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A wrapper for Koa route actions w/ schemas, middleware and more

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Launchcode Router

Licensed under MPL 2.0 Build Status npm

This is our main @lcdev/router node package, for centralizing the logic that all of our backend applications share. It's designed for usage in koa servers.

yarn add @lcdev/router@VERSION

It's built fairly simply, with a couple core ideas:

  • Routes are contained within one folder, with a flat structure
  • Routes are hierarchical, but usually one level deep
  • Routes typically consist of one "action" (where business logic lives), preceded by middleware

To help development remain consistent, we've made a package for encapsulating that logic. This is not a web server or framework - it's a wrapper for the organic structure of our backends.

So how do you use it?

import { join } from 'path';
import { createRouter } from '@lcdev/router';

// here, we load files from a folder (./routes) that contains many routers
// `api` here conglomerates all of them into one single koa router
const api = await createRouter(join(__dirname, 'routes'));

// you can use the router just like koa-router
const myServer = new Koa();

myServer
  .use(api.routes())
  .use(api.allowedMethods());

What about those files in ./routes? Let's look at their expected structure.

Below is one of the files in the routes folder:

import {
  RouteFactory,
  RouteActionWithContext,
  HttpMethod,
  route,
  bindRouteActions,
} from '@lcdev/router';

// we'll leave this blank for now
type Dependencies = {};

const factory: RouteFactory<Dependencies> = {
  getDependencies() {
    // here, we return whatever Dependencies is
    return {};
  },

  create(dependencies) {
    // here, bindRouteActions adds `dependencies` as `this` in actions
    // it's not required (returning an array is fine), but it makes things easier
    return bindRouteActions(dependencies, [
      // here, we'll wrap one of the route definitions in the `route` function
      // route is optional (an object works), but it adds better type inference
      route({
        path: '/hello-world',
        method: HttpMethod.GET,
        async action(ctx) {
          // returning here is the same as setting `ctx.body`
          return { hello: 'world!' };
        },
      }),
    ]);
  },
};

// important - default export needs to be a RouteFactory or a class implementing it
export default factory;

Alright, so we now have a 'RouteFactory', which can be consumed by our router. If this file was in ./routes, you'd now have a successful /hello-world GET route.

A few explanations:

  1. We export a RouteFactory to make the router side-effect free (you can import it without requiring everything to be initialized)
  2. We define Dependencies so that you can be explicit about what other modules are used, usually this is a database connection or other integration

So on to dependencies:

import {
  RouteFactory,
  RouteActionWithContext,
  HttpMethod,
  route,
  bindRouteActions,
} from '@lcdev/router';

type Dependencies = {
  // normally, you'd be a bit more concise and call this `kx` or `cx`
  databaseConnection: Postgres;
};

const factory: RouteFactory<Dependencies> = {
  getDependencies() {
    return {
      // we establish the database connection now
      // this avoids the need to have it ready until actually using this router
      databaseConnection: getTheDefaultDatabaseConnection(),
    };
  },

  create(dependencies) {
    return bindRouteActions(dependencies, [
      route({
        path: '/some-entity',
        method: HttpMethod.GET,
        async action(ctx) {
          // we now have access to `databaseConnection` through `this`!

          // and we can return whatever we want, which will end up as a json response!
          return this.databaseConnection.query('select * from some_entity');
        },
      }),
    ]);
  },
};

The key here is, that getDependencies is solely a helper. For testing, you might forgo it entirely, and create the router yourself with a mocked up database.

Testing

Before we go too deep, check out the testing package. It provides a very simple way to use these route factories as test fixtures.

Prefix

Prefixes get applied to all actions in a router. That means prefix: '/auth' puts all your actions within that path prefix. You can forgo this and specify absolute paths in your actions if you want.

const factory: RouteFactory<Dependencies> = {
  prefix: '/auth',

  getDependencies() { ... },
  create(dependencies) { ... },
};

Middleware

You can declare middleware for a router, and/or per route. This allows flexibility and coverage.

const factory: RouteFactory<Dependencies> = {
  // your normal getDependencies and create functions
  getDependencies() { ... },
  create(dependencies) { ... },

  middleware: (dependencies) => [
    // middleware here gets applied to all actions
    // you might put authentication middleware here, for example
  ],
};

The same interface is available per-action. Just specify middleware: [] beside path and friends.

