Windows 8 Metro 关于StreamSocket MSDN示例阅读
话题开始前首先鄙视下自己，博客园5年从未发过任何博文。理由很多不泛于没足够的能力、没足够的信心、没时间、没精力等等。
终于在失业且方向迷惘中写下第一篇博文。
文章能力有限，还望看客您多多指点。
废话到此进入正题。
8月15日我装上了WIN8正式版（订阅版），VS2012（订阅版）旗舰版，Blend + SketchFlow Preview for Visual Studio 2012。开始尝试Windows 8 Metro APP 的开发。一开始需要注册开发者授权按步骤走下去就是。
由于之前开发的Silverlight客户端连接服务器使用的是异步SOCKET连接（这个在园子里搜索下便有）。而 Metro应用与Silverlight的基本控件以及开发方式几乎一样，便有了把Silverlight的客户端移植到Metro应用中的想法。
我是个比较直接的人，第一个想到的就是连接通信的问题。看了微软的MSDN关于Windows 8 Metro的几种网络连接方式，我针对的看了 StreamWebSocket 以及StreamSocket。 我翻查了微软的MSDN 关于Windows 8 Metro StreamSocket （基本是英文的中文资料甚少，个人觉得自己英文很烂），下载到了关于StreamSocket 的示例 下载地址 。里面的代码具体讲述了 如何创建一个StreamSocket连接的服务器监听 如何利用StreamSocket 连接上服务器 如何发送消息 接收显示消息。一切看上去都是这么的全面。经过详细的阅读代码，我发现Windows 8 Metro StreamSocket 的发送接收都与之前的异步连接方式有相当大的区别。示例内用到了await/async 关键字（关于这个已经有很多博文解释了），对于两个关键字的理解是必要的。
现在让我们来解读下示例内的代码：（忽略App.xaml代码）
Scenario1.xaml.cs 情景1
这个情景片段（是这样翻译吧？英文太烂）的主要代码：
点击按钮开始创建一个服务器监听。
1 /// <summary> 2 /// This is the click handler for the 'StartListener' button. 3 /// </summary> 4 /// <param name="sender">Object for which the event was generated.</param> 5 /// <param name="e">Event's parameters.</param> 6 private async void StartListener_Click(object sender, RoutedEventArgs e) 7 { 8 // Overriding the listener here is safe as it will be deleted once all references to it are gone. However, in many cases this 9 // is a dangerous pattern to override data semi-randomly (each time user clicked the button) so we block it here. 10 if (CoreApplication.Properties.ContainsKey("listener")) 11 { 12 rootPage.NotifyUser("This step has already been executed. Please move to the next one.", NotifyType.ErrorMessage); 13 return; 14 } 15 16 if (String.IsNullOrEmpty(ServiceNameForListener.Text)) 17 { 18 rootPage.NotifyUser("Please provide a service name.", NotifyType.ErrorMessage); 19 return; 20 } 21 22 StreamSocketListener listener = new StreamSocketListener(); 23 listener.ConnectionReceived += OnConnection; 24 25 // Save the socket, so subsequent steps can use it. 26 CoreApplication.Properties.Add("listener", listener); 27 28 // Start listen operation. 29 try 30 { 31 await listener.BindServiceNameAsync(ServiceNameForListener.Text); 32 rootPage.NotifyUser("Listening", NotifyType.StatusMessage); 33 } 34 catch (Exception exception) 35 { 36 CoreApplication.Properties.Remove("listener"); 37 38 // If this is an unknown status it means that the error is fatal and retry will likely fail. 39 if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown) 40 { 41 throw; 42 } 43 44 rootPage.NotifyUser("Start listening failed with error: " + exception.Message, NotifyType.ErrorMessage); 45 } 46 }
我们可以看到 StreamSocketListener 创建监听是一件相当容易的事情。
其中代码 await listener.BindServiceNameAsync(ServiceNameForListener.Text);
listener.BindServiceNameAsync（端口号）为异步开启某端口监听代码。
listener.ConnectionReceived += OnConnection; 这个就类似于我们曾经写的异步SOCKET 数据过来时触发的委托事件。
OnConnection 代码：
