Blimp: add packet-level DEFLATE compression using zlib.

blimp/net/compressed_packet_writer.h

+// Copyright 2016 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.
+
+#ifndef BLIMP_NET_COMPRESSED_PACKET_WRITER_H_
+#define BLIMP_NET_COMPRESSED_PACKET_WRITER_H_
+
+#include "base/memory/weak_ptr.h"
+#include "blimp/net/blimp_net_export.h"
+#include "blimp/net/packet_writer.h"
+#include "net/base/completion_callback.h"
+#include "net/base/io_buffer.h"
+#include "third_party/zlib/zlib.h"
+
+namespace blimp {
+
+// Filter object which wraps a PacketWriter, adding a DEFLATE compression step
+// to outgoing packets.
+//
+// Each packet is appended as a DEFLATE block to a long-lived compression
+// stream.
+// Each block is prefixed with a 32-bit word representing the length of the
+// decompressed payload, used for sizing output buffers.

[Wez, 2016/03/29 21:38:38]

Looks like you got rid of that in the latest patch?

[Kevin M, 2016/03/29 23:48:24]

Done.

+// Blocks are explicitly flushed at each packet boundary, which prevents zlib's
+// internal buffers from introducing unwanted output latency.
+// Gzip headers and CRC checks are omitted from the stream output.
+class BLIMP_NET_EXPORT CompressedPacketWriter : public PacketWriter {
+ public:
+  // |source|: The PacketWriter which will receive compressed packets.
+  explicit CompressedPacketWriter(scoped_ptr<PacketWriter> sink);
+  ~CompressedPacketWriter() override;
+
+  // PacketWriter implementation.
+  void WritePacket(const scoped_refptr<net::DrainableIOBuffer>& buf,
+                   const net::CompletionCallback& cb) override;
+
+ private:
+  // Compresses |src_buf| into |dest_buf|, and sets |compressed_size| with the

[Wez, 2016/03/29 21:38:38]

There is no |compressed_size| - you mean it returns the length?

[Kevin M, 2016/03/29 23:48:24]

Done.

+  // length of the compressed packet (including decompressed length).

[Wez, 2016/03/29 21:38:38]

Not sure what "including decompressed length means"?

[Kevin M, 2016/03/29 23:48:24]

I meant "decompressed length header." But that's N/A now.

+  // On success, returns a >= 0 value indicating the size of the
+  // compressed payload.
+  // On failure, returns a negative value indicating the error code
+  // (see net_errors.h).
+  int Compress(const scoped_refptr<net::DrainableIOBuffer>& src_buf,
+               const scoped_refptr<net::GrowableIOBuffer>& dest_buf);
+
+  z_stream zlib_stream_{};
+  scoped_ptr<PacketWriter> sink_;
+  scoped_refptr<net::GrowableIOBuffer> compressed_buf_;
+  size_t uncompressed_size_total_ = 0;

[Wez, 2016/03/29 21:38:38]

nit: Do these need to be unsigned literals?

[Kevin M, 2016/03/29 23:48:24]

Done.

[Kevin M, 2016/03/29 23:48:24]

Done.

+  size_t compressed_size_total_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(CompressedPacketWriter);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_COMPRESSED_PACKET_WRITER_H_