From 9618ffe05feb13a0e7214c2095be97425fec62ef Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Mon, 7 Nov 2022 12:42:26 -0800
Subject: [PATCH] [next] Update rsc header handling (#8862)
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### Related Issues

Required for https://github.com/vercel/next.js/pull/42482

### 📋 Checklist

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#### Tests

- [ ] The code changed/added as part of this PR has been covered with
tests
- [ ] All tests pass locally with `yarn test-unit`

#### Code Review

- [ ] This PR has a concise title and thorough description useful to a
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- [ ] Issue from task tracker has a link to this PR
---
 packages/next/src/server-build.ts |  6 ++++--
 packages/next/src/utils.ts        | 11 +++++++++--
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/packages/next/src/server-build.ts b/packages/next/src/server-build.ts
index 590a327b920..5fd88e9b63c 100644
--- a/packages/next/src/server-build.ts
+++ b/packages/next/src/server-build.ts
@@ -1137,6 +1137,8 @@ export async function serverBuild({
     }
   }
 
+  const rscHeader = routesManifest.rsc?.header || '__rsc__';
+
   return {
     wildcard: wildcardConfig,
     images:
@@ -1390,7 +1392,7 @@ export async function serverBuild({
               has: [
                 {
                   type: 'header',
-                  key: '__rsc__',
+                  key: rscHeader,
                 },
               ],
               dest: path.posix.join('/', entryDirectory, '/index.rsc'),
@@ -1401,7 +1403,7 @@ export async function serverBuild({
               has: [
                 {
                   type: 'header',
-                  key: '__rsc__',
+                  key: rscHeader,
                 },
               ],
               dest: path.posix.join('/', entryDirectory, '/$1.rsc'),
diff --git a/packages/next/src/utils.ts b/packages/next/src/utils.ts
index c8a43b7906e..c1553fcf437 100644
--- a/packages/next/src/utils.ts
+++ b/packages/next/src/utils.ts
@@ -209,6 +209,10 @@ type RoutesManifestOld = {
       defaultLocale: string;
     }>;
   };
+  rsc?: {
+    header: string;
+    varyHeader: string;
+  };
 };
 
 type RoutesManifestV4 = Omit<RoutesManifestOld, 'dynamicRoutes' | 'version'> & {
@@ -1991,6 +1995,9 @@ export const onPrerenderRoute =
           allowQuery = [];
         }
       }
+      const rscVaryHeader =
+        routesManifest?.rsc?.varyHeader ||
+        '__rsc__, __next_router_state_tree__, __next_router_prefetch__';
 
       prerenders[outputPathPage] = new Prerender({
         expiration: initialRevalidate,
@@ -2008,7 +2015,7 @@ export const onPrerenderRoute =
         ...(isAppPathRoute
           ? {
               initialHeaders: {
-                vary: '__rsc__, __next_router_state_tree__, __next_router_prefetch__',
+                vary: rscVaryHeader,
               },
             }
           : {}),
@@ -2031,7 +2038,7 @@ export const onPrerenderRoute =
           ? {
               initialHeaders: {
                 'content-type': 'application/octet-stream',
-                vary: '__rsc__, __next_router_state_tree__, __next_router_prefetch__',
+                vary: rscVaryHeader,
               },
             }
           : {}),