How to assign static port to TCp server clients

[nirajgenius]

Hello Joel,

How can we make sure when the client gets connected then it uses the static port.
When I say static means once the client first time joined with the server then always assigned that same port one future connections.
Please see my screenshot below. I have the same client connected two times and each time It's assigned a different port.

[jchristn]

Hi @nirajgenius thanks for your note.

The library doesn't support that today, but the underlying TcpClient does: https://stackoverflow.com/questions/2869840/is-there-a-way-to-specify-the-local-port-to-used-in-tcpclient

Note that I don't know if there are multiplatform implications, i.e. it works on Windows but not on Mac. I haven't tested it.

Out of curiosity, why would you want to make the client port static? Generally by definition a client port is random, above 1024, and not something you should want to persist.

Please let me know more about the use case if you have some time; there might be an easy way to incorporate this into WatsonTcp without disturbing the codebase too much, but I want to make sure it's inline with the intent of the library.

Cheers, Joel

[jchristn]

Actually, give this a try and let me know if it works for you.

NuGet v4.8.6: https://www.nuget.org/packages/WatsonTcp/4.8.6
Commit: 23fd242

Usage:

client.Settings.LocalPort = 5000;

Note: a SocketException will be thrown when you call Connect() if the port number is already in use.

[nirajgenius]

Hello Joel,

Thank you for your reply.

We have Serial to WiFi ethernet Wireless devices that will be considered as clients and by using the Watson TCP library I build a server as you saw in the above screenshot. So far I am able to connect multiple clients but the problem is how to identify who is which client?

how to make sure if I want to communicate to a specific client?
I thought if I assign a specific dedicate port to each client then I can identify which client to send message Or Command.

I was thinking IP address but in my case, the client can be multiple in the same network so they will have the same IP so IP: PORT is what I think we can identify the unique client.

can you suggest how to identify clients?

[jchristn]

There could be a million reasons, honestly. It could be an intermittent disconnection on some intermediary router, too many dropped packets, packets routed across different networks and delivered out of an order and some upstream device thinks it's failed. The message header doesn't have anything to do with it though, it's just payload data to TCP. The null header data is because the call to read from the socket failed, thus it was unable to build the next message. Cheers, Joel

[nirajgenius]

Thank you Joel,
Some more information to get it more clear.

So, Joel,I am using SimpleTcpServer class Or WatsonTcpServer Class to build server. using _Server.Start(); method and seting options.

but my clients are not using "WatsonTcpClient" class Or "SimpleTcpClient" class to send Or receive data.
in my case clients are hardware devices and they are USR ethernet to serial wifi module

in USR devices, we are just allowed to enter the TCP server IP..NO code can be done there. as soon as we enter the TCP server address they start finding the listening server and automatically connected.

Watson server when started then automatically connect it but it keeps connecting and disconnecting client when the connection made over internet public IP.it works fine when the client and server made the connection in the same intranet.

[jchristn]

Hi @nirajgenius so these devices in the field where you can't add code, I doubt they're going to be compatible with WatsonTcp, since WatsonTcp has a framing layer in the TCP payload (in between the TCP headers and your data).

That 100% explains this in your logs:

[Debug    ] [WatsonTcpServer] accepted connection from X.X.X.X:1030
[Debug    ] [WatsonTcpServer] starting data receiver for X.X.X.X:1030
Client connected: X.X.X.X:1030
[Debug    ] [WatsonMessage] null header data, peer disconnect detected
[Debug    ] [WatsonTcpServer] disconnect detected for client X.X.X.X:1030

SimpleTcp however should work. It does not have a framing layer.

I really couldn't tell you why they keep disconnecting. The first step would be to get a network trace to see if there is a RST or FIN being sent in either direction.

[nirajgenius]

Yes, Joel, I can not do code on that client's wifi to serial modules...
Simple TCP works just fine when client and server are located in the intranet like in my office as an example.
same code when the server is built on my AWS production server then it keeps getting connected and disconnected.

So I tried different options and I get success to keep persistent connection by setting
_Server.Keepalive.TcpKeepAliveInterval = 3600;
uncommented from your example code...

So far going well with Simple TCP...I am just afraid as you said in a previous comment before that the setting I mentioned above purely depends on kernel and proven to be unreliable.

Separately..in YAT(Yet Another Terminal)...I can build a server on the same production box and also multiple clients are connected to that server and they remain persistent that's why I am hopeful with the Simple TCP plugin and considering no network-related issues otherwise YAT should have faced it...

[jchristn]

Hi @nirajgenius yes I'd definitely disable keepalives. I added them as part of a feature request (to support network cable removal, etc) and they tend to create problems with random disconnections. Cheers, Joel