Add example of (and fix) static asset proxy

packages/remix-oxygen/src/server.ts

@@ -23,6 +23,19 @@ export function createRequestHandler<Context = unknown>({
     request: Request,
     params: OxygenHandleRequestOptions,
   ) => Promise<Context> | Context;
+  /**
+   * By default, Hydrogen will prefix all static assets with a CDN url.
+   * If you need to serve static assets from the same domain or from the root,
+   * then update the `shouldProxyAsset: (url: string) => boolean` function below
+   * to return `true` when the url (pathname) matches your asset.
+   *
+   * @example
+   * ```ts
+   * shouldProxyAsset(url) {
+   *  return new URL(url).pathname === '/robots.txt';
+   * }
+   * ```
+   */
   shouldProxyAsset?: (url: string) => boolean;
 }) {
   const handleRequest = createRemixRequestHandler(build, mode);
@@ -39,8 +52,22 @@ export function createRequestHandler<Context = unknown>({
         shouldProxyAsset?.(request.url)
       ) {
         const url = new URL(request.url);
-        const assetBasePath = (build.publicPath || '').replace(/\/$/, '');
-        return fetch(request.url.replace(url.origin, assetBasePath), request);
+
+        /**
+         * Use the assetPrefix (publicPath) as the origin. Note that Remix expects client assets to be
+         * prefixed with `/build/*`, and as such, `/build/` is included in the Oxygen-created `assetPrefix`.
+         * However, we need strip out the leading `/build/` for this use case, as developers may wish to
+         * serve a static asset from the root `/public` folder (one level up from `/build`).
+         */
+        const newOriginAndPathPrefix = (build.publicPath || '').replace(
+          /\/build\/$/,
+          '',
+        );
+
+        return fetch(
+          request.url.replace(url.origin, newOriginAndPathPrefix),
+          request,
+        );
       }
 
       return await handleRequest(request, {