Implement WebSocketDeflater.

net/websockets/websocket_deflater.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/websockets/websocket_deflater.h"
+
+#include <string.h>
+#include <vector>
+
+#include "base/logging.h"
+#include "net/base/io_buffer.h"
+#include "third_party/zlib/zlib.h"
+
+namespace net {
+
+WebSocketDeflater::WebSocketDeflater(int window_bits,
+                                     ContextTakeOverMode mode)
+    : stream_(new z_stream),
+      mode_(mode),
+      are_bytes_added_(false) {
+  DCHECK_LE(8, window_bits);
+  DCHECK_GE(15, window_bits);
+  memset(stream_.get(), 0, sizeof(*stream_));
+  int result = deflateInit2(stream_.get(),
+                            Z_DEFAULT_COMPRESSION,
+                            Z_DEFLATED,
+                            -window_bits,
+                            8,  // default mem level
+                            Z_DEFAULT_STRATEGY);
+  DCHECK_EQ(Z_OK, result);
+}
+
+WebSocketDeflater::~WebSocketDeflater() {
+  if (stream_) {
+    deflateEnd(stream_.get());
+    stream_.reset(NULL);
+  }
+}
+
+bool WebSocketDeflater::AddBytes(const char* data, size_t size) {
+  if (!size)
+    return true;
+
+  stream_->next_in = reinterpret_cast<Bytef*>(const_cast<char*>(data));
+  stream_->avail_in = size;
+
+  // The estimation by deflateBound is not accurate if the zlib has some
+  // remaining input of the last compression.
+  size_t estimation = deflateBound(stream_.get(), size);
+  DCHECK_GT(estimation, 0u);
+  do {
+    size_t current = buffer_.size();
+    // TODO(yhirano): std::vector initializes the expanded area,
+    // but the initialization is actually not necessary.
+    buffer_.resize(buffer_.size() + estimation);
+    stream_->next_out = reinterpret_cast<Bytef*>(&buffer_[current]);
+    stream_->avail_out = buffer_.size() - current;
+
+    int result = deflate(stream_.get(), Z_NO_FLUSH);
+    if (result != Z_OK) {

[Adam Rice, 2013/08/30 07:16:11]

Probably these { } need to be removed too.

[yhirano, 2013/08/30 09:42:11]

Done.

+      return false;
+    }
+    buffer_.resize(buffer_.size() - stream_->avail_out);
+    estimation *= 2;
+  } while (!stream_->avail_out);
+  are_bytes_added_ = true;
+
+  return true;
+}
+
+scoped_refptr<IOBufferWithSize> WebSocketDeflater::Finish() {
+  scoped_refptr<IOBufferWithSize> result;
+  if (!are_bytes_added_) {
+    // Since consecutive calls of deflate with Z_SYNC_FLUSH and no input
+    // lead to an error, we create and return the output for the empty input
+    // manually.
+    DCHECK(buffer_.empty());
+    result = new IOBufferWithSize(2);
+    memcpy(result->data(), "\x02\x00", result->size());
+    Reset();
+    return result;
+  }
+  stream_->next_in = NULL;
+  stream_->avail_in = 0;
+
+  const size_t available_size = 4096;

[Adam Rice, 2013/08/30 07:16:11]

Where did the number 4096 come from?

[yhirano, 2013/08/30 07:26:34]

The deflater works for arbitrary value if it is not very small (less than 7 or
so).
Small values (like 32) can degrate compression.

+  do {

[Adam Rice, 2013/08/30 07:16:11]

I just realised that this loop is almost the same as the one in AddBytes(). You
should probably factor them out into a separate method. The only difference I
see is this one increases the buffer size linearly, whereas the AddBytes() loop
uses exponential increases. Since exponential increases are more efficient if
they are actually needed, I think it is okay to use exponential increases for
both.

[yhirano, 2013/08/30 09:42:11]

Done.

[yhirano, 2013/08/30 10:56:31]

I'm sorry, I was wrong.
Loop condition in AddBytes and Finish should differ and I fixed it.

+    size_t current = buffer_.size();
+    buffer_.resize(buffer_.size() + available_size);
+    stream_->next_out = reinterpret_cast<Bytef*>(&buffer_[current]);
+    stream_->avail_out = buffer_.size() - current;
+
+    int result = deflate(stream_.get(), Z_SYNC_FLUSH);
+    buffer_.resize(buffer_.size() - stream_->avail_out);
+    if (result != Z_OK && result != Z_BUF_ERROR) {
+      Reset();
+      return NULL;
+    }
+  } while (!stream_->avail_out);
+  // Remove 4 octets from the tail as the specification requires.
+  if (buffer_.size() < 4) {
+    Reset();
+    return NULL;
+  }
+  result = new IOBufferWithSize(buffer_.size() - 4);
+  memcpy(result->data(), buffer_.data(), result->size());
+  Reset();
+  return result;
+}
+
+void WebSocketDeflater::Reset() {
+  buffer_.clear();
+  if (mode_ == DO_NOT_TAKE_OVER_CONTEXT)
+    deflateReset(stream_.get());
+  are_bytes_added_ = false;
+}
+
+}  // namespace net