Add X-Prerender-Bypass-Mode header support

vercel · Feb 8, 2020 · c4e4a61 · c4e4a61
1 parent 8d4d990
commit c4e4a61
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Showing 2 changed files with 9 additions and 3 deletions.
diff --git a/packages/next/next-server/server/api-utils.ts b/packages/next/next-server/server/api-utils.ts
@@ -253,7 +253,6 @@ export function sendJson(res: NextApiResponse, jsonBody: any): void {
   res.send(jsonBody)
 }
 
-// X-Prerender-Bypass-Mode
 const COOKIE_NAME_PRERENDER_BYPASS = `__prerender_bypass`
 const COOKIE_NAME_PRERENDER_DATA = `__next_preview_data`
 

diff --git a/packages/next/next-server/server/next-server.ts b/packages/next/next-server/server/next-server.ts
@@ -1034,8 +1034,15 @@ export default class Server {
       return { html, pageData, sprRevalidate }
     })
 
-    // render fallback if cached data wasn't available
-    if (!isResSent(res) && !isDataReq && isDynamicRoute(pathname)) {
+    // render fallback if for a preview path or a non-seeded dynamic path
+    if (
+      !isResSent(res) &&
+      !isDataReq &&
+      ((isPreviewMode &&
+        // A header can opt into the blocking behavior.
+        req.headers['X-Prerender-Bypass-Mode'] !== 'Blocking') ||
+        isDynamicRoute(pathname))
+    ) {
       let html = ''
 
       if (!this.renderOpts.dev) {