root/remoting/host/native_messaging/native_messaging_reader.cc

DEFINITIONS

1. read_task_runner_
2. ReadMessage
3. NotifyEof
4. weak_factory_
5. Start
6. InvokeMessageCallback
7. InvokeEofCallback

// Copyright 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 "remoting/host/native_messaging/native_messaging_reader.h"

#include <string>

#include "base/bind.h"
#include "base/json/json_reader.h"
#include "base/location.h"
#include "base/sequenced_task_runner.h"
#include "base/single_thread_task_runner.h"
#include "base/stl_util.h"
#include "base/thread_task_runner_handle.h"
#include "base/threading/sequenced_worker_pool.h"
#include "base/values.h"
#include "net/base/file_stream.h"

namespace {

// uint32 is specified in the protocol as the type for the message header.
typedef uint32 MessageLengthType;

const int kMessageHeaderSize = sizeof(MessageLengthType);

// Limit the size of received messages, to avoid excessive memory-allocation in
// this process, and potential overflow issues when casting to a signed 32-bit
// int.
const MessageLengthType kMaximumMessageSize = 1024 * 1024;

}  // namespace

namespace remoting {

class NativeMessagingReader::Core {
 public:
  Core(base::PlatformFile handle,
       scoped_refptr<base::SingleThreadTaskRunner> caller_task_runner,
       scoped_refptr<base::SequencedTaskRunner> read_task_runner,
       base::WeakPtr<NativeMessagingReader> reader_);
  ~Core();

  // Reads a message from the Native Messaging client and passes it to
  // |message_callback_| on the originating thread. Called on the reader thread.
  void ReadMessage();

 private:
  // Notify the reader's EOF callback when an error occurs or EOF is reached.
  void NotifyEof();

  net::FileStream read_stream_;

  base::WeakPtr<NativeMessagingReader> reader_;

  // Used to post the caller-supplied reader callbacks on the caller thread.
  scoped_refptr<base::SingleThreadTaskRunner> caller_task_runner_;

  // Used to DCHECK that the reader code executes on the correct thread.
  scoped_refptr<base::SequencedTaskRunner> read_task_runner_;

  DISALLOW_COPY_AND_ASSIGN(Core);
};

NativeMessagingReader::Core::Core(
    base::PlatformFile handle,
    scoped_refptr<base::SingleThreadTaskRunner> caller_task_runner,
    scoped_refptr<base::SequencedTaskRunner> read_task_runner,
    base::WeakPtr<NativeMessagingReader> reader)
    : read_stream_(handle, base::PLATFORM_FILE_READ, NULL),
      reader_(reader),
      caller_task_runner_(caller_task_runner),
      read_task_runner_(read_task_runner) {
}

NativeMessagingReader::Core::~Core() {}

void NativeMessagingReader::Core::ReadMessage() {
  DCHECK(read_task_runner_->RunsTasksOnCurrentThread());

  // Keep reading messages until the stream is closed or an error occurs.
  while (true) {
    MessageLengthType message_length;
    int read_result = read_stream_.ReadUntilComplete(
        reinterpret_cast<char*>(&message_length), kMessageHeaderSize);
    if (read_result != kMessageHeaderSize) {
      // 0 means EOF which is normal and should not be logged as an error.
      if (read_result != 0) {
        LOG(ERROR) << "Failed to read message header, read returned "
                   << read_result;
      }
      NotifyEof();
      return;
    }

    if (message_length > kMaximumMessageSize) {
      LOG(ERROR) << "Message size too large: " << message_length;
      NotifyEof();
      return;
    }

    std::string message_json(message_length, '\0');
    read_result = read_stream_.ReadUntilComplete(string_as_array(&message_json),
                                                 message_length);
    if (read_result != static_cast<int>(message_length)) {
      LOG(ERROR) << "Failed to read message body, read returned "
                 << read_result;
      NotifyEof();
      return;
    }

    scoped_ptr<base::Value> message(base::JSONReader::Read(message_json));
    if (!message) {
      LOG(ERROR) << "Failed to parse JSON message: " << message;
      NotifyEof();
      return;
    }

    // Notify callback of new message.
    caller_task_runner_->PostTask(
        FROM_HERE, base::Bind(&NativeMessagingReader::InvokeMessageCallback,
                              reader_, base::Passed(&message)));
  }
}

void NativeMessagingReader::Core::NotifyEof() {
  DCHECK(read_task_runner_->RunsTasksOnCurrentThread());
  caller_task_runner_->PostTask(
      FROM_HERE,
      base::Bind(&NativeMessagingReader::InvokeEofCallback, reader_));
}

NativeMessagingReader::NativeMessagingReader(base::PlatformFile handle)
    : reader_thread_("Reader"),
      weak_factory_(this) {
  reader_thread_.Start();
  read_task_runner_ = reader_thread_.message_loop_proxy();
  core_.reset(new Core(handle, base::ThreadTaskRunnerHandle::Get(),
                       read_task_runner_, weak_factory_.GetWeakPtr()));
}

NativeMessagingReader::~NativeMessagingReader() {
  read_task_runner_->DeleteSoon(FROM_HERE, core_.release());
}

void NativeMessagingReader::Start(MessageCallback message_callback,
                                  base::Closure eof_callback) {
  message_callback_ = message_callback;
  eof_callback_ = eof_callback;

  // base::Unretained is safe since |core_| is only deleted via the
  // DeleteSoon task which is posted from this class's dtor.
  read_task_runner_->PostTask(
      FROM_HERE, base::Bind(&NativeMessagingReader::Core::ReadMessage,
                            base::Unretained(core_.get())));
}

void NativeMessagingReader::InvokeMessageCallback(
    scoped_ptr<base::Value> message) {
  message_callback_.Run(message.Pass());
}

void NativeMessagingReader::InvokeEofCallback() {
  eof_callback_.Run();
}

}  // namespace remoting