如何檢查TcpClient連接是否關閉？

Question

我正在玩TcpClient，我試圖弄清楚如何使連接屬性在斷開連接時發生錯誤。

我試着做

NetworkStream ns = client.GetStream(); 
ns.Write(new byte[1], 0, 0); 

但它仍然不會告訴我，如果TcpClient的斷開。你會如何使用TcpClient來解決這個問題？

Answer 1

據我所知/記住，沒有辦法測試套接字是否連接，而不是讀取或寫入它。

我還沒有使用過TcpClient，但是如果遠程端已經正常關閉，Socket類將從調用返回0來讀取。 如果遠端沒有正常關機[我認爲]你會得到一個超時異常，不記得類型抱歉。

使用像'if(socket.Connected) { socket.Write(...) }'這樣的代碼創建競爭條件。你最好只是調用socket.Write並處理異常和/或斷開連接。

Answer 2

試試這個，它爲我工作

private void timer1_Tick(object sender, EventArgs e) 
    { 
     if (client.Client.Poll(0, SelectMode.SelectRead)) 
      { 
       if (!client.Connected) sConnected = false; 
       else 
       { 
        byte[] b = new byte[1]; 
        try 
        { 
         if (client.Client.Receive(b, SocketFlags.Peek) == 0) 
         { 
          // Client disconnected 
          sConnected = false; 
         } 
        } 
        catch { sConnected = false; } 
       } 
      } 
     if (!sConnected) 
     { 
      //--Basically what you want to do afterwards 
      timer1.Stop(); 
      client.Close(); 
      ReConnect(); 
     } 

    } 

我使用定時器，因爲我想在固定時間間隔 檢查連接狀態，並且不能聽代碼的循環[我覺得這是減緩sending-接收過程]

Answer 3

我不會推薦你嘗試寫測試套接字。並且不要在.NET的Connected屬性上傳遞。

如果你想知道，如果遠程端點仍處於活動狀態，您可以使用TcpConnectionInformation：

TcpClient client = new TcpClient(host, port); 

IPGlobalProperties ipProperties = IPGlobalProperties.GetIPGlobalProperties(); 
TcpConnectionInformation[] tcpConnections = ipProperties.GetActiveTcpConnections().Where(x => x.LocalEndPoint.Equals(client.Client.LocalEndPoint) && x.RemoteEndPoint.Equals(client.Client.RemoteEndPoint)).ToArray(); 

if (tcpConnections != null && tcpConnections.Length > 0) 
{ 
    TcpState stateOfConnection = tcpConnections.First().State; 
    if (stateOfConnection == TcpState.Established) 
    { 
     // Connection is OK 
    } 
    else 
    { 
     // No active tcp Connection to hostName:port 
    } 

} 
client.Close(); 

另請參見：
TcpConnectionInformation MSDN上
IPGlobalProperties MSDN上
說明TcpState狀態
Netstat Wikipedia

---

這裏它是作爲TcpClient的擴展方法。

public static TcpState GetState(this TcpClient tcpClient) 
{ 
    var foo = IPGlobalProperties.GetIPGlobalProperties() 
    .GetActiveTcpConnections() 
    .SingleOrDefault(x => x.LocalEndPoint.Equals(tcpClient.Client.LocalEndPoint)); 
    return foo != null ? foo.State : TcpState.Unknown; 
} 

Answer 4

@ uriel的答案對我很好，但我需要用C++/CLI編寫代碼，這並不是完全無關緊要的。這裏是（大致相當的）C++/CLI代碼，並添加了一些健壯性檢查以實現良好的度量。

using namespace System::Net::Sockets; 
using namespace System::Net::NetworkInformation; 

TcpState GetTcpConnectionState(TcpClient^tcpClient) 
{ 
    TcpState tcpState = TcpState::Unknown; 

    if (tcpClient != nullptr) 
    { 
     // Get all active TCP connections 
     IPGlobalProperties^ipProperties = IPGlobalProperties::GetIPGlobalProperties(); 
     array<TcpConnectionInformation^>^tcpConnections = ipProperties->GetActiveTcpConnections(); 

     if ((tcpConnections != nullptr) && (tcpConnections->Length > 0)) 
     { 
      // Get the end points of the TCP connection in question 
      EndPoint^localEndPoint = tcpClient->Client->LocalEndPoint; 
      EndPoint^remoteEndPoint = tcpClient->Client->RemoteEndPoint; 

      // Run through all active TCP connections to locate TCP connection in question 
      for (int i = 0; i < tcpConnections->Length; i++) 
      { 
       if ((tcpConnections[i]->LocalEndPoint->Equals(localEndPoint)) && (tcpConnections[i]->RemoteEndPoint->Equals(remoteEndPoint))) 
       { 
        // Found active TCP connection in question 
        tcpState = tcpConnections[i]->State; 
        break; 
       } 
      } 
     } 
    } 

    return tcpState; 
} 

bool TcpConnected(TcpClient^tcpClient) 
{ 
    bool bTcpConnected = false; 

    if (tcpClient != nullptr) 
    { 
     if (GetTcpConnectionState(tcpClient) == TcpState::Established) 
     { 
      bTcpConnected = true; 
     } 
    } 
    return bTcpConnected; 
} 

希望這會幫助某人。

Answer 5

我已經創建了這個函數，併爲我檢查客戶端是否仍然與服務器連接。

/// <summary> 
/// THIS FUNCTION WILL CHECK IF CLIENT IS STILL CONNECTED WITH SERVER. 
/// </summary> 
/// <returns>FALSE IF NOT CONNECTED ELSE TRUE</returns> 
public bool isClientConnected() 
{ 
    IPGlobalProperties ipProperties = IPGlobalProperties.GetIPGlobalProperties(); 

    TcpConnectionInformation[] tcpConnections = ipProperties.GetActiveTcpConnections(); 

    foreach (TcpConnectionInformation c in tcpConnections) 
    { 
     TcpState stateOfConnection = c.State; 

     if (c.LocalEndPoint.Equals(ClientSocket.Client.LocalEndPoint) && c.RemoteEndPoint.Equals(ClientSocket.Client.RemoteEndPoint)) 
     { 
      if (stateOfConnection == TcpState.Established) 
      { 
       return true; 
      } 
      else 
      { 
       return false; 
      } 

     } 

    } 

    return false; 


} 

Answer 6

在我的情況，我被髮送一些命令到服務器（在同一計算機上的虛擬機上運行），並等待響應。但是，如果服務器在等待時意外停止，我沒有收到任何通知。我嘗試了其他海報提出的可能性，但都沒有工作（它總是說服務器仍然連接）。對於我來說，這是工作的唯一的事情就是寫0字節流：

var client = new TcpClient(); 
//... open the client 

var stream = client.GetStream(); 

//... send something to the client 

byte[] empty = { 0 }; 
//wait for response from server 
while (client.Available == 0) 
{ 
    //throws a SocketException if the connection is closed by the server 
    stream.Write(empty, 0, 0); 
    Thread.Sleep(10); 
} 

Answer 7

彼得Wone的解決方案和烏列是非常好的。但是您還需要檢查遠程端點，因爲您可以有多個到您的本地端點的開放連接。

public static TcpState GetState(this TcpClient tcpClient) 
    { 
     var foo = IPGlobalProperties.GetIPGlobalProperties() 
      .GetActiveTcpConnections() 
      .SingleOrDefault(x => x.LocalEndPoint.Equals(tcpClient.Client.LocalEndPoint) 
          && x.RemoteEndPoint.Equals(tcpClient.Client.RemoteEndPoint) 
     ); 

     return foo != null ? foo.State : TcpState.Unknown; 
    }