fix(rsc-mf): avoid host fallback refetching same expose URL

Author: cursoragent

tests/integration/rsc-mf/host/server/modern.server.ts

@@ -131,10 +131,12 @@ const fetchRemoteManifestFallbackAsset = async ({
   remoteOrigin,
   pathname,
   search,
+  requestUrl,
 }: {
   remoteOrigin: string;
   pathname: string;
   search: string;
+  requestUrl: string;
 }) => {
   if (!isManifestFallbackEligiblePath(pathname)) {
     return undefined;
@@ -175,6 +177,9 @@ const fetchRemoteManifestFallbackAsset = async ({
   if (!fallbackAssetUrl) {
     return undefined;
   }
+  if (fallbackAssetUrl === requestUrl) {
+    return undefined;
+  }
   const fallbackAssetResponse = await fetch(fallbackAssetUrl).catch(
     (): undefined => undefined,
   );
@@ -225,6 +230,7 @@ const proxyRemoteFederationAsset: MiddlewareHandler = async (c, next) => {
         remoteOrigin,
         pathname,
         search: reqUrl.search,
+        requestUrl: remoteUrl,
       });
 
   if (!resolvedUpstream || !resolvedUpstream.ok) {

tests/integration/rsc-mf/tests/modernServerConfig.test.ts

@@ -762,6 +762,55 @@ describe('rsc-mf host modern.server middleware contracts', () => {
     expect(context.res).toBeUndefined();
   });
 
+  it('falls through when manifest fallback resolves to original request URL', async () => {
+    const handler = getProxyMiddlewareHandler();
+    const next = jest.fn(async (): Promise<void> => undefined);
+    const fetchMock = installFetchMock(
+      jest
+        .fn()
+        .mockResolvedValueOnce(new Response('not-found', { status: 404 }))
+        .mockResolvedValueOnce(
+          new Response(
+            JSON.stringify({
+              exposes: [
+                {
+                  assets: {
+                    js: {
+                      sync: [
+                        'static/js/async/__federation_expose_RemoteClientCounter.js',
+                      ],
+                      async: [],
+                    },
+                    css: {
+                      sync: [],
+                      async: [],
+                    },
+                  },
+                },
+              ],
+            }),
+            {
+              status: 200,
+              headers: {
+                'content-type': 'application/json',
+              },
+            },
+          ),
+        ),
+    );
+    const context: { req: { url: string }; res?: Response } = {
+      req: {
+        url: 'http://127.0.0.1:3007/static/js/async/__federation_expose_RemoteClientCounter.js',
+      },
+    };
+
+    await withRemotePort('3999', () => handler(context, next));
+
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expect(next).toHaveBeenCalledTimes(1);
+    expect(context.res).toBeUndefined();
+  });
+
   it('matches fallback chunks when manifest hash suffix includes non-hex characters', async () => {
     const handler = getProxyMiddlewareHandler();
     const next = jest.fn(async (): Promise<void> => undefined);