mpc_client/protocols/
session.rs

use crate::{EventStream, NetworkTransport, Result, Transport};
use async_trait::async_trait;
use futures::StreamExt;
use mpc_protocol::{Event, SessionState};
use tokio::sync::Mutex;

/// Trait for types that handle session related events.
#[async_trait]
pub trait SessionEventHandler {
    /// Handle an event.
    async fn handle_event(
        &mut self,
        event: Event,
    ) -> Result<Option<SessionState>>;

    /// Consume this session handler into the underlying transport.
    fn into_transport(self) -> Transport;
}

/// Variants that can create or join a session.
pub enum SessionHandler {
    /// Session initiator.
    Initiator(SessionInitiator),
    /// Session participant.
    Participant(SessionParticipant),
}

#[async_trait]
impl SessionEventHandler for SessionHandler {
    async fn handle_event(
        &mut self,
        event: Event,
    ) -> Result<Option<SessionState>> {
        match self {
            Self::Initiator(s) => s.handle_event(event).await,
            Self::Participant(s) => s.handle_event(event).await,
        }
    }

    fn into_transport(self) -> Transport {
        match self {
            Self::Initiator(s) => s.into_transport(),
            Self::Participant(s) => s.into_transport(),
        }
    }
}

impl From<SessionHandler> for Transport {
    fn from(value: SessionHandler) -> Self {
        match value {
            SessionHandler::Initiator(s) => s.into(),
            SessionHandler::Participant(s) => s.into(),
        }
    }
}

/// Initiate a session.
pub struct SessionInitiator {
    transport: Transport,
    session_participants: Vec<Vec<u8>>,
    session_state: Mutex<Option<SessionState>>,
    requested_session: bool,
}

impl SessionInitiator {
    /// Create a new session handshake.
    pub fn new(
        transport: Transport,
        session_participants: Vec<Vec<u8>>,
    ) -> Self {
        Self {
            transport,
            session_participants,
            session_state: Mutex::new(None),
            requested_session: false,
        }
    }

    /// Lazily request to create new session only once.
    async fn new_session(&mut self) -> Result<()> {
        if !self.requested_session
            && self.transport.is_connected().await
        {
            self.transport
                .new_session(self.session_participants.clone())
                .await?;

            self.requested_session = true;
        }
        Ok(())
    }
}

#[async_trait]
impl SessionEventHandler for SessionInitiator {
    fn into_transport(self) -> Transport {
        self.transport
    }

    async fn handle_event(
        &mut self,
        event: Event,
    ) -> Result<Option<SessionState>> {
        self.new_session().await?;

        match event {
            Event::SessionCreated(session) => {
                tracing::info!(
                    id = ?session.session_id.to_string(),
                    "session created");

                let mut state = self.session_state.lock().await;
                *state = Some(session);
            }
            Event::SessionReady(session) => {
                tracing::info!(
                    id = ?session.session_id.to_string(),
                    "session ready");

                let connections =
                    session.connections(self.transport.public_key());

                for key in connections {
                    self.transport.connect_peer(key).await?;
                }
            }
            Event::PeerConnected { peer_key } => {
                let state = self.session_state.lock().await;
                let session = state.as_ref().unwrap();
                let connections =
                    session.connections(self.transport.public_key());
                if connections.contains(&peer_key) {
                    self.transport
                        .register_connection(
                            &session.session_id,
                            peer_key.as_slice(),
                        )
                        .await?;
                }
            }
            Event::SessionActive(session) => {
                return Ok(Some(session))
            }
            _ => {}
        }
        Ok(None)
    }
}

impl From<SessionInitiator> for Transport {
    fn from(value: SessionInitiator) -> Self {
        value.transport
    }
}

/// Participate in a session.
pub struct SessionParticipant {
    transport: Transport,
    session_state: Mutex<Option<SessionState>>,
}

impl SessionParticipant {
    /// Create a new session participant.
    pub fn new(transport: Transport) -> Self {
        Self {
            transport,
            session_state: Mutex::new(None),
        }
    }
}

#[async_trait]
impl SessionEventHandler for SessionParticipant {
    fn into_transport(self) -> Transport {
        self.transport
    }

    /// Handle joining a session for a participant.
    async fn handle_event(
        &mut self,
        event: Event,
    ) -> Result<Option<SessionState>> {
        match event {
            Event::SessionReady(session) => {
                let mut state = self.session_state.lock().await;
                *state = Some(session.clone());

                tracing::info!(
                    id = ?session.session_id.to_string(),
                    "session ready");

                for key in
                    session.connections(self.transport.public_key())
                {
                    self.transport.connect_peer(key).await?;
                }
            }
            Event::PeerConnected { peer_key } => {
                let state = self.session_state.lock().await;
                if let Some(session) = state.as_ref() {
                    let connections = session
                        .connections(self.transport.public_key());
                    if connections.contains(&peer_key) {
                        self.transport
                            .register_connection(
                                &session.session_id,
                                peer_key.as_slice(),
                            )
                            .await?;
                    }
                } else {
                    tracing::warn!(
                        "peer connected event without session"
                    );
                }
            }
            Event::SessionActive(session) => {
                return Ok(Some(session));
            }
            _ => {}
        }

        Ok(None)
    }
}

impl From<SessionParticipant> for Transport {
    fn from(value: SessionParticipant) -> Self {
        value.transport
    }
}

/// Wait for a session to become active.
pub async fn wait_for_session<S>(
    stream: &mut EventStream,
    mut client_session: S,
) -> Result<(Transport, SessionState)>
where
    S: SessionEventHandler + Into<Transport>,
{
    #[allow(unused_assignments)]
    let mut session: Option<SessionState> = None;
    while let Some(event) = stream.next().await {
        let event = event?;
        if let Some(active_session) =
            client_session.handle_event(event).await?
        {
            session = Some(active_session);
            break;
        }
    }
    Ok((client_session.into(), session.take().unwrap()))
}
mpc_client/protocols/session.rs

mpc_client/protocols/
session.rs
