fall back to GET when HEAD fails for redirect detection

some URL shorteners (e.g. amzn.eu) return 404 for HEAD requests
but 301 for GET. try HEAD first, fall back to GET on 404/405.
also replace the old test guard hack with proper fetchMock usage.

test/index.spec.ts

@@ -1,5 +1,5 @@
-import { env, createExecutionContext, waitOnExecutionContext, SELF } from "cloudflare:test";
-import { describe, it, expect, beforeAll } from "vitest";
+import { env, createExecutionContext, waitOnExecutionContext, fetchMock, SELF } from "cloudflare:test";
+import { describe, it, expect, beforeAll, beforeEach, afterEach } from "vitest";
 
 import worker, { RulesCache } from "../src/index";
 import type { ClearURLsRules } from "../src/types";
@@ -93,6 +93,24 @@ beforeAll(() => {
 });
 
 describe("URL Cleaner worker", () => {
+	beforeEach(() => {
+		fetchMock.activate();
+		fetchMock.disableNetConnect();
+		for (const origin of [
+			"https://example.com",
+			"https://youtube.com",
+			"https://amazon.com",
+			"https://google.com",
+			"https://tiktok.com",
+			"https://unknown-site.com",
+			"https://nonexistent.com",
+		]) {
+			fetchMock.get(origin).intercept({ path: /.*/, method: "HEAD" }).reply(200).persist();
+		}
+	});
+
+	afterEach(() => fetchMock.deactivate());
+
 	it("cleans global tracking parameters", async () => {
 		const testUrl = "https://example.com?utm_source=test&utm_medium=email&normal=keep";
 		const request = new IncomingRequest(`http://example.com/?url=${encodeURIComponent(testUrl)}`);
@@ -206,3 +224,81 @@ describe("URL Cleaner worker", () => {
 		expect(await putResponse.text()).toBe("Method not allowed");
 	});
 });
+
+describe("Redirect following", () => {
+	beforeEach(() => {
+		fetchMock.activate();
+		fetchMock.disableNetConnect();
+	});
+
+	afterEach(() => fetchMock.deactivate());
+
+	it("follows redirect when HEAD returns 3xx", async () => {
+		fetchMock
+			.get("https://short.test")
+			.intercept({ path: "/abc", method: "HEAD" })
+			.reply(301, "", { headers: { Location: "https://no-redirect.test/target" } });
+
+		const testUrl = "https://short.test/abc";
+		const response = await SELF.fetch(`https://example.com/?url=${encodeURIComponent(testUrl)}`);
+		expect(await response.text()).toBe("https://no-redirect.test/target");
+	});
+
+	it("falls back to GET when HEAD returns 404", async () => {
+		const pool = fetchMock.get("https://amzn-short.test");
+		pool.intercept({ path: "/d/abc123", method: "HEAD" }).reply(404);
+		pool
+			.intercept({ path: "/d/abc123", method: "GET" })
+			.reply(301, "", { headers: { Location: "https://amazon.com/dp/B123?ref_=tracking&tag=mytag" } });
+
+		const testUrl = "https://amzn-short.test/d/abc123";
+		const response = await SELF.fetch(`https://example.com/?url=${encodeURIComponent(testUrl)}`);
+		expect(await response.text()).toBe("https://amazon.com/dp/B123");
+	});
+
+	it("falls back to GET when HEAD returns 405", async () => {
+		const pool = fetchMock.get("https://head-unsupported.test");
+		pool.intercept({ path: "/link", method: "HEAD" }).reply(405);
+		pool
+			.intercept({ path: "/link", method: "GET" })
+			.reply(302, "", { headers: { Location: "https://no-redirect.test/destination" } });
+
+		const testUrl = "https://head-unsupported.test/link";
+		const response = await SELF.fetch(`https://example.com/?url=${encodeURIComponent(testUrl)}`);
+		expect(await response.text()).toBe("https://no-redirect.test/destination");
+	});
+
+	it("does not fall back to GET when HEAD returns 200", async () => {
+		fetchMock
+			.get("https://no-redirect.test")
+			.intercept({ path: "/page?utm_source=test", method: "HEAD" })
+			.reply(200);
+
+		const testUrl = "https://no-redirect.test/page?utm_source=test";
+		const response = await SELF.fetch(`https://example.com/?url=${encodeURIComponent(testUrl)}`);
+		expect(await response.text()).toBe("https://no-redirect.test/page");
+	});
+
+	it("cleans parameters on the redirect target", async () => {
+		fetchMock
+			.get("https://redir.test")
+			.intercept({ path: "/go", method: "HEAD" })
+			.reply(301, "", { headers: { Location: "https://youtube.com/watch?v=xyz&feature=share&si=track" } });
+
+		const testUrl = "https://redir.test/go";
+		const response = await SELF.fetch(`https://example.com/?url=${encodeURIComponent(testUrl)}`);
+		expect(await response.text()).toBe("https://youtube.com/watch?v=xyz");
+	});
+
+	it("handles relative redirect locations", async () => {
+		const pool = fetchMock.get("https://relative.test");
+		pool
+			.intercept({ path: "/short", method: "HEAD" })
+			.reply(301, "", { headers: { Location: "/full/path" } });
+		pool.intercept({ path: "/full/path", method: "HEAD" }).reply(200);
+
+		const testUrl = "https://relative.test/short";
+		const response = await SELF.fetch(`https://example.com/?url=${encodeURIComponent(testUrl)}`);
+		expect(await response.text()).toBe("https://relative.test/full/path");
+	});
+});