fix(core): App should not crash with a custom rest endpoint (#5911)

fixes #5880

packages/cli/src/Server.ts

@@ -10,7 +10,7 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
 /* eslint-disable @typescript-eslint/no-unsafe-member-access */
 /* eslint-disable @typescript-eslint/no-unsafe-assignment */
-
+import assert from 'assert';
 import { exec as callbackExec } from 'child_process';
 import { access as fsAccess } from 'fs/promises';
 import os from 'os';
@@ -452,6 +452,11 @@ class Server extends AbstractServer {
 			...excludeEndpoints.split(':'),
 		].filter((u) => !!u);
 
+		assert(
+			!ignoredEndpoints.includes(this.restEndpoint),
+			`REST endpoint cannot be set to any of these values: ${ignoredEndpoints.join()} `,
+		);
+
 		// eslint-disable-next-line no-useless-escape
 		const authIgnoreRegex = new RegExp(`^\/(${ignoredEndpoints.join('|')})\/?.*$`);
 

packages/cli/src/commands/start.ts

@@ -144,6 +144,7 @@ export class Start extends BaseCommand {
 	private async generateStaticAssets() {
 		// Read the index file and replace the path placeholder
 		const n8nPath = config.getEnv('path');
+		const restEndpoint = config.getEnv('endpoints.rest');
 		const hooksUrls = config.getEnv('externalFrontendHooksUrls');
 
 		let scriptsString = '';
@@ -167,6 +168,7 @@ export class Start extends BaseCommand {
 				];
 				if (filePath.endsWith('index.html')) {
 					streams.push(
+						replaceStream('{{REST_ENDPOINT}}', restEndpoint, { ignoreCase: false }),
 						replaceStream(closingTitleTag, closingTitleTag + scriptsString, {
 							ignoreCase: false,
 						}),