Restore handling of 204 "soft" redirects on data requests

.changeset/new-hornets-run.md

@@ -0,0 +1,9 @@
+---
+"react-router": patch
+---
+
+Update Single Fetch to also handle the 204 redirects used in `?_data` requests in Remix v2
+
+- This allows applications to return a redirect on `.data` requests from outside the scope of React Router (i.e., an `express`/`hono` middleware)
+- ⚠️ Please note that doing so relies on implementation details that are subject to change without a SemVer major release
+- This is primarily done to ease upgrading to Single Fetch for existing Remix v2 applications, but the recommended way to handle this is redirecting from a route middleware

integration/helpers/vite.ts

@@ -140,6 +140,7 @@ export const EXPRESS_SERVER = (args: {
   port: number;
   base?: string;
   loadContext?: Record<string, unknown>;
+  customLogic?: string;
 }) =>
   String.raw`
     import { createRequestHandler } from "@react-router/express";
@@ -166,6 +167,8 @@ export const EXPRESS_SERVER = (args: {
     }
     app.use(express.static("build/client", { maxAge: "1h" }));
 
+    ${args?.customLogic || ""}
+
     app.all(
       "*",
       createRequestHandler({

integration/single-fetch-test.ts

@@ -10,7 +10,14 @@ import {
   js,
 } from "./helpers/create-fixture.js";
 import { PlaywrightFixture } from "./helpers/playwright-fixture.js";
-import { reactRouterConfig } from "./helpers/vite.js";
+import {
+  EXPRESS_SERVER,
+  createProject,
+  customDev,
+  reactRouterConfig,
+  viteConfig,
+} from "./helpers/vite.js";
+import getPort from "get-port";
 
 const ISO_DATE = "2024-03-12T12:00:00.000Z";
 
@@ -1538,6 +1545,63 @@ test.describe("single-fetch", () => {
     expect(await app.getHtml("#target")).toContain("Target");
   });
 
+  test("processes redirects returned outside of react router", async ({
+    page,
+  }) => {
+    let port = await getPort();
+    let cwd = await createProject({
+      "vite.config.js": await viteConfig.basic({ port }),
+      "server.mjs": EXPRESS_SERVER({
+        port,
+        customLogic: js`
+          app.use(async (req, res, next) => {
+            if (req.url === "/page.data") {
+              res.status(204);
+              res.append('X-Remix-Status', '302');
+              res.append('X-Remix-Redirect', '/target');
+              res.end();
+            } else {
+              next();
+            }
+          });
+        `,
+      }),
+      "app/routes/_index.tsx": js`
+        import { Link } from "react-router";
+        export default function Component() {
+          return <Link to="/page">Go to /page</Link>
+        }
+      `,
+      "app/routes/page.tsx": js`
+        export function loader() {
+          return null
+        }
+        export default function Component() {
+          return <p>Should not see me</p>
+        }
+      `,
+      "app/routes/target.tsx": js`
+        export default function Component() {
+          return <h1 id="target">Target</h1>
+        }
+      `,
+    });
+    let stop = await customDev({ cwd, port });
+
+    try {
+      await page.goto(`http://localhost:${port}/`, {
+        waitUntil: "networkidle",
+      });
+      let link = page.locator('a[href="/page"]');
+      await expect(link).toHaveText("Go to /page");
+      await link.click();
+      await page.waitForSelector("#target");
+      await expect(page.locator("#target")).toHaveText("Target");
+    } finally {
+      stop();
+    }
+  });
+
   test("processes thrown loader errors", async ({ page }) => {
     let fixture = await createFixture({
       files: {

packages/react-router/lib/dom/ssr/single-fetch.tsx

@@ -56,6 +56,13 @@ interface StreamTransferProps {
   nonce?: string;
 }
 
+// We can't use a 3xx status or else the `fetch()` would follow the redirect.
+// We need to communicate the redirect back as data so we can act on it in the
+// client side router.  We use a 202 to avoid any automatic caching we might
+// get from a 200 since a "temporary" redirect should not be cached.  This lets
+// the user control cache behavior via Cache-Control
+export const SINGLE_FETCH_REDIRECT_STATUS = 202;
+
 // Some status codes are not permitted to have bodies, so we want to just
 // treat those as "no data" instead of throwing an exception:
 //   https://datatracker.ietf.org/doc/html/rfc9110#name-informational-1xx
@@ -535,6 +542,22 @@ async function fetchAndDecodeViaTurboStream(
     throw new ErrorResponseImpl(404, "Not Found", true);
   }
 
+  // Handle non-RR redirects (i.e., from express middleware)
+  if (res.status === 204 && res.headers.has("X-Remix-Redirect")) {
+    return {
+      status: SINGLE_FETCH_REDIRECT_STATUS,
+      data: {
+        redirect: {
+          redirect: res.headers.get("X-Remix-Redirect")!,
+          status: Number(res.headers.get("X-Remix-Status") || "302"),
+          revalidate: res.headers.get("X-Remix-Revalidate") === "true",
+          reload: res.headers.get("X-Remix-Reload-Document") === "true",
+          replace: res.headers.get("X-Remix-Replace") === "true",
+        },
+      },
+    };
+  }
+
   if (NO_BODY_STATUS_CODES.has(res.status)) {
     let routes: { [key: string]: SingleFetchResult } = {};
     // We get back just a single result for action requests - normalize that

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

@@ -29,7 +29,6 @@ import {
   getSingleFetchRedirect,
   singleFetchAction,
   singleFetchLoaders,
-  SINGLE_FETCH_REDIRECT_STATUS,
   SERVER_NO_BODY_STATUS_CODES,
 } from "./single-fetch";
 import { getDocumentHeaders } from "./headers";
@@ -38,7 +37,10 @@ import type {
   SingleFetchResult,
   SingleFetchResults,
 } from "../dom/ssr/single-fetch";
-import { SingleFetchRedirectSymbol } from "../dom/ssr/single-fetch";
+import {
+  SINGLE_FETCH_REDIRECT_STATUS,
+  SingleFetchRedirectSymbol,
+} from "../dom/ssr/single-fetch";
 import type { MiddlewareEnabled } from "../types/future";
 
 export type RequestHandler = (

packages/react-router/lib/server-runtime/single-fetch.ts

@@ -20,6 +20,7 @@ import type {
 } from "../dom/ssr/single-fetch";
 import {
   NO_BODY_STATUS_CODES,
+  SINGLE_FETCH_REDIRECT_STATUS,
   SingleFetchRedirectSymbol,
 } from "../dom/ssr/single-fetch";
 import type { AppLoadContext } from "./data";
@@ -28,13 +29,6 @@ import { ServerMode } from "./mode";
 import { getDocumentHeaders } from "./headers";
 import type { ServerBuild } from "./build";
 
-// We can't use a 3xx status or else the `fetch()` would follow the redirect.
-// We need to communicate the redirect back as data so we can act on it in the
-// client side router.  We use a 202 to avoid any automatic caching we might
-// get from a 200 since a "temporary" redirect should not be cached.  This lets
-// the user control cache behavior via Cache-Control
-export const SINGLE_FETCH_REDIRECT_STATUS = 202;
-
 // Add 304 for server side - that is not included in the client side logic
 // because the browser should fill those responses with the cached data
 // https://datatracker.ietf.org/doc/html/rfc9110#name-304-not-modified