1 /// <summary> 2 /// Invoked once a connection is accepted by StreamSocketListener. 3 /// </summary> 4 /// <param name="sender">The listener that accepted the connection.</param> 5 /// <param name="args">Parameters associated with the accepted connection.</param> 6 private async void OnConnection(StreamSocketListener sender, StreamSocketListenerConnectionReceivedEventArgs args) 7 { 8 DataReader reader = new DataReader(args.Socket.InputStream); 9 try 10 { 11 while (true) 12 { 13 // Read first 4 bytes (length of the subsequent string). 14 uint sizeFieldCount = await reader.LoadAsync(sizeof(uint)); 15 if (sizeFieldCount != sizeof(uint)) 16 { 17 // The underlying socket was closed before we were able to read the whole data. 18 return; 19 } 20 21 // Read the string. 22 uint stringLength = reader.ReadUInt32(); 23 uint actualStringLength = await reader.LoadAsync(stringLength); 24 if (stringLength != actualStringLength) 25 { 26 // The underlying socket was closed before we were able to read the whole data. 27 return; 28 } 29 30 // Display the string on the screen. The event is invoked on a non-UI thread, so we need to marshal the text back to the UI thread. 31 NotifyUserFromAsyncThread(String.Format("Receive data: \"{0}\"", reader.ReadString(actualStringLength)), NotifyType.StatusMessage); 32 } 33 } 34 catch (Exception exception) 35 { 36 // If this is an unknown status it means that the error is fatal and retry will likely fail. 37 if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown) 38 { 39 throw; 40 } 41 42 NotifyUserFromAsyncThread("Read stream failed with error: " + exception.Message, NotifyType.ErrorMessage); 43 } 44 }
在 OnConnection 内我们不难发现 StreamSocket 读取数据的方式：DataReader reader = new DataReader(args.Socket.InputStream);
StreamSocket读取数据依靠的是 DataReader 。在Windows 8 Metro APP 内有许多 InputStream 输入流格式的相关操作。
DataReader 是一个相当好的读取器。
代码：
uint stringLength = reader.ReadUInt32();
uint actualStringLength = await reader.LoadAsync(stringLength);
if (stringLength != actualStringLength)
{
// The underlying socket was closed before we were able to read the whole data.
return;
}
上面的一段代码意义为：读取 InputStream 内预先写好的长度reader.ReadUInt32();（注意非真实数据长度，发送数据时会讲到）
然后根据预先写好的长度异步读取实际数据 await reader.LoadAsync(stringLength);
其中reader.LoadAsync 返回的是DataReaderLoadOperation类继承了IAsyncOperation<uint> 。隐式转换为UINT类型。
if (stringLength != actualStringLength) 即为验证预先写好的数据长度与实际接收的数据长度是否一致。
如果不一致有可能是发送端过早关闭SOCKET，使数据不完整接收，不可用。
接下来代码：
NotifyUserFromAsyncThread(String.Format("Receive data: \"{0}\"", reader.ReadString(actualStringLength)), NotifyType.StatusMessage);
reader.ReadString(actualStringLength)通知输出reader读取到的数据。OK到这里StreamSocket的监听以及数据接收讲解完毕。
接下来我们看到Scenario2.xaml.cs 情景2 的代码：
1 private async void ConnectSocket_Click(object sender, RoutedEventArgs e) 2 { 3 if (CoreApplication.Properties.ContainsKey("clientSocket")) 4 { 5 rootPage.NotifyUser("This step has already been executed. Please move to the next one.", NotifyType.ErrorMessage); 6 return; 7 } 8 9 if (String.IsNullOrEmpty(ServiceNameForConnect.Text)) 10 { 11 rootPage.NotifyUser("Please provide a service name.", NotifyType.ErrorMessage); 12 return; 13 } 14 15 // By default 'HostNameForConnect' is disabled and host name validation is not required. When enabling the text 16 // box validating the host name is required since it was received from an untrusted source (user input). 17 // The host name is validated by catching ArgumentExceptions thrown by the HostName constructor for invalid 18 // input. 