fx_cast/app/src/daemon.ts

"use strict";

import { spawn } from "child_process";
import { Readable } from "stream";

import WebSocket from "ws";

import { DecodeTransform, EncodeTransform } from "./transforms";

export function init(port: number) {
    process.stdout.write("Starting WebSocket server... ");

    const wss = new WebSocket.Server({ port }, () => {
        // eslint-disable-next-line no-console
        console.log("Done!");
    });

    wss.on("error", err => {
        // eslint-disable-next-line no-console
        console.log("Failed!");
        console.error(err);
    });

    wss.on("connection", socket => {
        // Stream for incoming WebSocket messages
        const messageStream = new Readable({ objectMode: true });
        // eslint-disable-next-line @typescript-eslint/no-empty-function
        messageStream._read = () => {};

        socket.on("message", (message: string) => {
            messageStream.push(JSON.parse(message));
        });

        /**
         * Daemon and bridge are the same binary, so spawn a new
         * version of self in bridge mode.
         */
        const bridge = spawn(process.execPath, [process.argv[1]]);

        // socket -> bridge.stdin
        messageStream.pipe(new EncodeTransform()).pipe(bridge.stdin);

        // bridge.stdout -> socket
        bridge.stdout.pipe(new DecodeTransform()).on("data", data => {
            // Socket can be CLOSING here
            if (socket.readyState === WebSocket.OPEN) {
                socket.send(JSON.stringify(data));
            }
        });

        // Handle termination
        socket.on("close", () => bridge.kill());
        bridge.on("exit", () => socket.close());
    });
}