# Middlewares

Middleware is similar to the Express middleware with the difference that it's a class and you can use the IoC to inject other services on its constructor.

All middlewares decorated by Middleware have one method named use(). This method can use all parameters decorators as you could see with the Controllers and return a promise.

# Configuration

To begin, you must add the middlewares folder on the componentsScan attribute in your server settings as follows:

import {Configuration} from "@tsed/di";
import {MyController} from "./controllers/rest/MyController";

@Configuration({
  mount: {
    "/rest": [MyController]
  }
})
export class Server {}

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Then, create a new file in your middlewares folder. Create a new Class definition then add the Middleware decorator.

import {Context} from "@tsed/platform-params";
import {Middleware} from "@tsed/platform-middlewares";

@Middleware()
export class CustomMiddleware {
  use(@Context() $ctx: Context) {
    console.log("ID", $ctx.id);
  }
}

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You have different usecases to declare and use a middleware as following:

Global middleware: this middleware can be used on the Server,
Endpoint middleware: this middleware can be used on a controller method,
Error middleware: this middleware can be used to handle errors.

Note

Global middleware and endpoint middleware are similar, except that the Endpoint middleware can access to the last executed endpoint information.

# Global middleware

Global middlewares are generally used to handle requests before or after controllers.

import {Context} from "@tsed/platform-params";
import {Constant} from "@tsed/di";
import {MiddlewareMethods, Middleware} from "@tsed/platform-middlewares";
import {NotAcceptable} from "@tsed/exceptions";

@Middleware()
export default class AcceptMimesMiddleware implements MiddlewareMethods {
  @Constant("acceptMimes")
  acceptMimes: string[];

  use(@Context() $ctx: Context) {
    if (!$ctx.request.accepts(this.acceptMimes)) {
      throw new NotAcceptable("Accepted mimes are: " + this.acceptMimes.join(", "));
    }
  }
}

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Then add your middleware on the Server by using the right hook:

import {PlatformApplication} from "@tsed/common";
import {Configuration, Inject} from "@tsed/di";
import {GlobalAcceptMimeMiddleware} from "./GlobalAcceptMimeMiddleware";

@Configuration({
  acceptMimes: ["application/json"] // add your custom configuration here
})
export class Server {
  @Inject()
  app: PlatformApplication;

  $beforeRoutesInits() {
    this.app.use(GlobalAcceptMimeMiddleware);
  }

  // or
  $afterRoutesInit() {
    this.app.use(GlobalAcceptMimeMiddleware); // But maybe is too late ;)
  }
}

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TIP

Since v6.28.0, it's also possible to register middlewares from middlewares options on Configuration decorator. In addition, it's also possible to configure the environment for which the middleware should be loaded.

import {Configuration, ProviderScope, ProviderType} from "@tsed/di";

@Configuration({
  middlewares: [
    {hook: "$afterInit", use: helmet({contentSecurityPolicy: false})},
    {env: Env.PROD, use: EnsureHttpsMiddleware},
    cors(),
    cookieParser(),
    compress({}),
    methodOverride(),
    AuthTokenMiddleware
  ]
})
export class Server {}

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The middlewares added through middlewares options will always be registered after the middlewares registered through the hook methods!

# Endpoint middleware

Endpoint middleware is not really different from global middleware, but its goal is to handle a request before or after endpoint. It knows which endpoint is executed by using the EndpointInfo decorator.

The following example, show you how to implement the middleware and use it with a custom decorator.

Middleware can be used on a class controller or endpoint method with the following decorators:

UseBefore
Use
UseAfter
or routes decorators: Get , Post , Delete , Put and Patch

import {UseBefore} from "@tsed/platform-middlewares";
import {Get} from "@tsed/schema";
import {Controller} from "@tsed/di";
import {CustomMiddleware} from "./middlewares/CustomMiddleware";

@Controller("/test")
@UseBefore(CustomMiddleware) // global to the controller
class MyCtrl {
  @Get("/")
  @UseBefore(CustomMiddleware) // only to this endpoint
  getContent() {}
}

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# Error middleware

Express allows you to handle any error when your middleware have 4 parameters like this:

function (error, req, res, next){}

Ts.ED has the same mechanism with Err decorator. Use this decorator on a middleware to create a handler which will only called when an error occurs on th decorated endpoint.

import {Err, Middleware, Next} from "@tsed/common";

@Middleware()
export class MyMiddlewareError {
  use(@Err() err: unknown, @Next() next: Next) {
    console.log("===> Error:", err);
  }
}

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The following example is the GlobalErrorHandlerMiddleware used by Ts.ED to handle all errors thrown by your application.

