WP7应用开发笔记(5) 通信设计

WP7支持的通信方式

1. HTTP协议

主要是由WebClient或HttpWebRequest两个类提供，直接封装HTTP协议访问Web站点。最常用的通信方式。

2. WCF

WCF作为MS大力推广的通信方案非常强大，但是到了WP7上就变成了太监，只支持简单的BasicHttpBinding而且还有非常多的限制。

3 Socket

7.1SDK里新增的通信方式，支持TCP和UDP但只能使用异步的SocketAsyncEventArgs事件方式，也有不少限制。

 

选择通信方式

因为同时需要考虑到服务器端的实现，在服务器端尽量精简，最好不要有什么IIS之类大型依赖。

对应是服务器端实现方式如下：

HTTP协议	HttpListener
WCF	Wcf应用程序宿主
Socket	Socket

由于我使用的是Win7 HttpListener和BasicHttpBinding在监听外网IP时都需要管理员身份验证，这点很不友好，我每次开程序都提示一下，不爽。所以决定使用Socket。

 

SOCKET协议选择

而Socket分为TCP和UDP，为了稳定选择了有重传功能和回复的TCP（其实UDP也不是什么问题）。

TCP需要3次握手来维持链接，但是按照“偶尔连接”(Occasionally Connect)的设计准则，我不能让手机一直保持连接，而且断线检查也是个麻烦事。

所以决定采用HTTP1.0类似的短链接方式，就是连上、发一条消息、然后断开的流程（暂时没有回复）

 

 

应用层消息报文设计

这个程序比较简单设计的报文也很简单，

因为内网传输不需要考虑身份验证，加密、完整性等，而且短链接不会遇到粘包和拆包之类的，真是太轻松了。

报文结构如下

Length	长度	4字节 int
Action	动作	32字节 UTF8编码
Context	内容	长度由Length描述 UTF8编码

 

Length表示Context的长度，报文本身长度为Length+4+32

Action目前只有”TAP”按键 一种

Context表示按键的类型 有2种分类

• 一种是  Keyboard 直接对应键盘的键名称
• 另一种是 Media 媒体控制用 包括TogglePlayPause（播放暂停）、Forward（前进）、Backward（后退）IncreaseVolume（提高音量）等

表示方式是“Media.TogglePlayPause”

 Media 协议表

namespace VirtualKeyboard.Contract
{
    public static class KeyMethods
    {
        public const string KeyboardPackage = "Keyboard";
        public const string MediaPackage = "Media";

        public static class Keyboard
        {
            private const string KeyboardPre = KeyboardPackage + ".";

            /// <summary>
            /// Enter
            /// </summary>
            public const string Enter = KeyboardPre + "Enter";

            /// <summary>
            /// Esc
            /// </summary>
            public const string Esc = KeyboardPre + "Esc";
        }

        public static class Media
        {
            private const string MediaPre = MediaPackage + ".";

            /// <summary>
            ///  切换播放暂停
            /// </summary>
            public const string TogglePlayPause = MediaPre + "TogglePlayPause";

            /// <summary>
            /// 快进
            /// </summary>
            public const string FastForward = MediaPre + "FastForward";

            /// <summary>
            /// 快退
            /// </summary>
            public const string FastBackward = MediaPre + "FastBackward";

            /// <summary>
            /// 大步快进
            /// </summary>
            public const string VeryFastForward = MediaPre + "VeryFastForward";

            /// <summary>
            /// 大步快退
            /// </summary>
            public const string VeryFastBackward = MediaPre + "VeryFastBackward";

            /// <summary>
            /// 前进
            /// </summary>
            public const string Forward = MediaPre + "Forward";

            /// <summary>
            /// 前退
            /// </summary>
            public const string Backward = MediaPre + "Backward";

            /// <summary>
            /// 提高音量
            /// </summary>
            public const string IncreaseVolume = MediaPre + "IncreaseVolume";

            /// <summary>
            /// 降低音量
            /// </summary>
            public const string DecreaseVolume = MediaPre + "DecreaseVolume";

            /// <summary>
            /// 静音
            /// </summary>
            public const string MuteVolume = MediaPre + "MuteVolume";

            /// <summary>
            /// 上一集
            /// </summary>
            public const string PreviousTrack = MediaPre + "PreviousTrack";

