feat: update Deno.serve function signature (#15563)

This commit changes the `Deno.serve` function signature to be more
versatile and easier to use. It is now a drop in replacement for
std/http's `serve`.

The input validation has also been reworked.

cli/bench/http/deno_flash_hono_router.js

@@ -7,4 +7,4 @@ const [hostname, port] = addr.split(":");
 const app = new Hono();
 app.get("/", (c) => c.text("Hello, World!"));
 
-Deno.serve({ fetch: app.fetch, port: Number(port), hostname });
+Deno.serve(app.fetch, { port: Number(port), hostname });

cli/bench/http/deno_flash_send_file.js

@@ -6,9 +6,9 @@ const { serve } = Deno;
 
 const path = new URL("../testdata/128k.bin", import.meta.url).pathname;
 
-function fetch() {
+function handler() {
   const file = Deno.openSync(path);
   return new Response(file.readable);
 }
 
-serve({ fetch, hostname, port: Number(port) });
+serve(handler, { hostname, port: Number(port) });

cli/bench/http/deno_http_flash.js

@@ -4,12 +4,8 @@ const addr = Deno.args[0] || "127.0.0.1:4500";
 const [hostname, port] = addr.split(":");
 const { serve } = Deno;
 
-function fetch() {
+function handler() {
   return new Response("Hello World");
 }
 
-serve({
+serve(handler, { hostname, port });
-  fetch,
-  hostname,
-  port,
-});

cli/bench/http/deno_reactdom_ssr_flash.jsx

@@ -18,12 +18,6 @@ const headers = {
   },
 };
 
-serve(
+serve({ hostname, port }, async () => {
-  {
-    fetch: async () => {
   return new Response(await renderToReadableStream(<App />), headers);
-    },
+});
-    hostname,
-    port,
-  },
-);

cli/bench/testdata/deno_upgrade_http.js

@@ -1,14 +1,10 @@
 const { serve, upgradeHttp } = Deno;
 const u8 = Deno.core.encode("HTTP/1.1 101 Switching Protocols\r\n\r\n");
 
-async function fetch(req) {
+async function handler(req) {
   const [conn, _firstPacket] = upgradeHttp(req);
   await conn.write(u8);
   await conn.close();
 }
 
-serve({
+serve(handler, { hostname: "127.0.0.1", port: 9000 });
-  fetch,
-  hostname: "127.0.0.1",
-  port: 9000,
-});

cli/dts/lib.deno.unstable.d.ts

@@ -1230,27 +1230,21 @@ declare namespace Deno {
    */
   export function unrefTimer(id: number): void;
 
-  /**
-   * @category HTTP Server
-   */
-  export interface ServeInit extends Partial<Deno.ListenOptions> {
   /**
    * A handler for HTTP requests. Consumes a request and returns a response.
    *
-     * Handler allows `void` or `Promise<void>` return type to enable
-     * request upgrades using `Deno.upgradeHttp()` API. It is callers responsibility
-     * to write response manually to the returned connection. Failing to do so
-     * (or not returning a response without an upgrade) will cause the connection
-     * to hang.
-     *
    * If a handler throws, the server calling the handler will assume the impact
    * of the error is isolated to the individual request. It will catch the error
-     * and close the underlying connection.
+   * and if necessary will close the underlying connection.
+   *
+   * @category HTTP Server
    */
-    fetch: (
+  export type ServeHandler = (request: Request) => Response | Promise<Response>;
-      request: Request,
-    ) => Response | Promise<Response> | void | Promise<void>;
 
+  /**
+   * @category HTTP Server
+   */
+  export interface ServeOptions extends Partial<Deno.ListenOptions> {
     /** An AbortSignal to close the server and all connections. */
     signal?: AbortSignal;
 
@@ -1264,7 +1258,7 @@ declare namespace Deno {
   /**
    * @category HTTP Server
    */
-  export interface ServeTlsInit extends ServeInit {
+  export interface ServeTlsOptions extends ServeOptions {
     /** Server private key in PEM format */
     cert: string;
 
