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Editorial Team
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Asked: 2026-05-23T09:32:08+00:00

I wrote an server application in erlang and a client in C#. They communicate

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I wrote an server application in erlang and a client in C#. They communicate through 3 TCP ports. Port numbers are hardcoded. Now I’d like to do this dynamically. This is my first time doing network programming, so please pardon my inability to use proper terminology 😀

What I would like to do is make a supervisor which would accept a TCP connection from a client on a previously known port (say, 10000, or whatever), then find 3 free ports, start a server application on those 3 ports and tell the client those port numbers so client can connect to the server.

My particular problem is: how do I find 3 ports which are not in use? (clarification: which module:fun() to use to find a free port?)

My general problem is: I’m sure this kind of stuff (one server allocating ports and redirecting clients) is quite common network programming problem and there should be a bunch of (erlang-specific or general) resources about this, but I just don’t have the terminology to google it out.

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1 Answer

  1. Editorial Team

    According to the Erlang documentation here, if the Port argument to the gen_tcp:listen/2 function is 0, then the OS will assign any available port to the socket. The latter can then be retreived using inet:port/1 .

    You can therefore do something like this : 

    {ok, Listen} = gen_tcp:listen(0, [Options]),
Port = inet:port(Listen).
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