[inversify-express-utils] allow to inject dependencies into middleware constructor

[b1ff]

Expected Behavior

Middlewares should be created by http request scoped container. Since by default they are not singleton it does make sense to create them using per-request container, which allows to inject request-scoped dependencies in constructor instead calling this.httpContext.container.get(...). For middlewares that are registered as singleton nothing will be changed, so it should add any performance difference.

Current Behavior

Right now middlewares in express-utils are always created using root container which does not allow to inject request scoped variables in constructor.

Possible Solution

PR: https://github.com/inversify/inversify-express-utils/pull/325/files

Steps to Reproduce (for bugs)

    it("Should allow constructor injections from http-scope in middlewares", async () => {

        const TYPES = {
            Value: Symbol.for("Value"),
            ReadValue: Symbol.for("ReadValue"),
            HttpContextValueSetMiddleware: Symbol.for("HttpContextValueSetMiddleware"),
            HttpContextValueReadMiddleware: Symbol.for("HttpContextValueReadMiddleware"),
        };

        class HttpContextValueSetMiddleware extends BaseMiddleware {
            public handler(
                req: express.Request,
                res: express.Response,
                next: express.NextFunction
            ) {
                this.bind<string>(TYPES.Value).toConstantValue(`MyValue`);
                next();
            }
        }

        class HttpContextValueReadMiddleware extends BaseMiddleware {
            constructor(@inject(TYPES.Value) private value: string) {
                super();
            }

            public handler(
                req: express.Request,
                res: express.Response,
                next: express.NextFunction
            ) {
                this.bind(TYPES.ReadValue).toConstantValue(`${this.value} is read`);
                next();
            }
        }

        @controller("/http-scope-middleware-injection-test")
        class MiddlewareInjectionTestController extends BaseHttpController {

            constructor(@inject(TYPES.ReadValue) @optional() private value: string) {
                super();
            }

            @httpGet(
                "/get-value",
                TYPES.HttpContextValueSetMiddleware,
                TYPES.HttpContextValueReadMiddleware
            )
            public getValue() {
                return this.value;
            }
        }

        const container = new Container();

        container.bind<HttpContextValueReadMiddleware>(TYPES.HttpContextValueReadMiddleware)
            .to(HttpContextValueReadMiddleware);
        container.bind<HttpContextValueSetMiddleware>(TYPES.HttpContextValueSetMiddleware)
            .to(HttpContextValueSetMiddleware);
        container.bind<string>(TYPES.Value).toConstantValue("DefaultValue");
        const app = new InversifyExpressServer(container).build();

        await supertest(app)
            .get("/http-scope-middleware-injection-test/get-value")
            .expect(200, "MyValue is read");
    });

Context

In application I would like to register some values in middlewares at the beginning of the request and then use classes that abstract HTTP specific things for the consumers. Allowing to inject dependencies into middleware constructor simplifies unit testing of those middlewares.

Your Environment

NodeJS 12.x.x Windows

[PodaruDragos]

hey @b1ff .

I saw that you've made a PR for this. but it's already possible to do this in inversify-express-utils. Let me give you an example.

@injectable()
export class AuthorizationMiddleware extends BaseMiddleware {
  @inject(TYPES.USER_REPOSITORY)
  private readonly userRepository!: EntityRepository<User>;

  constructor(
    @inject(TYPES.USER_REPOSITORY)
    private readonly userRepositoryFromConstructor: EntityRepository<User>
  ) {
    super();
  }

  public handler(_req: Request, _res: Response, next: NextFunction): void {
    console.log(this.userRepository);
    console.log(this.userRepositoryFromConstructor);
    next();
  }
}

And then for the container binding

container.bind(AuthorizationMiddleware).toSelf();

Is this what you were looking for ?

[b1ff]

@PodaruDragos hey there, not really. The issue is when I do

this.bind(..).to...();

in middleware, I cannot inject it using constructor to middleware. I have to use httpContext.containter.get(). While it works as workaround, it is better from testability and cleanness to inject it via middleware constructor, even if it was bound to container on httpContext. You might see that behavior in test that I have added.