Publish/Subscribe Operations | Fern Documentation

Operations in AsyncAPI are defined underneath the operations key, with channels defined under the channels key. Below is an example of defining publish and subscribe operations:

asyncapi.yml

channels:
  user/notifications:
    address: user/notifications
    messages:
      UserNotification:
        $ref: '#/components/messages/UserNotification'
operations:
  onUserNotification:
    action: receive
    channel:
      $ref: '#/channels/user~1notifications'
    summary: Receive user notifications
    description: Subscribe to user notification events
  sendUserNotification:
    action: send
    channel:
      $ref: '#/channels/user~1notifications'
    summary: Send user notification
    description: Publish a user notification event

Message examples

You can provide examples of messages by using the examples key in your message definitions:

asyncapi.yml

components:
  messages:
    UserNotification:
      name: UserNotification
      title: User Notification
      summary: Notification sent to a user
      contentType: application/json
      payload:
        $ref: '#/components/schemas/Notification'
      examples:
        - name: EmailNotification
          summary: Example email notification
          payload:
            userId: "123e4567-e89b-12d3-a456-426614174000"
            type: "email"
            message: "Welcome to our service!"
            priority: "medium"

Publish operations

Publish operations represent messages that your service sends to a channel:

asyncapi.yml

operations:
  publishOrderStatus:
    action: send
    channel:
      $ref: '#/channels/order~1status'
    summary: Publish order status update
    description: Send order status updates to subscribers
    message:
      $ref: '#/components/messages/OrderStatus'

Subscribe operations represent messages that your service receives from a channel:

asyncapi.yml

operations:
  subscribeToUserSignups:
    action: receive
    channel:
      $ref: '#/channels/user~1signup'
    summary: Subscribe to user signups
    description: Receive notifications when users sign up
    message:
      $ref: '#/components/messages/UserSignup'

Bi-directional communication

You can define both publish and subscribe operations for the same channel to enable bi-directional communication:

asyncapi.yml

operations:
  sendChatMessage:
    action: send
    channel:
      $ref: '#/channels/chat~1room'
    summary: Send chat message
    description: Send a message to a chat room
  receiveChatMessage:
    action: receive
    channel:
      $ref: '#/channels/chat~1room'
    summary: Receive chat message
    description: Receive messages from a chat room