Simplify go brotli wrapper. (#540)

Based on PR #533.

Kudos to Bryan (bcmillis@).

8 files changed, 349 insertions, 532 deletions

diff --git a/go/cbrotli/BUILD b/go/cbrotli/BUILD
index 4bea8a0..e045b61 100755
--- a/go/cbrotli/BUILD
+++ b/go/cbrotli/BUILD
@@ -2,16 +2,19 @@ package(default_visibility = ["//visibility:public"])
 
 licenses(["notice"])  # MIT
 
-load("@io_bazel_rules_go//go:def.bzl", "go_prefix", "go_library", "go_test")
+load("@io_bazel_rules_go//go:def.bzl", "go_prefix", "cgo_library", "go_test")
 
 go_prefix("github.com/google/brotli")
 
-go_library(
+cgo_library(
     name = "cbrotli",
-    srcs = ["cbrotli.go"],
-    deps = [
-        "//go/cbrotli/internal:decoder",
-        "//go/cbrotli/internal:encoder",
+    srcs = [
+        "reader.go",
+        "writer.go",
+    ],
+    cdeps = [
+        "//:brotlidec",
+        "//:brotlienc",
     ],
 )
 
diff --git a/go/cbrotli/cbrotli.go b/go/cbrotli/cbrotli.go
deleted file mode 100755
index a7009d0..0000000
--- a/go/cbrotli/cbrotli.go
+++ /dev/null
@@ -1,254 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Distributed under MIT license.
-// See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
-
-// Package cbrotli compresses and decompresses data with C-Brotli library.
-package cbrotli
-
-import (
-	"bytes"
-	"io"
-
-	"github.com/google/brotli/go/cbrotli/internal/decoder"
-	"github.com/google/brotli/go/cbrotli/internal/encoder"
-)
-
-// An internalError reports an error in the (c-)brotli code itself.
-type internalError string
-
-func (e internalError) Error() string {
-	return "cbrotli: internal error: " + string(e)
-}
-
-//------------------------------------------------------------------------------
-// Encoder
-//------------------------------------------------------------------------------
-
-// WriterOptions configures Writer.
-type WriterOptions struct {
-	// Quality controls the compression-speed vs compression-density trade-offs.
-	// The higher the quality, the slower the compression. Range is 0 to 11.
-	Quality int
-	// LGWin is the base 2 logarithm of the sliding window size.
-	// Range is 10 to 24. 0 indicates automatic configuration based on Quality.
-	LGWin int
-}
-
-// Writer implements io.WriteCloser, an io.Writer decorator that produces
-// Brotli-encoded data.
-type Writer struct {
-	dst     io.Writer
-	encoder encoder.Encoder
-	closed  bool
-}
-
-// NewWriter initializes new Writer instance.
-// Close MUST be called to free resources.
-func NewWriter(dst io.Writer, options WriterOptions) *Writer {
-	return &Writer{
-		dst:     dst,
-		encoder: encoder.New(options.Quality, options.LGWin),
-	}
-}
-
-// Close implements io.Closer. Close MUST be invoked to free native resources.
-// Also Close implicitly flushes remaining data to the decorated writer.
-func (z *Writer) Close() error {
-	if z.closed {
-		return nil
-	}
-	defer z.encoder.Close()
-	_, err := z.writeChunk(nil, encoder.Finish)
-	z.closed = true
-	return err
-}
-
-func (z *Writer) writeChunk(p []byte, op encoder.Operation) (int, error) {
-	if z.closed {
-		return 0, internalError("write after close")
-	}
-	var totalBytesConsumed int
-	var err error
-	for {
-		bytesConsumed, output, status := z.encoder.CompressStream(p, op)
-		if status == encoder.Error {
-			err = internalError("encoder failure")
-			break
-		}
-		p = p[bytesConsumed:]
-		totalBytesConsumed += bytesConsumed
-		_, err = z.dst.Write(output)
-		if err != nil {
-			break
-		}
-		if len(p) == 0 && status == encoder.Done {
-			break
-		}
-	}
-	return totalBytesConsumed, err
-}
-
-// Write implements io.Writer.
