fix(prerenderer): write responses with json signature to original path (#1963)

Author: pi0

src/prerender.ts

@@ -14,6 +14,8 @@ import { compressPublicAssets } from "./compress";
 
 const allowedExtensions = new Set(["", ".json"]);
 
+const JsonSigRx = /^\s*["[{]|^\s*-?\d{1,16}(\.\d{1,17})?([Ee][+-]?\d+)?\s*$/; // From unjs/destr
+
 const linkParents = new Map<string, Set<string>>();
 
 export async function prerender(nitro: Nitro) {
@@ -220,7 +222,9 @@ export async function prerender(nitro: Nitro) {
     // Guess route type and populate fileName
     const contentType = res.headers.get("content-type") || "";
     const isImplicitHTML =
-      !route.endsWith(".html") && contentType.includes("html");
+      !route.endsWith(".html") &&
+      contentType.includes("html") &&
+      !JsonSigRx.test(dataBuff.subarray(0, 32).toString("utf8"));
     const routeWithIndex = route.endsWith("/") ? route + "index" : route;
     const htmlPath =
       route.endsWith("/") || nitro.options.prerender.autoSubfolderIndex

test/fixture/routes/json-string.ts

@@ -0,0 +1,3 @@
+export default eventHandler(() => {
+  return '{"foo":"bar"}';
+});

test/fixture/routes/prerender.ts

@@ -12,6 +12,7 @@ export default defineEventHandler((event) => {
     "../api/hey",
     "/api/param/foo.json",
     "/api/param/foo.css",
+    "/json-string",
     event.path.includes("?") ? "/api/param/hidden" : "/prerender?withQuery",
   ];
 

test/presets/cloudflare-pages.test.ts

@@ -53,6 +53,7 @@ describe("nitro:preset:cloudflare-pages", async () => {
           "/build/*",
           "/favicon.ico",
           "/icon.png",
+          "/json-string",
           "/api/hello",
           "/prerender/index.html",
           "/prerender/index.html.br",