Extract server responses
Redis connection failure behavior

Previously when the Redis connection failed, open connections kept open
and resumed streaming events when Redis came back online, but could have
missed events in between. New connections were also accepted and resumed
streaming when possible but crashed the server if history was requested.

Now open connections are closed when the Redis connection fails, which
allows the client to automatically retry with Last-Event-Id, which makes
possible to send missed events as history, while new connections fail
with a 503 Service Unavailable status.