[QUIC] QuicListener.ListenEndPoint returns a port of 0 if Start() hasn't been called

[scalablecory]

We should probably make this property throw if the listener hasn't been started.

var listener = new QuicListener(new IPEndPoint(IPAddress.Loopback, 0), sslOpts);
IPEndPoint endPoint = listener.ListenEndPoint; // will have a port of 0.
listener.Start();
endPoint = listener.ListenEndPoint; // will now have a valid port.

CC @jkotalik

[geoffkizer]

Having a property throw usually isn't great, but I suppose you can argue that this is incorrect usage and thus reasonable.

I do think it raises the question: why do we have a separate call to Start()?

What would you ever do between calling the QuicListener constuctor and Start()? Seems like the answer is "nothing useful", and as such we should just get rid of Start.

[geoffkizer]

I suppose another option would be to make the constructor do the equivalent of calling Socket.Bind, but not Socket.Listen. This would at least give you a useful value for LocalEndPoint. Then, Start() would do the equivalent of Listen.

[karelz]

Triage: We want to merge Start into constructor -- no point in having them separate.
Affects API.

[scalablecory]

@jkotalik @Tratcher we're considering getting rid of Start()/Stop() and just having ctor/Dispose() do these things. This would avoid the 0 port issue as well. How will this impact Kestrel?

[Tratcher]

@halter73 @JamesNK

[Tratcher]

Not much, Kestrel immediately calls Start:
https://github.com/dotnet/aspnetcore/blob/ea2f5594e4f817c828904421b33bed3f921907ec/src/Servers/Kestrel/Transport.Quic/src/Internal/QuicConnectionListener.cs#L46-L47