`EmbeddedChannel.writeOutbound` doesn't throw if only `context.fireErrorCaught` is called

[Davidde94]

Expected behavior

I would have expected writeOutbound to have identical behaviour to writeInbound in that it should throw if either or both of the following are true:

• A promise is failed
• A handler calls context.fireErrorCaught

Actual behavior

If the promise isn't failed but fireErrorCaught is called then writeOutbound doesn't throw, but writeInbound does.

Note

This should probably be fixed as part of NIO 3, as it's possible for a lot of project's tests to suddenly begin failing if this is fixed.

[t089]

Please correct me if I’m wrong, but I thought that errorCaught is explicitly only for inbound handlers and thus inbound errors. Outbound errors are only propagated through the given promise/future.

[weissi]

@t089 errorCaught is only served to inbound handlers indeed. writeInbound/writeOutbound are methods on EmbeddedChannel only that you use for testing.

Because in unit tests when making sure that something doesn't fail, you typically also want to check that no errors have been delivered through the pipeline. (Most of the time in EmbeddedChannels, you test handlers in isolation actually).

Sure, this functionality is not needed, you can in tests add another handler that tells you about any errors that went through the pipeline. But if you forget that, then you may miss an error. Hence, when using writeInbound we also tell you about errors that hit the channel. I think we should (for NIO 3) do the same for writeOutbound. If a write fails, you typically fail the promise and fire an error through the pipeline.

[t089]

Thanks a lot for the explanation. I missed the EmbeddedEventLoop part. Makes sense now 😀