Forward headers from React to static output and dynamic render

packages/next/src/export/routes/app-page.ts

@@ -1,6 +1,5 @@
 import type { ExportRouteResult, FileWriter } from '../types'
 import type { RenderOpts } from '../../server/app-render/types'
-import type { OutgoingHttpHeaders } from 'http'
 import type { NextParsedUrlQuery } from '../../server/request-meta'
 import type { RouteMetadata } from './types'
 
@@ -184,9 +183,10 @@ export async function exportAppPage(
       )
     }
 
-    let headers: OutgoingHttpHeaders | undefined
+    const headers = { ...metadata.extraHeaders }
+
     if (fetchTags) {
-      headers = { [NEXT_CACHE_TAGS_HEADER]: fetchTags }
+      headers[NEXT_CACHE_TAGS_HEADER] = fetchTags
     }
 
     // Writing static HTML to a file.

packages/next/src/server/app-render/app-render.tsx

@@ -736,9 +736,21 @@ async function renderToHTMLOrFlightImpl(
         hasPostponed,
       })
 
+      function onHeaders(headers: Headers): void {
+        // Copy headers created by React into the response object.
+        headers.forEach((value: string, key: string) => {
+          res.appendHeader(key, value)
+          if (!extraRenderResultMeta.extraHeaders) {
+            extraRenderResultMeta.extraHeaders = {}
+          }
+          extraRenderResultMeta.extraHeaders[key] = value
+        })
+      }
+
       try {
         const renderStream = await renderer.render(content, {
           onError: htmlRendererErrorHandler,
+          onHeaders: onHeaders,
           nonce,
           bootstrapScripts: [bootstrapScript],
           formState,

packages/next/src/server/app-render/static/static-renderer.ts

@@ -1,5 +1,6 @@
 type StreamOptions = {
   onError?: (error: Error) => void
+  onHeaders?: (headers: Headers) => void
   nonce?: string
   bootstrapScripts?: {
     src: string
@@ -38,6 +39,10 @@ class StaticResumeRenderer implements Renderer {
   constructor(private readonly postponed: object) {}
 
   public async render(children: JSX.Element, streamOptions: StreamOptions) {
+    // TODO: Refactor StreamOptions because not all options apply to all React
+    // functions so this factoring of trying to reuse a single render() doesn't
+    // make sense. This is passing multiple invalid options that React should
+    // error for.
     const stream = await this.resume(children, this.postponed, streamOptions)
 
     return { stream }

packages/next/src/server/base-server.ts

@@ -2373,10 +2373,11 @@ export default abstract class Server<ServerOptions extends Options = Options> {
 
       // Add any fetch tags that were on the page to the response headers.
       const cacheTags = metadata.fetchTags
+
+      headers = { ...metadata.extraHeaders }
+
       if (cacheTags) {
-        headers = {
-          [NEXT_CACHE_TAGS_HEADER]: cacheTags,
-        }
+        headers[NEXT_CACHE_TAGS_HEADER] = cacheTags
       }
 
       // Pull any fetch metrics from the render onto the request.
@@ -2769,6 +2770,23 @@ export default abstract class Server<ServerOptions extends Options = Options> {
         )
       }
 
+      if (cachedData.headers) {
+        const resHeaders = cachedData.headers
+        for (const key of Object.keys(resHeaders)) {
+          if (key === NEXT_CACHE_TAGS_HEADER) {
+            // Not sure if needs to be special.
+            continue
+          }
+          let v = resHeaders[key]
+          if (typeof v !== 'undefined') {
+            if (typeof v === 'number') {
+              v = v.toString()
+            }
+            res.setHeader(key, v)
+          }
+        }
+      }
+
       if (
         this.minimalMode &&
         isSSG &&

packages/next/src/server/render-result.ts

@@ -1,4 +1,4 @@
-import type { ServerResponse } from 'http'
+import type { OutgoingHttpHeaders, ServerResponse } from 'http'
 import type { StaticGenerationStore } from '../client/components/static-generation-async-storage.external'
 import type { Revalidate } from './lib/revalidate'
 
@@ -23,6 +23,7 @@ export type RenderResultMetadata = {
   isRedirect?: boolean
   fetchMetrics?: StaticGenerationStore['fetchMetrics']
   fetchTags?: string
+  extraHeaders?: OutgoingHttpHeaders
   waitUntil?: Promise<any>
   postponed?: string
 }