WebSockets — Fern

Pro Feature

This feature is only available on paid plans. Please schedule a demo or email us to get started.

Fern’s SDKs support sending and receiving messages over WebSockets. You can specify your WebSocket API Definition by using AsyncAPI or the Fern Definition.

How it works

Specify your WebSocket API Definition

AsyncAPI

See below for how to specify the contract for your WebSocket channel using AsyncAPI.

1     asyncapi: 2.6.0
2     info:
3       title: Chat API
4       version: 1.1.2
5     servers:
6       production:
7         host: wss.chat.com
8     channels:
9       /:
10         bindings:
11           ws:
12             query:
13               type: object
14               properties:
15                 channel_id:
16                   type: string
17                   description: Unique identifier assigned to the channel
18         publish:
19           description: Send messages to the WebSocket
20           operationId: sendMessage
21           message:
22             oneOf:
23               - $ref: "#/components/messages/SendChat"
24         subscribe:
25           description: Receive messages from the WebSocket
26           operationId: receiveMessage
27           message:
28             oneOf:
29               - $ref: "#/components/messages/ReceiveChat"
30     components:
31       messages:
32         SendChat:
33           summary: Action triggered when the channel receives a new reaction-added event
34           payload:
35             $ref: '#/components/schemas/SendChat'
36         ReceiveChat:
37           summary: Action triggered when a successful WebSocket connection is established
38           payload:
39             $ref: '#/components/schemas/ReceiveChat'
40     schemas:
41       SendChat:
42         type: object
43         properties:
44           message:
45             type: string
46       ReceiveChat:
47         type: object
48         properties:
49           message:
50             type: string

Fern Definition

If you have a Fern Definition, you can specify your websocket in a yaml file. See the example in chat.yml below:

chat.yml

1 channel: 
2   query-parameters: 
3     channel_id: 
4       type: string
5       docs: Unique identifier assigned to the channel
6   messages: 
7     send: 
8       payload: 
9         message: 
10           type: string
11           docs: The message to send over the WebSocket
12     receive: 
13       payload: 
14         message: string

Generate the SDK

1 import { ChatClient } from "chat";
2 
3 const client = new ChatClient();
4 
5 const socket = client.chat.connect({
6   channelId: "123",
7   onOpen: () => {
8     console.log("Connected to the WebSocket");
9   },
10   onMessage: (message) => {
11     console.log(message);
12   },
13 });
14 
15 await socket.send("Hello, world!");
16 
17 socket.on("close", () => {
18   console.log("WebSocket connection closed");
19 });
20 
21 await socket.send("Bye, world!");
22 
23 socket.close();

1	asyncapi: 2.6.0
2	info:
3	title: Chat API
4	version: 1.1.2
5	servers:
6	production:
7	host: wss.chat.com
8	channels:
9	/:
10	bindings:
11	ws:
12	query:
13	type: object
14	properties:
15	channel_id:
16	type: string
17	description: Unique identifier assigned to the channel
18	publish:
19	description: Send messages to the WebSocket
20	operationId: sendMessage
21	message:
22	oneOf:
23	- $ref: "#/components/messages/SendChat"
24	subscribe:
25	description: Receive messages from the WebSocket
26	operationId: receiveMessage
27	message:
28	oneOf:
29	- $ref: "#/components/messages/ReceiveChat"
30	components:
31	messages:
32	SendChat:
33	summary: Action triggered when the channel receives a new reaction-added event
34	payload:
35	$ref: '#/components/schemas/SendChat'
36	ReceiveChat:
37	summary: Action triggered when a successful WebSocket connection is established
38	payload:
39	$ref: '#/components/schemas/ReceiveChat'
40	schemas:
41	SendChat:
42	type: object
43	properties:
44	message:
45	type: string
46	ReceiveChat:
47	type: object
48	properties:
49	message:
50	type: string

1	channel:
2	query-parameters:
3	channel_id:
4	type: string
5	docs: Unique identifier assigned to the channel
6	messages:
7	send:
8	payload:
9	message:
10	type: string
11	docs: The message to send over the WebSocket
12	receive:
13	payload:
14	message: string

1	import { ChatClient } from "chat";
2
3	const client = new ChatClient();
4
5	const socket = client.chat.connect({
6	channelId: "123",
7	onOpen: () => {
8	console.log("Connected to the WebSocket");
9	},
10	onMessage: (message) => {
11	console.log(message);
12	},
13	});
14
15	await socket.send("Hello, world!");
16
17	socket.on("close", () => {
18	console.log("WebSocket connection closed");
19	});
20
21	await socket.send("Bye, world!");
22
23	socket.close();