-func (z *Writer) Write(p []byte) (int, error) {
-	return z.writeChunk(p, encoder.Process)
-}
-
-// Flush outputs encoded data for all input provided to Write. The resulting
-// output can be decoded to match all input before Flush, but the stream is
-// not yet complete until after Close.
-// Flush has a negative impact on compression.
-func (z *Writer) Flush() error {
-	_, err := z.writeChunk(nil, encoder.Finish)
-	return err
-}
-
-// Encode returns content encoded with Brotli.
-func Encode(content []byte, options WriterOptions) ([]byte, error) {
-	var buf bytes.Buffer
-	writer := NewWriter(&buf, options)
-	defer writer.Close()
-	_, err := writer.Write(content)
-	if err != nil {
-		return nil, err
-	}
-	if err := writer.Close(); err != nil {
-		return nil, err
-	}
-	return buf.Bytes(), nil
-}
-
-//------------------------------------------------------------------------------
-// Decoder
-//------------------------------------------------------------------------------
-
-// Reader implements io.ReadCloser, an io.Reader decorator that decodes
-// Brotli-encoded data.
-type Reader struct {
-	src     io.Reader
-	decoder decoder.Decoder
-	buf     []byte // intermediate read buffer pointed to by next
-	eof     bool   // true if all compressed stream is decoded
-	next    []byte // buffered data to be passed to decoder
-	output  []byte // data produced by decoder, but not yet consumed
-	srcErr  error  // last source reader error
-	err     error  // reader state; nil if it is OK to read further
-	closed  bool   // true is stream is already closed
-}
-
-// NewReader initializes new Reader instance.
-// Close MUST be called to free resources.
-func NewReader(src io.Reader) *Reader {
-	return &Reader{
-		src:     src,
-		decoder: decoder.New(),
-		buf:     make([]byte, 32*1024),
-		eof:     false,
-	}
-}
-
-// Close implements io.Closer. Close MUST be invoked to free native resources.
-func (z *Reader) Close() error {
-	if z.closed {
-		return nil
-	}
-	z.decoder.Close()
-	z.err = internalError("read after close")
-	z.closed = true
-	return nil
-}
-
-func isEOF(src io.Reader) bool {
-	n, err := src.Read(make([]byte, 1))
-	return n == 0 && err == io.EOF
-}
-
-// Read implements io.Reader.
-func (z *Reader) Read(p []byte) (int, error) {
-	// Any error state is unrecoverable.
-	if z.err != nil {
-		return 0, z.err
-	}
-	// See io.Reader documentation.
-	if len(p) == 0 {
-		return 0, nil
-	}
-
-	var totalOutBytes int
-
-	// There is no practical limit for amount of bytes being consumed by decoder
-	// before producing any output. Continue feeding decoder until some data is
-	// produced
-	for {
-		// Push already produced output first.
-		if outBytes := len(z.output); outBytes != 0 {
-			outBytes = copy(p, z.output)
-			p = p[outBytes:]
-			z.output = z.output[outBytes:]
-			totalOutBytes += outBytes
-			// Output buffer is full.
-			if len(p) == 0 {
-				break
-			}
-			continue
-		}
-		// No more produced output left.
-		// If no more output is expected, then we are finished.
-		if z.eof {
-			z.err = io.EOF
-			break
-		}
-		// Replenish buffer (might cause blocking read), only if necessary.
-		if len(z.next) == 0 && totalOutBytes == 0 && z.srcErr != io.EOF {
-			var n int
-			n, z.srcErr = z.src.Read(z.buf)
-			z.next = z.buf[:n]
-			if z.srcErr != nil && z.srcErr != io.EOF {
-				z.err = z.srcErr
-				break
-			}
-		}
-		// Do decoding.
-		consumed, output, status := z.decoder.DecompressStream(z.next)
-		z.output = output
-		z.next = z.next[consumed:]
-		if status == decoder.Error {
-			// When error happens, the remaining output does not matter.
-			z.err = internalError("decoder failure")
-			break
-		} else if status == decoder.Done {
-			// Decoder stream is closed; no further input is expected.
-			if len(z.next) != 0 || (z.srcErr != io.EOF && !isEOF(z.src)) {
-				z.err = internalError("excessive input")
-				break
-			}
-			// No more output is expected; keep pushing output.
