Improve normalisation of percent-encoded request URLs

Summary:
When processing requests, Metro compares path prefixes and "extensions" to specific magic strings, eg `/[metro-project]/`. Currently, this matching is performed on the literal requested path, which makes it sensitive to URL (percent) encoding.

In particular, iOS (`NSURL urlWithString`) encodes some characters more aggressively than other clients, including encoding `[` and `]`. This causes a request for `/[metro-project]/foo.js` to fail with a 404 when executed through `NSURLRequest`, because `urlObj.pathname` begins `/%5Bmetro-project%5D/`.

Metro should ideally be insensitive to percent-encoding on all requests. This fix isn't complete, but addresses the particular blocking issue with source URLs.

```
 - **[Fix]**: Improve dev server insensitivity to percent encoding on source requests.
```

Reviewed By: motiz88

Differential Revision: D58289369

fbshipit-source-id: 616da5d5e44539996c16f103254f1b5aaa83704c

packages/metro/src/Server.js

@@ -540,7 +540,7 @@ class Server {
   ) {
     const originalUrl = req.url;
     req.url = this._rewriteAndNormalizeUrl(req.url);
-    const urlObj = url.parse(req.url, true);
+    const urlObj = url.parse(decodeURI(req.url), true);
     const {host} = req.headers;
     debug(
       `Handling request: ${host ? 'http://' + host : ''}${req.url}` +
@@ -597,11 +597,11 @@ class Server {
       for (const [pathnamePrefix, normalizedRootDir] of this
         ._sourceRequestRoutingMap) {
         if (pathname.startsWith(pathnamePrefix)) {
+          const relativePathname = pathname.substr(pathnamePrefix.length);
           await this._processSourceRequest(
-            req,
-            res,
-            pathnamePrefix,
+            relativePathname,
             normalizedRootDir,
+            res,
           );
           handled = true;
           break;
@@ -614,15 +614,10 @@ class Server {
   }
 
   async _processSourceRequest(
-    req: IncomingMessage,
-    res: ServerResponse,
-    pathnamePrefix: string,
+    relativePathname: string,
     rootDir: string,
+    res: ServerResponse,
   ): Promise<void> {
-    const urlObj = url.parse(req.url, true);
-    const relativePathname = nullthrows(urlObj.pathname).substr(
-      pathnamePrefix.length,
-    );
     if (
       !this._allowedSuffixesForSourceRequests.some(suffix =>
         relativePathname.endsWith(suffix),

packages/metro/src/integration_tests/__tests__/server-test.js

@@ -195,5 +195,20 @@ describe('Metro development server serves bundles via HTTP', () => {
         ),
       );
     });
+
+    test('requested with aggressive URL encoding /%5Bmetro-project%5D', async () => {
+      const response = await fetch(
+        'http://localhost:' +
+          config.server.port +
+          '/%5Bmetro-project%5D/Foo%2Ejs',
+      );
+      expect(response.status).toBe(200);
+      expect(await response.text()).toEqual(
+        await fs.promises.readFile(
+          path.join(__dirname, '../basic_bundle/Foo.js'),
+          'utf8',
+        ),
+      );
+    });
   });
 });