akka/akka-http

Exception in failed CompletionStage is always wrapped in CompletionException

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#1,267 opened on Jul 5, 2017

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1 - triagedhelp wantedt:javat:routingt:server

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Description

When using the completeOKWithFutureString or completeOKWithFuture directives from the javadsl, the exception in a failed CompletionStage is always wrapped in a CompletionException.

This is unfortunate, as you end up writing ExceptionHandlers like this:

    ExceptionHandler exceptionHandler = ExceptionHandler.newBuilder()
            .match(CompletionException.class, e -> {
              if (e.getCause() instanceof IllegalStateException) return complete(StatusCodes.NOT_FOUND);
              // Etc.
              else return complete(StatusCodes.INTERNAL_SERVER_ERROR);
            })
            .build();

The CompletionException doesn't appear to contain any useful information (not in the stacktrace either), perhaps we should consider unwrapping it in akka-http - though that would be a breaking change. Perhaps we could deprecate completeOKWithFuture(String) and add completeOKWithCompletionStage(String) that unwraps, as that's the native terminology anyway?

Contributor guide

Research direction
Investigate the exception handling in completeOKWithFuture directives and propose unwrapping CompletionException. Consider deprecating the old methods and adding new ones that unwrap, ensuring backward compatibility.
Tech stack
scalajava
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
ScalaAkka HTTPJava
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35