-			z.eof = true
-			continue
-		} else {
-			// If can not move any further...
-			if consumed == 0 && len(z.output) == 0 {
-				// Unexpected end of input.
-				if z.srcErr == io.EOF || totalOutBytes == 0 {
-					z.err = io.ErrUnexpectedEOF
-				}
-				// Postpone blocking reads for the next invocation.
-				break
-			}
-			// Continue pushing output.
-		}
-	}
-	return totalOutBytes, z.err
-}
-
-// Decode decodes Brotli encoded data.
-func Decode(encodedData []byte) ([]byte, error) {
-	var buf bytes.Buffer
-	reader := NewReader(bytes.NewReader(encodedData))
-	defer reader.Close()
-	_, err := io.Copy(&buf, reader)
-	if err != nil {
-		return nil, err
-	}
-	return buf.Bytes(), nil
-}
diff --git a/go/cbrotli/cbrotli_test.go b/go/cbrotli/cbrotli_test.go
index 4fe0960..0a9368b 100755
--- a/go/cbrotli/cbrotli_test.go
+++ b/go/cbrotli/cbrotli_test.go
@@ -91,7 +91,7 @@ func TestEncoderStreams(t *testing.T) {
 	// to fill the window.
 	const lgWin = 16
 	windowSize := int(math.Pow(2, lgWin))
-	input := make([]byte, 2*windowSize)
+	input := make([]byte, 8*windowSize)
 	rand.Read(input)
 	out := bytes.Buffer{}
 	e := NewWriter(&out, WriterOptions{Quality: 11, LGWin: lgWin})
@@ -106,7 +106,7 @@ func TestEncoderStreams(t *testing.T) {
 	// We've fed more data than the sliding window size. Check that some
 	// compressed data has been output.
 	if out.Len() == 0 {
-		t.Errorf("Output length is after %d bytes written", n)
+		t.Errorf("Output length is 0 after %d bytes written", n)
 	}
 	if err := e.Close(); err != nil {
 		t.Errorf("Close Error after copied %d bytes: %v", n, err)
@@ -151,6 +151,9 @@ func TestEncoderFlush(t *testing.T) {
 	if err := e.Flush(); err != nil {
 		t.Fatalf("Flush(): %v", err)
 	}
+	if out.Len() == 0 {
+		t.Fatalf("0 bytes written after Flush()")
+	}
 	decompressed := make([]byte, 1000)
 	reader := NewReader(bytes.NewReader(out.Bytes()))
 	n, err := reader.Read(decompressed)
@@ -187,8 +190,8 @@ func TestReader(t *testing.T) {
 			"Reader output:\n"+
 			"%q\n"+
 			"want:\n"+
-			"%q",
-			got, content)
+			"<%d bytes>",
+			got, len(content))
 	}
 }
 
@@ -204,8 +207,8 @@ func TestDecode(t *testing.T) {
 			"Decode content:\n"+
 			"%q\n"+
 			"want:\n"+
-			"%q",
-			decoded, content)
+			"<%d bytes>",
+			decoded, len(content))
 	}
 }
 
@@ -213,7 +216,13 @@ func TestDecodeFuzz(t *testing.T) {
 	// Test that the decoder terminates with corrupted input.
 	content := bytes.Repeat([]byte("hello world!"), 100)
 	src := rand.NewSource(0)
-	encoded, _ := Encode(content, WriterOptions{Quality: 5})
+	encoded, err := Encode(content, WriterOptions{Quality: 5})
+	if err != nil {
+		t.Fatalf("Encode(<%d bytes>, _) = _, %s", len(content), err)
+	}
+	if len(encoded) == 0 {
+		t.Fatalf("Encode(<%d bytes>, _) produced empty output", len(content))
+	}
 	for i := 0; i < 100; i++ {
 		enc := append([]byte{}, encoded...)
