# # Custom API Hooks

> Custom API Hooks allow running custom logic when a specified event occurs within your project. There are different types of events to choose from.

## # Extension Entrypoint

The entrypoint of your hook is the `index` file inside the `src/` folder of your extension package. It exports a register function to register one or more event listeners.

Example of an entrypoint:

    export default ({ filter, action }) => {
    	filter('items.create', () => {
    		console.log('Creating Item!');
    	});

    	action('items.create', () => {
    		console.log('Item created!');
    	});
    };

## # Events

Your hook can trigger on a variety of different events. An event is defined by its type and its name.

There are four event types to choose from:

- Filter
- Action
- Init
- Schedule

Use filter hooks when you want the hook to fire before the event. Use action hooks when you want the hook to fire after the event.

### # Filter

Filter hooks act on the event's payload before the event is fired. They allow you to check, modify, or cancel an event.

Below is an example of canceling a `create` event by throwing a standard Gitaflow exception.

    export default ({ filter }, { exceptions }) => {
    	const { InvalidPayloadException } = exceptions;

    	filter('items.create', async (input) => {
    		if (LOGIC_TO_CANCEL_EVENT) {
    			throw new InvalidPayloadException(WHAT_IS_WRONG);
    		}

    		return input;
    	});
    };

The filter register function receives two parameters:

- The event name
- A callback function that is executed whenever the event fires.

The callback function itself receives three parameters:

- The modifiable payload
- An event-specific meta object
- A context object

The context object has the following properties:

- `database` — The current database transaction
- `schema` — The current API schema in use
- `accountability` — Information about the current user

Performance

Filters can impact performance when not carefully implemented, as they are executed in a blocking manner. This applies in particular to filters firing on `read` events, where a single request can result in a large amount of database reads.

### # Action

Action hooks execute after a defined event and receive data related to the event. Use action hooks when you need to automate responses to CRUD events on items or server actions.

The action register function receives two parameters:

- The event name
- A callback function that is executed whenever the event fires.

The callback function itself receives two parameters:

- An event-specific meta object
- A context object

The context object has the following properties:

- `database` — The current database transaction
- `schema` — The current API schema in use
- `accountability` — Information about the current user

### # Init

Init hooks execute at a defined point within the lifecycle of Gitaflow. Use init hook objects to inject logic into internal services.

The init register function receives two parameters:

- The event name
- A callback function that is executed whenever the event fires.

The callback function itself receives one parameter:

- An event-specific meta object

### # Schedule

Schedule hooks execute at certain points in time rather than when Gitaflow performs a specific action. This is supported through `node-cron`
(opens new window).

To set up a scheduled event, provide a cron statement as the first parameter to the `schedule()` function. For example `schedule('15 14 1 * *', <...>)` (at 14:15 on day-of-month 1) or `schedule('5 4 * * sun', <...>)` (at 04:05 on Sunday).

Below is an example of registering a schedule hook.

    import axios from 'axios';

    export default ({ schedule }) => {
    	schedule('*/15 * * * *', async () => {
    		await axios.post('http://example.com/webhook', { message: 'Another 15 minutes passed...' });
    	});
    };

## # Available Events

### # Filter Events

Name | Payload | Meta
--- | --- | ---
`request.not_found` | `false` | `request`, `response`
`request.error` | The request errors | --
`database.error` | The database error | `client`
`auth.login` | The login payload | `status`, `user`, `provider`
`auth.jwt` | The auth token | `status`, `user`, `provider`, `type`
`authenticate` | The empty accountability object | `req`
`(<collection>.)items.read` | The read item | `query`, `collection`
`(<collection>.)items.create` | The new item | `collection`
`(<collection>.)items.update` | The updated item | `keys`, `collection`
`(<collection>.)items.delete` | The keys of the item | `collection`
`<system-collection>.create` | The new item | `collection`
`<system-collection>.update` | The updated item | `keys`, `collection`
`<system-collection>.delete` | The keys of the item | `collection`

System Collections

`<system-collection>` should be replaced with one of the system collection names `activity`, `collections`, `fields`, `files` (except create/update), `folders`, `permissions`, `presets`, `relations`, `revisions`, `roles`, `settings`, `users` or `webhooks`.

### # Action Events

Name | Meta
--- | ---
`server.start` | `server`
`server.stop` | `server`
`response` | `request`, `response`, `ip`, `duration`, `finished`
`auth.login` | `payload`, `status`, `user`, `provider`
`files.upload` | `payload`, `key`, `collection`
`(<collection>.)items.read` | `payload`, `query`, `collection`
`(<collection>.)items.create` | `payload`, `key`, `collection`
`(<collection>.)items.update` | `payload`, `keys`, `collection`
`(<collection>.)items.delete` | `keys`, `collection`
`(<collection>.)items.sort` | `collection`, `item`, `to`
`<system-collection>.create` | `payload`, `key`, `collection`
`<system-collection>.update` | `payload`, `keys`, `collection`
`<system-collection>.delete` | `keys`, `collection`

System Collections

`<system-collection>` should be replaced with one of the system collection names `activity`, `collections`, `fields`, `files` (except create/update), `folders`, `permissions`, `presets`, `relations`, `revisions`, `roles`, `settings`, `users` or `webhooks`.

### # Init Events

Name | Meta
--- | ---
`cli.before` | `program`
`cli.after` | `program`
`app.before` | `app`
`app.after` | `app`
`routes.before` | `app`
`routes.after` | `app`
`routes.custom.before` | `app`
`routes.custom.after` | `app`
`middlewares.before` | `app`
`middlewares.after` | `app`

## # Register Function

The register function receives an object containing the type-specific register functions as the first parameter:

- `filter` — Listen for a filter event
- `action` — Listen for an action event
- `init` — Listen for an init event
- `schedule` — Execute a function at certain points in time

The second parameter is a context object with the following properties:

- `services` — All API internal services
- `exceptions` — API exception objects that can be used for throwing "proper" errors
- `database` — Knex instance that is connected to the current database
- `getSchema` — Async function that reads the full available schema for use in services
- `env` — Parsed environment variables
- `logger` — Pino
  (opens new window) instance.
- `emitter` — Event emitter
  (opens new window) instance that can be used to trigger custom events for other extensions.

Event loop

When implementing custom events using the emitter make sure you never directly or indirectly emit the same event your hook is currently handling as that would result in an infinite loop!

## # Example: Sync with External

    import axios from 'axios';

    export default ({ filter }, { services, exceptions }) => {
    	const { MailService } = services;
    	const { ServiceUnavailableException, ForbiddenException } = exceptions;

    	// Sync with external recipes service, cancel creation on failure
    	filter('items.create', async (input, { collection }, { schema }) => {
    		if (collection !== 'recipes') return input;

    		const mailService = new MailService({ schema });

    		try {
    			await axios.post('https://example.com/recipes', input);
    			await mailService.send({
    				to: 'person@example.com',
    				template: {
    					name: 'item-created',
    					data: {
    						collection: collection,
    					},
    				},
    			});
    		} catch (error) {
    			throw new ServiceUnavailableException(error);
    		}

    		input.syncedWithExample = true;

    		return input;
    	});
    };