Fix local registry being able to start only once in unstable_dev (#2044)

* Fix local registry being able to start only once in unstable_dev

When using `unstable_dev`, it's not possible to start multiple workers in a sequence. Once you stop one worker, the local registry is closed and cannot be started again. This fixed that by clearing the `server` variable once the server is stopped

* Add a test for the fix

* Add changeset

* Move tests to Wrangler unit tests

---------

Co-authored-by: Pete Bacon Darwin <pete@bacondarwin.com>

.changeset/purple-books-lie.md

@@ -0,0 +1,5 @@
+---
+"wrangler": patch
+---
+
+fix: allow programmatic dev workers to be stopped and started in a single session

packages/wrangler/src/__tests__/api-devregistry.test.ts

@@ -0,0 +1,121 @@
+import { fetch } from "undici";
+import { unstable_dev } from "../api";
+
+jest.unmock("undici");
+
+/**
+ * a huge caveat to how testing multi-worker scripts works:
+ * you can't shutdown the first worker you spun up, or it'll kill the devRegistry
+ */
+describe("multi-worker testing", () => {
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
+	let childWorker: any;
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
+	let parentWorker: any;
+
+	beforeAll(async () => {
+		childWorker = await unstable_dev(
+			"src/__tests__/helpers/worker-scripts/hello-world-worker.js",
+			{
+				config: "src/__tests__/helpers/worker-scripts/child-wrangler.toml",
+				experimental: {
+					disableExperimentalWarning: true,
+				},
+			}
+		);
+		parentWorker = await unstable_dev(
+			"src/__tests__/helpers/worker-scripts/parent-worker.js",
+			{
+				config: "src/__tests__/helpers/worker-scripts/parent-wrangler.toml",
+				experimental: {
+					disableExperimentalWarning: true,
+				},
+			}
+		);
+	});
+
+	afterAll(async () => {
+		await childWorker.stop();
+		await parentWorker.stop();
+	});
+
+	it("parentWorker and childWorker should be added devRegistry", async () => {
+		const resp = await fetch("http://localhost:6284/workers");
+		if (resp) {
+			const parsedResp = (await resp.json()) as {
+				parent: unknown;
+				child: unknown;
+			};
+			expect(parsedResp.parent).toBeTruthy();
+			expect(parsedResp.child).toBeTruthy();
+		}
+	});
+
+	it("childWorker should return Hello World itself", async () => {
+		const resp = await childWorker.fetch();
+		if (resp) {
+			const text = await resp.text();
+			expect(text).toMatchInlineSnapshot(`"Hello World!"`);
+		}
+	});
+
+	it("parentWorker should return Hello World by invoking the child worker", async () => {
+		const resp = await parentWorker.fetch();
+		if (resp) {
+			const parsedResp = await resp.text();
+			expect(parsedResp).toEqual("Parent worker sees: Hello World!");
+		}
+	});
+
+	it("should be able to stop and start the server with no warning logs", async () => {
+		// Spy on all the console methods
+		let logs = "";
+		(["debug", "info", "log", "warn", "error"] as const).forEach((method) =>
+			jest
+				.spyOn(console, method)
+				.mockImplementation((...args: unknown[]) => (logs += `\n${args}`))
+		);
+
+		// Spy on the std out that is written to by Miniflare 2
+		jest
+			.spyOn(process.stdout, "write")
+			.mockImplementation((chunk: unknown) => ((logs += `\n${chunk}`), true));
+
+		async function startWorker() {
+			return await unstable_dev(
+				"src/__tests__/helpers/worker-scripts/hello-world-worker.js",
+				{
+					// We need the wrangler.toml config to specify a Worker name
+					// otherwise unstable_dev will not register the worker with the DevRegistry
+					config: "src/__tests__/helpers/worker-scripts/child-wrangler.toml",
+					// We need debug logs because this is where the message is written if registering the worker fails.
+					logLevel: "debug",
+					experimental: {
+						disableExperimentalWarning: true,
+					},
+				}
+			);
+		}
+
+		// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		let worker: any;
+		try {
+			worker = await startWorker();
+
+			// Stop the worker and start it again
+			await worker.stop();
+			await new Promise((r) => setTimeout(r, 2000));
+
+			worker = await startWorker();
+
+			const resp = await worker.fetch();
+			expect(resp).not.toBe(undefined);
+
+			expect(logs).not.toMatch(
+				/Failed to register worker in local service registry/
+			);
+		} finally {
+			await worker?.stop();
+		}
+	}, 10000);
+});

packages/wrangler/src/dev-registry.ts

@@ -13,7 +13,7 @@ import type { HttpTerminator } from "http-terminator";
 const DEV_REGISTRY_PORT = "6284";
 const DEV_REGISTRY_HOST = `http://localhost:${DEV_REGISTRY_PORT}`;
 
-let server: Server;
+let server: Server | null;
 let terminator: HttpTerminator;
 
 export type WorkerRegistry = Record<string, WorkerDefinition>;
@@ -102,6 +102,7 @@ export async function startWorkerRegistry() {
  */
 export async function stopWorkerRegistry() {
 	await terminator?.terminate();
+	server = null;
 }
 
 /**