fix: handle thrown exceptions in runAsyncTransaction callback

[thebrianchen]

Fixes #667.

The callback onFailure is only triggered if the ApiFuture contains the exception. When a runtime exception is thrown neither the onFailure nor onSuccess handler is called, leading the ApiFuture to hang and never complete.

The fix adds a catchingAsync() around updateCallback to guard against thrown exceptions. Added a system test for redundancy, but I can remove it. Both tests fail (never complete) when run against master.

[schmidt-sebastian]

Did you look at

java-firestore/google-cloud-firestore/src/main/java/com/google/cloud/firestore/FirestoreImpl.java

Line 465 in f2c76a1

private static class TransactionAsyncAdapter<T> implements Transaction.AsyncFunction<T> {

? It might be cleaner to follow the same pattern here.

[thebrianchen]

? It might be cleaner to follow the same pattern here.

I saw that, but it's only clean for synchronous functions. For async callbacks that return an ApiFuture, I think the only way is to add a callback.

[schmidt-sebastian]

I think this code would be easier to understand if you did something like this:

try { const result = userCallback.updateCallback(transaction) ApiFutures.addCallback(...) } catch (Exception e) { callbackResult.setException(e); } 

It's very hard to tell what the try/catch block addresses. The other alternative is to wrap the callback in a try/catch before passing it here like in TransactionAsyncAdapter.

[thebrianchen]

Done, moved it out into a separate variable.