[GCM] Initial work to set up directory structure and introduce socket integration

google_apis/gcm/base/socket_stream.h

+// 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.
+//
+// Protobuf ZeroCopy[Input/Output]Stream implementations capable of using a
+// net::StreamSocket. Built to work with Protobuf CodedStreams.
+
+#ifndef GOOGLE_APIS_GCM_BASE_SOCKET_STREAM_H_
+#define GOOGLE_APIS_GCM_BASE_SOCKET_STREAM_H_
+
+#include "base/basictypes.h"
+#include "base/callback_forward.h"
+#include "base/compiler_specific.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "google/protobuf/io/zero_copy_stream.h"
+#include "google_apis/gcm/base/gcm_export.h"
+
+namespace net {
+class DrainableIOBuffer;
+class IOBufferWithSize;
+class StreamSocket;
+}

[akalin, 2013/10/04 18:37:04]

// namespace net

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+
+namespace gcm {
+
+// A helper class for interacting with a net::StreamSocket that is receiving
+// protobuf encoded messages. A SocketInputStream does not take ownership of
+// the socket itself, and it is expected that the life of the input stream
+// should match the life of the socket itself (while the socket remains
+// connected). If an error is encounters, the input stream will store the error
+// input last_error_, and state will be set to CLOSED.

[akalin, 2013/10/04 18:37:04]

input last_error_ -> in |last_error_|
state -> the state or state()

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+// Typical usage:
+// 1. Check the state() of the input stream before using it. If CLOSED, the
+//    input stream must be rebuilt (and the socket likely needs to be
+//    reconnected as an error was encountered).
+// 2. If state() is EMPTY, call Refresh(..), passing the maximum byte size for
+//    a message, and wait until the callback is invoked. It is invalid to
+//    attempt to Refresh or read data while another Refresh is pending.
+// 3. Check state() again to ensure the Refresh was successful.
+// 4. Use a CodedInputStream to read from the ZeroCopyInputStream interface of
+//    the SocketInputStream. Next(..) will return true until there is no data
+//    remaining.
+// 5. Call RebuildBuffer when done reading, to shift any unread data to the
+//    start of the buffer.
+// 6. Repeat as necessary.
+class GCM_EXPORT SocketInputStream
+    : public google::protobuf::io::ZeroCopyInputStream {
+ public:
+  enum State {
+    // No valid data to read. This means the buffer is either empty or all data
+    // in the buffer has already been consumed.
+    EMPTY,
+    // Valid data to read.
+    READY,
+    // In the process of reading new data from the socket.
+    READING,
+    // An permanent error occurred and the stream is now closed.
+    CLOSED,
+  };
+
+  // |socket| should already be connected.
+  explicit SocketInputStream(net::StreamSocket* socket);
+  virtual ~SocketInputStream();
+
+  // ZeroCopyInputStream implementation.
+  virtual bool Next(const void** data, int* size) OVERRIDE;
+  virtual void BackUp(int count) OVERRIDE;
+  virtual bool Skip(int count) OVERRIDE;
+  virtual int64 ByteCount() const OVERRIDE;
+
+  // Reads and appends a max of |byte_limit| bytes onto the read buffer.
+  // |callback| is invoked upon read completion, even if an error was
+  // encountered (state() and ByteCount() must be checked to see if forward
+  // progress was made).
+  void Refresh(const base::Closure& callback, int byte_limit);

[akalin, 2013/10/04 18:37:04]

so |callback| can be invoked directly by Refresh, right? It seems worth calling
this out, esp. since it departs from net:: convention

[Nicolas Zea, 2013/10/04 20:55:28]

I've gone ahead and made it so synchronous callbacks don't happen (seems
cleaner/safer), here and in flush.

+
+  // Rebuilds the buffer state by copying over any unread data to the beginning
+  // of the buffer and resetting the buffer read/write positions.
+  // Note: it is not valid to call Rebuild() if state() == CLOSED. The stream
+  // must be recreated from scratch in such a scenario.
+  void RebuildBuffer();
+
+  // Returns the last fatal error encountered. Only valid if state() == CLOSED.
+  int last_error() const;

[akalin, 2013/10/04 18:37:04]

net::Error?

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+
+  // Returns the current state.
+  State state() const;
+
+ private:
+  // Clears the local state.
+  void ResetInternal();
+
+  // Callback for Socket::Read calls.
+  void RefreshCompletionCallback(const base::Closure& callback, int result);
+
+  // Permanently closes the stream.
+  void CloseStream(int error, const base::Closure& callback);
+
+  // Internal net components.
+  net::StreamSocket* socket_;

[akalin, 2013/10/04 18:37:04]

* const socket_?

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+  scoped_refptr<net::IOBufferWithSize> io_buffer_;

[akalin, 2013/10/04 18:37:04]

since drainable_io_buffer_ stores the size already, does io_buffer_ need to be
IOBufferWithSize? Can it be IOBuffer instead?

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+  scoped_refptr<net::DrainableIOBuffer> drainable_io_buffer_;

[akalin, 2013/10/04 18:37:04]

do we need this to be a member variable? Seems to violate the DRY principle
since drainable_io_buffer_'s offset is basically buffer_read_pos_, but we have
to keep them in sync. Maybe eliminate one or the other?

[Nicolas Zea, 2013/10/04 20:55:28]

The offset is actually buffer_write_pos_. You're right though that I can
therefore replace buffer_write_pos_ usage with
drainable_io_buffer_->BytesConsumed().

