fix(core): docusaurus serve redirects should include the site `/bas…

…eUrl/` prefix (#10090)

packages/docusaurus/src/commands/serve.ts

@@ -12,11 +12,19 @@ import logger from '@docusaurus/logger';
 import {DEFAULT_BUILD_DIR_NAME} from '@docusaurus/utils';
 import serveHandler from 'serve-handler';
 import openBrowser from 'react-dev-utils/openBrowser';
+import {applyTrailingSlash} from '@docusaurus/utils-common';
 import {loadSiteConfig} from '../server/config';
 import {build} from './build';
 import {getHostPort, type HostPortOptions} from '../server/getHostPort';
 import type {LoadContextParams} from '../server/site';
 
+function redirect(res: http.ServerResponse, location: string) {
+  res.writeHead(302, {
+    Location: location,
+  });
+  res.end();
+}
+
 export type ServeCLIOptions = HostPortOptions &
   Pick<LoadContextParams, 'config'> & {
     dir?: string;
@@ -62,15 +70,24 @@ export async function serve(
   const server = http.createServer((req, res) => {
     // Automatically redirect requests to /baseUrl/
     if (!req.url?.startsWith(baseUrl)) {
-      res.writeHead(302, {
-        Location: baseUrl,
-      });
-      res.end();
+      redirect(res, baseUrl);
+      return;
+    }
+
+    // We do the redirect ourselves for a good reason
+    // server-handler is annoying and won't include /baseUrl/ in redirects
+    const normalizedUrl = applyTrailingSlash(req.url, {trailingSlash, baseUrl});
+    if (req.url !== normalizedUrl) {
+      redirect(res, normalizedUrl);
       return;
     }
 
     // Remove baseUrl before calling serveHandler, because /baseUrl/ should
     // serve /build/index.html, not /build/baseUrl/index.html (does not exist)
+    // Note server-handler is really annoying here:
+    // - no easy way to do rewrites such as "/baseUrl/:path" => "/:path"
+    // - no easy way to "reapply" the baseUrl to the redirect "Location" header
+    // See also https://github.com/facebook/docusaurus/pull/10090
     req.url = req.url.replace(baseUrl, '/');
 
     serveHandler(req, res, {