@@ -1272,7 +1266,17 @@ declare namespace Deno {
     key: string;
   }
 
-  /** Serves HTTP requests with the given handler.
+  /**
+   * @category HTTP Server
+   */
+  export interface ServeInit {
+    /** The handler to invoke to process each incoming request. */
+    handler: ServeHandler;
+  }
+
+  /** **UNSTABLE**: new API, yet to be vetted.
+   *
+   * Serves HTTP requests with the given handler.
    *
    * You can specify an object with a port and hostname option, which is the
    * address to listen on. The default is port 9000 on hostname "127.0.0.1".
@@ -1280,69 +1284,64 @@ declare namespace Deno {
    * The below example serves with the port 9000.
    *
    * ```ts
-   * Deno.serve({
+   * Deno.serve((_req) => new Response("Hello, world"));
-   *   fetch: (_req) => new Response("Hello, world")
-   * });
    * ```
    *
-   * You can change the listening address by the `hostname` and `port` options.
+   * You can change the address to listen on using the `hostname` and `port`
-   * The below example serves with the port 3000.
+   * options. The below example serves on port 3000.
    *
    * ```ts
-   * Deno.serve({
+   * Deno.serve({ port: 3000 }, (_req) => new Response("Hello, world"));
-   *   fetch: (_req) => new Response("Hello, world"),
-   *   port: 3000
-   * });
    * ```
    *
-   * You can close the server by passing a `signal` option. To wait for the server
+   * You can stop the server with an AbortSignal. The abort signal needs to be
-   * to close, await the promise returned from the `Deno.serve` API.
+   * passed as the `signal` option in the options bag. The server aborts when
+   * the abort signal is aborted. To wait for the server to close, await the
+   * promise returned from the `Deno.serve` API.
    *
    * ```ts
    * const ac = new AbortController();
    *
-   * Deno.serve({
+   * Deno.serve({ signal: ac.signal }, (_req) => new Response("Hello, world"))
-   *   fetch: (_req) => new Response("Hello, world"),
+   *  .then(() => console.log("Server closed"));
-   *   signal: ac.signal
-   * }).then(() => {
-   *   console.log("Server closed");
-   * });
    *
    * console.log("Closing server...");
    * ac.abort();
    * ```
    *
-   * `Deno.serve` function prints the message `Listening on http://<hostname>:<port>/`
+   * By default `Deno.serve` prints the message `Listening on http://<hostname>:<port>/`
-   * on start-up by default. If you like to change this message, you can specify
+   * on start up. If you like to change this behaviour, you can specify a custom
-   * `onListen` option to override it.
+   * `onListen` callback.
    *
    * ```ts
    * Deno.serve({
-   *   fetch: (_req) => new Response("Hello, world"),
    *   onListen({ port, hostname }) {
    *     console.log(`Server started at http://${hostname}:${port}`);
    *     // ... more info specific to your server ..
    *   },
+   *   handler: (_req) => new Response("Hello, world"),
    * });
    * ```
    *
-   * To enable TLS you must specify `key` and `cert` options.
+   * To enable TLS you must specify the `key` and `cert` options.
    *
    * ```ts
    * const cert = "-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----\n";
    * const key = "-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----\n";
-   * Deno.serve({
+   * Deno.serve({ cert, key }, (_req) => new Response("Hello, world"));
-   *   fetch: (_req) => new Response("Hello, world"),
-   *   cert,
-   *   key
-   * });
-   *
-   * @param options The options. See `ServeInit` and `ServeTlsInit` documentation for details.
    *
    * @category HTTP Server
    */
   export function serve(
-    options?: ServeInit | ServeTlsInit,
+    handler: ServeHandler,
+    options?: ServeOptions | ServeTlsOptions,
+  ): Promise<void>;
+  export function serve(
+    options: ServeOptions | ServeTlsOptions,
+    handler: ServeHandler,
+  ): Promise<void>;
+  export function serve(
+    options: ServeInit & (ServeOptions | ServeTlsOptions),
   ): Promise<void>;
 
   /** **UNSTABLE**: new API, yet to be vetter.

cli/tests/unit/flash_test.ts

@@ -12,11 +12,9 @@ import {
   assert,
   assertEquals,
   assertRejects,
-  assertStrictEquals,
   assertThrows,
   Deferred,
   deferred,
-  delay,
   fail,
 } from "./test_util.ts";
 
