fix(workers-shared): guard against undefined user_worker static_routing rules (#13668)

Author: for-the-kidz

.changeset/fix-router-worker-user-worker-rules-iterable.md

@@ -0,0 +1,8 @@
+---
+"@cloudflare/workers-shared": patch
+"miniflare": patch
+---
+
+Fix `TypeError: rules is not iterable` in the router-worker when `static_routing` is configured without `user_worker` rules
+
+The router-worker's static-routing include-rule evaluation passed `config.static_routing.user_worker` directly to the matcher, which iterates with `for...of`. When `static_routing` was set but `user_worker` was omitted, the matcher threw `TypeError: rules is not iterable` and failed the request. The adjacent `asset_worker` branch already falls back to `[]` in this case; the `user_worker` branch now does the same.

packages/workers-shared/router-worker/src/worker.ts

@@ -219,7 +219,7 @@ export default {
 				}
 				// evaluate "include" rules
 				const includeRulesMatcher = generateStaticRoutingRuleMatcher(
-					config.static_routing.user_worker
+					config.static_routing.user_worker ?? []
 				);
 				if (
 					includeRulesMatcher({

packages/workers-shared/router-worker/tests/index.test.ts

@@ -201,6 +201,41 @@ describe("unit tests", () => {
 		expect(await response.text()).toEqual("hello from asset worker");
 	});
 
+	// Regression test for WC-5014 / Sentry #31445454: previously threw
+	// `TypeError: rules is not iterable` when static_routing was defined but
+	// user_worker was undefined.
+	it("does not throw when static_routing is defined without user_worker rules", async ({
+		expect,
+	}) => {
+		const request = new Request("https://example.com/unmatched-path");
+		const ctx = createExecutionContext();
+
+		const env = {
+			CONFIG: {
+				has_user_worker: true,
+				static_routing: {
+					asset_worker: ["/assets/*"],
+				},
+			},
+			USER_WORKER: {
+				async fetch(_request: Request): Promise<Response> {
+					return new Response("hello from user worker");
+				},
+			},
+			ASSET_WORKER: {
+				async fetch(_request: Request): Promise<Response> {
+					return new Response("hello from asset worker");
+				},
+				async unstable_canFetch(_request: Request): Promise<boolean> {
+					return true;
+				},
+			},
+		} as Env;
+
+		const response = await worker.fetch(request, env, ctx);
+		expect(await response.text()).toEqual("hello from asset worker");
+	});
+
 	it("returns fetch from asset worker when no static_routing rule matches but asset exists", async ({
 		expect,
 	}) => {