 		for j := 0; j < 5; j++ {
@@ -260,12 +269,18 @@ func TestEncodeDecode(t *testing.T) {
 			t.Errorf("Decode: %v", err)
 		}
 		if !bytes.Equal(decoded, input) {
+			var want string
+			if len(input) > 320 {
+				want = fmt.Sprintf("<%d bytes>", len(input))
+			} else {
+				want = fmt.Sprintf("%q", input)
+			}
 			t.Errorf(""+
 				"Decode content:\n"+
 				"%q\n"+
 				"want:\n"+
-				"%q",
-				decoded, input)
+				"%s",
+				decoded, want)
 		}
 	}
 }
diff --git a/go/cbrotli/internal/BUILD b/go/cbrotli/internal/BUILD
deleted file mode 100755
index a3e3b87..0000000
--- a/go/cbrotli/internal/BUILD
+++ /dev/null
@@ -1,19 +0,0 @@
-package(default_visibility = ["//visibility:public"])
-
-licenses(["notice"])  # MIT
-
-load("@io_bazel_rules_go//go:def.bzl", "cgo_library")
-
-cgo_library(
-    name = "decoder",
-    srcs = ["decoder.go"],
-    visibility = ["//go/cbrotli:__subpackages__"],
-    cdeps = ["//:brotlidec"],
-)
-
-cgo_library(
-    name = "encoder",
-    srcs = ["encoder.go"],
-    visibility = ["//go/cbrotli:__subpackages__"],
-    cdeps = ["//:brotlienc"],
-)
diff --git a/go/cbrotli/internal/decoder.go b/go/cbrotli/internal/decoder.go
deleted file mode 100755
index 74d4c21..0000000
--- a/go/cbrotli/internal/decoder.go
+++ /dev/null
@@ -1,110 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Distributed under MIT license.
-// See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
-
-// Package decoder wraps the brotli decoder C API used by package brotli.
-package decoder
-
-/*
-#include <brotli/decode.h>
-
-// Wrap BrotliDecoderDecompressStream so that it doesn't take variable (in-out)
-// pointers. Instead of updated pointer, deltas are saved in auxiliary struct.
-
-struct DecompressStreamResult {
-  size_t bytes_consumed;
-  const uint8_t* output_data;
-  size_t output_data_size;
-  BrotliDecoderResult status;
-};
-
-struct DecompressStreamResult DecompressStream(BrotliDecoderState* s,
-    const uint8_t* encoded_data, size_t encoded_data_size) {
-  struct DecompressStreamResult result;
-  size_t available_in = encoded_data_size;
-  const uint8_t* next_in = encoded_data;
-  size_t available_out = 0;
-  result.status = BrotliDecoderDecompressStream(s,
-      &available_in, &next_in, &available_out, 0, 0);
-  result.bytes_consumed = encoded_data_size - available_in;
-  result.output_data = 0;
-  result.output_data_size = 0;
-  if (result.status != BROTLI_DECODER_RESULT_ERROR) {
-    result.output_data = BrotliDecoderTakeOutput(s, &result.output_data_size);
-    if (BrotliDecoderIsFinished(s)) {
-      result.status = BROTLI_DECODER_RESULT_SUCCESS;
-    }
-  }
-  return result;
-}
-
-*/
-import "C"
-import (
-	"unsafe"
-)
-
-// Status represents internal state after DecompressStream invokation
-type Status int
-
-const (
-	// Error happened
-	Error Status = iota
-	// Done means that no more output will be produced
-	Done
-	// Ok means that more output might be produced with no additional input
-	Ok
-)
-
-// Decoder is the Brotli c-decoder handle.
-type Decoder struct {
-	state *C.BrotliDecoderState
-}
-
-// New returns a new Brotli c-decoder handle.
-// Close MUST be called to free resources.
-func New() Decoder {
-	return Decoder{state: C.BrotliDecoderCreateInstance(nil, nil, nil)}
-}
-
-// Close frees resources used by decoder.
-func (z *Decoder) Close() {
-	C.BrotliDecoderDestroyInstance(z.state)
-	z.state = nil
-}
-
-func goStatus(cStatus C.BrotliDecoderResult) (status Status) {
-	switch cStatus {
-	case C.BROTLI_DECODER_RESULT_SUCCESS:
-		return Done
-	case C.BROTLI_DECODER_RESULT_NEEDS_MORE_INPUT:
-		return Ok
-	case C.BROTLI_DECODER_RESULT_NEEDS_MORE_OUTPUT:
-		return Ok
-	}
-	return Error
-}
-
-// cBytes casts a Go []byte into a C uint8_t*. We pass &buf[0] directly to C,
-// which is legal because C doesn't save the pointer longer than the call and
-// the byte array itself doesn't contain any pointers.
