fix: enable redirection to a relative path (#168)

Author: ajfAfg

src/no-dead-link.ts

@@ -183,16 +183,29 @@ const createCheckAliveURL = (ruleOptions: Options) => {
             const res = await fetchWithDefaults(uri, opts);
             // redirected
             if (isRedirect(res.status)) {
-                const redirectedUrl = res.headers.get("Location");
+                const location = res.headers.get("Location");
                 // Status code is 301 or 302, but Location header is not set
-                if (redirectedUrl === null) {
+                if (location === null) {
                     return {
                         ok: false,
                         redirected: true,
                         redirectTo: null,
                         message: `${res.status} ${res.statusText}`
                     };
                 }
+
+                const redirectedUrl = isRelative(location)
+                    ? URL.parse(location, URL.parse(uri)?.origin)?.href
+                    : location;
+                if (!redirectedUrl) {
+                    return {
+                        ok: false,
+                        redirected: true,
+                        redirectTo: null,
+                        message: `${res.status} ${res.statusText}`
+                    };
+                }
+
                 const finalRes = await fetchWithDefaults(redirectedUrl, { ...opts, redirect: "follow" });
                 const url = URL.parse(uri);
                 const hash = url?.hash || null;

test/no-dead-link.ts

@@ -121,6 +121,13 @@ tester.run("no-dead-link", rule, {
                 ignoreRedirects: true
             }
         },
+        // Test whether redirection to a relative path is possible
+        {
+            text: `should handle relative redirect: ${TEST_SERVER_URL}/301-relative`,
+            options: {
+                ignoreRedirects: true
+            }
+        },
         // Test User-Agent requirement
         {
             text: `should treat 200 OK when User-Agent is provided: ${TEST_SERVER_URL}/user-agent-required`,

test/test-server.ts

@@ -72,6 +72,15 @@ export async function startTestServer(options: TestServerOptions = {}): Promise<
                 res.end("Moved Permanently");
                 break;
 
+            case "/301-relative":
+                // Redirect to a relative URL
+                res.writeHead(301, {
+                    Location: `200`,
+                    "Content-Type": "text/plain"
+                });
+                res.end("Moved Permanently");
+                break;
+
             case "/user-agent-required":
                 // Requires specific User-Agent header
                 if (req.headers["user-agent"] && req.headers["user-agent"].includes("Mozilla")) {