Stream

To return a response streaming out of the box by using a generator function with yield keyword.

import { Elysia } from 'elysia'

const app = new Elysia()
	.get('/ok', function* () {
		yield 1
		yield 2
		yield 3
	})

This this example, we may stream a response by using yield keyword.

Set headers

Elysia will defers returning response headers until the first chunk is yielded.

This allows us to set headers before the response is streamed.

import { Elysia } from 'elysia'

const app = new Elysia()
	.get('/ok', function* ({ set }) {
		// This will set headers
		set.headers['x-name'] = 'Elysia'
		yield 1
		yield 2

		// This will do nothing
		set.headers['x-id'] = '1'
		yield 3
	})

Once the first chunk is yielded, Elysia will send the headers and the first chunk in the same response.

Setting headers after the first chunk is yielded will do nothing.

Conditional Stream

If the response is returned without yield, Elysia will automatically convert stream to normal response instead.

import { Elysia } from 'elysia'

const app = new Elysia()
	.get('/ok', function* ({ set }) {
		if (Math.random() > 0.5) return 'ok'

		yield 1
		yield 2
		yield 3
	})

This allows us to conditionally stream a response or return a normal response if necessary.

Abort

While streaming a response, it's common that request may be cancelled before the response is fully streamed.

Elysia will automatically stop the generator function when the request is cancelled.

Eden

Eden will will interpret a stream response as AsyncGenerator allowing us to use for await loop to consume the stream.

import { Elysia } from 'elysia'
import { treaty } from '@elysiajs/eden'

const app = new Elysia()
	.get('/ok', function* () {
		yield 1
		yield 2
		yield 3
	})

const { data, error } = await treaty(app).ok.get()
if (error) throw error

for await (const chunk of data)
	console.log(chunk)