-func cBytes(buf []byte) (*C.uint8_t, C.size_t) {
-	if len(buf) == 0 {
-		return (*C.uint8_t)(nil), 0
-	}
-	return (*C.uint8_t)(unsafe.Pointer(&buf[0])), C.size_t(len(buf))
-}
-
-// DecompressStream reads Brotli-encoded bytes from in, and returns produced
-// bytes. Output contents should not be modified. Liveness of output is
-// hard-limited by Decoder liveness; slice becomes invalid when any Decoder
-// method is invoked.
-func (z *Decoder) DecompressStream(in []byte) (
-	bytesConsumed int, output []byte, status Status) {
-	cin, cinSize := cBytes(in)
-	result := C.DecompressStream(z.state, cin, cinSize)
-	output = C.GoBytes(
-		unsafe.Pointer(result.output_data), C.int(result.output_data_size))
-	return int(result.bytes_consumed), output, goStatus(result.status)
-}
diff --git a/go/cbrotli/internal/encoder.go b/go/cbrotli/internal/encoder.go
deleted file mode 100755
index 13526f3..0000000
--- a/go/cbrotli/internal/encoder.go
+++ /dev/null
@@ -1,134 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Distributed under MIT license.
-// See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
-
-// Package encoder wraps the brotli encoder C API used by package brotli.
-package encoder
-
-/*
-#include <brotli/encode.h>
-
-// Wrap BrotliEncoderCompressStream so that it doesn't take variable (in-out)
-// pointers. Instead of updated pointer, deltas are saved in auxiliary struct.
-struct CompressStreamResult {
-  size_t bytes_consumed;
-  const uint8_t* output_data;
-  size_t output_data_size;
-  int success;
-  int has_more;
-};
-
-struct CompressStreamResult CompressStream(
-    BrotliEncoderState* s, BrotliEncoderOperation op,
-    const uint8_t* data, size_t data_size) {
-  struct CompressStreamResult result;
-  size_t available_in = data_size;
-  const uint8_t* next_in = data;
-  size_t available_out = 0;
-  result.success = BrotliEncoderCompressStream(s, op,
-      &available_in, &next_in, &available_out, 0, 0) ? 1 : 0;
-  result.bytes_consumed = data_size - available_in;
-  result.output_data = 0;
-  result.output_data_size = 0;
-  if (result.success) {
-    result.output_data = BrotliEncoderTakeOutput(s, &result.output_data_size);
-  }
-  result.has_more = BrotliEncoderHasMoreOutput(s) ? 1 : 0;
-  return result;
-}
-*/
-import "C"
-import (
-	"unsafe"
-)
-
-// Operation represents type of request to CompressStream
-type Operation int
-
-const (
-	// Process input
-	Process Operation = iota
-	// Flush input processed so far
-	Flush
-	// Finish stream
-	Finish
-)
-
-// Status represents internal state after CompressStream invocation
-type Status int
-
-const (
-	// Error happened
-	Error Status = iota
-	// Done means that no more output will be produced
-	Done
-	// Ok means that more output might be produced with no additional input
-	Ok
-)
-
-// Encoder is the Brotli c-encoder handle.
-type Encoder struct {
-	state *C.BrotliEncoderState
-}
-
-// New returns a new Brotli c-encoder handle.
-// quality and lgWin are described in third_party/Brotli/enc/encode.h.
-// Close MUST be called to free resources.
-func New(quality, lgWin int) Encoder {
-	state := C.BrotliEncoderCreateInstance(nil, nil, nil)
-	C.BrotliEncoderSetParameter(
-		state, C.BROTLI_PARAM_QUALITY, (C.uint32_t)(quality))
-	C.BrotliEncoderSetParameter(
-		state, C.BROTLI_PARAM_LGWIN, (C.uint32_t)(lgWin))
-	return Encoder{state}
-}
-
-// Close frees resources used by encoder.
-func (z *Encoder) Close() {
-	C.BrotliEncoderDestroyInstance(z.state)
-	z.state = nil
-}
-
-// cBytes casts a Go []byte into a C uint8_t*. We pass &buf[0] directly to C,
-// which is legal because C doesn't save the pointer longer than the call and
-// the byte array itself doesn't contain any pointers.
