使用 VB.net 监控远程 FTP 服务器

Question

我正在尝试使用此代码为远程 FTP 服务器创建一个简单的监视器 （在 Martin Prikryl 的大力帮助下构建）

    Private Function TestFTP(ByVal target As String, ByVal time As Integer) As Object
    Dim responseTime As Integer = 0
    Dim answer As Boolean
    Dim startTime As Integer = DateTime.Now.Millisecond
    Dim endTime As Integer
    Dim socket As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)

    Try
        With socket
            .ReceiveTimeout = time
            .Ttl = 64
            .SendTimeout = time
            .Connect(target, 21)
            .Dispose()
            .Close()
        End With
        endTime = DateTime.Now.Millisecond
        IIf(endTime - startTime < 0, responseTime = endTime + 1000, responseTime = endTime)
        answer = True

    Catch ex As Exception
        responseTime = time
        answer = False
    End Try

    Return {responseTime, answer}
End Function

当 FTP 服务器启动并响应时，没有问题，但当它不存在时，我会在发送异常之前将我的应用挂起约 15 秒。

套接字本身没有超时连接（仅用于发送和接收命令 - 在函数中使用）。

我试图用计时器包裹它，但没有运气， 请帮忙。

男人

Answer 1

好的，在这件事上挣扎了几个小时后，我找到了解决问题的方法

我实际上使用了 System.Net.Sockets.TcpClient 类

我将异步 BeginConnect 与一个非常简单的 While 循环相结合，检查是否已连接，检查套接字是否已连接

 Private Function TestFTP(ByVal target As String, ByVal time As Integer) As Object
    Dim responseTime As Integer = 0
    Dim answer As Boolean
    Dim startTime As Integer = DateTime.Now.Millisecond
    Dim endTime As Integer
    Dim t As TcpClient = New TcpClient(AddressFamily.InterNetwork)
    Dim loops As Integer
    time *= 2
    t.BeginConnect(target, 21, Nothing, t)
    While Not t.Connected
        Thread.Sleep(Int(time / 6))
        loops += 1
        If loops >= 6 Then Exit While
    End While
    endTime = DateTime.Now.Millisecond
    t.Close()
    If loops >= 6 Then
        answer = False
        responseTime = 300
    Else
        answer = True
        If endTime >= startTime Then
            responseTime = endTime - startTime
        Else
            responseTime = endTime - startTime + 1000
        End If
    End If


    Return {responseTime, answer}
End Function

这对我有用，希望对某人有所帮助。