Question

我是Visual Basic和.NET的菜鸟，所以请原谅我可能简单而愚蠢的问题。我想创建一个简单的服务器客户端连接。这现在有效，我的客户端可以连接到服务器。但是，如果我关闭客户端，服务器仍然认为客户端已连接。这是我的代码：

Private server As TcpListener
Private serverPort As Integer = 8000
Private connectionMonitor As Tasks.Task
Private clientList As New List(Of Connection)

Public Structure Connection
    Dim client As TcpClient
End Structure

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    StartServer()
End Sub

Private Sub StartServer()
    server = New TcpListener(IPAddress.Any, serverPort)
    server.Start()
    server.BeginAcceptTcpClient(AddressOf DoAcceptClient, server)
    Console.WriteLine("Server started")
    connectionMonitor = Tasks.Task.Factory.StartNew(AddressOf DoMonitorConnections)
End Sub

Private Sub DoAcceptClient(result As IAsyncResult)
    ' Get the listener that handles the client request.
    Dim listener As TcpListener = CType(result.AsyncState, TcpListener)

    Dim client As TcpClient = listener.EndAcceptTcpClient(result)

    ' Process the connection here.
    Console.WriteLine("Client connected")
    Dim c As Connection = New Connection
    c.client = client
    clientList.Add(c)
End Sub

Private Sub DoMonitorConnections()
    Dim a As Integer = 0
    While True
        For index As Integer = 0 To clientList.Count - 1 Step 1
            Dim conn As Connection = clientList(index)
            If conn.client.Connected Then
                Console.WriteLine("Client still conncected" & a)
                Console.WriteLine(conn.client.Connected)
            Else
                Console.WriteLine("Client connection lost")
                clientList.Remove(conn)
            End If
            a += 1
        Next
        ' throttle loop
        connectionMonitor.Wait(1000)
    End While
End Sub

在DoMonitorConnections()我检查，如果客户端仍然连接。虽然客户端应用程序已关闭，但我仍然得到输出＆＃34;仍然连接＆＃34;，因为TcpClient的连接属性始终为True。

Answer 1

尝试向客户发送内容并抓住错误......：

Private Sub DoMonitorConnections()
         While ...
            For index ...
            .
            .
                Try
                    Dim tmp(0) As Byte
                    conn.client.Client.Send(tmp)
                    Console.WriteLine("---Connected!---")
                Catch e As SocketException
                    Console.WriteLine("--Disconnected: error code {0}!", e.NativeErrorCode)
                End Try
            .
            .
        .
End Sub

Answer 2

要手动发送/接收套接字，您必须设计一个实体模式，以便双方知道何时应完成事务。完成连接后，双方必须呼叫关机，然后呼叫断开连接。

使用套接字后，请务必查看WCF，因为它使一切变得更加简单和清洁。

Answer 3

套接字仅代表连接的一端。如果没有正常关闭连接（Socket.Shutdown，等待0个字节，然后调用socket.Close()），则在另一端检测到断开连接之前可能需要一些时间。

断开连接的明确指示是Send或Receive报告已传输0个字节。这是检查连接是否仍处于活动状态的最佳方法。

TcpListener不会失去联系

3 个答案: