Trace

Performance is an important aspect for Elysia.

We don't want to be fast for benchmarking purposes, we want you to have a real fast server in real-world scenario.

There are many factors that can slow down our app - and it's hard to identify them, but trace can helps solve that problem by injecting start and stop code to each life-cycle.

Trace allows us to inject code to before and after of each life-cycle event, block and interact with the execution of the function.

Trace

Trace use a callback listener to ensure that callback function is finished before moving on to the next lifecycle event.

To use trace, you need to call trace method on the Elysia instance, and pass a callback function that will be executed for each life-cycle event.

You may listen to each lifecycle by adding on prefix follows by life-cycle name, for example onHandle to listen to handle event.

import { Elysia } from 'elysia'

const app = new Elysia()
    .trace(async ({ onHandle }) => {
	    onHandle(({ begin, onStop }) => {
			onStop(({ end }) => {
        		console.log('handle took', end - begin, 'ms')
			})
	    })
    })
    .get('/', () => 'Hi')
    .listen(3000)

Please refer to Life Cycle Events for more information:

Children

Every events except handle have a children, which is an array of events that are executed inside for each life-cycle event.

You can use onEvent to listen to each child event in order

import { Elysia } from 'elysia'

const sleep = (time = 1000) =>
    new Promise((resolve) => setTimeout(resolve, time))

const app = new Elysia()
    .trace(async ({ onBeforeHandle }) => {
        onBeforeHandle(({ total, onEvent }) => {
            console.log('total children:', total)

            onEvent(({ onStop }) => {
                onStop(({ elapsed }) => {
                    console.log('child took', elapsed, 'ms')
                })
            })
        })
    })
    .get('/', () => 'Hi', {
        beforeHandle: [
            function setup() {},
            async function delay() {
                await sleep()
            }
        ]
    })
    .listen(3000)

In this example, total children will be 2 because there are 2 children in the beforeHandle event.

Then we listen to each child event by using onEvent and print the duration of each child event.

Trace Parameter

When each lifecycle is called

import { Elysia } from 'elysia'

const app = new Elysia()
	// This is trace parameter
	// hover to view the type
	.trace((parameter) => {
	})
	.get('/', () => 'Hi')
	.listen(3000)

trace accept the following parameters:

id - number

Randomly generated unique id for each request

context - Context

Elysia's Context, eg. set, store, query, params`

set - Context.set

Shortcut for context.set, to set a headers or status of the context

store - Singleton.store

Shortcut for context.store, to access a data in the context

time - number

Timestamp of when request is called

on[Event] - TraceListener

An event listener for each life-cycle event.

You may listen to the following life-cycle:

• onRequest - get notified of every new request
• onParse - array of functions to parse the body
• onTransform - transform request and context before validation
• onBeforeHandle - custom requirement to check before the main handler, can skip the main handler if response returned.
• onHandle - function assigned to the path
• onAfterHandle - interact with the response before sending it back to the client
• onMapResponse - map returned value into a Web Standard Response
• onError - handle error thrown during processing request
• onAfterResponse - cleanup function after response is sent

Trace Listener

A listener for each life-cycle event

import { Elysia } from 'elysia'

const app = new Elysia()
	.trace(({ onBeforeHandle }) => {
		// This is trace listener
		// hover to view the type
		onBeforeHandle((parameter) => {

		})
	})
	.get('/', () => 'Hi')
	.listen(3000)

Each lifecycle listener accept the following

name - string

The name of the function, if the function is anonymous, the name will be anonymous

begin - number

The time when the function is started

end - Promise<number>

The time when the function is ended, will be resolved when the function is ended

error - Promise<Error | null>

Error that was thrown in the lifecycle, will be resolved when the function is ended

onStop - callback?: (detail: TraceEndDetail) => any

A callback that will be executed when the lifecycle is ended

import { Elysia } from 'elysia'

const app = new Elysia()
	.trace(({ onBeforeHandle, set }) => {
		onBeforeHandle(({ onStop }) => {
			onStop(({ elapsed }) => {
				set.headers['X-Elapsed'] = elapsed.toString()
			})
		})
	})
	.get('/', () => 'Hi')
	.listen(3000)

It's recommended to mutate context in this function as there's a lock mechanism to ensure the context is mutate successfully before moving on to the next lifecycle event

TraceEndDetail

A parameter that passed to onStop callback

end - number

The time when the function is ended

error - Error | null

Error that was thrown in the lifecycle

elapsed - number

Elapsed time of the lifecycle or end - begin