Allow refusing all client connections with max_conns: 0

[neilalexander]

By setting max_conns to 0, we will refuse all client, MQTT and WebSocket connections. On reloading max_conns to 0, we will disconnect all clients.

Signed-off-by: Neil Twigg neil@nats.io

[MauriceVanVeen]

Principally LGTM, but should the server config be max_conns: 0?

The users generally know -1 to mean 'infinite', so having max_conns: -1 might be interpreted as "allow infinite connections".
We could detect max_conns is explicitly set to 0 and update the internal opts.MaxConn to -1 still, but then at least it's a bit clearer that max_conns: 0 actually means "no connections allowed" and the internal opts.MaxConn: 0 still means "default connections".

[neilalexander]

Updated so that you can do so with max_conns: 0 instead. Note this doesn't prevent getting the same effect with -1, as there's no "unlimited" when it comes to max_conns (otherwise you'd likely hit the file descriptor limit).

[MauriceVanVeen]

LGTM