Register Express middleware per application

[ghost]

As a user migrating from Express, or simply wishing to leverage an existing Express middleware in lb4 application, I would like to enable this middleware to be executed before/after lb4 route.

Consider the following definition in an Express app:

// before route 
app.use(function (req, res, next) {
  console.log('Time:', Date.now())
  next()
})

app.get('/api/info', 
  function getInfo(req, res, next) {
    // the route
  });

// after route 
app.use(function (req, res, next) {
  console.log('Time:', Date.now())
  next()
})

loopback 4 currently not support before/after route/requestHandler middleware.

I use the following short term workaround to support after route middleware

export async function setupMiddleware(restApp: Application): Promise<void> {
    const expressApp = restApp.restServer.requestHandler;
    (<express.Application>expressApp).use(async (req,res,next)=>{
        // ...
        next();
    });
}

[ghost]

just an idea :
middleware directory that holding all middlewares classes each class should have PreRoute and postRoute method (PreRoute before invoke controller , postRoute after invoke the controller).
with keeping in minds the order of the middleware.

class MyMiddleWare{
 readonly order =  1;
  preRoute(req,res,next){
    next();
  }
  postRoute(req,res,next){
    next(); 
  }
}

[ghost]

@bajtos following our discussion #2035

lets discuss high level first ,
i think loopback should support this feature

[bajtos]

Thank you @sanadHaj for the comments. We already have a different GH issue opened to keep track of this feature - see #1293, let's close this one as a duplicate. Feel free to re-post your comments above to #1293.

Please note that as a temporary workaround, you can mount the LB4 app on a new Express instance and then register the app-wide middleware on that Express instance. See #1982 and https://loopback.io/doc/en/lb4/express-with-lb4-rest-tutorial.html.

[bajtos]

I would like to enable this middleware to be executed before/after lb4 route.

#1293 is for executing middleware before LB4 routing kicks in.

We want to allow developes to register routing middleware handling additional non-LB4 routes too, see #2389 (already in progress).