Links & Callbacks

These decorators document advanced OpenAPI features: response-driven navigation (links) and webhook delivery (callbacks). Both are optional — most APIs don't need them.

Response links

OpenAPI links describe how values from a response can be used as input to another operation. This is useful for HATEOAS-style navigation in the generated spec.

Basic usage

import { SwaggerLink } from '@moostjs/swagger'

@SwaggerLink('GetUser', {
  operationId: 'getUser',
  parameters: { userId: '$response.body#/id' },
})
@SwaggerResponse(201, UserDto)
@Post()
create(@Body() dto: CreateUserDto) {
  // The 201 response includes a link: "use the id from this response to call getUser"
}

Target modes

A link must reference a target operation. Three modes are supported:

By operationId string — references any operation by its operationId:

@SwaggerLink('GetUser', {
  operationId: 'getUser',
  parameters: { userId: '$response.body#/id' },
})

By handler reference — type-safe, resolved to the actual operationId at mapping time:

@SwaggerLink('GetUser', {
  handler: [UserController, 'getUser'],
  parameters: { userId: '$response.body#/id' },
})

This is the recommended approach within a Moost application. If the target handler is renamed or moved, TypeScript flags the reference at compile time.

By operationRef — JSON pointer for cross-document or non-standard references:

@SwaggerLink('ExternalOp', {
  operationRef: '#/paths/~1users~1{id}/get',
  parameters: { id: '$response.body#/userId' },
})

Multiple links

Stack multiple @SwaggerLink decorators to add several links to the same response:

@SwaggerLink('GetUser', {
  handler: [UserController, 'getUser'],
  parameters: { userId: '$response.body#/id' },
})
@SwaggerLink('ListOrders', {
  handler: [OrderController, 'listByUser'],
  parameters: { userId: '$response.body#/id' },
})
@SwaggerResponse(201, UserDto)
@Post()
create(@Body() dto: CreateUserDto) { /* ... */ }

Status codes

By default, a link attaches to the default success status code for the HTTP method (200 for GET/PUT, 201 for POST, 204 for DELETE). Target a specific status code with the 3-argument form:

@SwaggerLink(201, 'GetCreated', {
  operationId: 'getItem',
  parameters: { id: '$response.body#/id' },
})
@SwaggerLink(200, 'GetUpdated', {
  operationId: 'getItem',
  parameters: { id: '$response.body#/id' },
})

Options reference

Field	Type	Description
operationId	string	Target operation by operationId
operationRef	string	Target operation by JSON pointer
handler	[Class, string]	Target by controller class + method name (resolved at mapping time)
parameters	Record<string, string>	Map of parameter names to runtime expressions
requestBody	string	Runtime expression for the request body
description	string	Human-readable description of the link
server	{ url, description? }	Alternative server for the link target

Exactly one of operationId, operationRef, or handler must be provided. If handler cannot be resolved (e.g., the target controller is not registered), the link is silently skipped.

---

Callbacks (webhooks)

OpenAPI callbacks document requests your server sends to a client-provided URL — typically for webhook delivery after an event.

Basic usage

import { SwaggerCallback } from '@moostjs/swagger'

@SwaggerCallback('onEvent', {
  expression: '{$request.body#/callbackUrl}',
  requestBody: EventPayloadDto,
  description: 'Event notification sent to subscriber',
})
@Post('subscribe')
subscribe(@Body() dto: SubscribeDto) {
  // Documents: "after subscribing, server POSTs EventPayloadDto to the callbackUrl"
}

The expression is an OpenAPI runtime expression that resolves to the callback URL at runtime. The most common pattern is '{$request.body#/callbackUrl}' — a URL provided in the request body.

Custom method, content type, and response

By default, callbacks use POST, application/json, and expect a 200 OK response. Override any of these:

@SwaggerCallback('onUpdate', {
  expression: '{$request.body#/webhookUrl}',
  method: 'put',
  contentType: 'text/plain',
  responseStatus: 204,
  responseDescription: 'Acknowledged',
})
@Post('subscribe')
subscribe(@Body() dto: SubscribeDto) { /* ... */ }

Multiple callbacks

Stack multiple @SwaggerCallback decorators to document several webhooks on the same operation:

@SwaggerCallback('onCreated', {
  expression: '{$request.body#/callbackUrl}',
  requestBody: CreatedEventDto,
})
@SwaggerCallback('onUpdated', {
  expression: '{$request.body#/callbackUrl}',
  requestBody: UpdatedEventDto,
})
@Post('subscribe')
subscribe(@Body() dto: SubscribeDto) { /* ... */ }

Options reference

Field	Type	Default	Description
expression	string	(required)	Runtime expression resolving to the callback URL
requestBody	type/schema	—	Schema for the payload your server sends. Resolved via the schema pipeline
method	string	'post'	HTTP method your server uses
contentType	string	'application/json'	Content type for the payload
description	string	—	Description for the callback operation
responseStatus	number	200	Expected response status from the receiver
responseDescription	string	'OK'	Description for the expected response