A Koa middleware to handle timeouts correctly

How it works | Usage

koa-timeout uses Promise.race to race a setTimeout against your Koa middlewares/response.

Middlewares
              A 1s     B 2s       C 3s      D 4s
         ╭─────┴────────┴─────╳╌╌╌╌┴╌╌╌╌╌╌╌╌╌┴╌╌╌╌╌
Req ─────┤
         ╰────────────────────┬──→ 408 - 2500ms
                           Timeout
                             2.5s

In this example, a request has come in and the timeout is racing middlewares, A, B, C & D. However, the timeout is triggered causing a 408 response after 2500ms.

The ╳ signifys a short circuit and prevents middlewares C & D from running.

Middlewares
              A 1s     B 2s      C 3s      D 4s
         ╭─────┴────────┴─────────┴─────────┴──────╮
         │                                         │
Req ─────┤                                         ╰──→ 200 - 4500ms
         │
         ╰─────────────────────────────────────────╳╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╮
                                                                     Timeout
                                                                        5s

In this example, all 4 middlewares - A, B, C & D - have finished, resulting in a 200 response after ~4500ms. The timeout is then cleared, signified by the ╳.

The middleware can be configured with a custom timeout time and status code.

import Koa from 'koa'
import timeout from '@uswitch/koa-timeout'

const app = new Koa()

app.use(timeout(1000))                     // 1s timeout
app.use(timeout(1000, { status: 499 }))    // 1s timeout with 499 status

N.B. By default, koa-timeout does not short circuit the other middlewares. This means that the in-flight request will continue to be processed even though a response has already been sent.

This behaviour can be useful in development to see where the slow parts of the request are, however, in production you probably want to kill the request as soon as possible.

This will prevent the next middleware after a timeout from triggering.

import { shortCircuit } from '@uswitch/koa-timeout'

app.use(timeout(5000))

app.get('*', shortCircuit(handleInitialState))
app.get('*', shortCircuit(handleRendering))
app.get('*', shortCircuit(handleReturn))

// Or

app.get('*', ...shortCircuit(handleInitialState, handleRendering, handleReturn))

N.B. when calling with multiple middlewares, make sure to spread the result! i.e. ...shortCircuit(a, b, c)