-func cBytes(buf []byte) (*C.uint8_t, C.size_t) {
-	if len(buf) == 0 {
-		return (*C.uint8_t)(nil), 0
-	}
-	return (*C.uint8_t)(unsafe.Pointer(&buf[0])), C.size_t(len(buf))
-}
-
-func cOperation(op Operation) (cOp C.BrotliEncoderOperation) {
-	switch op {
-	case Flush:
-		return C.BROTLI_OPERATION_FLUSH
-	case Finish:
-		return C.BROTLI_OPERATION_FINISH
-	}
-	return C.BROTLI_OPERATION_PROCESS
-}
-
-// CompressStream processes data and produces Brotli-encoded bytes. Encoder may
-// consume considerable amount of input before the first output bytes come out.
-// Flush and Finish operations force Encoder to produce output that corresponds
-// to input consumed so far. Output contents should not be modified. Liveness of
-// output is hard-limited by Encoder liveness; slice becomes invalid when any
-// Encoder method is invoked.
-func (z *Encoder) CompressStream(in []byte, op Operation) (
-	bytesConsumed int, output []byte, status Status) {
-	cin, cinSize := cBytes(in)
-	result := C.CompressStream(z.state, cOperation(op), cin, cinSize)
-	output = C.GoBytes(
-		unsafe.Pointer(result.output_data), C.int(result.output_data_size))
-	var outcome Status
-	if result.success == 0 {
-		outcome = Error
-	} else if result.has_more != 0 {
-		outcome = Ok
-	} else {
-		outcome = Done
-	}
-	return int(result.bytes_consumed), output, outcome
-}
diff --git a/go/cbrotli/reader.go b/go/cbrotli/reader.go
new file mode 100755
index 0000000..a05809b
--- /dev/null
+++ b/go/cbrotli/reader.go
@@ -0,0 +1,156 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Distributed under MIT license.
+// See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+
+// Package cbrotli compresses and decompresses data with C-Brotli library.
+package cbrotli
+
+/*
+#include <stddef.h>
+#include <stdint.h>
+
+#include <brotli/decode.h>
+
+static BrotliDecoderResult DecompressStream(BrotliDecoderState* s,
+                                            uint8_t* out, size_t out_len,
+                                            const uint8_t* in, size_t in_len,
+                                            size_t* bytes_written,
+                                            size_t* bytes_consumed) {
+  size_t in_remaining = in_len;
+  size_t out_remaining = out_len;
+  BrotliDecoderResult result = BrotliDecoderDecompressStream(
+      s, &in_remaining, &in, &out_remaining, &out, NULL);
+  *bytes_written = out_len - out_remaining;
+  *bytes_consumed = in_len - in_remaining;
+  return result;
+}
+*/
+import "C"
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"io/ioutil"
+)
+
+type decodeError C.BrotliDecoderErrorCode
+
+func (err decodeError) Error() string {
+	return "cbrotli: " +
+		C.GoString(C.BrotliDecoderErrorString(C.BrotliDecoderErrorCode(err)))
+}
+
+var errExcessiveInput = errors.New("cbrotli: excessive input")
+var errInvalidState = errors.New("cbrotli: invalid state")
+var errReaderClosed = errors.New("cbrotli: Reader is closed")
+
+// Reader implements io.ReadCloser by reading Brotli-encoded data from an
+// underlying Reader.
+type Reader struct {
+	src   io.Reader
+	state *C.BrotliDecoderState
+	buf   []byte // scratch space for reading from src
+	in    []byte // current chunk to decode; usually aliases buf
+}
+
+// readBufSize is a "good" buffer size that avoids excessive round-trips
+// between C and Go but doesn't waste too much memory on buffering.
+// It is arbitrarily chosen to be equal to the constant used in io.Copy.
+const readBufSize = 32 * 1024
+
+// NewReader initializes new Reader instance.
+// Close MUST be called to free resources.
+func NewReader(src io.Reader) *Reader {
+	return &Reader{
+		src:   src,
+		state: C.BrotliDecoderCreateInstance(nil, nil, nil),
+		buf:   make([]byte, readBufSize),
+	}
+}
+
+// Close implements io.Closer. Close MUST be invoked to free native resources.
