Channels

Lightyear introduces the concept of a Channel to handle reliability.

A Channel is a way to send packets with specific reliability, ordering and priority guarantees.

You register a channel on the app like so (this must be shared between client and server, so it usually lives in the protocol plugin):

pub struct Channel1;

pub(crate) struct ProtocolPlugin;

impl Plugin for ProtocolPlugin {
    fn build(&self, app: &mut App) {
        app.add_channel::<Channel1>(ChannelSettings {
            mode: ChannelMode::OrderedReliable(ReliableSettings::default()),
            ..default()
        })
        .add_direction(NetworkDirection::ServerToClient);
    }
}

Any Send + Sync + 'static struct can be a channel; there is a blanket Channel impl, so no derive needed.

Mode

The mode field of ChannelSettings defines the reliability/ordering guarantees of the channel.

Reliability:

• Unreliable: packets are not guaranteed to arrive (UnorderedUnreliable, UnorderedUnreliableWithAcks, SequencedUnreliable)
• Reliable: packets are guaranteed to arrive. We will resend the packet until we receive an acknowledgement from the remote. You can tune how often we resend via the ReliableSettings field (rtt_resend_factor, rtt_resend_min_delay).

Ordering:

• Ordered: packets are guaranteed to arrive in the order they were sent (client sends 1,2,3,4,5, server receives 1,2,3,4,5)
• Unordered: packets are not guaranteed to arrive in the order they were sent (client sends 1,2,3,4,5, server receives 1,3,2,5,4)
• Sequenced: packets are not guaranteed to arrive in the order they were sent, but we will discard packets that are older than the last received packet (client sends 1,2,3,4,5, server receives 1,3,5 (2 and 4 are discarded))

Direction

The direction (NetworkDirection::ClientToServer, ServerToClient or Bidirectional) can be used to restrict a Channel (or a message) to one way of traffic.