// Close previous writer, if any.
if w.output != nil {
close(w.output)
w.writerWg.Wait()
w.output = nil
}
w.errState = nil
w.ibuf = w.ibuf[:0]
w.wroteStreamHeader = false
w.written = 0
w.writer = writer
w.uncompWritten = 0
w.index.reset(w.blockSize)
// If we didn't get a writer, stop here.
if writer == nil {
return
}
// If no concurrency requested, don't spin up writer goroutine.
if w.concurrency == 1 {
return
}
toWrite := make(chan chan result, w.concurrency)
w.output = toWrite
w.writerWg.Add(1)
// Start a writer goroutine that will write all output in order.
go func() {
defer w.writerWg.Done()
// Get a queued write.
for write := range toWrite {
// Wait for the data to be available.
input := <-write
in := input.b
if len(in) > 0 {
if w.err(nil) == nil {
// Don't expose data from previous buffers.
toWrite := in[:len(in):len(in)]
// Write to output.
n, err := writer.Write(toWrite)
if err == nil && n != len(toWrite) {
err = io.ErrShortBuffer
}
_ = w.err(err)
w.err(w.index.add(w.written, input.startOffset))
w.written += int64(n)
}
}
if cap(in) >= w.obufLen {
w.buffers.Put(in)
}
// close the incoming write request.
// This can be used for synchronizing flushes.
close(write)
}
}()
}
// Write satisfies the io.Writer interface.
func (w *Writer) Write(p []byte) (nRet int, errRet error) {
if err := w.err(nil); err != nil {
return 0, err
}
if w.flushOnWrite {
return w.write(p)
}
// If we exceed the input buffer size, start writing
for len(p) > (cap(w.ibuf)-len(w.ibuf)) && w.err(nil) == nil {
var n int
if len(w.ibuf) == 0 {
// Large write, empty buffer.
// Write directly from p to avoid copy.
n, _ = w.write(p)
} else {
n = copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p)
w.ibuf = w.ibuf[:len(w.ibuf)+n]
w.write(w.ibuf)
w.ibuf = w.ibuf[:0]
}
nRet += n
p = p[n:]
}
if err := w.err(nil); err != nil {
return nRet, err
}
// p should always be able to fit into w.ibuf now.
n := copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p)
w.ibuf = w.ibuf[:len(w.ibuf)+n]
nRet += n
return nRet, nil
}
// ReadFrom implements the io.ReaderFrom interface.
// Using this is typically more efficient since it avoids a memory copy.
// ReadFrom reads data from r until EOF or error.
// The return value n is the number of bytes read.
// Any error except io.EOF encountered during the read is also returned.
func (w *Writer) ReadFrom(r io.Reader) (n int64, err error) {
if err := w.err(nil); err != nil {
return 0, err
}
if len(w.ibuf) > 0 {
err := w.Flush()
if err != nil {
return 0, err
}
}
if br, ok := r.(byter); ok {
buf := br.Bytes()
if err := w.EncodeBuffer(buf); err != nil {
return 0, err
}
return int64(len(buf)), w.Flush()
}
for {
inbuf := w.buffers.Get().([]byte)[:w.blockSize+obufHeaderLen]
n2, err := io.ReadFull(r, inbuf[obufHeaderLen:])
if err != nil {
if err == io.ErrUnexpectedEOF {
err = io.EOF
}
if err != io.EOF {
return n, w.err(err)
}
}
if n2 == 0 {
break
}
n += int64(n2)
err2 := w.writeFull(inbuf[:n2+obufHeaderLen])
if w.err(err2) != nil {
break
}
if err != nil {
// We got EOF and wrote everything
break
}
}
return n, w.err(nil)
}
// AddSkippableBlock will add a skippable block to the stream.
// The ID must be 0x80-0xfe (inclusive).
