fix(webClientServer): include basePath in createRequestUrl

This patches the createRequestUrl convenience method to ensure that the basePath
is included in the returned URL in case code-server is being served behind a
reverse proxy.

An example of this would be using Caddy to server code-server on
localhost:8082/code/

This fix ensures request urls are created against localhost:8082/code/ instead
of localhost:8082/

Author: jsjoeio

src/vs/server/webClientServer.ts

@@ -164,7 +164,16 @@ export class WebClientServer {
 	private createRequestUrl(req: http.IncomingMessage, parsedUrl: url.UrlWithParsedQuery, pathname: string): URL {
 		const pathPrefix = getPathPrefix(parsedUrl.pathname!);
 		const remoteAuthority = this.getRemoteAuthority(req);
-		return new URL(path.join('/', pathPrefix, pathname), remoteAuthority);
+		/**
+		 * Prepend URL with basePath.
+		 *
+		 * This ensures the request URL includes the correct base
+		 * in case code-server is being served behind a reverse proxy.
+		 * @author coder
+		 */
+		const basePath = new URL(req.headers.referer || 'https://example.com').pathname.slice(0, -1);
+
+		return new URL(path.join(basePath, '/', pathPrefix, pathname), remoteAuthority);
 	}
 
 	private _iconSizes = [192, 512];