@@ -37,10 +35,10 @@ function onListen<T>(
 }
 
 Deno.test(async function httpServerInvalidHostname() {
-  assertThrows(
+  await assertRejects(
     () =>
       Deno.serve({
-        fetch: (_req) => new Response("ok"),
+        handler: (_req) => new Response("ok"),
         hostname: "localhost",
       }),
     TypeError,
@@ -54,7 +52,7 @@ Deno.test({ permissions: { net: true } }, async function httpServerBasic() {
   const listeningPromise = deferred();
 
   const server = Deno.serve({
-    fetch: async (request) => {
+    handler: async (request) => {
       // FIXME(bartlomieju):
       // make sure that request can be inspected
       console.log(request);
@@ -84,11 +82,103 @@ Deno.test({ permissions: { net: true } }, async function httpServerBasic() {
   await server;
 });
 
+Deno.test({ permissions: { net: true } }, async function httpServerOverload1() {
+  const ac = new AbortController();
+  const promise = deferred();
+  const listeningPromise = deferred();
+
+  const server = Deno.serve({
+    port: 4501,
+    signal: ac.signal,
+    onListen: onListen(listeningPromise),
+    onError: createOnErrorCb(ac),
+  }, async (request) => {
+    // FIXME(bartlomieju):
+    // make sure that request can be inspected
+    console.log(request);
+    assertEquals(new URL(request.url).href, "http://127.0.0.1:4501/");
+    assertEquals(await request.text(), "");
+    promise.resolve();
+    return new Response("Hello World", { headers: { "foo": "bar" } });
+  });
+
+  await listeningPromise;
+  const resp = await fetch("http://127.0.0.1:4501/", {
+    headers: { "connection": "close" },
+  });
+  await promise;
+  const clone = resp.clone();
+  const text = await resp.text();
+  assertEquals(text, "Hello World");
+  assertEquals(resp.headers.get("foo"), "bar");
+  const cloneText = await clone.text();
+  assertEquals(cloneText, "Hello World");
+  ac.abort();
+  await server;
+});
+
+Deno.test({ permissions: { net: true } }, async function httpServerOverload2() {
+  const ac = new AbortController();
+  const promise = deferred();
+  const listeningPromise = deferred();
+
+  const server = Deno.serve(async (request) => {
+    // FIXME(bartlomieju):
+    // make sure that request can be inspected
+    console.log(request);
+    assertEquals(new URL(request.url).href, "http://127.0.0.1:4501/");
+    assertEquals(await request.text(), "");
+    promise.resolve();
+    return new Response("Hello World", { headers: { "foo": "bar" } });
+  }, {
+    port: 4501,
+    signal: ac.signal,
+    onListen: onListen(listeningPromise),
+    onError: createOnErrorCb(ac),
+  });
+
+  await listeningPromise;
+  const resp = await fetch("http://127.0.0.1:4501/", {
+    headers: { "connection": "close" },
+  });
+  await promise;
+  const clone = resp.clone();
+  const text = await resp.text();
+  assertEquals(text, "Hello World");
+  assertEquals(resp.headers.get("foo"), "bar");
+  const cloneText = await clone.text();
+  assertEquals(cloneText, "Hello World");
+  ac.abort();
+  await server;
+});
+
+Deno.test(
+  { permissions: { net: true } },
+  async function httpServerErrorOverloadMissingHandler() {
+    // @ts-ignore - testing invalid overload
+    await assertRejects(() => Deno.serve(), TypeError, "handler");
+    // @ts-ignore - testing invalid overload
+    await assertRejects(() => Deno.serve({}), TypeError, "handler");
+    await assertRejects(
+      // @ts-ignore - testing invalid overload
+      () => Deno.serve({ handler: undefined }),
+      TypeError,
+      "handler",
+    );
+    await assertRejects(
+      // @ts-ignore - testing invalid overload
+      () => Deno.serve(undefined, { handler: () => {} }),
+      TypeError,
+      "handler",
+    );
+  },
+);
+
 Deno.test({ permissions: { net: true } }, async function httpServerPort0() {
   const ac = new AbortController();
 
   const server = Deno.serve({
-    fetch() {
+    handler() {
       return new Response("Hello World");
     },
     port: 0,
@@ -120,7 +210,7 @@ Deno.test(
 
     try {
       const server = Deno.serve({
-        fetch() {
+        handler() {
           return new Response("Hello World");
         },
         hostname: "0.0.0.0",
@@ -145,7 +235,7 @@ Deno.test(
 
