> Markdown version of https://www.asyncapi.com/docs/tutorials/websocket/websocket-request-reply > Index: https://www.asyncapi.com/llms.txt # Implement Request/Reply in an AsyncAPI document for a Slack app > In this tutorial, you'll learn how to write an AsyncAPI document that implements the request/reply feature in a Slack application using the WebSocket protocol. ## Introduction In the [Create an AsyncAPI Document for a Slackbot with WebSockets](https://www.asyncapi.com/docs/tutorials/websocket) tutorial, you learned how to write an AsyncAPI document for a Slackbot `Heart-Counter` that actively monitored reactions associated with a message. In this lesson, let's go a step further. After receiving a reaction, `Heart-Counter` responds via a message back to the Slack server through WebSocket to confirm the event reception. The interaction where the Slackbot acknowledges the event and replies with a specific response sets the stage for the Request/Reply messaging pattern discussed in this context. > Refer to the [Request/Reply pattern tutorial](https://www.asyncapi.com/docs/tutorials/getting-started/request-reply) for an introduction to its implementation. ```mermaid sequenceDiagram participant Heart-Counter participant Slack Server (Socket Mode) participant User User-->>Slack Server (Socket Mode): Adds emoji to a message. Slack Server (Socket Mode)->>Heart-Counter: Sending "reaction_added" payload Note left of Heart-Counter: Event received Heart-Counter->>Slack Server (Socket Mode): Sending acknowledgement ``` ## Background context The [Request-Reply Messaging Pattern](https://www.asyncapi.com/docs/concepts/asyncapi-document/reply-info) in AsyncAPI is an exciting and highly anticipated feature. The messaging pattern mirrors a traditional conversation, where one "requester" entity initiates a query or request, and the "responder" entity provides a specific and expected response. The messaging pattern can work in both synchronous and asynchronous environments and is very beneficial to decouple components by allowing them to operate independently in a distributed system. ```mermaid sequenceDiagram participant Client participant Server Client->>Server: Request note right of Client: Continue with other tasks Server-->>Client: Acknowledgment Server->>Server: Process Request Server-->>Client: Reply ``` ## Define messages In the `Heart-Counter` tutorial, you dealt with the `hello` event triggered when the WebSocket connection was established and the `reaction` event expected when a new reaction-added event was triggered. In this tutorial, you'll add the `acknowledge` message to your AsyncAPI document to represent the acknowledgment sent by the Slack application back to the server to indicate that it has successfully received the message. ```yaml components: messages: reaction: summary: Action triggered when the channel receives a new reaction-added event payload: $ref: '#/components/schemas/reaction' hello: summary: Action triggered when a successful WebSocket connection is established payload: $ref: '#/components/schemas/hello' acknowledge: summary: Acknowledgement response sent to Server payload: $ref: '#/components/schemas/acknowledge' ``` ## Define schemas Previously, the `reaction` schema was simplified to include the `event` payload. However, in this instance, you will be able to elaborate on the schema for the complete request it is expected to receive. > **Remember** > > The sample request and response payloads are extracted from Slack's official documentation. ```yaml schemas: hello: type: object properties: type: type: string description: A hello string confirming WebSocket connection connection_info: type: object properties: app_id: type: string num_connections: type: integer debug_info: type: object properties: host: type: string started: type: string build_number: type: integer approximate_connection_time: type: integer reaction: type: object properties: envelope_id: type: string description: 'Unique ID assigned to payload' payload: type: object description: 'Payload of the reaction added event' properties: token: type: string team_id: type: string event: type: object properties: user: type: string description: User ID who performed this event reaction: type: string description: The only reaction that you need is a heart emoji item_user: type: string description: | User ID that created the original item that has been reacted to item: type: object properties: channel: type: string description: Channel information of original message ts: type: string description: Timestamp information of original message event_ts: type: string description: Reaction timestamp type: type: string accepts_response_payload: type: boolean ``` Additionally, you will also be adding the `acknowledge` schema that makes use of the `envelope_id` attribute to send a reply back to Slack acknowledging that event has been received. ```yaml acknowledge: type: object properties: envelope_id: type: string description: 'Unique ID of acknowledged payload' payload: type: object description: 'Optional payload of