Add on-error hook (#4233)

* Add on-error hook

Closes #2906

* Ignore unspecified listeners

* Document error hook

api/src/emitter.ts

@@ -1,7 +1,14 @@
 import { EventEmitter2 } from 'eventemitter2';
 import logger from './logger';
 
-const emitter = new EventEmitter2({ wildcard: true, verboseMemoryLeak: true, delimiter: '.' });
+const emitter = new EventEmitter2({
+	wildcard: true,
+	verboseMemoryLeak: true,
+	delimiter: '.',
+
+	// This will ignore the "unspecified event" error
+	ignoreErrors: true,
+});
 
 /**
  * Emit async events without throwing errors. Just log them out as warnings.

api/src/middleware/error-handler.ts

@@ -3,6 +3,7 @@ import { BaseException } from '../exceptions';
 import logger from '../logger';
 import env from '../env';
 import { toArray } from '../utils/to-array';
+import { emitAsyncSafe } from '../emitter';
 
 const errorHandler: ErrorRequestHandler = (err, req, res, next) => {
 	let payload: any = {
@@ -66,7 +67,9 @@ const errorHandler: ErrorRequestHandler = (err, req, res, next) => {
 		}
 	}
 
-	return res.json(payload);
+	emitAsyncSafe('error', payload.errors).then(() => {
+		return res.json(payload);
+	});
 };
 
 export default errorHandler;

docs/guides/api-hooks.md

@@ -81,8 +81,9 @@ module.exports = function registerHook({ exceptions }) {
 | `middlewares.init`   | `before` and `after`               | No       |
 | `request`            | `not_found`                        | No       |
 | `response`           |                                    | No†      |
-| `items`              | `create`, `update` and `delete`    | Optional |
+| `error`              |                                    | No       |
 | `auth`               | `success`†, `fail`† and `refresh`† | No       |
+| `items`              | `create`, `update` and `delete`    | Optional |
 | `activity`           | `create`, `update` and `delete`    | Optional |
 | `collections`        | `create`, `update` and `delete`    | Optional |
 | `fields`             | `create`, `update` and `delete`    | Optional |