Factor out the shared parts of IPC channel reading.

ipc/ipc_channel_reader.h

Index: ipc/ipc_channel_reader.h
diff --git a/ipc/ipc_channel_reader.h b/ipc/ipc_channel_reader.h
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+++ b/ipc/ipc_channel_reader.h
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+// Copyright (c) 2012 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 IPC_IPC_CHANNEL_READER_H_
+#define IPC_IPC_CHANNEL_READER_H_
+
+#include "base/basictypes.h"
+#include "ipc/ipc_channel.h"
+
+namespace IPC {
+namespace internal {
+
+// This class provides common pipe reading functionality for the
+// platform-specific IPC channel implementations.
+//
+// It does the common input buffer management and message dispatch, while the
+// platform-specific parts provide the pipe management through a virtual
+// interface implemented on a per-platform basis.
+//
+// Note that there is no "writer" corresponding to this because the code for
+// writing to the channel is much simpler and has very little common
+// functionality that would benefit from being factored out. If we add
+// something like that in the future, it would be more appropriate to add it
+// here (and rename appropriately) rather than writing a different class.
+class ChannelReader {
+ public:
+  explicit ChannelReader(Channel::Listener* listener);
+  virtual ~ChannelReader();
+
+  void set_listener(Channel::Listener* listener) { listener_ = listener; }
+
+  // Call to process messages received from the IPC connection and dispatch
+  // them. Returns false on channel error. True indicates that everything
+  // succeeded, although there may not have been any messages processed.
+  bool ProcessIncomingMessages();
+
+  // Handles asynchronously read data.
+  //
+  // Optionally call this after returning READ_PENDING from ReadData to
+  // indicate that buffer was filled with the given number of bytes of
+  // data. See ReadData for more.
+  bool AsyncReadComplete(int bytes_read);
+
+  // Returns true if the given message is the "hello" message sent on channel
+  // set-up.
+  bool IsHelloMessage(const Message& m) const;
+
+ protected:
+  enum ReadState { READ_SUCCEEDED, READ_FAILED, READ_PENDING };
+
+  Channel::Listener* listener() const { return listener_; }
+
+  // Populates the given buffer with data from the pipe.
+  //
+  // Returns the state of the read. On READ_SUCCESS, the number of bytes
+  // read will be placed into |*bytes_read| (which can be less than the
+  // buffer size). On READ_FAILED, the channel will be closed.
+  //
+  // If the return value is READ_PENDING, it means that there was no data
+  // ready for reading. The implementation is then responsible for either
+  // calling AsyncReadComplete with the number of bytes read into the
+  // buffer, or ProcessIncomingMessages to try the read again (depending
+  // on whether the platform's async I/O is "try again" or "write
+  // asynchronously into your buffer").
+  virtual ReadState ReadData(char* buffer, int buffer_len, int* bytes_read) = 0;
+
+  // Loads the required file desciptors into the given message. Returns true
+  // on success. False means a fatal channel error.
+  //
+  // This will read from the input_fds_ and read more handles from the FD
+  // pipe if necessary.
+  virtual bool WillDispatchInputMessage(Message* msg) = 0;
+
+  // Performs post-dispatch checks. Called when all input buffers are empty,
+  // though there could be more data ready to be read from the OS.
+  virtual bool DidEmptyInputBuffers() = 0;
+
+  // Handles the first message sent over the pipe which contains setup info.
+  virtual void HandleHelloMessage(const Message& msg) = 0;
+
+ private:
+  // Takes the given data received from the IPC channel and dispatches any
+  // fully completed messages.
+  //
+  // Returns true on success. False means channel error.
+  bool DispatchInputData(const char* input_data, int input_data_len);
+
+  Channel::Listener* listener_;
+
+  // We read from the pipe into this buffer. Managed by DispatchInputData, do
+  // not access directly outside that function.
+  char input_buf_[Channel::kReadBufferSize];
+
+  // Large messages that span multiple pipe buffers, get built-up using
+  // this buffer.
+  std::string input_overflow_buf_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChannelReader);
+};
+
+}  // namespace internal
+}  // namespace IPC
+
+#endif  // IPC_IPC_CHANNEL_READER_H_