Global interceptor's tap function is not executed if exception has been thrown

[weeco]

I'm submitting a...

[ ] Regression 
[X] Bug report
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

I created a global interceptor (literally copy pasted from the interceptor docs) and applied it as global interceptor to my NestJS app:

import { ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
import { Observable } from 'rxjs';
// tslint:disable-next-line:no-submodule-imports
import { tap } from 'rxjs/operators';

@Injectable()
export class GlobalMetricsInterceptor implements NestInterceptor {
  public intercept(context: ExecutionContext, call$: Observable<unknown>): Observable<unknown> {
    console.log('Before...');

    const now: number = Date.now();

    return call$.pipe(tap(() => console.log(`After... ${Date.now() - now}ms`)));
  }
}

If an exception is thrown on a called route the "After..." logline will never be printed:

Before...
After... 0ms
Before...
After... 0ms
Before...
After... 0ms
Before...
{"level":60,"time":1543875905200,"msg":"Exception in 'getPlayerProfile'. ECONNREFUSED - connect ECONNREFUSED 127.0.0.1:4400'","name":"ApiClientService","severity":"ERROR","v":1}

Expected behavior

I expected it to always print before and after.

What is the motivation / use case for changing the behavior?

I want to create prometheus metrics (#967 ) for all routes (e. g. HTTP response duration grouped by HTTP status code) and therefore I always need it to execute a function afterwards.

Environment

Nest version: 5.4.1

 
For Tooling issues:
- Node version: 10
- Platform: Windows

[marcus-sa]

tap is not supposed to be called if an error was thrown.
You need to combine it with the catchError operator.
https://www.learnrxjs.io/operators/error_handling/catch.html

[weeco]

@marcus-sa Is there no operator which would execute a function regardless if the "middleware" throws or not?

[kamilmysliwiec]

tap takes 3 parameters, next, error, and complete. If you want to capture errors as well, just add another function (second param)

[weeco]

Apparently finalize() offers what I was looking for. Thank you for your comments though!

Happy Birthday @kamilmysliwiec

[lock]

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