+func (r *Reader) Close() error {
+	if r.state == nil {
+		return errReaderClosed
+	}
+	// Close despite the state; i.e. there might be some unread decoded data.
+	C.BrotliDecoderDestroyInstance(r.state)
+	r.state = nil
+	return nil
+}
+
+func (r *Reader) Read(p []byte) (n int, err error) {
+	if int(C.BrotliDecoderHasMoreOutput(r.state)) == 0 && len(r.in) == 0 {
+		m, readErr := r.src.Read(r.buf)
+		if m == 0 {
+			// If readErr is `nil`, we just proxy underlying stream behavior.
+			return 0, readErr
+		}
+		r.in = r.buf[:m]
+	}
+
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	for n == 0 {
+		var written, consumed C.size_t
+		var data *C.uint8_t
+		if len(r.in) != 0 {
+			data = (*C.uint8_t)(&r.in[0])
+		}
+		result := C.DecompressStream(r.state,
+			(*C.uint8_t)(&p[0]), C.size_t(len(p)),
+			data, C.size_t(len(r.in)),
+			&written, &consumed)
+		r.in = r.in[int(consumed):]
+		n = int(written)
+
+		switch result {
+		case C.BROTLI_DECODER_RESULT_SUCCESS:
+			if len(r.in) > 0 {
+				return n, errExcessiveInput
+			}
+			return n, nil
+		case C.BROTLI_DECODER_RESULT_ERROR:
+			return n, decodeError(C.BrotliDecoderGetErrorCode(r.state))
+		case C.BROTLI_DECODER_RESULT_NEEDS_MORE_OUTPUT:
+			if n == 0 {
+				return 0, io.ErrShortBuffer
+			}
+			return n, nil
+		case C.BROTLI_DECODER_NEEDS_MORE_INPUT:
+		}
+
+		if len(r.in) != 0 {
+			return 0, errInvalidState
+		}
+
+		// Top off the buffer.
+		encN, err := r.src.Read(r.buf)
+		if encN == 0 && n == 0 {
+			// Not enough data to complete decoding.
+			if err == io.EOF {
+				return 0, io.ErrUnexpectedEOF
+			}
+			return 0, err
+		}
+		r.in = r.buf[:encN]
+	}
+
+	return n, nil
+}
+
+// Decode decodes Brotli encoded data.
+func Decode(encodedData []byte) ([]byte, error) {
+	r := &Reader{
+		src:   bytes.NewReader(nil),
+		state: C.BrotliDecoderCreateInstance(nil, nil, nil),
+		buf:   make([]byte, 4), // arbitrarily small but nonzero so that r.src.Read returns io.EOF
+		in:    encodedData,
+	}
+	defer r.Close()
+	return ioutil.ReadAll(r)
+}
diff --git a/go/cbrotli/writer.go b/go/cbrotli/writer.go
new file mode 100755
index 0000000..279a2f2
--- /dev/null
+++ b/go/cbrotli/writer.go
@@ -0,0 +1,160 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Distributed under MIT license.
+// See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+
+package cbrotli
+
+/*
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <brotli/encode.h>
+
+struct CompressStreamResult {
+  size_t bytes_consumed;
+  const uint8_t* output_data;
+  size_t output_data_size;
+  int success;
+  int has_more;
+};
+
+static struct CompressStreamResult CompressStream(
+    BrotliEncoderState* s, BrotliEncoderOperation op,
+    const uint8_t* data, size_t data_size) {
+  struct CompressStreamResult result;
+  size_t available_in = data_size;
+  const uint8_t* next_in = data;
+  size_t available_out = 0;
+  result.success = BrotliEncoderCompressStream(s, op,
+      &available_in, &next_in, &available_out, 0, 0) ? 1 : 0;
+  result.bytes_consumed = data_size - available_in;
+  result.output_data = 0;
+  result.output_data_size = 0;
+  if (result.success) {
+    result.output_data = BrotliEncoderTakeOutput(s, &result.output_data_size);
+  }
+  result.has_more = BrotliEncoderHasMoreOutput(s) ? 1 : 0;
+  return result;
+}
+*/
+import "C"
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"unsafe"
+)
+
+// WriterOptions configures Writer.