event' ``` ## Define acknowledge message to channel Extend the channel the `Heart-Counter` used to include the `acknowledge` message. ```yaml channels: root: address: / messages: hello: $ref: '#/components/messages/hello' reaction: $ref: '#/components/messages/reaction' acknowledge: $ref: '#/components/messages/acknowledge' ``` ## Define operations Now you've reached the most important part of the tutorial; it's time to represent the Request/Reply pattern. Both `helloListener` and `reactionListener` operations are set to `receive` events. However, in the case of `reactionListener`, you also want to represent the message sent back to the server. This is where the `reply` attribute comes into play. Since both the request and reply function happens over the same WebSocket URL, both `channel` values stay the same. However, you can differentiate each operation's message by specifying the messages sent or received. Thus, you can say that for a `reaction` message received over the `root` channel, the `reactionListener` operation will reply with the `acknowledge` message over the same channel. ```yaml operations: helloListener: action: receive channel: $ref: '#/channels/root' messages: - $ref: '#/channels/root/messages/hello' reactionListener: action: receive channel: $ref: '#/channels/root' messages: - $ref: '#/channels/root/messages/reaction' reply: messages: - $ref: '#/channels/root/messages/acknowledge' channel: $ref: '#/channels/root' ``` Putting all this together, you have your AsyncAPI document ready to go! ```yaml asyncapi: 3.1.0 info: title: Implement Request/Reply in an AsyncAPI document for a Slack app version: 1.0.0 description: > The Heart-Counter manages popular messages in a Slack workspace by monitoring message reaction data. It also sends an acknowledgment message back to the Slack Server to indicate it has received the message. servers: production: host: wss-primary.slack.com pathname: /link protocol: wss description: Slack's server in Socket Mode for real-time communication channels: root: address: / messages: hello: $ref: '#/components/messages/hello' reaction: $ref: '#/components/messages/reaction' acknowledge: $ref: '#/components/messages/acknowledge' bindings: ws: query: type: object description: >- Tokens are produced in the WebSocket URL generated from the [apps.connections.open](https://api.slack.com/methods/apps.connections.open) method from Slack's API properties: ticket: type: string description: Temporary token generated when connection is initiated const: 13748dac-b866-4ea7-b98e-4fb7895c0a7f app_id: type: string description: Unique identifier assigned to the Slack app const: fe684dfa62159c6ac646beeac31c8f4ef415e4f39c626c2dbd1530e3a690892f operations: helloListener: action: receive channel: $ref: '#/channels/root' messages: - $ref: '#/channels/root/messages/hello' reactionListener: action: receive channel: $ref: '#/channels/root' messages: - $ref: '#/channels/root/messages/reaction' reply: messages: - $ref: '#/channels/root/messages/acknowledge' channel: $ref: '#/channels/root' components: messages: reaction: summary: Action triggered when the channel receives a new reaction-added event payload: $ref: '#/components/schemas/reaction' hello: summary: Action triggered when a successful WebSocket connection is established payload: $ref: '#/components/schemas/hello' acknowledge: summary: Acknowledgement response sent to Server payload: $ref: '#/components/schemas/acknowledge' schemas: hello: type: object properties: type: type: string description: A hello string confirming WebSocket connection connection_info: type: object properties: app_id: type: string num_connections: type: integer debug_info: type: object properties: host: type: string started: type: string build_number: type: integer approximate_connection_time: type: integer reaction: type: object properties: envelope_id: type: string description: 'Unique ID assigned to payload' payload: type: object description: 'Payload of the reaction added event' properties: token: type: string team_id: type: string event: type: object properties: user: type: string description: User ID who performed this event reaction: type: string description: The only reaction that you need is a heart emoji item_user: type: string description: | User ID that created the original item that has been reacted to item: type: object properties: channel: type: string description: Channel information of original message ts: type: string description: Timestamp information of original message event_ts: type: string description: Reaction timestamp type: type: string accepts_response_payload: type: boolean acknowledge: type: object properties: envelope_id: type: string description: 'Unique ID of acknowledged payload' payload: type: object description: 'Optional payload of event' ``` ## Summary Great job getting to the end! In this tutorial, you learned how to create an AsyncAPI document for a use case that implemented the Request-Reply messaging pattern. Now, you can explore this pattern with sub-patterns to see how it works with real-life use cases.