If you planed to catch errors globally see our Exception filter page.

# Specifics parameters decorators

In addition, you have these specifics parameters decorators for the middlewares:

Signature	Description
Err	Inject the `Express.Err` service.
Context	Provide all information about the called endpoint

# Call sequences

As you see in the previous section, a middleware can be used on different contexts:

A middleware added to a controller or endpoint level has the same constraint as the endpoint method itself. It'll be played only when the url request matches with the path associated to the controller and its endpoint method.

When a request is sent to the server all middlewares added in the Server, Controller or Endpoint with decorators will be called while a response isn't sent by one of the handlers/middlewares in the stack.

For each executed endpoints and middlewares, Platform API store the return value to the Context . We have two scenarios:

If a data is stored in the Context object, the response will be immediately send to your consumer after the UseAfterEach middleware (if present).
If no data is stored in the Context object, the call sequence middlewares continue to the next endpoint (if present) or to the UseAfter then Global middlewares until a data isn't returned by a handler.

TIP

The middlewares shown in the Endpoints box will be replayed as many times as it has endpoint that matches the request url.

For example:

import {Next} from "@tsed/common";
import {Use, UseAfter, UseBefore, UseBeforeEach} from "@tsed/platform-middlewares";
import {Get} from "@tsed/schema";
import {Controller} from "@tsed/di";

@Controller("/")
@UseAfter(MdlwCtrlAfter)
@UseBefore(MdlwCtrlBefore)
@UseBeforeEach(MdlwCtrlBeforeEach)
@Use(MdlwCtrl)
export class MyCtrl {
  @Get("/")
  @UseBefore(MdlwBefore)
  @Use(Mdlw)
  @UseAfter(MdlwAfter)
  endpointA(@Next() next: Next) {
    console.log("EndpointA");
    next();
  }

  @Get("/")
  endpointB() {
    console.log("EndpointB");

    return {};
  }
}

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According to the call sequence scheme, the stack calls will be there:

Middlewares added in Server (logger, express middleware, etc...),
MdlwCtrlBefore,
MdlwCtrlBeforeEach
MdlwBefore,
MdlwCtrl,
MyCtrl.endpointA,
MdlwAfter,
SendResponse, (but no data is returned by the endpointA)
MdlwCtrlBeforeEach
MdlwCtrl,
MyCtrl.endpointB,
MdlwAfter,
SendResponse, send a response because endpointB returns data,
MdlwCtrlAfter, but this middleware will not be called because a response is sent.
Middleware added in Server (not called too).

# Override existing middlewares

The decorator OverrideProvider gives you the ability to override some internal Ts.ED middlewares.

import {OriginalMiddleware} from "@tsed/common";
import {Context} from "@tsed/platform-params";
import {OverrideProvider} from "@tsed/di";

@OverrideProvider(OriginalMiddleware)
export class CustomMiddleware extends OriginalMiddleware {
  public use(@Context() $ctx: Context) {
    $ctx.response; // Ts.ED response
    $ctx.request; // Ts.ED resquest
    $ctx.getResponse(); // return Express.js or Koa.js response
    $ctx.getRequest(); // return Express.js or Koa.js request

    // Do something
    return super.use();
  }
}

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Here we use the new Platform API to write our middleware. By using Context decorator and PlatformContext class we can get some information:

The data returned by the last executed endpoint,
The EndpointMetadata itself,
The PlatformRequest and PlatformResponse classes abstraction. These classes allow better code abstraction by exposing methods that are agnostic to Express.js.

TIP

By default, the server imports automatically your middlewares matching with this rules ${rootDir}/middlewares/**/*.ts (See componentScan configuration).

.
├── src
│   ├── controllers
│   ├── services
│   ├── middlewares
│   └── Server.ts
└── package.json

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If not, just import your middleware in your server or edit the componentScan configuration.

import {Configuration} from "@tsed/common";
import "./src/other/directory/CustomMiddleware";

@Configuration({
    ...
})
export class Server {

}

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# Provided middlewares

Loading in progress...

# Middlewares

# Configuration

# Global middleware

# Endpoint middleware

# Error middleware

# Specifics parameters decorators

# Call sequences

# Override existing middlewares

# Provided middlewares

Other topics