Connection errors not reported for akka-http client backend

[jrudolph]

Connection errors are not reported i.e. the response Future of a call is not failed.

The reason is that currently the akka-http PersistentConnection fails the connection stream if the connection fails ultimately. When that happens, we might have a request on the akka-http side outstanding (and more in the queue on the akka-grpc side).

We could try to report an error on the akka-http side but that is prone to race conditions (send error response vs stream failure, but also possibly send new request vs. stage failed).

To add that feature in akka-grpc, we need to keep track of ongoing requests. Is that what we want?

See also akka/akka-http#3892.

[johanandren]

Trying out a possible upstream solution/precondition to solution here: akka/akka-http#4299

[johanandren]

Better upstream fix for the request triggering the failure: akka/akka-http#4322

[jtjeferreira]

@johanandren Since akka/akka-http#4322 was merged and released this is no longer needed?

[johanandren]

There is still an open PR with further fixes needed waiting (#1851)