h3x 0.6.1

Peer-to-peer DHTTP/3 transport over QUIC
Documentation
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use std::{
    collections::{HashMap, HashSet},
    sync::{
        Arc, Mutex, Weak,
        atomic::{AtomicBool, Ordering},
    },
};

use futures::{StreamExt, future::BoxFuture, stream::FuturesUnordered};
use snafu::ResultExt;
use tokio::sync::{mpsc, watch};
use tracing::Instrument;

use super::{
    WebTransportSessionId, WebTransportStreamCount,
    error::{
        CloseReason, RegisterSessionError, SessionCloseReason, SessionClosed, SessionDrain,
        SessionFlowControlError, session_flow_control_error,
    },
    session::{
        RoutedBiStream, RoutedUniStream,
        stream::{TrackedStreamReader, TrackedStreamWriter},
    },
};
use crate::{
    error::Code,
    quic::{ResetStreamExt, StopStreamExt},
    stream_id::StreamId,
    varint::VarInt,
};

const SESSION_STREAM_CHANNEL_SIZE: usize = 16;

#[derive(Debug, Default)]
struct RegistryInner {
    active: HashMap<WebTransportSessionId, Weak<SessionState>>,
    closed: HashSet<WebTransportSessionId>,
}

#[derive(Debug, Default, Clone)]
pub(super) struct Registry {
    inner: Arc<Mutex<RegistryInner>>,
}

pub(super) enum RouteBiError {
    Unknown(RoutedBiStream),
    Closed(RoutedBiStream),
    FlowControl(RoutedBiStream),
    Rejected(RoutedBiStream),
}

pub(super) enum RouteUniError {
    Unknown(RoutedUniStream),
    Closed(RoutedUniStream),
    FlowControl(RoutedUniStream),
    Rejected(RoutedUniStream),
}

impl Registry {
    pub(super) fn register(
        &self,
        session_id: WebTransportSessionId,
    ) -> Result<RegisteredSession, RegisterSessionError> {
        let default_credit = default_initial_stream_credit();
        self.register_with_credit(session_id, default_credit, default_credit)
    }

    pub(super) fn register_with_credit(
        &self,
        session_id: WebTransportSessionId,
        bidi_credit: WebTransportStreamCount,
        uni_credit: WebTransportStreamCount,
    ) -> Result<RegisteredSession, RegisterSessionError> {
        let bidi_queue_capacity = incoming_stream_queue_capacity(bidi_credit);
        let uni_queue_capacity = incoming_stream_queue_capacity(uni_credit);
        let (bidi_tx, bidi_rx) = mpsc::channel(bidi_queue_capacity);
        let (uni_tx, uni_rx) = mpsc::channel(uni_queue_capacity);

        let Ok(mut inner) = self.inner.lock() else {
            return Err(RegisterSessionError::RegistryPoisoned);
        };

        if inner.active.contains_key(&session_id) || inner.closed.contains(&session_id) {
            return Err(RegisterSessionError::AlreadyRegistered { session_id });
        }

        let state = Arc::new(SessionState::new(
            session_id,
            self.clone(),
            bidi_tx,
            uni_tx,
            bidi_credit,
            uni_credit,
            bidi_queue_capacity,
            uni_queue_capacity,
        ));

        inner.active.insert(session_id, Arc::downgrade(&state));

        Ok(RegisteredSession {
            state,
            bidi_rx,
            uni_rx,
        })
    }

    pub(super) fn unregister(&self, session_id: WebTransportSessionId) {
        self.close(session_id);
    }

    fn close(&self, session_id: WebTransportSessionId) {
        let Ok(mut inner) = self.inner.lock() else {
            tracing::debug!(?session_id, "webtransport session registry lock poisoned");
            return;
        };
        inner.active.remove(&session_id);
        inner.closed.insert(session_id);
    }

    pub(super) fn route_bi(
        &self,
        session_id: WebTransportSessionId,
        stream: RoutedBiStream,
    ) -> Result<(), RouteBiError> {
        let state = {
            let Ok(inner) = self.inner.lock() else {
                tracing::debug!(session_id = %session_id, "webtransport session registry lock poisoned");
                return Err(RouteBiError::Rejected(stream));
            };
            let Some(state) = inner
                .active
                .get(&session_id)
                .and_then(std::sync::Weak::upgrade)
            else {
                if inner.closed.contains(&session_id) {
                    tracing::debug!(session_id = %session_id, "webtransport bidi stream belongs to closed session");
                    return Err(RouteBiError::Closed(stream));
                }
                tracing::debug!(session_id = %session_id, "no registered session for webtransport bidi stream");
                return Err(RouteBiError::Unknown(stream));
            };
            state
        };

