Custom Middleware

For this article, it is necessary to have a understanding of Middleware component, Controllers, Routes & HTTP Handlers

Main

Custom middleware are used to provide interceptions to certain endpoints in your Application. The use cases may vary, but the most common use cases are verifications.

In order for a middleware to be considered a mandarine middleware, your middleware class needs to implement the class MiddlewareTarget.

MiddlewareTarget contains two key methods which you will need to provide functionality.

• onPreRequest(...args): boolean

  • It is executed before the request reaches to the HTTP Handler.

  • If it returns true, the request is authorized to continue to the HTTP handler & then to the post-request handler.

  • If it returns false, the request will be stopped and the HTTP handler nor the post-request handler will be reached.

• onPostRequest(...args): void

  • It is executed after the request has reached & called the HTTP handler.

Note that both onPreRequest and onPostRequest can absolutely use all HTTP parameter decorators.

Usage

Syntax: See syntax and extra information here

middleware.ts

import { Middleware, MiddlewareTarget } from "https://deno.land/x/mandarinets/mod.ts";

@Middleware(new RegExp('/api/*'))
export class Middleware1 implements MiddlewareTarget {

    public onPreRequest(@ResponseParam() response: any): boolean {
        console.log("pre-request()");
        return true;
    }
    
    public onPostRequest(): void {
        console.log("post-request()");
    }
}

controller.ts

import { Controller, MandarineMVC } from "https://deno.land/x/mandarinets/mod.ts";

@Controller()
export class MyController {

    @GET('/api/hello-world')
    public helloWorldApi() {
        return "Hello world";
    }

}

Index file

import { MandarineCore } from "https://deno.land/x/mandarinets/mod.ts";

import { MyController } from "./controller.ts";
import { Middleware1 } from "./middleware.ts";

const controllers = [MyController1];
const middleware = [Middleware1];

new MandarineCore().MVC().run();

Deno execution

deno run --config tsconfig.json --allow-net --allow-read index.ts

Result

# http://localhost:8080/api/hello-world
[Console] pre-request()
Hello world
[Console] post-request()