Add rudimentary command line parsing to express app

express/app.ts

@@ -3,6 +3,7 @@ import express, {
     Response as ExpressResponse,
 } from "express";
 import { match } from "path-to-regexp";
+import { cli } from "./cli";
 import { contentTypes } from "./content-types";
 import { httpCodes } from "./http-codes";
 import { routes } from "./routes";
@@ -117,4 +118,6 @@ app.use(async (req: ExpressRequest, res: ExpressResponse) => {
     res.status(code).send(result);
 });
 
-app.listen(3000);
+app.listen(cli.listen.port, cli.listen.host, () => {
+    console.log(`Listening on ${cli.listen.host}:${cli.listen.port}`);
+});

express/cli.ts

@@ -0,0 +1,49 @@
+import { parseArgs } from "node:util";
+
+const { values } = parseArgs({
+    options: {
+        listen: {
+            type: "string",
+            short: "l",
+        },
+    },
+    strict: true,
+    allowPositionals: false,
+});
+
+function parseListenAddress(listen: string | undefined): {
+    host: string;
+    port: number;
+} {
+    const defaultHost = "127.0.0.1";
+    const defaultPort = 3000;
+
+    if (!listen) {
+        return { host: defaultHost, port: defaultPort };
+    }
+
+    const lastColon = listen.lastIndexOf(":");
+    if (lastColon === -1) {
+        // Just a port number
+        const port = parseInt(listen, 10);
+        if (isNaN(port)) {
+            throw new Error(`Invalid listen address: ${listen}`);
+        }
+        return { host: defaultHost, port };
+    }
+
+    const host = listen.slice(0, lastColon);
+    const port = parseInt(listen.slice(lastColon + 1), 10);
+
+    if (isNaN(port)) {
+        throw new Error(`Invalid port in listen address: ${listen}`);
+    }
+
+    return { host, port };
+}
+
+const listenAddress = parseListenAddress(values.listen);
+
+export const cli = {
+    listen: listenAddress,
+};

express/run.sh

@@ -6,4 +6,4 @@ DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
 cd "$DIR"
 
-exec ../cmd node dist/index.js
+exec ../cmd node dist/index.js "$@"