Schemas

We support JSON Schema natively to validate incoming request bodies. Simply put a schema property next to your action.

route({
  path: '/resource/:id',
  method: HttpMethod.POST,
  // we give you @serafin/schema-builder through the `emptySchema` export
  // you can also using a json schema directly, using the `JSONSchema` export
  schema: emptySchema()
    .addNumber('x')
    .addNumber('y'),
  async action(_, body) {
    // here, typescript will actually know the type of x and y!
    const { x, y } = body;
  },
})

This does depend on having bodyparser middleware. We export bodyparser, for common use cases, from this module. It's good practice to include this bodyparser per-route-factory.

import { RouteFactory, bodyparser, propagateErrors, propagateValues } from '@lcdev/router';

const factory: RouteFactory<Dependencies> = {
  getDependencies() { ... },

  // a normal normal middleware stack looks like this
  middleware: ({ auth }) => [
    propagateErrors(true),
    propagateValues(),
    bodyparser(),
    auth.authenticate(),
  ],

  create(dependencies) { ... },
};

Nesting

The lcdev router is usually used in mostly flat contexts, but you can easily nest your routers.

import {
  RouteFactory,
  findRoutes,
} from '@lcdev/router';

const factory: RouteFactory<Dependencies> = {
  prefix: '/support',
  nested: () => findRoutes(join(__dirname, 'support')),

  getDependencies() { ... },
  create(dependencies) { ... },
};

The example above nests routes found in the ./support folder.

Errors

The lcdev router normalizes errors that come from your actions. This pairs nicely with @lcdev/logger.

What you need to know:

  • @lcdev/router exports BaseError (you can use err), which is "a user visible error"
  • In development, you'll always see your error messages
  • In production, only errors that are BaseErrors propagate up (see internalMessage for full details)

Throwing errors: it happens, you'll need a way to throw an error up when things go wrong.

import { err } from '@lcdev/router';

// is it okay for your API consumers to see this error?
throw err(401, 'Your error message');

// no? keep it private by throwing any other error type
throw { status: 401, message: 'Your error message' };

You'll likely want to use propagateErrors, though it is, strictly speaking, optional.

import { propagateErrors } from '@lcdev/router';

// try to keep this as high as you can in your middleware stack
myServer.use(propagateErrors());

myServer.use(api.routes());
myServer.use(api.allowedMethods());

This will catch normalized errors, and return them in our standard json body format (and set the HTTP code).

{
  "success": false,
  "code": "ERRCODE|num",
  "message": "User visible message"
}

You're encouraged to add this middleware at the top of your app, as well as on every RouteFactory. Doing so per-factory will make testing those factories in isolation a lot easier.

Return Format

In a similar way to errors, it's handy to have all of your routes return JSON in the same structured format.

{
  "success": true,
  "data": { ... }
}

Instead of doing this yourself, we have middleware to help. Again, this is optional but encouraged.

import { propagateValues } from '@lcdev/router';

myServer.use(propagateValues());

When this middleware is above your route actions, you don't need to do anything. JSON responses will be wrapped in the above format. This makes parsing your API responses a lot easier.

By default, this supports a third "meta" property in return objects. We normally use this for pagination state. You can add data the ctx.state.meta or call addMeta(ctx, { ... }) to fill this in in an action.

Pagination

Actions will look basically like this:

import { paginate, addPagination, paginationSchema, Pagination } from '@lcdev/router';

route({
  path: '/',
  method: HttpMethod.GET,
  middleware: [
    // wrapping middleware around your action
    // verifies 'page: number' and 'count?: number' query parameters
    // 100 is the default count/pageSize when not provided
    paginate(100), // second (optional) parameter here is the maximum limit allowed
  ],
  querySchema: paginationSchema,
  returning: [getApiFields(MyEntity)],
  async action(ctx) {
    // this is populated by the paginate middleware
    const { page, pageSize } = ctx.state.pagination as Pagination;

    // just use page and pageSize as you normally would
    const { results, total } = await MyEntity.query(this.kx)
      .page(page, pageSize);

    // pushes the resulting total into ctx state
    addPagination(ctx, total);

    // after this, 'total' and 'pages' are added as meta properties to the response
    return results;
  },
}),

Extracting Returns

Taking an example route action:

route({
  path: '/users',
  method: HttpMethod.GET,
  async action(ctx) {
    return myDatabase.select('* from user');
  },
}),

You might prefer not to include the password field here (excuse the contrived example).

