UDPClient.Send 到特定的 IP/Port 没有发送，也没有抛出异常

Question

我正在尝试将一个小型 python 脚本的功能提取到 VB 应用程序中。该应用程序正在测试与自定义 PCBA 的 UDP 通信。 PCBA 将向 App 发送特定消息，App 应接收该消息并将其回显，从而完成测试。我想将此功能迁移到 VB 中，这样我就没有 python 脚本的 shell，它可以工作，但不那么容易分发。

问题在于，虽然 python 代码按预期工作，但 VB 代码没有回显。它不会抛出异常，它会接收初始消息，检查消息中是否存在“Loopback”一词，并尝试通过将接收到的字节发回来做出响应。但是，没有发送字节。为什么？

有效的python脚本是：

import socket
import sys
import string

lb = "Loopback"
# Create a UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
# Bind the socket to the port
server_address = ('192.168.1.99', 10000)
sock.bind(server_address)
while True:
    print('\nWaiting to receive message')
    data, address = sock.recvfrom(512)
    print('>>> %s' % data)
    if lb in data.decode():
        #if lb in data:
        sock.sendto(data, address)
        print('Sent %d bytes back to %s' % (len(data), address))

尝试在 Visual Basic 中实现相同的功能（不起作用）是：

Dim udpClient As New UdpClient(10000)
        Dim RemoteIpEndPoint As New IPEndPoint(IPAddress.Parse("192.168.1.99"), 10000)
        Dim receiveBytes As Byte()
        Dim returnData As String

        While True
            receiveBytes = udpClient.Receive(RemoteIpEndPoint)
            returnData = Encoding.ASCII.GetString(receiveBytes)

            Console.WriteLine(RemoteIpEndPoint.Address.ToString() + ":" + returnData.ToString())
            Try
                If returnData.ToString().Contains("Loopback") Then
                    udpClient.Connect(RemoteIpEndPoint)
                    Dim reply As Integer = udpClient.Send(receiveBytes, receiveBytes.Length, RemoteIpEndPoint)
                    Console.WriteLine("Replied:" + reply.ToString() + " to : " + RemoteIpEndPoint.Address.ToString() + ", Port: " + RemoteIpEndPoint.Port.ToString())
                End If
            Catch ex As SocketException
                Console.WriteLine(ex.ErrorCode.ToString())
            End Try
        End While

当我在运行 VB Echo 代码时通过 WireShark 监控通信时，我可以看到接收到的数据包，但没有像 Python Echo 代码那样回显。

任何帮助将不胜感激！

Answer 1

我不知道发送部分，所以我不知道这是否是正确的答案。

1. 检查你的防火墙

2. 删除 udpClient.Connect(RemoteIpEndPoint) 源部分

Dim udpClient As New UdpClient(10000)
Dim RemoteIpEndPoint As New IPEndPoint(IPAddress.Parse("192.168.1.99"), 10000)
Dim receiveBytes As Byte()
Dim returnData As String

receiveBytes = udpClient.Receive(RemoteIpEndPoint)
returnData = Encoding.ASCII.GetString(receiveBytes)

      While True
            receiveBytes = udpClient.Receive(RemoteIpEndPoint)
            returnData = Encoding.ASCII.GetString(receiveBytes)

            Console.WriteLine(RemoteIpEndPoint.Address.ToString() + ":" + returnData.ToString())
            Try
               If returnData.ToString().Contains("Loopback") Then
                  ' udpClient.Connect(RemoteIpEndPoint)
                  Dim reply As Integer = udpClient.Send(receiveBytes, receiveBytes.Length, RemoteIpEndPoint)
                  Console.WriteLine("Replied:" + reply.ToString() + " to : " + RemoteIpEndPoint.Address.ToString() + ", Port: " + RemoteIpEndPoint.Port.ToString())
               End If
            Catch ex As SocketException
               Console.WriteLine(ex.ErrorCode.ToString())
            End Try
         End While