How to listen to a TCP port which is already being listened by another app

I've a plugin which always listening to the port 6002, and i have an ASP.net application which sending messages to the same port and receiving the reply from the plugin on the same port, Sending is working 开发者_JAVA技巧fine, and the plugin sends a reply on the same port but i don't know how to catch this reply, when i try to listen to the same port using Tcplistener the start method throws this exception : Only one usage of each socket address (protocol/network address/port) is normally permitted,

is there any way to catch the received message Thanks

It sounds like you are wrongly assuming that the Socket which you get from TcpListener.AcceptSocket can only be used in one direction.

Sockets can actually be bidirectional. You can use Send to send something, and Receive to listen for get the replies. Open one socket, and then use it for both sending and receiving.

In short, no.

Once a port is opened an exception will be thrown if further attempts are made to utilise that same port from a different source - as you are experiencing right now. There isn't a way to get around this.

I've solved this problem using this way ,, I know it's old method but it's working !! :

'/*Variables Initialization*/
dim objSocket, strServicePort, strIpAddr, strResult, strMsgTo, strMsgResponse   
strServicePort = "6002"
strIpAddr = "127.0.0.1"

'/* Create a TCP/IP socket. */
objSocket = Server.CreateObject("Intrafoundation.TCPClient.3")
objSocket.ClearLog()

'/* Establish socket connection. */
objSocket.Open (strIpAddr,strServicePort)
objSocket.Timeout=60.0 
strMsgTo ="---- Message here ----"

'/* Send request message to plugin  */

objSocket.SendRN(strMsgTo) 

'/* receive XML Request Message from plugin  */
strMsgResponse = objSocket.Recv()
strMsgResponse = Replace(strMsgResponse, vbLf, "")

objSocket.Close()

If you want to inspect traffic you can use winpcap.
edit: I don't think you are asking the right question. In this case the plugin is the server (listening on port 6002) and your ASP.net app is the client listening on some arbitrary port. You only need to bind to a different port in your ASP.net app if it also needs to run as a server with the plugin acting s the client. In this case you should pick a different port even though there are, in fact, ways to make it work when they are both bound to the same port.
In your case though you should just read back responses from the connection you established from the client.