Koa Integration

The @feathersjs/koa package provides integration between Feathers and Koa, bringing async/await middleware patterns and lightweight HTTP handling to your Feathers services.

Installation

npm install @feathersjs/koa koa

Basic Setup

Create the Koa application

The Koa integration wraps a Feathers application with Koa functionality:

import { feathers } from '@feathersjs/feathers'
import { koa } from '@feathersjs/koa'

const app = koa(feathers())

Add body parsing middleware

Enable request body parsing for POST/PUT/PATCH requests:

import { bodyParser } from '@feathersjs/koa'

app.use(bodyParser())

Configure REST transport

Enable the REST transport to expose services via HTTP:

import { rest } from '@feathersjs/koa'

app.configure(rest())

Services are automatically exposed as REST endpoints:

app.use('/users', {
  async find() {
    return [{ id: 1, name: 'Alice' }]
  },
  async get(id) {
    return { id, name: 'Alice' }
  }
})

Add error handling

Use the error handler middleware to catch and format errors:

import { errorHandler } from '@feathersjs/koa'

app.use(errorHandler())

Start the server

The listen method automatically calls setup() on all services:

await app.listen(3030)
console.log('Feathers app started on http://localhost:3030')

Complete Example

import { feathers } from '@feathersjs/feathers'
import { koa, rest, bodyParser, errorHandler, cors } from '@feathersjs/koa'

const app = koa(feathers())

// Middleware must be added before REST configuration
app.use(errorHandler())
app.use(cors())
app.use(bodyParser())

// Configure REST transport
app.configure(rest())

// Register services
app.use('/messages', {
  async find() {
    return [
      { id: 1, text: 'Hello world' },
      { id: 2, text: 'How are you?' }
    ]
  },
  async create(data) {
    return { id: 3, ...data }
  }
})

// Custom Koa middleware
app.use(async (ctx, next) => {
  if (ctx.path === '/health') {
    ctx.body = { status: 'ok' }
  } else {
    await next()
  }
})

// Start server
const server = await app.listen(3030)
console.log('Server ready on http://localhost:3030')

Service Middleware

Koa middleware can be added before and after service calls using the koa option:

import { Middleware } from '@feathersjs/koa'

const logRequest: Middleware = async (ctx, next) => {
  console.log(`${ctx.method} ${ctx.path}`)
  await next()
}

const addTimestamp: Middleware = async (ctx, next) => {
  await next()
  ctx.body = { ...ctx.body, timestamp: new Date() }
}

app.use('/todos', todoService, {
  koa: {
    before: [logRequest],
    after: [addTimestamp]
  },
  methods: ['find', 'get', 'create']
})

Middleware Patterns

Before Middleware
After Middleware
Combined

Middleware in the before array runs before the service method:

const validateRequest: Middleware = async (ctx, next) => {
  if (!ctx.request.headers.authorization) {
    ctx.throw(401, 'Unauthorized')
  }
  await next()
}

app.use('/protected', service, {
  koa: {
    before: [validateRequest]
  }
})

Middleware in the after array runs after the service method and can modify ctx.body:

const formatResponse: Middleware = async (ctx, next) => {
  await next()
  ctx.body = {
    status: 'success',
    data: ctx.body,
    timestamp: new Date()
  }
}

app.use('/api/users', userService, {
  koa: {
    after: [formatResponse]
  }
})

Use both before and after middleware together:

app.use('/todos', todoService, {
  koa: {
    before: [
      async (ctx, next) => {
        ctx.state.startTime = Date.now()
        await next()
      }
    ],
    after: [
      async (ctx, next) => {
        await next()
        const duration = Date.now() - ctx.state.startTime
        ctx.set('X-Response-Time', `${duration}ms`)
      }
    ]
  }
})

Context and Feathers Params

Koa’s ctx.feathers object contains Feathers-specific parameters:

app.use(async (ctx, next) => {
  // Access Feathers params
  console.log(ctx.feathers.provider)  // 'rest'
  console.log(ctx.feathers.headers)   // Request headers

  // Add custom params that services will receive
  ctx.feathers.customData = { userId: 123 }

  await next()
})

app.use('/items', {
  async find(params) {
    // params includes ctx.feathers properties
    console.log(params.customData)  // { userId: 123 }
    console.log(params.provider)     // 'rest'
    return []
  }
})

Authentication

Integrate Feathers authentication with Koa middleware:

import { authenticate } from '@feathersjs/koa'

// Protect routes with authentication
app.use('/admin', authenticate('jwt'), adminService)

// Authentication middleware
const requireAuth: Middleware = authenticate('jwt')

app.use(async (ctx, next) => {
  if (ctx.path.startsWith('/api/')) {
    await requireAuth(ctx, next)
  } else {
    await next()
  }
})

Authentication Configuration

import { rest, parseAuthentication } from '@feathersjs/koa'

// Configure REST with automatic authentication parsing
app.configure(rest({
  authentication: {
    service: 'authentication',
    strategies: ['jwt', 'local']
  }
}))

// Or add authentication parsing globally
app.use(parseAuthentication({
  service: 'authentication',
  strategies: ['jwt']
}))

Error Handling

Koa error handling is done through middleware:

import { errorHandler } from '@feathersjs/koa'

// Use default error handler (must be first middleware)
app.use(errorHandler())
app.use(bodyParser())
app.configure(rest())

Static Files

Serve static files using Koa’s static middleware:

import { serveStatic } from '@feathersjs/koa'
import path from 'path'

// Serve static files from public directory
app.use(serveStatic(path.join(__dirname, 'public')))