+
+  // The amount of data within |io_buffer_| that has already been read.
+  int buffer_read_pos_;
+
+  // The amount of data written within |io_buffer_|.
+  int buffer_write_pos_;

[akalin, 2013/10/04 18:37:04]

the name suggests that it's analogous to buffer_read_pos_, but this is more like
a limit to buffer_read_pos_. Perhaps rename to 'buffer_valid_size_' or
something?

[Nicolas Zea, 2013/10/04 20:55:28]

Removed in favor of reusing DrainableIOBuffer::BytesConsumed()

+
+  // The number of bytes the stream has been backed up by. These bytes need to
+  // be returned on the subsequent Next(..) call.
+  // 0 <= backup_bytes_ <= buffer_pos_
+  int backup_bytes_;

[akalin, 2013/10/04 18:37:04]

https://developers.google.com/protocol-buffers/docs/reference/cpp/google.prot...
is ambiguous on how to handle a call to BackUp(0). (Should the next call to
Next() return 0 for size?) Perhaps document the assumption you make? (i.e.,
backup_bytes_ == 0 means BackUp() hasn't been called)

[akalin, 2013/10/04 18:37:04]

is it possible to omit backup_bytes_ entirely and just adjust buffer_read_pos_
appropriately? It might be, if we assume that it's called only at most once
after a successful call to Next

[Nicolas Zea, 2013/10/04 20:55:28]

Good point. It seemed easier at dev time to track them separately, so I
understood what was going on better, but at this point just updating
buffer_read_pos_ is simpler. Done.

+
+  // The number of bytes to skip from the next successful refresh.
+  int skipped_bytes_;

[akalin, 2013/10/04 18:37:04]

i suppose we're assuming it's not true that both BackUp() and Skip() will be
called?

[Nicolas Zea, 2013/10/04 20:55:28]

Fair enough. I had originally written this to support all the CodedStream usage,
but for my purposes Skip isn't used, and it's better to just keep things simple.
Removed and made it NOTIMPLEMENTED().

+
+  // If < net::OK, the last net error received.
+  int last_error_;

[akalin, 2013/10/04 18:37:04]

net::Error?

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+
+  // The current state.
+  State state_;
+
+  base::WeakPtrFactory<SocketInputStream> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SocketInputStream);
+};
+
+// A helper class for writing to a SocketStream with protobuf encoded data.
+// A SocketOutputStream does not take ownership of the socket itself, and it is
+// expected that the life of the output stream should match the life of the
+// socket itself (while the socket remains connected).
+// Typical usage:
+// 1. Check the state() of the output stream before using it. If CLOSED, the
+//    output stream must be rebuilt (and the socket likely needs to be
+//    reconnected, as an error was encountered).
+// 2. If EMPTY, the output stream can be written via a CodedOutputStream using
+//    the ZeroCopyOutputStream interface.
+// 3. Once done writing, state() should be READY, so call Flush(..) to write
+//    the buffer into the StreamSocket. Wait for the callback to be invoked
+//    (it's invalid to write to an output stream while it's flushing).
+// 4. Check the state() again to ensure the Flush was successful. state() should
+//    be EMPTY again.
+// 5. Repeat.
+class GCM_EXPORT SocketOutputStream
+    : public google::protobuf::io::ZeroCopyOutputStream {
+ public:
+  enum State {
+    // No valid data yet.
+    EMPTY,
+    // Ready for flushing (some data is present).
+    READY,
+    // In the process of flushing into the socket.
+    FLUSHING,
+    // A permanent error occurred, and the stream is now closed.
+    CLOSED,
+  };
+
+  // |socket| should already be connected.
+  explicit SocketOutputStream(net::StreamSocket* socket);
+  virtual ~SocketOutputStream();
+
+  // ZeroCopyOutputStream implementation.
+  virtual bool Next(void** data, int* size) OVERRIDE;
+  virtual void BackUp(int count) OVERRIDE;
+  virtual int64 ByteCount() const OVERRIDE;
+
+  // Writes the buffer into the Socket.
+  void Flush(const base::Closure& callback);
+
+  // Returns the current state.
+  State state() const;
+
+  // Returns the last fatal error encountered. Only valid if state() == CLOSED.
+  int last_error() const;

[akalin, 2013/10/04 18:37:04]

net::Error

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+
+ private:
+  void FlushCompletionCallback(const base::Closure& callback, int result);
+
+  // Internal net components.
+  net::StreamSocket* socket_;
+  scoped_refptr<net::IOBufferWithSize> io_buffer_;

[akalin, 2013/10/04 18:37:04]

IOBufferWithSize -> IOBuffer

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+  scoped_refptr<net::DrainableIOBuffer> drainable_io_buffer_;
+
+  // The amount of valid buffer data. This is the amount of data written on the
+  // next call to Flush().
+  int buffer_used_;
+
+  // If < net::OK, the last net error received.
+  int last_error_;

[akalin, 2013/10/04 18:37:04]

net::Error?

[Nicolas Zea, 2013/10/04 20:55:28]

Done.

+
+  // The current state.
+  State state_;
+
+  base::WeakPtrFactory<SocketOutputStream> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SocketOutputStream);
+};
+
+}  // namespace gcm
+
+#endif  // GOOGLE_APIS_GCM_BASE_SOCKET_STREAM_H_