Elysia.js

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WebSocket ​

Elysia WebSocket extends Bun's WebSocket which uses uWebSocket under the hood.

To start working with a WebSocket, register the Elysia WebSocket plugin, and declare a WebSocket route with .ws.

typescript
import { Elysia, ws } from 'elysia'

new Elysia()
    .use(ws())
    .ws('/ws', {
        message(ws, message) {
            ws.send(message)
        }
    })
    .listen(8080)
import { Elysia, ws } from 'elysia'

new Elysia()
    .use(ws())
    .ws('/ws', {
        message(ws, message) {
            ws.send(message)
        }
    })
    .listen(8080)

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

Configuration ​

Elysia's WebSocket plugin extends Bun's WebSocket configuration so if you wish to configure the websocket you can refer to Bun's WebSocket documentation to learn more about this.

Below is a config that extends 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 plugin

ws ​

Create a websocket handler

Example:

typescript
import { Elysia, ws } from 'elysia'

new Elysia()
    .use(ws())
    .ws('/ws', {
        message(ws, message) {
            ws.send(message)
        }
    })
    .listen(8080)
import { Elysia, ws } from 'elysia'

new Elysia()
    .use(ws())
    .ws('/ws', {
        message(ws, message) {
            ws.send(message)
        }
    })
    .listen(8080)

Type:

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

schema ​

Validatation for an incoming WebSocket request.

  • headers: validate headers before upgrade to WebSocket
  • params: validate path paramters
  • query: validate query parameters
  • body: validate websocket message
  • response: validate websocket response

TIP

It's recommended to use query parameters instead of path parameters in WebSocket, as parsing path parameters is expensive and sometime unrealiable for multiple data with long value.

open ​

Callback function for new websocket connection.

Type:

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

message ​

Callback function for incoming websocket message.

Type:

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

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

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

Additional headers to add before upgrade connection to WebSocket.

Pattern ​

Below you can find the common patterns to use the plugin.

WebSocket message validation: ​

Validate incoming WebSocket message.

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

typescript
import { Elysia, ws } from 'elysia'

new Elysia()
    .use(ws())
    .ws('/ws', {
        // validate incoming message
        body: t.Object({
            message: t.String()
        })
        message(ws, { message }) {
            ws.send({
                message,
                time: Date.now()
            })
        }
    )
    .listen(8080)
import { Elysia, ws } from 'elysia'

new Elysia()
    .use(ws())
    .ws('/ws', {
        // validate incoming message
        body: t.Object({
            message: t.String()
        })
        message(ws, { message }) {
            ws.send({
                message,
                time: Date.now()
            })
        }
    )
    .listen(8080)