// Length of the skippable block must be <= 16777215 bytes.
func (w *Writer) AddSkippableBlock(id uint8, data []byte) (err error) {
if err := w.err(nil); err != nil {
return err
}
if len(data) == 0 {
return nil
}
if id < 0x80 || id > chunkTypePadding {
return fmt.Errorf("invalid skippable block id %x", id)
}
if len(data) > maxChunkSize {
return fmt.Errorf("skippable block excessed maximum size")
}
var header [4]byte
chunkLen := 4 + len(data)
header[0] = id
header[1] = uint8(chunkLen >> 0)
header[2] = uint8(chunkLen >> 8)
header[3] = uint8(chunkLen >> 16)
if w.concurrency == 1 {
write := func(b []byte) error {
n, err := w.writer.Write(b)
if err = w.err(err); err != nil {
return err
}
if n != len(data) {
return w.err(io.ErrShortWrite)
}
w.written += int64(n)
return w.err(nil)
}
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
if w.snappy {
if err := write([]byte(magicChunkSnappy)); err != nil {
return err
}
} else {
if err := write([]byte(magicChunk)); err != nil {
return err
}
}
}
if err := write(header[:]); err != nil {
return err
}
if err := write(data); err != nil {
return err
}
}
// Create output...
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
hWriter := make(chan result)
w.output <- hWriter
if w.snappy {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
} else {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
}
}
// Copy input.
inbuf := w.buffers.Get().([]byte)[:4]
copy(inbuf, header[:])
inbuf = append(inbuf, data...)
output := make(chan result, 1)
// Queue output.
w.output <- output
output <- result{startOffset: w.uncompWritten, b: inbuf}
return nil
}
// EncodeBuffer will add a buffer to the stream.
// This is the fastest way to encode a stream,
// but the input buffer cannot be written to by the caller
// until Flush or Close has been called when concurrency != 1.
//
// If you cannot control that, use the regular Write function.
//
// Note that input is not buffered.
// This means that each write will result in discrete blocks being created.
// For buffered writes, use the regular Write function.
func (w *Writer) EncodeBuffer(buf []byte) (err error) {
if err := w.err(nil); err != nil {
return err
}
if w.flushOnWrite {
_, err := w.write(buf)
return err
}
// Flush queued data first.
if len(w.ibuf) > 0 {
err := w.Flush()
if err != nil {
return err
}
}
if w.concurrency == 1 {
_, err := w.writeSync(buf)
return err
}
// Spawn goroutine and write block to output channel.
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
hWriter := make(chan result)
w.output <- hWriter
if w.snappy {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
} else {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
}
}
for len(buf) > 0 {
// Cut input.
uncompressed := buf
if len(uncompressed) > w.blockSize {
uncompressed = uncompressed[:w.blockSize]
}
buf = buf[len(uncompressed):]
// Get an output buffer.
obuf := w.buffers.Get().([]byte)[:len(uncompressed)+obufHeaderLen]
output := make(chan result)
// Queue output now, so we keep order.
w.output <- output
res := result{
startOffset: w.uncompWritten,
}
w.uncompWritten += int64(len(uncompressed))
go func() {
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
n2 := w.encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
// Check if we should use this, or store as uncompressed instead.
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
// copy uncompressed
copy(obuf[obufHeaderLen:], uncompressed)
}
// Fill in the per-chunk header that comes before the body.
obuf[0] = chunkType
obuf[1] = uint8(chunkLen >> 0)
obuf[2] = uint8(chunkLen >> 8)
obuf[3] = uint8(chunkLen >> 16)
obuf[4] = uint8(checksum >> 0)
obuf[5] = uint8(checksum >> 8)
obuf[6] = uint8(checksum >> 16)
obuf[7] = uint8(checksum >> 24)
// Queue final output.
res.b = obuf
output <- res
}()
}
return nil
}
func (w *Writer) encodeBlock(obuf, uncompressed []byte) int {
if w.snappy {
switch w.level {
case levelFast:
return encodeBlockSnappy(obuf, uncompressed)
case levelBetter:
return encodeBlockBetterSnappy(obuf, uncompressed)
case levelBest:
return encodeBlockBestSnappy(obuf, uncompressed)
}
return 0
}
switch w.level {
case levelFast:
return encodeBlock(obuf, uncompressed)
case levelBetter:
return encodeBlockBetter(obuf, uncompressed)
case levelBest:
return encodeBlockBest(obuf, uncompressed)
}
return 0
}
func (w *Writer) write(p []byte) (nRet int, errRet error) {
if err := w.err(nil); err != nil {
return 0, err
}
if w.concurrency == 1 {
return w.writeSync(p)
}
// Spawn goroutine and write block to output channel.
for len(p) > 0 {
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
hWriter := make(chan result)
w.output <- hWriter
if w.snappy {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
} else {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
}
}
var uncompressed []byte
if len(p) > w.blockSize {
uncompressed, p = p[:w.blockSize], p[w.blockSize:]
} else {
uncompressed, p = p, nil
}
// Copy input.
