解释 C# TcpClient/TcpListener 在 Net Core 上的怪异行为

Question

我运行在 Windows 10 上使用 NetCore，我有两个程序 - 服务器和客户端，我都在本地运行使用。

执行顺序如下：

运行服务器 - 有一个处理客户端的循环
运行客户端 - 客户端执行其工作并且进程终止
运行第二次客户

此序列使用以下代码从服务器生成以下输出：

Waiting for client.
Reading message.
Incoming message: This message is longer than what
Sending message.
Closing connection.
Waiting for client.
Reading message.
Incoming message: This message is longer than what
Sending message.
Closing connection.
Waiting for client.

以及客户端的以下输出：

Connecting to server.
Sending message.
Reading message.
Incoming message: Thank you!


Connecting to server.
Sending message.
Reading message.

Unhandled Exception: System.AggregateException: One or more errors occurred. (Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.) ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host

换句话说 - 运行客户端的第二次尝试以异常结束。那是奇怪的部分。

这是我用于重现问题的最小代码示例。

服务器代码：

public static async Task StartServerAsync()
{
  TcpListener listener = new TcpListener(IPAddress.Any, 1234);
  listener.Server.NoDelay = true;
  listener.Server.LingerState = new LingerOption(true, 0);
  listener.Start();

  while (true)
  {
    Console.WriteLine("Waiting for client.");
    using (TcpClient client = await listener.AcceptTcpClientAsync())
    {
      client.NoDelay = true;
      client.LingerState = new LingerOption(true, 0);

      Console.WriteLine("Reading message.");
      using (NetworkStream stream = client.GetStream())
      {
        byte[] buffer = new byte[32];
        int len = await stream.ReadAsync(buffer, 0, buffer.Length);
        string incomingMessage = Encoding.UTF8.GetString(buffer, 0, len);
        Console.WriteLine("Incoming message: {0}", incomingMessage);


        Console.WriteLine("Sending message.");
        byte[] message = Encoding.UTF8.GetBytes("Thank you!");
        await stream.WriteAsync(message, 0, message.Length);
        Console.WriteLine("Closing connection.");
      }
    }
  }
}

客户代码：

public static async Task StartClientAsync()
{
  using (TcpClient client = new TcpClient())
  {
    client.NoDelay = true;
    client.LingerState = new LingerOption(true, 0);

    Console.WriteLine("Connecting to server.");
    await client.ConnectAsync("127.0.0.1", 1234);

    Console.WriteLine("Sending message.");
    using (NetworkStream stream = client.GetStream())
    {
      byte[] buffer = Encoding.UTF8.GetBytes("This message is longer than what the server is willing to read.");
      await stream.WriteAsync(buffer, 0, buffer.Length);

      Console.WriteLine("Reading message.");
      int len = await stream.ReadAsync(buffer, 0, buffer.Length);
      string message = Encoding.UTF8.GetString(buffer, 0, len);

      Console.WriteLine("Incoming message: {0}", message);
    }
  }
}

奇怪的是，如果我们将客户端的消息从

"This message is longer than what the server is willing to read."

至

"This message is short."

客户端的两个实例在没有崩溃的情况下完成并产生相同的输出。

请注意，如果我省略了设置 LingerState 的所有三行，则没有任何区别。如果我将 LingerState 设置为

，行为也没有区别

new LingerState(true, 5)

如果我将NoDelay 设置为false 也没有区别。换句话说，在任一侧为 LingerState 和 NoDelay 设置任何值似乎对崩溃没有任何影响。防止崩溃的唯一方法是在服务器端从客户端读取整个输入。

这很奇怪，我想知道是否有人可以解释一下。我不确定它是否也适用于 .NET Framework，仅在 NetCore 1.0.0 和 Windows 10.

上进行了测试

Answer 1

我已经获取了您的代码片段并创建了一个实际的可运行文件 demo solution 仍处于未答复状态。

只需稍作改动即可获得预期的行为。在您的服务器端代码中，您需要确保实际读取整个字符串。调整以下行：

byte[] buffer = new byte[32];
int len = await stream.ReadAsync(buffer, 0, buffer.Length);
string incomingMessage = Encoding.UTF8.GetString(buffer, 0, len);
Console.WriteLine("Incoming message: {0}", incomingMessage);

与：

StringBuilder sb = new StringBuilder();
byte[] buffer = new byte[32];
int len;
do
{
    len = await stream.ReadAsync(buffer, 0, buffer.Length);
    sb.Append(Encoding.UTF8.GetString(buffer, 0, len));
} while (len == buffer.Length);
Console.WriteLine("Incoming message: {0}", sb.ToString());

看看 the demo solution 的历史，你会发现所有的变化都是最小的。

Answer 2

.NET Core 团队终于在 GitHub 上回答了这个问题。

长答案 - 请参阅 https://github.com/dotnet/corefx/issues/13114

的最后一条评论

简答 -

The behavior is expected, and is by-design.

解释 C# TcpClient/TcpListener 在 Net Core 上的怪异行为

Explain weird behavior of C# TcpClient/TcpListener on NetCore

c#

.net

tcpclient

.net-core

tcplistener