gotosocial/vendor/github.com/klauspost/compress/s2/writer.go

1025 lines
26 KiB
Go
Raw Normal View History

// 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"
"runtime"
"sync"
"github.com/klauspost/compress/internal/race"
)
const (
levelUncompressed = iota + 1
levelFast
levelBetter
levelBest
)
// 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
customEnc func(dst, src []byte) int
// wroteStreamHeader is whether we have written the stream header.
wroteStreamHeader bool
paramsOK bool
snappy bool
flushOnWrite bool
appendIndex bool
level uint8
}
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 := 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(b) {
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
}
return write(data)
}
// 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]
race.WriteSlice(obuf)
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() {
race.ReadSlice(uncompressed)
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.customEnc != nil {
if ret := w.customEnc(obuf, uncompressed); ret >= 0 {
return ret
}
}
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, nil)
}
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.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
n2 := w.encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
obuf = obuf[:8]
}
// 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)
n, err := w.writer.Write(obuf)
if err != nil {
return 0, w.err(err)
}
if n != len(obuf) {
return 0, w.err(io.ErrShortWrite)
}
w.err(w.index.add(w.written, w.uncompWritten))
w.written += int64(n)
w.uncompWritten += int64(len(uncompressed))
if chunkType == chunkTypeUncompressedData {
// Write uncompressed data.
n, err := w.writer.Write(uncompressed)
if err != nil {
return 0, w.err(err)
}
if n != len(uncompressed) {
return 0, w.err(io.ErrShortWrite)
}
w.written += int64(n)
}
w.buffers.Put(obuf)
// Queue final output.
nRet += len(uncompressed)
}
return nRet, nil
}
// Flush flushes the Writer to its underlying io.Writer.
// This does not apply padding.
func (w *Writer) Flush() error {
if err := w.err(nil); err != nil {
return err
}
// Queue any data still in input buffer.
if len(w.ibuf) != 0 {
if !w.wroteStreamHeader {
_, err := w.writeSync(w.ibuf)
w.ibuf = w.ibuf[:0]
return w.err(err)
} else {
_, err := w.write(w.ibuf)
w.ibuf = w.ibuf[:0]
err = w.err(err)
if err != nil {
return err
}
}
}
if w.output == nil {
return w.err(nil)
}
// Send empty buffer
res := make(chan result)
w.output <- res
// Block until this has been picked up.
res <- result{b: nil, startOffset: w.uncompWritten}
// When it is closed, we have flushed.
<-res
return w.err(nil)
}
// Close calls Flush and then closes the Writer.
// Calling Close multiple times is ok,
// but calling CloseIndex after this will make it not return the index.
func (w *Writer) Close() error {
_, err := w.closeIndex(w.appendIndex)
return err
}
// CloseIndex calls Close and returns an index on first call.
// This is not required if you are only adding index to a stream.
func (w *Writer) CloseIndex() ([]byte, error) {
return w.closeIndex(true)
}
func (w *Writer) closeIndex(idx bool) ([]byte, error) {
err := w.Flush()
if w.output != nil {
close(w.output)
w.writerWg.Wait()
w.output = nil
}
var index []byte
if w.err(err) == nil && w.writer != nil {
// Create index.
if idx {
compSize := int64(-1)
if w.pad <= 1 {
compSize = w.written
}
index = w.index.appendTo(w.ibuf[:0], w.uncompWritten, compSize)
// Count as written for padding.
if w.appendIndex {
w.written += int64(len(index))
}
}
if w.pad > 1 {
tmp := w.ibuf[:0]
if len(index) > 0 {
// Allocate another buffer.
tmp = w.buffers.Get().([]byte)[:0]
defer w.buffers.Put(tmp)
}
add := calcSkippableFrame(w.written, int64(w.pad))
frame, err := skippableFrame(tmp, add, w.randSrc)
if err = w.err(err); err != nil {
return nil, err
}
n, err2 := w.writer.Write(frame)
if err2 == nil && n != len(frame) {
err2 = io.ErrShortWrite
}
_ = w.err(err2)
}
if len(index) > 0 && w.appendIndex {
n, err2 := w.writer.Write(index)
if err2 == nil && n != len(index) {
err2 = io.ErrShortWrite
}
_ = w.err(err2)
}
}
err = w.err(errClosed)
if err == errClosed {
return index, nil
}
return nil, err
}
// calcSkippableFrame will return a total size to be added for written
// to be divisible by multiple.
// The value will always be > skippableFrameHeader.
// The function will panic if written < 0 or wantMultiple <= 0.
func calcSkippableFrame(written, wantMultiple int64) int {
if wantMultiple <= 0 {
panic("wantMultiple <= 0")
}
if written < 0 {
panic("written < 0")
}
leftOver := written % wantMultiple
if leftOver == 0 {
return 0
}
toAdd := wantMultiple - leftOver
for toAdd < skippableFrameHeader {
toAdd += wantMultiple
}
return int(toAdd)
}
// skippableFrame will add a skippable frame with a total size of bytes.
