Imports System
Imports System.Net.Sockets
Imports System.Text
 
Public Class PortChecker
    Public Function CheckPortOpen(ipAddress As String, portNumber As Integer) As Boolean
        ' 创建一个TcpClient实例
        Using tcpClient As New TcpClient()
            Try
                ' 尝试连接到目标IP和端口
                tcpClient.Connect(ipAddress, portNumber)
                ' 如果连接成功，则返回True
                Return True
            Catch ex As SocketException
                ' 如果连接失败，则根据SocketException的类型判断原因
                ' 这里只检查最常见的错误代码，实际使用中可能需要处理更多情况
                If ex.SocketErrorCode = SocketError.ConnectionRefused Then
                    ' 连接被拒绝，通常表示端口关闭
                    Return False
                ElseIf ex.SocketErrorCode = SocketError.TimedOut Then
                    ' 连接超时，可能表示网络问题或端口响应慢
                    Return False
                ' 其他错误情况可能需要根据具体需求来处理
                Else
                    ' 未知错误或其他原因导致的连接失败
                    Return False
                End If
            Finally
                ' 确保关闭TcpClient连接，即使发生异常也要执行
                If tcpClient.Connected Then
                    tcpClient.Close()
                End If
            End Try
        End Using
    End Function
 
    ' 示例用法
    Public Sub Main()
        Dim targetIP As String = "192.168.1.100" ' 替换为目标计算机的IP地址
        Dim targetPort As Integer = 80 ' 替换为要检测的端口号
        Dim isPortOpen As Boolean = CheckPortOpen(targetIP, targetPort)
        If isPortOpen Then
            Console.WriteLine("端口 {0} 是开放的。", targetPort)
        Else
            Console.WriteLine("端口 {0} 是关闭的或不可访问的。", targetPort)
        End If
    End Sub
End Class