Handle 404 status code in the proxyResponse.

CHANGELOG.md

@@ -0,0 +1 @@
+- Fixes issue with custom 404 pages not being returned in Next.js in the emulator (#8035).

src/frameworks/utils.ts

@@ -23,7 +23,7 @@
 
 // Use "true &&"" to keep typescript from compiling this file and rewriting
 // the import statement into a require
 const { dynamicImport } = require(true && "../dynamicImport");
 
 const NPM_ROOT_TIMEOUT_MILLIES = 5_000;
 const NPM_ROOT_MEMO = new Map<string, string>();
@@ -40,7 +40,7 @@
  *
  * Note: `throws: false` won't work with the async function: https://github.com/jprichardson/node-fs-extra/issues/542
  */
 export function readJSON<JsonType = any>(
   file: string,
   options?: ReadOptions | BufferEncoding | string,
 ): Promise<JsonType> {
@@ -57,10 +57,10 @@
   defaultBuildScripts: string[],
 ): Promise<void> {
   const packageJsonBuffer = await readFile(join(dir, "package.json"));
   const packageJson = JSON.parse(packageJsonBuffer.toString());
   const buildScript = packageJson.scripts?.build;
 
   if (buildScript && !defaultBuildScripts.includes(buildScript)) {
     console.warn(
       `\nWARNING: Your package.json contains a custom build that is being ignored. Only the ${framework} default build script (e.g, "${defaultBuildScripts[0]}") is respected. If you have a more advanced build process you should build a custom integration https://firebase.google.com/docs/hosting/express\n`,
     );
@@ -149,7 +149,7 @@
         next();
       } else {
         for (const [fn, args] of buffer) {
           (res as any)[fn](...args);
         }
         res.end(...args);
         buffer.length = 0;
@@ -208,7 +208,12 @@
         originalRes.end();
       });
     } else {
-      const proxiedRes = proxyResponse(originalReq, originalRes, next);
+      const proxiedRes = proxyResponse(originalReq, originalRes, () => {
+        // This next function is called when the proxied response is a 404
+        // In that case we want to let the handler to use the original response
+        void hostOrRequestHandler(originalReq, originalRes, next);
+      });
+
       await hostOrRequestHandler(originalReq, proxiedRes, next);
     }
   };