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Middlewares & Interceptors

In fact, middleware and interceptors are exactly the same thing: they are injectables that have a certain interface to correspond to an express middleware.

Middlewares

The middlewares are Kodexo are very often used in the following cases:

  • data validation
  • authentication & access control
  • logging

They run before the method in your controllers and are applied to them using the @Use decorator which we will see next.

To create your first middleware, you must respect the following implementation:

typescript
import {
  Request,
  Response,
  NextFunction,
  Middleware,
  MiddlewareHandling
} from '@kodexo/common'

@Middleware()
export class MyMiddleware implements MiddlewareHandling {
  constructor() {} // Inject your providers if they are needed

  async use(req: Request, res: Response, next: NextFunction) {
    // Do something on req or throw an error

    // Remember to call next() function to go further
    next()
  }
}

Then you have to apply it to your route on your controllers:

typescript
import { Use, Controller, Get } from '@kodexo/common'
import { MyMiddleware } from './middlewares/my-middleware'

@Controller('/cars')
export class CarsController {

  @Use(MyMiddleware)
  @Get('/')
  async getCars() {
    return []
  }
}

Interceptors

Basically, interceptors are also middleware but they are applied after the response of your controllers' methods. They also share the same MiddlewareHandling interface.

Interceptors are generally used to modify the result before sending the response to the client.

typescript
import {
  Request,
  Response,
  NextFunction,
  Interceptor,
  MiddlewareHandling
} from '@kodexo/common'

@Interceptor()
export class MyInterceptor implements MiddlewareHandling {
  constructor() {} // Inject your providers if they are needed

  async use(req: Request, res: Response, next: NextFunction) {
    req.result = req.result.map((car: any) => {
      return {
        ...car,
        price: car.price * 1.1
      }
    })

    // Remember to call next() function to go further
    next()
  }
}

To override the result, simply rewrite the req.result variable and voilà, your Interceptor works.