Creator of Rambo here. Don’t use libraries if you’re writing your own port. Libraries are for working around external programs that cannot be changed.

Your minimal program is a good start, just need to read (block on) standard input on another thread so your MS Project job can run.

If you don’t care about JVM startup time, just run your port with System.cmd on demand. Otherwise if your Java process is long-lived, you’ll need to consider the communication protocol between your Java and Erlang processes.

OK, problem exists between chair & keyboard. My main loop was badly behaved. I stripped it back to the most basic stdin read loop and it terminates ok. Time to start building it up again and see where it fails.

For reference, here’s a minimal Java program that works nicely over ports, terminating when the process or BEAM terminates (including brutally killing from Windows task manager):

package com.thing;
import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        int ch;
        while(true) {
            ch = System.in.read();
            if (ch == -1) {break;} // This is the EOF signal in Java
            if (ch == 'q') {break;}
            if (ch == 't') {System.out.println("tasks");}
            System.out.println(" got " + ch + " - " + (char)ch);
        }
    }
}

Thanks for the mention. To clarify, Rambo only requires the Rust compiler if you are not using Linux, macOS or Windows. Bundled binaries should cover most users.

Besides of the already mentioned erlport there are a couple of other projects available, like porcelain which relies on a wrapper written in Golang, which has to be installed seperately, or rambo which explicitely not only manages the lifecycle of the program, but also is able to wrap those programs that do only print their own reply after stdin got closed. Its wrapper is written in Rust, and as far as I remember you need to have rust installed to compile the library.

Thanks @jayjun - yes, the java process will be long lived. I’ve worked up a more extended example that uses Erlang ETF to transmit the payload back and forth. The Ericsson JInterface library has all the parsing and packaging routines. There are a couple of gotchas that I’ll write up (eg the OtpOutputStream doesn’t write the first byte - 131 - for some reason so you have to do that by hand), but it seems pretty straightforward otherwise. The Java side can respond synchronously to each call in my case which simplifies things on that side.