Add rudimentary command line parsing to express app

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,
+};