19 // Note that when enabling the text box users may provide names for hosts on the intErnet that require the 20 // "Internet (Client)" capability. 21 HostName hostName; 22 try 23 { 24 hostName = new HostName(HostNameForConnect.Text); 25 } 26 catch (ArgumentException) 27 { 28 rootPage.NotifyUser("Error: Invalid host name.", NotifyType.ErrorMessage); 29 return; 30 } 31 32 StreamSocket socket = new StreamSocket(); 33 34 // Save the socket, so subsequent steps can use it. 35 CoreApplication.Properties.Add("clientSocket", socket); 36 37 rootPage.NotifyUser("Connecting to: " + HostNameForConnect.Text, NotifyType.StatusMessage); 38 39 try 40 { 41 // Connect to the server (in our case the listener we created in previous step). 42 await socket.ConnectAsync(hostName, ServiceNameForConnect.Text); 43 44 rootPage.NotifyUser("Connected", NotifyType.StatusMessage); 45 46 // Mark the socket as connected. Set the value to null, as we care only about the fact that the property is set. 47 CoreApplication.Properties.Add("connected", null); 48 } 49 catch (Exception exception) 50 { 51 // If this is an unknown status it means that the error is fatal and retry will likely fail. 52 if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown) 53 { 54 throw; 55 } 56 57 rootPage.NotifyUser("Connect failed with error: " + exception.Message, NotifyType.ErrorMessage); 58 } 59 }
嗯。Scenario2就这点代码。这个片段介绍的是如何利用StreamSocket 创建一个连接 连到正在监听的服务器。
首先接收一个IP或者是计算机网络名称用于创建一个HostName类。这里的HostName有点类似于曾经的Socket连接需要 用到IPEndPoint的IPAddress类。
然后是声明一个StreamSocket 实例 。
代码：await socket.ConnectAsync(hostName, ServiceNameForConnect.Text); 异步连接服务器，hostName 为上面的HostName类，ServiceNameForConnect.Text为接收一个端口号。
可以这样写 socket.ConnectAsync（new HostName("127.0.0.1"), "4518"）
到这里 连接的部分也完成了。
接下来就是发数据。我们看到Scenario3.xaml.cs 情景3的代码：
private async void SendHello_Click(object sender, RoutedEventArgs e)
{
if (!CoreApplication.Properties.ContainsKey("connected"))
{
rootPage.NotifyUser("Please run previous steps before doing this one.", NotifyType.ErrorMessage);
return;
}
object outValue;
StreamSocket socket;
if (!CoreApplication.Properties.TryGetValue("clientSocket", out outValue))
{
rootPage.NotifyUser("Please run previous steps before doing this one.", NotifyType.ErrorMessage);
return;
}
socket = (StreamSocket)outValue;
// Create a DataWriter if we did not create one yet. Otherwise use one that is already cached.
DataWriter writer;
if (!CoreApplication.Properties.TryGetValue("clientDataWriter", out outValue))
{
writer = new DataWriter(socket.OutputStream);
CoreApplication.Properties.Add("clientDataWriter", writer);
}
else
{
writer = (DataWriter)outValue;
}
// Write first the length of the string as UINT32 value followed up by the string. Writing data to the writer will just store data in memory.
string stringToSend = "Hello";
writer.WriteUInt32(writer.MeasureString(stringToSend));
writer.WriteString(stringToSend);
// Write the locally buffered data to the network.
try
{
await writer.StoreAsync();
SendOutput.Text = "\"" + stringToSend + "\" sent successfully.";
}
catch (Exception exception)
{
// If this is an unknown status it means that the error if fatal and retry will likely fail.
