c# - 如何在客户端检测关闭的 StreamSocket

Question

DataReader.LoadAsync 不检测关闭的套接字(使用 InputStreamOptions::Partial)

我正在通过 TCP 连接向服务器发送数据并读取响应，但之后一切正常。但是在 5-6 条消息之后，我的项目已经完成，我没有发现错误在哪里。

有时我发现通过主机关闭了连接所以我怎么知道StreamSocket是否已连接

============代码=============

public async Task<bool> Connect(string host, string port)
        {
            try
            {
                socket = new StreamSocket();
                HostName hostName = new HostName(host);
                CancellationTokenSource _cts = new CancellationTokenSource();
                _cts.CancelAfter(5000);

                // Connect to the server
                await socket.ConnectAsync(hostName, port).AsTask(_cts.Token);
                return true;
            }
            catch (Exception ex)
            {
                throw ex;
            }


        }


      public async Task<String> SendMessageToServer(string message)
            {
                try
                {
                    // Create the data writer object backed by the in-memory stream. 
                    using (writer = new DataWriter(socket.OutputStream))
                    {
                        writer.WriteString(message);
                        await writer.StoreAsync();
                        await writer.FlushAsync();
                        writer.DetachStream();
                        return await ReadResponse();
                    }
                }
                catch (Exception ex)
                {

                    throw ex;
                }

            }
            private async Task<String> ReadResponse()
            {
                DataReader reader;
                StringBuilder strBuilder = new StringBuilder();
                try
                {
                    using (reader = new DataReader(socket.InputStream))
                    {
                        uint ReadBufferLength = 1024;
                        // If task cancellation was requested, comply
                        //cancellationToken.ThrowIfCancellationRequested();
                        // Set InputStreamOptions to complete the asynchronous reask(cancellationToken);
                        reader.InputStreamOptions = Windows.Storage.Streams.InputStreamOptions.Partial;

                        IAsyncOperation<uint> taskLoad = reader.LoadAsync(ReadBufferLength);
                        taskLoad.AsTask().Wait(2000);

                        string msg = string.Empty;
                        while (reader.UnconsumedBufferLength > 0)
                        {
                            strBuilder.Append(reader.ReadString(reader.UnconsumedBufferLength));
                            msg = strBuilder.ToString();
                        }

                        reader.DetachStream();
                        reader.Dispose();

                    }
                }
                catch (Exception ex)
                {

                    return "0";
                    throw ex;

                }
                finally
                {
                    // Cleanup once complete


                }
                return strBuilder.ToString();
            }

Answer 1

How can i found that is StreamSocket is connected or not

我在我这边测试了你的代码。如您所知，DataReader/DataWriter 本身并不关心“连接”。但是关闭的连接将通过方法 Task.Wait 检测到，用于同步等待任务完成或抛出异常。因此，在您的场景中，如果 StreamSocked 在 DataReader.LoadAsync 之前关闭, taskLoad.AsTask().Wait(2000); 将抛出异常:

One or more errors occurred. (An existing connection was forcibly closed by the remote host. )

如果套接字连接在DataReader.LoadAsync 处理期间关闭，此时客户端无法检测到关闭，它将在客户端下次向服务器发送消息时检测到连接关闭。在您的场景中，客户端将继续向服务器发送消息，服务器在发送新消息时将始终捕获连接关闭。如果服务器关闭连接，您将在 await writer.StoreAsync(); 代码行收到连接关闭异常。

But after 5-6 message my project is hand I didn't find where is error

您可能已经捕获了有关连接关闭的异常。所以这可能是由其他一些原因导致的。我在你的代码片段中看到 DataReader 只加载一次长度为 1024 的消息。所以如果从服务器发送的消息长度超过 1024，客户端将只收到部分消息，下次服务器发送时新消息，客户端仍然会收到上次的剩余消息，而不是新消息。几次后服务器将返回记录许多数据并可能导致问题。我建议您按如下方式更新 reader.LoadAsync 代码:

  string msg = string.Empty;  
  var loadsize = await reader.LoadAsync(ReadBufferLength);
  while (loadsize >= ReadBufferLength)
  {
      loadsize = await reader.LoadAsync(ReadBufferLength);
  }
  if (reader.UnconsumedBufferLength > 0)
  {
      strBuilder.Append(reader.ReadString(reader.UnconsumedBufferLength));
  }

此外，我强烈建议您使用 StreamReader相反，它不会像 DataReader 那样受到关注，而您的 ReadResponse() 方法可以简单如下:

private async Task<String> ReadResponse()
{
    Stream streamIn = socket.InputStream.AsStreamForRead();
    StreamReader reader2 = new StreamReader(streamIn);
    string response = await reader2.ReadLineAsync();
    return response; 
} 

关于 uwp 中 StreamSocket 的更多细节请引用 official sample .