     let headers: Headers;
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         await request.text();
         headers = request.headers;
         promise.resolve();
@@ -182,7 +272,7 @@ Deno.test(
 
     let req: Request;
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         await request.text();
         req = request;
         promise.resolve();
@@ -226,7 +316,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: (request) => {
+      handler: (request) => {
         assertEquals(request.body, null);
         promise.resolve();
         return new Response("", { headers: {} });
@@ -270,7 +360,7 @@ Deno.test(
     const listeningPromise = deferred();
     const ac = new AbortController();
     const server = Deno.serve({
-      fetch: (request) => {
+      handler: (request) => {
         assert(!request.body);
         return new Response(stream.readable);
       },
@@ -300,7 +390,7 @@ Deno.test(
     const listeningPromise = deferred();
     const ac = new AbortController();
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         const reqBody = await request.text();
         assertEquals("hello world", reqBody);
         return new Response("yo");
@@ -328,7 +418,7 @@ Deno.test({ permissions: { net: true } }, async function httpServerClose() {
   const ac = new AbortController();
   const listeningPromise = deferred();
   const server = Deno.serve({
-    fetch: () => new Response("ok"),
+    handler: () => new Response("ok"),
     port: 4501,
     signal: ac.signal,
     onListen: onListen(listeningPromise),
@@ -348,7 +438,7 @@ Deno.test(
     const ac = new AbortController();
     const listeningPromise = deferred();
     const server = Deno.serve({
-      fetch: () => new Response(new Blob([])),
+      handler: () => new Response(new Blob([])),
       port: 4501,
       signal: ac.signal,
       onListen: onListen(listeningPromise),
@@ -369,7 +459,7 @@ Deno.test({ permissions: { net: true } }, async function httpServerWebSocket() {
   const ac = new AbortController();
   const listeningPromise = deferred();
   const server = Deno.serve({
-    fetch: async (request) => {
+    handler: async (request) => {
       const {
         response,
         socket,
@@ -409,7 +499,7 @@ Deno.test(
 
     let headers: Headers;
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         headers = request.headers;
         promise.resolve();
         return new Response("");
@@ -448,7 +538,7 @@ Deno.test(
     let headers: Headers;
     let text: string;
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         headers = request.headers;
         text = await request.text();
         promise.resolve();
@@ -493,7 +583,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: () => {
+      handler: () => {
         promise.resolve();
         return new Response("");
       },
@@ -643,7 +733,7 @@ Deno.test(
     }
 
     const finished = Deno.serve({
-      fetch: () => {
+      handler: () => {
         promise.resolve();
         return new Response(periodicStream());
       },
@@ -674,7 +764,7 @@ Deno.test(
     const promise = deferred();
     const ac = new AbortController();
     const server = Deno.serve({
-      fetch: (request) => {
+      handler: (request) => {
         assertEquals(request.headers.get("X-Header-Test"), "á");
         promise.resolve();
         return new Response("hello", { headers: { "X-Header-Test": "Æ" } });
@@ -720,7 +810,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         // FIXME:
         // assertEquals(new URL(request.url).href, "http://127.0.0.1:4501/");
         assertEquals(await request.text(), "");
@@ -774,7 +864,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(await request.text(), "");
         assertEquals(request.headers.get("cookie"), "foo=bar, bar=foo");
         promise.resolve();
@@ -817,7 +907,7 @@ Deno.test(
     file.close();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         const f = await Deno.open(tmpFile, { read: true });
         promise.resolve();
         return new Response(f.readable);
@@ -853,7 +943,7 @@ Deno.test(
     const port = 4501;
 
     const server = Deno.serve({
-      fetch: () => {
+      handler: () => {
         promise.resolve();
         return new Response("ok");
       },
@@ -888,7 +978,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.body, null);
         promise.resolve();
         return new Response(new Uint8Array([128]));
@@ -918,7 +1008,7 @@ Deno.test("upgradeHttp tcp", async () => {
   const promise2 = deferred();
   const ac = new AbortController();
   const signal = ac.signal;
-  const fetch = async (req: Request) => {
+  const handler = async (req: Request) => {
     const [conn, _] = await Deno.upgradeHttp(req);
 