            /// <summary>
            /// 下一集
            /// </summary>
            public const string NextTrack = MediaPre + "NextTrack ";

            /// <summary>
            /// 停止
            /// </summary>
            public const string Stop = MediaPre + "Stop";

            /// <summary>
            /// 全屏
            /// </summary>
            public const string FullScreen = MediaPre + "FullScreen";
        }
    }
}

 

客户端通信代码实现

 public class SendCommandCompletedEventArgs : EventArgs
    {
        public bool Success { get; internal set; }
        public string ErrMessage { get; internal set; }
    }

    public class Client
    {
        const int ActionSize = 32;
        const int BufferSize = 1024;

        public event EventHandler<SendCommandCompletedEventArgs> SendCommandCompleted;

        private void OnSendCommandCompleted(SendCommandCompletedEventArgs e)
        {
            EventHandler<SendCommandCompletedEventArgs> handler = SendCommandCompleted;
            if (handler != null) handler(this, e);
        }

        public Client()
        {

        }

        public void SendCommandAsync(EndPoint endPoint, string action, string command)
        {
            var actionBuffer = Encoding.UTF8.GetBytes(action);
            var contextBuffer = Encoding.UTF8.GetBytes(command);

            var bufferSize = contextBuffer.Length + ActionSize + 4;
            var lengthBuffer = BitConverter.GetBytes(contextBuffer.Length);

            var buffer = new byte[BufferSize];
            int offset = 0;
            Array.Copy(lengthBuffer, 0, buffer, offset, lengthBuffer.Length);
            offset += 4;
            Array.Clear(buffer, offset, ActionSize);
            Array.Copy(actionBuffer, 0, buffer, offset, actionBuffer.Length);
            offset += ActionSize;
            Array.Copy(contextBuffer, 0, buffer, offset, contextBuffer.Length);

            var socketAsyncEventArgs = new SocketAsyncEventArgs
                                           {
                                               UserToken =
                                                   new Socket(AddressFamily.InterNetwork, SocketType.Stream,
                                                              ProtocolType.Tcp)
                                           };
            socketAsyncEventArgs.Completed += AsyncCompleted;
            socketAsyncEventArgs.SetBuffer(buffer, 0, bufferSize);
            socketAsyncEventArgs.RemoteEndPoint = endPoint;
            ProcessConnect(socketAsyncEventArgs);
        }

        #region Private
        private void ProcessConnect(SocketAsyncEventArgs e)
        {
            var socket = (Socket)e.UserToken;
            bool willRaiseEvent = socket.ConnectAsync(e);
            if (!willRaiseEvent)
            {
                ConnectCompleted(e);
            }
        }

        private void ProcessSend(SocketAsyncEventArgs e)
        {
            var socket = (Socket)e.UserToken;
            bool willRaiseEvent = socket.SendAsync(e);
            if (!willRaiseEvent)
            {
                SendCompleted(e);
            }
        }

        private void AsyncCompleted(object sender, SocketAsyncEventArgs e)
        {
            switch (e.LastOperation)
            {
                case SocketAsyncOperation.Connect:
                    ConnectCompleted(e);
                    break;
                case SocketAsyncOperation.Send:
                    SendCompleted(e);
                    break;
                case SocketAsyncOperation.Receive:
                    ReceiveCompleted(e);
                    break;
                default:
                    return;
            }

        }

        private void ReceiveCompleted(SocketAsyncEventArgs e)
        {
        }
        private void ConnectCompleted(SocketAsyncEventArgs e)
        {
            if (e.SocketError == SocketError.Success)
            {
                ProcessSend(e);
            }
            else
            {
                OnSendCommandCompleted(new SendCommandCompletedEventArgs { Success = false, ErrMessage = "接收器无法连接" });
            }
        }

        private void SendCompleted(SocketAsyncEventArgs e)
        {
            var socket = (Socket)e.UserToken;
            socket.Close();
            if (e.SocketError == SocketError.Success)
            {
                OnSendCommandCompleted(new SendCommandCompletedEventArgs { Success = true });
            }
            else
            {
                OnSendCommandCompleted(new SendCommandCompletedEventArgs { Success = false, ErrMessage = "发送命令失败" });
            }

        }
        #endregion

    }