akka/akka-http

Exception in failed CompletionStage is always wrapped in CompletionException

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#1267 opened on Jul 5, 2017

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 (4 comments) (1 reaction) (0 assignees)Scala (1,311 stars) (598 forks)batch import
1 - triagedhelp wantedt:javat:routingt:server

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

Tech stack
javascala
Domain
backenddeveloper experience
Issue type
feature
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
Java CompletionStageakka http basicsExceptionHandlerJava DSL
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Look into the implementation of `completeOKWithFuture` and `completeOKWithFutureString` directives in the Java DSL, likely in `akka http/javadsl/server/directives/`. Understand how the CompletionStage is handled and where the CompletionException wrapping occurs. Consider adding new methods that unwrap the exception or modify the existing ones. Review the discussion in the issue comments for additional context.