To do so, the manual approach is:

const { values, to, return } = { ... };

return { values, to, return };

This is clearly not great. Lots of duplication and possibility for errors. It doesn't work for nesting objects well, and with multiple branches in an action, requires duplication.

You might opt to use our returning field instead.

route({
  path: '/users',
  method: HttpMethod.GET,
  returning: {
    firstName: true,
    lastName: true,
    permissions: [{
      role: true,
      authority: ['access'],
    }],
  },
  async action(ctx) {
    return myDatabase.select('* from user');
  },
}),

You can think of this as the inverse of schema. Some examples of this:

INPUT:
{
  firstName: 'Bob',
  lastName: 'Albert',
  password: 'secure!',
  permissions: [
    { role: 'admin', timestamp: new Date(), authority: { access: 33 } },
    { role: 'user', timestamp: new Date(), extra: false },
  ],
}

RETURNING:
{
  firstName: true,
  lastName: true,
  permissions: [{
    role: true,
    authority: ['access'],
  }],
}

RESULT:
{
  firstName: 'Bob',
  lastName: 'Albert',
  permissions: [
    { role: 'admin', authority: { access: 33 } },
    { role: 'user' },
  ],
}

Note a couple things:

  • ['access'] means "pull these fields from the object" - it's the same as { access: true }
  • [{ ... }] means "map this array with this selector"
  • { foo: true } means "take only 'foo'"

Mismatching types, like an array selector when the return is an object, are ignored.

This is pulled directly from the @lcdev/mapper package, you can read more there.

API Fields

You might want to reduce the duplication when using the returning feature. Most of the time, you want to return the same fields for the same entities, records, etc.

Please see the @lcdev/api-fields package for that. It defines a decorator, called @ApiField(), which you can use to automatically fill in the returning field of a route action.

import { ApiField } from '@lcdev/api-fields';

class User extends BaseEntity {
  @ApiField()
  id: number;

  privateField: number;

  @ApiField()
  firstName: string;

  @ApiField(() => Permission)
  permission: Permission;

  ...
}

In your route action, simply:

import { getApiFields } from '@lcdev/api-fields';

route({
  path: '/users/:id',
  method: HttpMethod.GET,
  // getApiFields returns an object with the same format that `returning` expects
  returning: getApiFields(User),
  async action(ctx) {
    return myDatabase.select('from user where id = $0', id).first();
  },
}),
route({
  path: '/users',
  method: HttpMethod.GET,
  // can be composed easily - an array of users is just like this
  returning: [getApiFields(User)],
  async action(ctx) {
    return myDatabase.select('from user where id = $0', id);
  },
}),

Please read more on the docs.

Incremental Adoption

For apps that are using a basic koa-router and don't want the module loading of this package, this enables you to still use route (giving you schema validation, middleware, error handling, api fields / returning extraction).

import * as Router from 'koa-router';
import { route, addRouteToRouter, addRoutesToRouter, HttpMethod } from '@lcdev/router';

const router = new Router();

addRouteToRouter(
  route({
    path: '/my-route',
    method: HttpMethod.GET,
    returning: {
      foo: true,
    },
    async action() {
      return {
        foo: 'bar',
        bar: 'baz',
      };
    },
  }),
  router,
);

// or

addRoutesToRouter(router, [
  route({
    path: '/my-route',
    method: HttpMethod.GET,
    async action() {
      return {
        foo: 'bar',
        bar: 'baz',
      };
    },
  }),
]);

export default router;

This enable incremental adoption, though without the benefit of DI, nesting, etc.

Open API

There is early support for generating API documentation from your routers. Check out the createOpenAPI function for more about this. For now, we encourage you to use Insomnia for testing of APIs.

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