WebSocket

WebSocket is a realtime protocol for communication between your client and server.

Unlike HTTP where our client repeatedly asking the website for information and waiting for a reply each time, WebSocket sets up a direct line where our client and server can send messages back and forth directly, making the conversation quicker and smoother without having to start over each message.

SocketIO is a popular library for WebSocket, but it is not the only one. Elysia uses uWebSocket which Bun uses under the hood with the same API.

To use websocket, simply call Elysia.ws():

import { Elysia } from 'elysia'

new Elysia()
    .ws('/ws', {
        message(ws, message) {
            ws.send(message)
        }
    })
    .listen(3000)

WebSocket message validation:

Same as normal route, WebSockets also accepts a schema object to strictly type and validate requests.

import { Elysia, t } from 'elysia'

const app = new Elysia()
    .ws('/ws', {
        // validate incoming message
        body: t.Object({
            message: t.String()
        }),
        message(ws, { message }) {
            ws.send({
                message,
                time: Date.now()
            })
        }
    })
    .listen(3000)

WebSocket schema can validate the following:

• message - An incoming message.
• query - query string or URL parameters.
• params - Path parameters.
• header - Request's headers.
• cookie - Request's cookie
• response - Value returned from handler

By default Elysia will parse incoming stringified JSON message as Object for validation.

Configuration

You can set Elysia constructor to set the Web Socket value.

import { Elysia } from 'elysia'

new Elysia({
    websocket: {
        idleTimeout: 30
    }
})

Elysia's WebSocket implementation extends Bun's WebSocket configuration, please refer to Bun's WebSocket documentation for more information.

The following are a brief configuration from Bun WebSocket

perMessageDeflate

@default false

Enable compression for clients that support it.

By default, compression is disabled.

maxPayloadLength

The maximum size of a message.

idleTimeout

@default 120

After a connection has not received a message for this many seconds, it will be closed.

backpressureLimit

@default 16777216 (16MB)

The maximum number of bytes that can be buffered for a single connection.

closeOnBackpressureLimit

@default false

Close the connection if the backpressure limit is reached.

Methods

Below are the new methods that are available to the WebSocket route

ws

Create a websocket handler

Example:

import { Elysia } from 'elysia'

const app = new Elysia()
    .ws('/ws', {
        message(ws, message) {
            ws.send(message)
        }
    })
    .listen(3000)

Type:

.ws(endpoint: path, options: Partial<WebSocketHandler<Context>>): this

endpoint: A path to exposed as websocket handler options: Customize WebSocket handler behavior

WebSocketHandler

WebSocketHandler extends config from config.

Below is a config which is accepted by ws.

open

Callback function for new websocket connection.

Type:

open(ws: ServerWebSocket<{
    // uid for each connection
    id: string
    data: Context
}>): this

message

Callback function for incoming websocket message.

Type:

message(
    ws: ServerWebSocket<{
        // uid for each connection
        id: string
        data: Context
    }>,
    message: Message
): this

Message type based on schema.message. Default is string.

close

Callback function for closing websocket connection.

Type:

close(ws: ServerWebSocket<{
    // uid for each connection
    id: string
    data: Context
}>): this

drain

Callback function for the server is ready to accept more data.

Type:

drain(
    ws: ServerWebSocket<{
        // uid for each connection
        id: string
        data: Context
    }>,
    code: number,
    reason: string
): this

parse

Parse middleware to parse the request before upgrading the HTTP connection to WebSocket.

beforeHandle

Before Handle middleware which execute before upgrading the HTTP connection to WebSocket.

Ideal place for validation.

transform

Transform middleware which execute before validation.

transformMessage

Like transform, but execute before validation of WebSocket message

header

Additional headers to add before upgrade connection to WebSocket.