// If the block is incompressible, this is used for the result.
inbuf := w.buffers.Get().([]byte)[:len(uncompressed)+obufHeaderLen]
obuf := w.buffers.Get().([]byte)[:w.obufLen]
copy(inbuf[obufHeaderLen:], uncompressed)
uncompressed = inbuf[obufHeaderLen:]
output := make(chan result)
// Queue output now, so we keep order.
w.output <- output
res := result{
startOffset: w.uncompWritten,
}
w.uncompWritten += int64(len(uncompressed))
go func() {
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
n2 := w.encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
// Check if we should use this, or store as uncompressed instead.
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
// Use input as output.
obuf, inbuf = inbuf, obuf
}
// Fill in the per-chunk header that comes before the body.
obuf[0] = chunkType
obuf[1] = uint8(chunkLen >> 0)
obuf[2] = uint8(chunkLen >> 8)
obuf[3] = uint8(chunkLen >> 16)
obuf[4] = uint8(checksum >> 0)
obuf[5] = uint8(checksum >> 8)
obuf[6] = uint8(checksum >> 16)
obuf[7] = uint8(checksum >> 24)
// Queue final output.
res.b = obuf
output <- res
// Put unused buffer back in pool.
w.buffers.Put(inbuf)
}()
nRet += len(uncompressed)
}
return nRet, nil
}
// writeFull is a special version of write that will always write the full buffer.
// Data to be compressed should start at offset obufHeaderLen and fill the remainder of the buffer.
// The data will be written as a single block.
// The caller is not allowed to use inbuf after this function has been called.
func (w *Writer) writeFull(inbuf []byte) (errRet error) {
if err := w.err(nil); err != nil {
return err
}
if w.concurrency == 1 {
_, err := w.writeSync(inbuf[obufHeaderLen:])
return err
}
// Spawn goroutine and write block to output channel.
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
hWriter := make(chan result)
w.output <- hWriter
if w.snappy {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
} else {
hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
}
}
// Get an output buffer.
obuf := w.buffers.Get().([]byte)[:w.obufLen]
uncompressed := inbuf[obufHeaderLen:]
output := make(chan result)
// Queue output now, so we keep order.
w.output <- output
res := result{
startOffset: w.uncompWritten,
}
w.uncompWritten += int64(len(uncompressed))
go func() {
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
n2 := w.encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
// Check if we should use this, or store as uncompressed instead.
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
// Use input as output.
obuf, inbuf = inbuf, obuf
}
// Fill in the per-chunk header that comes before the body.
obuf[0] = chunkType
obuf[1] = uint8(chunkLen >> 0)
obuf[2] = uint8(chunkLen >> 8)
obuf[3] = uint8(chunkLen >> 16)
obuf[4] = uint8(checksum >> 0)
obuf[5] = uint8(checksum >> 8)
obuf[6] = uint8(checksum >> 16)
obuf[7] = uint8(checksum >> 24)
// Queue final output.
res.b = obuf
output <- res
// Put unused buffer back in pool.
w.buffers.Put(inbuf)
}()
return nil
}
func (w *Writer) writeSync(p []byte) (nRet int, errRet error) {
if err := w.err(nil); err != nil {
return 0, err
}
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
var n int
var err error
if w.snappy {
n, err = w.writer.Write([]byte(magicChunkSnappy))
} else {
n, err = w.writer.Write([]byte(magicChunk))
}
if err != nil {
return 0, w.err(err)
}
if n != len(magicChunk) {
return 0, w.err(io.ErrShortWrite)
}
w.written += int64(n)
}
for len(p) > 0 {
var uncompressed []byte
if len(p) > w.blockSize {
uncompressed, p = p[:w.blockSize], p[w.blockSize:]
} else {
uncompressed, p = p, nil
}
obuf := w.buffers.Get().([]byte)[:w.obufLen]
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.