Bump github.com/mattermost/mattermost-server/v6 from 6.1.0 to 6.3.0 (#1686)

Bumps [github.com/mattermost/mattermost-server/v6](https://github.com/mattermost/mattermost-server) from 6.1.0 to 6.3.0.
- [Release notes](https://github.com/mattermost/mattermost-server/releases)
- [Changelog](https://github.com/mattermost/mattermost-server/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mattermost/mattermost-server/compare/v6.1.0...v6.3.0)

---
updated-dependencies:
- dependency-name: github.com/mattermost/mattermost-server/v6
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

1 files changed, 1172 insertions, 0 deletions

diff --git a/vendor/github.com/klauspost/compress/s2/encode.go b/vendor/github.com/klauspost/compress/s2/encode.go
new file mode 100644
index 00000000..aa8b108d
--- /dev/null
+++ b/vendor/github.com/klauspost/compress/s2/encode.go
@@ -0,0 +1,1172 @@
+// 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
+	output      chan chan result
+	buffers     sync.Pool
+	pad         int
+
+	writer   io.Writer
+	randSrc  io.Reader
+	writerWg sync.WaitGroup
+
+	// wroteStreamHeader is whether we have written the stream header.
+	wroteStreamHeader bool
+	paramsOK          bool
+	snappy            bool
+	flushOnWrite      bool
+	level             uint8
+}
+
+const (
+	levelUncompressed = iota + 1
+	levelFast
+	levelBetter
+	levelBest
+)
+
+type result []byte
+
+// 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
+	// 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.
+			in := <-write
+			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.written += int64(n)
+				}
+			}
+			if cap(in) >= w.obufLen {
+				w.buffers.Put([]byte(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 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 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)
+}
+
+// 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 <- []byte(magicChunkSnappy)
+		} else {
+			hWriter <- []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
+		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.
+			output <- obuf
+		}()
+	}
+	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 <- []byte(magicChunkSnappy)
+			} else {
+				hWriter <- []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
+		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.
+			output <- obuf
+
+			// 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 <- []byte(magicChunkSnappy)
+		} else {
+			hWriter <- []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
+	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.
+		output <- obuf
+
+		// 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.written += int64(n)
+		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 <- nil
+	// 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.
+func (w *Writer) Close() error {
+	err := w.Flush()
+	if w.output != nil {
+		close(w.output)
+		w.writerWg.Wait()
+		w.output = nil
+	}
+	if w.err(nil) == nil && w.writer != nil && w.pad > 0 {
+		add := calcSkippableFrame(w.written, int64(w.pad))
+		frame, err := skippableFrame(w.ibuf[:0], add, w.randSrc)
+		if err = w.err(err); err != nil {
+			return err
+		}
+		_, err2 := w.writer.Write(frame)
+		_ = w.err(err2)
+	}
+	_ = w.err(errClosed)
+	if err == errClosed {
+		return nil
+	}
+	return err
+}
+
+const skippableFrameHeader = 4
+
+// 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
+}
+
+// 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
+	}
+}
+
+// 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
+	}
+}