     await conn.write(
@@ -938,7 +1028,7 @@ Deno.test("upgradeHttp tcp", async () => {
     conn.close();
   };
   const server = Deno.serve({
-    fetch,
+    handler: handler as any,
     port: 4501,
     signal,
     onListen: onListen(listeningPromise),
@@ -980,7 +1070,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "GET");
         assertEquals(request.headers.get("host"), "deno.land");
         promise.resolve();
@@ -1014,7 +1104,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "GET");
         assertEquals(request.headers.get("server"), "hello\tworld");
         promise.resolve();
@@ -1048,7 +1138,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "GET");
         assertEquals(await request.text(), "");
         promise.resolve();
@@ -1084,7 +1174,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "POST");
         assertEquals(await request.text(), "I'm a good request.");
         promise.resolve();
@@ -1130,7 +1220,7 @@ function createServerLengthTest(name: string, testCase: TestCase) {
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "GET");
         promise.resolve();
         return new Response(testCase.body, testCase.headers ?? {});
@@ -1262,7 +1352,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "GET");
         promises[reqCount].resolve();
         reqCount++;
@@ -1325,7 +1415,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "POST");
         assertEquals(request.headers.get("content-length"), "5");
         assertEquals(await request.text(), "hello");
@@ -1361,7 +1451,7 @@ Deno.test(
     const ac = new AbortController();
     const listeningPromise = deferred();
     const server = Deno.serve({
-      fetch: () => {
+      handler: () => {
         throw new Error("unreachable");
       },
       port: 4503,
@@ -1401,7 +1491,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(request.method, "POST");
         assertEquals(await request.text(), "qwert");
         promise.resolve();
@@ -1438,7 +1528,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: async (r) => {
+      handler: async (r) => {
         promise.resolve();
         assertEquals(await r.text(), "12345");
         return new Response("ok");
@@ -1474,7 +1564,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: () => {
+      handler: () => {
         promise.resolve();
         return new Response("foo bar baz");
       },
@@ -1522,7 +1612,7 @@ Deno.test(
     await file.write(data);
     file.close();
     const server = Deno.serve({
-      fetch: async () => {
+      handler: async () => {
         const f = await Deno.open(tmpFile, { read: true });
         promise.resolve();
         return new Response(f.readable, { status: 200 });
@@ -1557,7 +1647,7 @@ Deno.test(
     file.close();
 
     const server = Deno.serve({
-      fetch: async (request) => {
+      handler: async (request) => {
         assertEquals(new Uint8Array(await request.arrayBuffer()), data);
         promise.resolve();
         return new Response("ok");
@@ -1594,7 +1684,7 @@ Deno.test(
     const port = 4501;
 
     const server = Deno.serve({
-      fetch: () => new Response("Hello World"),
+      handler: () => new Response("Hello World"),
       hostname,
       port,
       signal: ac.signal,
@@ -1629,7 +1719,7 @@ Deno.test(
     const promise = deferred();
 
     const server = Deno.serve({
-      fetch: async (req) => {
+      handler: async (req) => {
         assertEquals(await req.text(), "");
         promise.resolve();
         return new Response("ok");
@@ -1664,7 +1754,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: () => {
+      handler: () => {
         throw new Error("oops");
       },
       port: 4503,
@@ -1713,7 +1803,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: () => {
+      handler: () => {
         promise.resolve();
         return new Response(null, { status: 304 });
       },
@@ -1757,7 +1847,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: async (req) => {
+      handler: async (req) => {
         promise.resolve();
         assertEquals(await req.text(), "hello");
         return new Response(null, { status: 304 });
@@ -1818,7 +1908,7 @@ Deno.test(
     const ac = new AbortController();
 
     const server = Deno.serve({
-      fetch: async (req) => {
+      handler: async (req) => {
         promise.resolve();
         assertEquals(await req.text(), "");
         return new Response(null, { status: 304 });
@@ -1872,7 +1962,7 @@ for (const [name, req] of badRequests) {
       const listeningPromise = deferred();
 
       const server = Deno.serve({
-        fetch: () => {
+        handler: () => {
           throw new Error("oops");
         },
         port: 4503,
@@ -1917,7 +2007,7 @@ Deno.test(
     const listeningPromise = deferred();
 
