Custom Middleware — Series 3

Preview — 3 of 10 questions

What does exclude() do here, and what is the common mistake?

javascript

consumer
  .apply(AuthMiddleware)
  .exclude({ path: 'auth/(.*)', method: RequestMethod.ALL })
  .forRoutes('*');

AIt removes the excluded routes from the application entirely

BIt applies the middleware only to the excluded paths, inverting forRoutes

CIt excludes the paths from every middleware registered in this module

DIt carves the auth subtree out of this middleware's coverage; the usual mistake is assuming the pattern is matched against the raw URL — it is matched against the registered route path, so a global prefix or a mismatched wildcard syntax silently leaves the routes covered after all

When does the middleware run?

javascript

consumer.apply(MetricsMiddleware).forRoutes({ path: 'reports', method: RequestMethod.GET });
// no controller declares GET /reports

AOn every request, since an unmatched path falls through to all middleware

BNever for requests to /reports: middleware is mounted on the path, but a request only reaches it through the router, and with no route registered the request is answered with a 404 by the adapter — so middleware bound to a non-existent route is silently dead code

COnce at startup, to validate the path

DOn /reports requests only, returning 404 afterwards

Is normalising the body here a good idea?

javascript

use(req: Request, res: Response, next: NextFunction) {
  if (typeof req.body?.email === 'string') req.body.email = req.body.email.trim().toLowerCase();
  next();
}

AIt works — the body is already parsed and @Body() reads the same object — but it hides a transformation from everyone reading the DTO, and it runs for every route the middleware covers whether or not the field is meaningful there; @Transform() on the DTO expresses the same rule where the shape is declared

BIt has no effect, because @Body() reads from a copy of the request

CIt throws, since the parsed body is frozen

DIt works and is preferred, since middleware runs before validation

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