// total should be >= skippableFrameHeader and < maxBlockSize + skippableFrameHeader
func skippableFrame(dst []byte, total int, r io.Reader) ([]byte, error) {
if total == 0 {
return dst, nil
}
if total < skippableFrameHeader {
return dst, fmt.Errorf("s2: requested skippable frame (%d) < 4", total)
}
if int64(total) >= maxBlockSize+skippableFrameHeader {
return dst, fmt.Errorf("s2: requested skippable frame (%d) >= max 1<<24", total)
}
// Chunk type 0xfe "Section 4.4 Padding (chunk type 0xfe)"
dst = append(dst, chunkTypePadding)
f := uint32(total - skippableFrameHeader)
// Add chunk length.
dst = append(dst, uint8(f), uint8(f>>8), uint8(f>>16))
// Add data
start := len(dst)
dst = append(dst, make([]byte, f)...)
_, err := io.ReadFull(r, dst[start:])
return dst, err
}
var errClosed = errors.New("s2: Writer is closed")
// WriterOption is an option for creating a encoder.
type WriterOption func(*Writer) error
// WriterConcurrency will set the concurrency,
// meaning the maximum number of decoders to run concurrently.
// The value supplied must be at least 1.
// By default this will be set to GOMAXPROCS.
func WriterConcurrency(n int) WriterOption {
return func(w *Writer) error {
if n <= 0 {
return errors.New("concurrency must be at least 1")
}
w.concurrency = n
return nil
}
}
// WriterAddIndex will append an index to the end of a stream
// when it is closed.
func WriterAddIndex() WriterOption {
return func(w *Writer) error {
w.appendIndex = true
return nil
}
}
// WriterBetterCompression will enable better compression.
// EncodeBetter compresses better than Encode but typically with a
// 10-40% speed decrease on both compression and decompression.
func WriterBetterCompression() WriterOption {
return func(w *Writer) error {
w.level = levelBetter
return nil
}
}
// WriterBestCompression will enable better compression.
// EncodeBetter compresses better than Encode but typically with a
// big speed decrease on compression.
func WriterBestCompression() WriterOption {
return func(w *Writer) error {
w.level = levelBest
return nil
}
}
// WriterUncompressed will bypass compression.
// The stream will be written as uncompressed blocks only.
// If concurrency is > 1 CRC and output will still be done async.
func WriterUncompressed() WriterOption {
return func(w *Writer) error {
w.level = levelUncompressed
return nil
}
}
// WriterBlockSize allows to override the default block size.
// Blocks will be this size or smaller.
// Minimum size is 4KB and and maximum size is 4MB.
//
// Bigger blocks may give bigger throughput on systems with many cores,
// and will increase compression slightly, but it will limit the possible
// concurrency for smaller payloads for both encoding and decoding.
// Default block size is 1MB.
//
// When writing Snappy compatible output using WriterSnappyCompat,
// the maximum block size is 64KB.
func WriterBlockSize(n int) WriterOption {
return func(w *Writer) error {
if w.snappy && n > maxSnappyBlockSize || n < minBlockSize {
return errors.New("s2: block size too large. Must be <= 64K and >=4KB on for snappy compatible output")
}
if n > maxBlockSize || n < minBlockSize {
return errors.New("s2: block size too large. Must be <= 4MB and >=4KB")
}
w.blockSize = n
return nil
}
}
// WriterPadding will add padding to all output so the size will be a multiple of n.
// This can be used to obfuscate the exact output size or make blocks of a certain size.
// The contents will be a skippable frame, so it will be invisible by the decoder.
// n must be > 0 and <= 4MB.
// The padded area will be filled with data from crypto/rand.Reader.
// The padding will be applied whenever Close is called on the writer.
func WriterPadding(n int) WriterOption {
return func(w *Writer) error {
if n <= 0 {
return fmt.Errorf("s2: padding must be at least 1")
}
// No need to waste our time.
if n == 1 {
w.pad = 0
}
if n > maxBlockSize {
return fmt.Errorf("s2: padding must less than 4MB")
}
w.pad = n
return nil
}
}
// WriterPaddingSrc will get random data for padding from the supplied source.
// By default crypto/rand is used.
func WriterPaddingSrc(reader io.Reader) WriterOption {
return func(w *Writer) error {
w.randSrc = reader
return nil
}
}
// WriterSnappyCompat will write snappy compatible output.
// The output can be decompressed using either snappy or s2.
// If block size is more than 64KB it is set to that.
func WriterSnappyCompat() WriterOption {
return func(w *Writer) error {
w.snappy = true
if w.blockSize > 64<<10 {
// We choose 8 bytes less than 64K, since that will make literal emits slightly more effective.
// And allows us to skip some size checks.
w.blockSize = (64 << 10) - 8
}
return nil
}
}
// WriterFlushOnWrite will compress blocks on each call to the Write function.
//
// This is quite inefficient as blocks size will depend on the write size.
//
// Use WriterConcurrency(1) to also make sure that output is flushed.
// When Write calls return, otherwise they will be written when compression is done.
func WriterFlushOnWrite() WriterOption {
return func(w *Writer) error {
w.flushOnWrite = true
return nil
}
}
// WriterCustomEncoder allows to override the encoder for blocks on the stream.
// The function must compress 'src' into 'dst' and return the bytes used in dst as an integer.
// Block size (initial varint) should not be added by the encoder.
// Returning value 0 indicates the block could not be compressed.
// Returning a negative value indicates that compression should be attempted.
// The function should expect to be called concurrently.
func WriterCustomEncoder(fn func(dst, src []byte) int) WriterOption {
return func(w *Writer) error {
w.customEnc = fn
return nil
}
}