wrong redirect in local server (mdn#2179)

* wrong redirect in local server

Part of #350

* end-to-end tests

server/index.js

@@ -192,34 +192,23 @@ app.get("/*", async (req, res) => {
       clearKumascriptRenderCache: true,
     });
     console.timeEnd(`buildDocumentFromURL(${lookupURL})`);
-    if (!built) {
-      return res
-        .status(404)
-        .sendFile(path.join(STATIC_ROOT, "en-us", "_spas", "404.html"));
+    if (built) {
+      document = built.doc;
+      bcdData = built.bcdData;
     }
-    document = built.doc;
-    bcdData = built.bcdData;
   } catch (error) {
     console.error(`Error in buildDocumentFromURL(${lookupURL})`, error);
     return res.status(500).send(error.toString());
   }
 
   if (!document) {
-    // redirect resolving can take some time, so we only do it when there's no document
-    // for the current route
     const redirectURL = Redirect.resolve(lookupURL);
     if (redirectURL !== lookupURL) {
       return res.redirect(301, redirectURL + extraSuffix);
     }
-
-    // It doesn't resolve to a file on disk and it's not a redirect.
-    // Try to send a slightly better error at least.
     return res
       .status(404)
-      .send(
-        `From URL ${lookupURL} no folder on disk could be found. ` +
-          `Tried to find a folder called ${Document.urlToFolderPath(lookupURL)}`
-      );
+      .sendFile(path.join(STATIC_ROOT, "en-us", "_spas", "404.html"));
   }
 
   if (bcdDataURL) {

testing/tests/developing.test.js

@@ -76,6 +76,36 @@ describe("Testing the Express server", () => {
     expect(response.headers.location).toBe("/en-US/docs/Web");
   });
 
+  withDeveloping("redirect based on _redirects.txt", async () => {
+    // Yes, this is a bit delicate since it depends on non-fixtures, but
+    // it's realistic and it's a good end-to-end test.
+    // See mdn/content/files/en-us/_redirects.txt
+
+    // First redirect *out* to an external URL.
+    let response = await got(
+      serverURL(
+        "/en-US/docs/Mozilla/Add-ons/WebExtensions/Publishing_your_WebExtension"
+      ),
+      { followRedirect: false }
+    );
+    expect(response.statusCode).toBe(301);
+    expect(response.headers.location).toBe(
+      "https://extensionworkshop.com/documentation/publish/package-your-extension/"
+    );
+
+    // Redirect within.
+    response = await got(
+      serverURL(
+        "/en-US/docs/Mozilla/Add-ons/WebExtensions/Extension_API_differences"
+      ),
+      { followRedirect: false }
+    );
+    expect(response.statusCode).toBe(301);
+    expect(response.headers.location).toBe(
+      "/en-US/docs/Mozilla/Add-ons/WebExtensions/Differences_between_API_implementations"
+    );
+  });
+
   withDeveloping("redirect by preferred locale cookie", async () => {
     let response = await got(serverURL("/"), {
       followRedirect: false,