// Serve with options
app.use(serveStatic('assets', {
  maxage: 86400000, // 1 day
  hidden: false
}))

Custom Response Formatting

Customize how service results are sent as HTTP responses:

import { rest, Middleware } from '@feathersjs/koa'

const customFormatter: Middleware = async (ctx, next) => {
  await next()

  // Wrap all responses
  if (ctx.body) {
    ctx.body = {
      success: true,
      result: ctx.body,
      timestamp: Date.now()
    }
  }
}

app.configure(rest({ formatter: customFormatter }))

Using Existing Koa App

Integrate Feathers into an existing Koa application:

import Koa from 'koa'
import { koa as feathersKoa } from '@feathersjs/koa'
import { feathers } from '@feathersjs/feathers'

// Existing Koa app
const koaApp = new Koa()
koaApp.use(async (ctx, next) => {
  if (ctx.path === '/health') {
    ctx.body = { status: 'ok' }
  } else {
    await next()
  }
})

// Add Feathers to it
const app = feathersKoa(feathers(), koaApp)
app.configure(rest())
app.use('/api/users', userService)

await app.listen(3030)

Pure Koa Middleware

You can mix Feathers services with pure Koa middleware:

import { koa, rest, bodyParser } from '@feathersjs/koa'
import Router from '@koa/router'

const app = koa(feathers())
app.use(bodyParser())

// Use Koa router
const router = new Router()
router.get('/status', (ctx) => {
  ctx.body = { status: 'ok', uptime: process.uptime() }
})

app.use(router.routes())
app.use(router.allowedMethods())

// Configure Feathers REST
app.configure(rest())

// Register Feathers services
app.use('/api/todos', todoService)

Lifecycle Methods

listen()
setup()
teardown()

The listen() method starts the server and calls setup() on all services:

const server = await app.listen(3030)
console.log('Server started on port 3030')

Manually call setup() when using a custom server:

import http from 'http'

const server = http.createServer(app.callback())
await app.setup(server)
server.listen(3030)

Clean shutdown closes the HTTP server and calls teardown on services:

// Graceful shutdown
process.on('SIGTERM', async () => {
  await app.teardown()
  console.log('Server stopped')
  process.exit(0)
})

TypeScript Support

import { feathers, Service } from '@feathersjs/feathers'
import { koa, Application } from '@feathersjs/koa'

interface User {
  id: number
  email: string
  name: string
}

interface ServiceTypes {
  users: Service<User>
}

const app: Application<ServiceTypes> = koa(feathers())

app.use('/users', {
  async find() {
    return [{ id: 1, email: '[email protected]', name: 'User' }]
  }
})

await app.listen(3030)

Middleware Execution Order

Understanding middleware order is crucial in Koa:

import { koa, rest, bodyParser, errorHandler } from '@feathersjs/koa'

const app = koa(feathers())

// 1. Error handler (first to catch all errors)
app.use(errorHandler())

// 2. Global middleware
app.use(async (ctx, next) => {
  console.log('Request:', ctx.method, ctx.path)
  await next()
  console.log('Response:', ctx.status)
})

// 3. Body parser
app.use(bodyParser())

// 4. REST configuration (sets up service routing)
app.configure(rest())

// 5. Custom routes
app.use(async (ctx, next) => {
  if (ctx.path === '/custom') {
    ctx.body = { custom: true }
  } else {
    await next()
  }
})

// 6. Services (handled by REST transport)
app.use('/users', userService)

API Reference

koa(feathersApp?, koaApp?)

Wraps a Feathers application with Koa. Parameters:

feathersApp - A Feathers application instance
koaApp - Optional existing Koa app

Returns: Combined Feathers + Koa application

rest(options?)

Configures the REST transport. Options:

formatter - Custom response formatter middleware
authentication - Authentication settings
- service - Authentication service name
- strategies - Array of strategy names

errorHandler()

Koa error handling middleware that catches errors and formats them as JSON.

bodyParser(options?)

Parses request bodies. Wraps koa-body. Options: See koa-body documentation

cors(options?)

Enables CORS. Wraps @koa/cors. Options: See @koa/cors documentation

Getting Started

Core Concepts

Guides

Installation

Basic Setup

Complete Example

Service Middleware

Middleware Patterns

Context and Feathers Params

Authentication

Authentication Configuration

Error Handling

Static Files

Custom Response Formatting

Using Existing Koa App

Pure Koa Middleware

Lifecycle Methods

TypeScript Support

Middleware Execution Order

API Reference

koa(feathersApp?, koaApp?)

rest(options?)

errorHandler()

bodyParser(options?)

cors(options?)

Build docs developers (and LLMs) love

Getting Started

Core Concepts

Guides

​Installation

​Basic Setup

​Complete Example

​Service Middleware

​Middleware Patterns

​Context and Feathers Params

​Authentication

​Authentication Configuration

​Error Handling

​Static Files

​Custom Response Formatting

​Using Existing Koa App

​Pure Koa Middleware

​Lifecycle Methods

​TypeScript Support

​Middleware Execution Order

​API Reference

​koa(feathersApp?, koaApp?)

​rest(options?)

​errorHandler()

​bodyParser(options?)

​cors(options?)

Build docs developers (and LLMs) love

Installation

Basic Setup

Complete Example

Service Middleware

Middleware Patterns

Context and Feathers Params

Authentication

Authentication Configuration

Error Handling

Static Files

Custom Response Formatting

Using Existing Koa App

Pure Koa Middleware

Lifecycle Methods

TypeScript Support

Middleware Execution Order

API Reference

koa(feathersApp?, koaApp?)

rest(options?)

errorHandler()

bodyParser(options?)

cors(options?)