Koa Middleware Adapter

Functions and promises can be used as middleware in koa.

​

const Koa = require('koa');
const adapter = require('koa-middleware-adapter');

const app = new Koa();

app.use(adapter.create(() => 'Hello, World!'));

const port = 4000;
app.listen(port, () => {
  console.log(`server is listening to port ${port}`);
});

​

Document

• example
• source

​

Install

$ npm i koa-middleware-adapter

​

Usage

const Koa = require('koa');
const Router = require('koa-router');
const bodyParser = require('koa-bodyparser');
const adapter = require('koa-middleware-adapter');

const UserDao = require('./userDao');

const userDao = new UserDao();

async function findUserInfo(userId, userDao) {
  const user = await userDao.findById(Number(userId));
  if (!user) throw new adapter.NotFound('User Not Found');

  return user;
}

async function createUserInfo(user, userDao) {
  await userDao.insert(user);
  return user;
}

const findUserMiddleware = adapter.create(findUserInfo, {
  status: 200,
  parameters: [
    new adapter.parameter.Parameter(adapter.parameter.where.params, { name: 'id', index: 0 }),
    new adapter.parameter.Parameter(userDao, { index: 1 }),
  ],
});

const findUserInContextMiddleware = adapter.create(findUserInfo, {
  status: 200,
  parameters: [
    new adapter.parameter.Parameter(new adapter.parameter.where.Where('user', true), { name: 'id', index: 0 }),
    new adapter.parameter.Parameter(userDao, { index: 1 }),
  ],
});

const createUserMiddleware = adapter.create(createUserInfo, {
  status: null,
  parameters: [
    new adapter.parameter.Parameter(adapter.parameter.where.body, { index: 0 }),
    new adapter.parameter.Parameter(userDao, { index: 1 }),
  ],
  response: new adapter.response.Response(adapter.response.where.context, { name: 'user' }),
});

const router = new Router();

router.get('/users/:id', findUserMiddleware);
router.post('/user', createUserMiddleware, findUserInContextMiddleware);

const app = new Koa();

app.use(bodyParser());

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

const port = 4000;
app.listen(port, () => {
  console.log(`server is listening to port ${port}`);
});

Request

• POST http://localhost:4000/user

  {
  	"username": "test",
  	"password": "test"
  }

Response

• status: 200

  {
      "username": "test",
      "password": "test",
      "id": 0
  }

​

Request

• GET http://localhost:4000/users/0

Response

• status: 200

  {
      "username": "test",
      "password": "test",
      "id": 0
  }

​

Spec

Adapt

adapter.create(listener, { status, type, parameters, response, handlers, thisArg });

​

Parameters

function Parameter(
  where = new Where(null, true, true, true),
  options = {},
) {
  this.where = where;
  this.name = options.name || null;
  this.as = options.as || null;
  this.index = options.index || 0;
  this.combineLevel = options.combineLevel || 0;
}

• Parameters defines the information of the parameters to pass.

  • where defines where to find the parameter.
    • If where is not an instance of Where, the parameter is where .
    • If where is an instance of Where, the parameter is found in ctx with information from where.
  • name is the name of the parameter.
    • If name exists, the same name is taken from the parameter's location.
  • combineLevel is the level at which the imported arguments are to be combined.
    • 0 means the imported parameter is the parameter to pass.
    • 1 means the imported parameter is a child of the parameter to pass.
  • as specifies a name when passing a parameter.
  • index is index of the parameter to pass.

• The default value is params, query, header, body, cookies defined.

​

Response

function Response(
  where = new Where(null, true, true, true),
  options = {},
) {
  this.where = where;
  this.name = options.name || null;
  this.type = options.type;
}

• The response determines how to handle the lister's response
  • where defines where to bind the response.
    • If where is not an instance of Where, the response is injected in where .
    • If where is an instance of Where, the position is found in ctx with information from where and inject the response.
  • name is the name of the response.
    • If name exists, the same name is defined in the position to inject the response.
• The default value is body, which binds the request value to the body of the response.

​

Where

function Where(name, context, koa, node, setterAndGetter) {
  this.name = name;
  this.context = context;
  this.koa = koa;
  this.node = node;
  this.setterAndGetter = setterAndGetter;
}

• Where defines where to find the parameter.
  • name is the name of the location from which to retrieve the parameter.
  • context means to find the location of a parameter in ctx.
  • koa means to find the location of a parameter in ctx.request.
  • node means to find the location of a parameter in ctx.req.
• setterAndGetter means to use set or get method to extract or inject object, if set or get method is exist.

​

Handlers

const handlers = { extractParameterHandler, injectResponseHandler, errorHandler };

Extract Parameter Handler

function extractParameterHandler(ctx, parameters) {}

Inject Response Handler

function injectResponseHandler(ctx, result, options = { response, status, type }) {}

Error Handler

function errorHandler(ctx, error) {}

​

thisArg

• If this is exist, listener call by thisArg.
• If this type is function, listener call by result of thisArg.