koa-detour-addons

A small collection of helpful middleware for koa-detour.

koa-detour and koa-detour-addons are designed to simplify the development of REST APIs.

const R = require("@nickbottomley/responses");

// this whole object is considered a single "resource"
const resource = {

  // if this method resolves to something falsy, response is a 400
  // otherwise, processing continues
  validate (ctx) {
    if (ctx.method !== "POST" && ctx.method !== "PUT") return;
    return applySchema(ctx, { title: String, isbn: String });
  },

  // something upstream is (in this case) responsible for populating ctx.user
  // if this method resolves to something falsy, response is 401
  // otherwise, processing continues
  authenticate (ctx) {
    return ctx.user && ctx.user.type === "author";
  },

  // if this method resolves to something falsy, response is 403
  // otherwise processing continues
  allow (ctx) {
    // ctx.user is defined now
    return Books.isByAuthor(ctx.body.isbn, ctx.user);
  },

  // if this method resolves to null/undefind, response is 404
  // otherwise, the value is provided as "ctx.fetched"
  fetch (ctx) {
    return Books.findByIsbn(ctx.body.isbn)
  },

  // handles GET requests
  GET (ctx) {
    return R.Ok(ctx.fetched);
  },

  // handles DELETE requests
  DELETE (ctx) {
    const {id} = ctx.fetched;
    // R.NoContent() is a 204 response; `respond` add-on takes care of the details
    return Books.deleteById(id).then(R.NoContent)
  }

  POST (ctx) {
    // `validate` middleware already checked the validity of `ctx.body`
    // R.Created() is a 201 response; `respond` add-on takes care of the details
    return Books.create(ctx.body).then(R.Created)
  }
};

const KoaDetourRouter = require("koa-detour");
const router = new KoaDetourRouter()
  .apply(require("koa-detour-addons"))
  .route("/books", booksResource);

const Koa = require("koa");
const app = new Koa().use(router);

validate middleware

type ValidateFn = (ctx: KoaContext) => Boolean | Promise<Boolean>

The validate should return a Promise or value representing whether the request is valid or not. If that value is falsy, a 400 response (Bad Request) is sent automatically. If validateFn throws or rejects, a 400 is sent with that error message. This is different from how the other middleware work -- they re-throw errors. This behavior makes it easy to use validation functions which throw errors. However, it can be dangerous where there is e.g. a programmer error in the validation function.

authenticate middleware

type AuthenticateFn = (ctx: KoaContext) => Boolean | Promise<Boolean>

The authenticate should return a Promise or value representing whether the request is from a properly authenticated user. If that value is falsy, a 401 response (Unauthorized) is sent automatically.

allow middleware

type ForbidFn = (ctx: KoaContext) => Boolean | Promise<Boolean>

The allow should return a Promise or value representing whether the current user has access to the requested resource. If that value is falsy, a 403 response (Forbidden) is sent automatically.

fetch middleware

type FetchFn = (ctx: KoaContext) => Object? | Promise<Object?>

The fetch should return a Promise or value of the business object being requested. If that value is null or undefined, a 404 response (NotFound) is sent automatically.

respond plugin

The respond plugin is responsible for interfacing between response objects and the Koa context object. In particular, it allows middleware and resources to return or throw response objects and have them handled properly.