+type WriterOptions struct {
+	// Quality controls the compression-speed vs compression-density trade-offs.
+	// The higher the quality, the slower the compression. Range is 0 to 11.
+	Quality int
+	// LGWin is the base 2 logarithm of the sliding window size.
+	// Range is 10 to 24. 0 indicates automatic configuration based on Quality.
+	LGWin int
+	// BufferSize is the number of bytes to use to buffer encoded output.
+	// 0 indicates an implementation-defined default.
+	BufferSize int
+}
+
+// Writer implements io.WriteCloser by writing Brotli-encoded data to an
+// underlying Writer.
+type Writer struct {
+	dst          io.Writer
+	state        *C.BrotliEncoderState
+	buf, encoded []byte
+}
+
+var (
+	errEncode       = errors.New("cbrotli: encode error")
+	errWriterClosed = errors.New("cbrotli: Writer is closed")
+)
+
+// NewWriter initializes new Writer instance.
+// Close MUST be called to free resources.
+func NewWriter(dst io.Writer, options WriterOptions) *Writer {
+	state := C.BrotliEncoderCreateInstance(nil, nil, nil)
+	C.BrotliEncoderSetParameter(
+		state, C.BROTLI_PARAM_QUALITY, (C.uint32_t)(options.Quality))
+	C.BrotliEncoderSetParameter(
+		state, C.BROTLI_PARAM_LGWIN, (C.uint32_t)(options.LGWin))
+	return &Writer{
+		dst:   dst,
+		state: state,
+	}
+}
+
+func (w *Writer) writeChunk(p []byte, op C.BrotliEncoderOperation) (n int, err error) {
+	if w.state == nil {
+		return 0, errWriterClosed
+	}
+
+	for {
+		var data *C.uint8_t
+		if len(p) != 0 {
+			data = (*C.uint8_t)(&p[0])
+		}
+		result := C.CompressStream(w.state, op, data, C.size_t(len(p)))
+		if result.success == 0 {
+			return n, errEncode
+		}
+		p = p[int(result.bytes_consumed):]
+		n += int(result.bytes_consumed)
+
+		length := int(result.output_data_size)
+		if length != 0 {
+			// It is a workaround for non-copying-wrapping of native memory.
+			// C-encoder never pushes output block longer than ((2 << 25) + 502).
+			// TODO: use natural wrapper, when it becomes available, see
+			//               https://golang.org/issue/13656.
+			output := (*[1 << 30]byte)(unsafe.Pointer(result.output_data))[:length:length]
+			_, err = w.dst.Write(output)
+			if err != nil {
+				return n, err
+			}
+		}
+		if len(p) == 0 && result.has_more == 0 {
+			return n, nil
+		}
+	}
+}
+
+// Flush outputs encoded data for all input provided to Write. The resulting
+// output can be decoded to match all input before Flush, but the stream is
+// not yet complete until after Close.
+// Flush has a negative impact on compression.
+func (w *Writer) Flush() error {
+	_, err := w.writeChunk(nil, C.BROTLI_OPERATION_FLUSH)
+	return err
+}
+
+// Close flushes remaining data to the decorated writer and frees C resources.
+func (w *Writer) Close() error {
+	// If stream is already closed, it is reported by `writeChunk`.
+	_, err := w.writeChunk(nil, C.BROTLI_OPERATION_FINISH)
+	// C-Brotli tolerates `nil` pointer here.
+	C.BrotliEncoderDestroyInstance(w.state)
+	w.state = nil
+	return err
+}
+
+// Write implements io.Writer. Flush or Close must be called to ensure that the
+// encoded bytes are actually flushed to the underlying Writer.
+func (w *Writer) Write(p []byte) (n int, err error) {
+	return w.writeChunk(p, C.BROTLI_OPERATION_PROCESS)
+}
+
+// Encode returns content encoded with Brotli.
+func Encode(content []byte, options WriterOptions) ([]byte, error) {
+	var buf bytes.Buffer
+	writer := NewWriter(&buf, options)
+	_, err := writer.Write(content)
+	if closeErr := writer.Close(); err == nil {
+		err = closeErr
+	}
+	return buf.Bytes(), err
+}