if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown)
{
throw;
}
rootPage.NotifyUser("Send failed with error: " + exception.Message, NotifyType.ErrorMessage);
}
}
嗯。这个发数据就这点代码。
首先我们看到的是如何获取之前连接好的StreamSocket 实例。
代码：
object outValue;
StreamSocket socket;
if (!CoreApplication.Properties.TryGetValue("clientSocket", out outValue))
{
rootPage.NotifyUser("Please run previous steps before doing this one.", NotifyType.ErrorMessage);
return;
}
socket = (StreamSocket)outValue;
这里我们不讨论CoreApplication相关的东西。我们只需要知道通过这个我们获取到了前面连接上的StreamSocket 实例。
在前面我们看到 Metro应用内 读取InputStream 的DataReader ，现在我们要声明一个DataWriter。
代码：
DataWriter writer;
if (!CoreApplication.Properties.TryGetValue("clientDataWriter", out outValue))
{
writer = new DataWriter(socket.OutputStream);
CoreApplication.Properties.Add("clientDataWriter", writer);
}
else
{
writer = (DataWriter)outValue;
}
好吧。暂且我们把 CoreApplication当成一个缓存工具。
代码大概的意思是 尝试从缓存中取到DataWriter实例，如果没有就创建一个。
我们看到在创建一个DataWriter时将StreamSocket 的 OutputStream 作为参数传入。
传入OutputStream 在于将DataWriter与建立好连接的StreamSocket进行绑定关联。
然后我们开始制造数据 代码：
string stringToSend = "Hello";
writer.WriteUInt32(writer.MeasureString(stringToSend));
writer.WriteString(stringToSend);
这里我们需要发送的数据是"Hello"。
writer.WriteUInt32(writer.MeasureString(stringToSend));便是我们前面的 情景1 读取数据时需要用到 预先写好的数据长度。
writer.MeasureString()返回的是要发送数据的字符串长度，writer.WriteUInt32()将字符串长度写入到输出流。
然后writer.WriteString(stringToSend);是将字符串写入输出流。
到这里我们不难发现StreamSocket 利用DataReader DataWriter 读取和写入数据的同时帮助我们制造数据包格式。
如果您是原异步Socket的使用经验者，应该会考虑到数据包格式定义的问题。
比如 数据包 包头+数据包长度+（数据包类型+数据包命令+数据包内容）+包尾 类似的设计。
数据包设计必然会出现的数据包长度，在StreamSocket 的读取写入 已是单独实现，不需要再到数据包里面找了。
接下来是异步发送数据：
await writer.StoreAsync();
这个异步方法的注解为：将缓冲区的数据提交到备份存储区。
这个注解我本人比较笨理解不过来，大概是说将数据流数据放入发送的SOCKET BUFFER内 等待计算机网络空闲时才把数据发送出去。（这个理解为个人理解，希望有高人指点）
到此我们的发送情景也就完结了。
Scenario4.xam.cs 情景4 为一系列移除CoreApplication 以及释放StreamSocket StreamSocketListener DataWriter 。DataWriter的释放比较有意思，代码贴上具体就不再解读了：
CloseSockets
1 private void CloseSockets_Click(object sender, RoutedEventArgs e) 2 { 3 object outValue; 4 if (CoreApplication.Properties.TryGetValue("clientDataWriter", out outValue)) 5 { 6 // Remove the data writer from the list of application properties as we are about to close it. 7 CoreApplication.Properties.Remove("clientDataWriter"); 8 DataWriter dataWriter = (DataWriter)outValue; 9 10 // To reuse the socket with other data writer, application has to detach the stream from the writer 11 // before disposing it. This is added for completeness, as this sample closes the socket in 12 // very next block. 13 dataWriter.DetachStream(); 14 dataWriter.Dispose(); 15 } 16 17 if (CoreApplication.Properties.TryGetValue("clientSocket", out outValue)) 18 { 19 // Remove the socket from the list of application properties as we are about to close it. 20 CoreApplication.Properties.Remove("clientSocket"); 21 StreamSocket socket = (StreamSocket)outValue; 22 socket.Dispose(); 23 } 24 25 if (CoreApplication.Properties.TryGetValue("listener", out outValue)) 26 { 27 // Remove the listener from the list of application properties as we are about to close it. 28 CoreApplication.Properties.Remove("listener"); 29 StreamSocketListener listener = (StreamSocketListener)outValue; 30 listener.Dispose(); 31 } 32 33 if (CoreApplication.Properties.ContainsKey("connected")) 34 { 35 CoreApplication.Properties.Remove("connected"); 36 } 37 38 rootPage.NotifyUser("Socket and listener closed", NotifyType.StatusMessage); 39 }
以上为鄙人解读的 MSDN内关于StreamSocket示例代码。
解读完后问题才刚刚开始，在原有的异步Socket连接方式与现在WIN8 Metro App 的StreamSocket 如何通信呢？
StreamSocket在原有的数据包格式如何读取到数据？（没有DataWriter.WriteUInt32()，DataReader.ReadUInt32();）
WIN8 Metro App 如何像之前的Silverlight一样与服务器进行异步收发数据（问答数据）？
嗯。现在已是凌晨5点，这几个问题的解答与实验将会在下一章博文里出现。当然如果有人写了，鄙人就不再重复了。
解答的下一篇连接 《Windows 8 Metro 关于StreamSocket与原异步Socket》
国际惯例如果您看得起鄙人，转载请注明出处谢谢。
