HostFilter Not Used for Control Connection

[amcrn]

The HostFilter is not being used for the Control Connection (aka the controlConn). This can be problematic, especially if the host is being filtered due to it being in a bad state, as it can hold up the creation of the Control Connection (and therefore the Session itself) for quite some time.

This also fixes an issue if disableControlConn=true and/or DisableInitialHostLookup=true, where the Ring is updated with the host, prior to filtering:
https://github.com/gocql/gocql/blob/db6d5564dd6843cc08cc1d6c3642612adf94c618/session.go#L265-L268

Closes: #1723

[testisnullus]

We can refactor to something like:

newHosts := hosts[:0]

to avoid allocating a new slice, but in general, it is a good suggestion to fix an issue.

[testisnullus]

LGTM

[OleksiienkoMykyta]

LGTM. Could you please make it up to date, update CHANGELOG.md, and refactor commit log according to CONTRIBUTING.md, as an example you can check f35d463, or any other last merged PR.
@joao-r-reis, @jameshartig, please check it out.

[jameshartig]

Unfortunately, I don't think this is the right way for this to be fixed. The problem is that most HostFilter's expect the information about the host to be filled in (such as DataCenter, ConnectAddress, HostID), but in this case, so early in the process we don't have the correct, or really any information. I'm concerned that this will be pointless (because they'll all be filtered) and very confusing.

Right after we connect, we filter the hosts which seems about as good as we can do.

cassandra-gocql-driver/session.go

Line 247 in bf16ec3

filteredHosts := make([]*HostInfo, 0, len(newHosts))

This also fixes an issue if disableControlConn=true and/or DisableInitialHostLookup=true, where the Ring is updated with the host, prior to filtering:

My understanding is that the ring should always contain all hosts in the cluster and that we should only be filtering before adding a host to the pool so I believe this is working as intended.

[joao-r-reis]

This also fixes an issue if disableControlConn=true and/or DisableInitialHostLookup=true, where the Ring is updated with the host, prior to filtering:

My understanding is that the ring should always contain all hosts in the cluster and that we should only be filtering before adding a host to the pool so I believe this is working as intended.

There's a separate PR to address the issue with DisableInitialHostLookup=true, I posted this comment there. Are your thoughts in line with what my suggestion there @jameshartig ?