     const server = Deno.serve({
-      fetch: () => new Response(null),
+      handler: () => new Response(null),
       port: 4503,
       signal: ac.signal,
       onListen: onListen(listeningPromise),
@@ -1957,7 +2047,7 @@ Deno.test(
     let reqCount = -1;
     let timerId: number | undefined;
     const server = Deno.serve({
-      fetch: async (req) => {
+      handler: async (req) => {
         reqCount++;
         if (reqCount === 0) {
           const msg = new TextEncoder().encode("data: hello\r\n\r\n");

ext/flash/01_http.js

@@ -25,7 +25,9 @@
   } = window.__bootstrap.webSocket;
   const { _ws } = window.__bootstrap.http;
   const {
+    Function,
     ObjectPrototypeIsPrototypeOf,
+    PromiseResolve,
     TypedArrayPrototypeSubarray,
     TypeError,
     Uint8Array,
@@ -185,48 +187,76 @@
     return hostname === "0.0.0.0" ? "localhost" : hostname;
   }
 
-  function serve(opts = {}) {
+  async function serve(arg1, arg2) {
-    if (!("fetch" in opts)) {
+    let options = undefined;
-      throw new TypeError("Options is missing 'fetch' handler");
+    let handler = undefined;
+    if (arg1 instanceof Function) {
+      handler = arg1;
+      options = arg2;
+    } else if (arg2 instanceof Function) {
+      handler = arg2;
+      options = arg1;
+    } else {
+      options = arg1;
     }
-    if ("cert" in opts && !("key" in opts)) {
+    if (handler === undefined) {
-      throw new TypeError("Options is missing 'key' field");
+      if (options === undefined) {
+        throw new TypeError(
+          "No handler was provided, so an options bag is mandatory.",
+        );
       }
-    if ("key" in opts && !("cert" in opts)) {
+      handler = options.handler;
-      throw new TypeError("Options is missing 'cert' field");
     }
-    opts = { hostname: "127.0.0.1", port: 9000, ...opts };
+    if (!(handler instanceof Function)) {
-    const handler = opts.fetch;
+      throw new TypeError("A handler function must be provided.");
-    delete opts.fetch;
+    }
-    const signal = opts.signal;
+    if (options === undefined) {
-    delete opts.signal;
+      options = {};
-    const onError = opts.onError ?? function (error) {
+    }
+
+    const signal = options.signal;
+
+    const onError = options.onError ?? function (error) {
       console.error(error);
       return new Response("Internal Server Error", { status: 500 });
     };
-    delete opts.onError;
+
-    const onListen = opts.onListen ?? function ({ port }) {
+    const onListen = options.onListen ?? function ({ port }) {
       console.log(
-        `Listening on http://${hostnameForDisplay(opts.hostname)}:${port}/`,
+        `Listening on http://${
+          hostnameForDisplay(listenOpts.hostname)
+        }:${port}/`,
       );
     };
-    delete opts.onListen;
+
-    const serverId = core.ops.op_flash_serve(opts);
+    const listenOpts = {
+      hostname: options.hostname ?? "127.0.0.1",
+      port: options.port ?? 9000,
+    };
+    if (options.cert || options.key) {
+      if (!options.cert || !options.key) {
+        throw new TypeError(
+          "Both cert and key must be provided to enable HTTPS.",
+        );
+      }
+      listenOpts.cert = options.cert;
+      listenOpts.key = options.key;
+    }
+
+    const serverId = core.ops.op_flash_serve(listenOpts);
     const serverPromise = core.opAsync("op_flash_drive_server", serverId);
 
     core.opAsync("op_flash_wait_for_listening", serverId).then((port) => {
-      onListen({ hostname: opts.hostname, port });
+      onListen({ hostname: listenOpts.hostname, port });
     });
 
     const server = {
       id: serverId,
-      transport: opts.cert && opts.key ? "https" : "http",
+      transport: listenOpts.cert && listenOpts.key ? "https" : "http",
-      hostname: opts.hostname,
+      hostname: listenOpts.hostname,
-      port: opts.port,
+      port: listenOpts.port,
       closed: false,
-      finished: (async () => {
+      finished: PromiseResolve(serverPromise),
-        return await serverPromise;
-      })(),
       async close() {
         if (server.closed) {
           return;
@@ -520,7 +550,7 @@
       }, 1000);
     }
 
-    return server.serve().catch(console.error);
+    return await server.serve().catch(console.error);
   }
 
   function createRequestBodyStream(serverId, token) {