fix(react-router): Preserve headers on action redirects

integration/redirects-test.ts

@@ -150,6 +150,42 @@ test.describe("redirects", () => {
                 return <h1 id="d">D</h1>
               }
             `,
+
+            "app/routes/headers.tsx": js`
+              import * as React from 'react';
+              import { Link, Form, redirect, useLocation } from 'react-router';
+
+              export function action() {
+                return redirect('/headers?action-redirect', {
+                  headers: { 'X-Test': 'Foo' }
+                })
+              }
+
+              export function loader({ request }) {
+                let url = new URL(request.url);
+                if (url.searchParams.has('redirect')) {
+                  return redirect('/headers?loader-redirect', {
+                    headers: { 'X-Test': 'Foo' }
+                  })
+                }
+                return null
+              }
+
+              export default function Component() {
+                let location = useLocation()
+                return (
+                  <>
+                    <Link id="loader-redirect" to="/headers?redirect">Redirect</Link>
+                    <Form method="post">
+                      <button id="action-redirect" type="submit">Action Redirect</button>
+                    </Form>
+                    <p id="search-params">
+                      Search Params: {location.search}
+                    </p>
+                  </>
+                );
+              }
+            `,
           },
         });
 
@@ -224,6 +260,49 @@ test.describe("redirects", () => {
         await page.goBack();
         await page.waitForSelector("#a"); // [/a]
       });
+
+      test("maintains custom headers on redirects", async ({ page }) => {
+        let app = new PlaywrightFixture(appFixture, page);
+
+        let hasGetHeader = false;
+        let hasPostHeader = false;
+        page.on("request", async (request) => {
+          let extension = /^rsc/.test(templateName) ? "rsc" : "data";
+          if (
+            request.method() === "GET" &&
+            request.url().endsWith(`headers.${extension}?redirect=`)
+          ) {
+            const headers = (await request.response())?.headers() || {};
+            hasGetHeader = headers["x-test"] === "Foo";
+          }
+          if (
+            request.method() === "POST" &&
+            request.url().endsWith(`headers.${extension}`)
+          ) {
+            const headers = (await request.response())?.headers() || {};
+            hasPostHeader = headers["x-test"] === "Foo";
+          }
+        });
+
+        await app.goto("/headers", true);
+        await app.clickElement("#loader-redirect");
+        await expect(page.locator("#search-params")).toHaveText(
+          "Search Params: ?loader-redirect"
+        );
+        expect(hasGetHeader).toBe(true);
+        expect(hasPostHeader).toBe(false);
+
+        hasGetHeader = false;
+        hasPostHeader = false;
+
+        await app.goto("/headers", true);
+        await app.clickElement("#action-redirect");
+        await expect(page.locator("#search-params")).toHaveText(
+          "Search Params: ?action-redirect"
+        );
+        expect(hasGetHeader).toBe(false);
+        expect(hasPostHeader).toBe(true);
+      });
     });
   }
 });

packages/react-router/lib/rsc/server.rsc.ts

@@ -649,13 +649,24 @@ function generateRedirectResponse(
     status: response.status,
     actionResult,
   };
+
+  // Preserve non-internal headers on the user-created redirect
+  let headers = new Headers(response.headers);
+  headers.delete("Location");
+  headers.delete("X-Remix-Reload-Document");
+  headers.delete("X-Remix-Replace");
+  // Remove Content-Length because node:http will truncate the response body
+  // to match the Content-Length header, which can result in incomplete data
+  // if the actual encoded body is longer.
+  // https://nodejs.org/api/http.html#class-httpclientrequest
+  headers.delete("Content-Length");
+  headers.set("Content-Type", "text/x-component");
+  headers.set("Vary", "Content-Type");
+
   return generateResponse(
     {
       statusCode: SINGLE_FETCH_REDIRECT_STATUS,
-      headers: new Headers({
-        "Content-Type": "text/x-component",
-        Vary: "Content-Type",
-      }),
+      headers,
       payload,
     },
     { temporaryReferences }
@@ -708,6 +719,12 @@ async function generateStaticContextResponse(
     (match) => (match as RouteMatch<string, RSCRouteConfigEntry>).route.headers
   );
 
+  // Remove Content-Length because node:http will truncate the response body
+  // to match the Content-Length header, which can result in incomplete data
+  // if the actual encoded body is longer.
+  // https://nodejs.org/api/http.html#class-httpclientrequest
+  headers.delete("Content-Length");
+
   const baseRenderPayload: Omit<RSCRenderPayload, "matches" | "patches"> = {
     type: "render",
     actionData: staticContext.actionData,