feathers/docs/api/koa.md

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Koa

npm install @feathersjs/koa --save

The @feathersjs/koa module contains the KoaJS framework integrations for Feathers. It will turn the Feathers app into a fully compatible KoaJS application.

koa(app)

koa(app) -> app is a function that turns a Feathers application into a fully KoaJS compatible application that additionally to Feathers functionality also lets you use the KoaJS API.

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

// Create an app that is a Feathers AND Express application
const app = koa(feathers())

app.use(errorHandler())
app.use(authentication())
app.use(bodyParser())
app.configure(rest())

@feathersjs/koa also exposes the following middleware:

• rest - A middleware to expose services as REST APIs
• authentication - A middleware for parsing HTTP headers for Feathers authentication information
• bodyParser - The koa-bodyparser middleware for parsing request bodies
• errorHandler - A JSON error handler middleware. Should always be registered as the very first middleware.

koa(app, koaApp)

koa(app, koaApp) -> app allows to extend an existing Koa application with the Feathers application app.

koa()

If no Feathers application is passed, koa() -> app returns a plain Koa application (new Koa()).

app.use(location|mw[, service])

app.use(location|mw[, service]) -> app registers either a service object, or a Koa middleware. If a path and service object is passed it will use Feathers registration mechanism, for a middleware function Koa.

Koa middleware

In a Koa middleware, ctx.feathers is an object which will be extended as params in a service method call.

import type { NextFunction } from '@feathersjs/koa'
import type { Id, Params } from '@feathersjs/feathers'

class TodoService {
  async get(id: Id, params: Params & { fromMiddleware: string }) {
    const { fromMiddleware } = params

    return { id, fromMiddleware }
  }
}

// Register Koa middleware
app.use(async (ctx: any, next: NextFunction) => {
  ctx.feathers.fromMiddleware = 'Hello from Koa middleware'

  await next()
})

// Register a service
app.use('todos', new TodoService())

Service middleware

When registering a service, it is also possible to pass custom Koa middleware that should run before the specific service method in the koa service option:

app.use('/todos', new TodoService(), {
  koa: {
    before: [async (ctx, next) => {
      ctx.feathers // data that will be merged into sevice `params`
      
      // This will run all subsequent middleware and the service call
      await next()

      // Then we have additional properties available on the context
      ctx.hook // the hook context from the method call
      ctx.body // the return value
    }]
  }
})

Note that the order of middleware will be [...before, serviceMethod].

app.listen(port)

app.listen(port) -> HttpServer will first call Koa app.listen and then internally also call the Feathers app.setup(server).

// Listen on port 3030
const server = await app.listen(3030)

app.setup(server)

app.setup(server) -> app is usually called internally by app.listen but in the cases described below needs to be called explicitly.

Middleware

rest

import { rest } from '@feathersjs/koa'

app.configure(rest())

Configures the middleware for handling service calls via HTTP. It will also register authentication header parsing. The following (optional) options are available:

• formatter - A middleware that formats the response body
• authentication - The authentication service and strategies to use for parsing authentication information

errorHandler

import { errorHandler } from '@feathersjs/koa'

app.configure(errorHandler())

A middleware that formats errors as a Feathers error and sets the proper status code. Needs to be the first middleware registered in order to catch all other errors.

authenticate

A middleware that allows to authenticate a user (or other authentication entity) setting ctx.feathers.user. Not necessary for use with services but can be used in custom middleware.

bodyParser

A reference to the koa-bodyparser module.