It seems like the

ApacheClient

does not handle

SocketException

, which can be thrown from the underlying Apache HTTP client. https://github.com/http4k/http4k/issues/866

This is fixed and released in v4.40.2.0. Thanks for reporting! 🙃

Would it make sense to "invent" a new code for this, like

UNKNOWN_HOST

, to distinguish from 503 from server?

Maybe - do we know under which conditions it occurs?

I think it can happen when the server does not respond with proper HTTP response, or if the TLS handshake fails in case of HTTPS. In my case, it was probably due to mixing up HTTP with HTTPS.