        state.route_incoming_bi(stream)
    }

    pub(super) fn route_uni(
        &self,
        session_id: WebTransportSessionId,
        stream: RoutedUniStream,
    ) -> Result<(), RouteUniError> {
        let state = {
            let Ok(inner) = self.inner.lock() else {
                tracing::debug!(session_id = %session_id, "webtransport session registry lock poisoned");
                return Err(RouteUniError::Rejected(stream));
            };
            let Some(state) = inner
                .active
                .get(&session_id)
                .and_then(std::sync::Weak::upgrade)
            else {
                if inner.closed.contains(&session_id) {
                    tracing::debug!(session_id = %session_id, "webtransport uni stream belongs to closed session");
                    return Err(RouteUniError::Closed(stream));
                }
                tracing::debug!(session_id = %session_id, "no registered session for webtransport uni stream");
                return Err(RouteUniError::Unknown(stream));
            };
            state
        };

        state.route_incoming_uni(stream)
    }
}

impl Registry {
    pub(super) fn len(&self) -> usize {
        self.inner
            .lock()
            .map(|inner| inner.active.len())
            .unwrap_or(0)
    }
}

#[derive(Debug, Clone, Copy)]
struct IncomingStreamCredit {
    advertised_max: WebTransportStreamCount,
    received: WebTransportStreamCount,
    queued: usize,
}

impl IncomingStreamCredit {
    const fn new(advertised_max: WebTransportStreamCount) -> Self {
        Self {
            advertised_max,
            received: WebTransportStreamCount::ZERO,
            queued: 0,
        }
    }

    fn reserve_incoming(&mut self, queue_capacity: usize) -> Result<(), SessionFlowControlError> {
        if self.received >= self.advertised_max {
            return Err(SessionFlowControlError::ExceededStreamCredit);
        }
        if self.queued >= queue_capacity {
            return Err(SessionFlowControlError::QueueCapacityInvariant);
        }
        self.received = self
            .received
            .checked_increment()
            .context(session_flow_control_error::StreamCountSnafu)?;
        self.queued += 1;
        Ok(())
    }

    fn accept_one(&mut self) -> Result<WebTransportStreamCount, SessionFlowControlError> {
        self.queued = self.queued.saturating_sub(1);
        self.advertised_max = self
            .advertised_max
            .checked_increment()
            .context(session_flow_control_error::StreamCountSnafu)?;
        Ok(self.advertised_max)
    }
}

#[derive(Debug)]
struct LocalOpenCredit {
    peer_max: WebTransportStreamCount,
    opened: WebTransportStreamCount,
    last_blocked_sent: Option<WebTransportStreamCount>,
    changed: watch::Sender<WebTransportStreamCount>,
}

impl LocalOpenCredit {
    fn new(peer_max: WebTransportStreamCount) -> Self {
        let (changed, _rx) = watch::channel(peer_max);
        Self {
            peer_max,
            opened: WebTransportStreamCount::ZERO,
            last_blocked_sent: None,
            changed,
        }
    }

    fn try_reserve(&mut self) -> Result<(), WebTransportStreamCount> {
        if self.opened >= self.peer_max {
            return Err(self.peer_max);
        }
        self.opened = self
            .opened
            .checked_increment()
            .expect("opened stream count cannot overflow below peer maximum");
        Ok(())
    }

    fn block(&mut self) -> LocalStreamCreditBlock {
        let maximum = self.peer_max;
        let send_blocked = self.last_blocked_sent != Some(maximum);
        if send_blocked {
            self.last_blocked_sent = Some(maximum);
        }
        LocalStreamCreditBlock {
            maximum,
            send_blocked,
            changed: self.changed.subscribe(),
        }
    }

    fn update_peer_max(
        &mut self,
        peer_max: WebTransportStreamCount,
    ) -> Result<(), SessionFlowControlError> {
        if peer_max < self.peer_max {
            return Err(SessionFlowControlError::DecreasingMaxStreams);
        }
        if peer_max > self.peer_max {
            self.peer_max = peer_max;
            self.last_blocked_sent = None;
            let _ = self.changed.send(peer_max);
        }
        Ok(())
    }
}

pub(super) struct LocalStreamCreditBlock {
    pub(super) maximum: WebTransportStreamCount,
    pub(super) send_blocked: bool,
    pub(super) changed: watch::Receiver<WebTransportStreamCount>,
}

pub(super) enum LocalStreamCreditReservation {
    Reserved,
    Blocked(LocalStreamCreditBlock),
}

#[derive(Debug)]
pub(super) struct RegisteredSession {
    pub(super) state: Arc<SessionState>,
    pub(super) bidi_rx: mpsc::Receiver<RoutedBiStream>,
    pub(super) uni_rx: mpsc::Receiver<RoutedUniStream>,
}

#[derive(Debug)]
pub(super) struct SessionState {
    session_id: WebTransportSessionId,
    registry: Registry,
    closed: AtomicBool,
    close_reason: watch::Sender<Option<CloseReason>>,
    drain_status: watch::Sender<Option<SessionDrain>>,
    bidi_tx: mpsc::Sender<RoutedBiStream>,
    uni_tx: mpsc::Sender<RoutedUniStream>,
    bidi_credit: Mutex<IncomingStreamCredit>,
    uni_credit: Mutex<IncomingStreamCredit>,
    local_bidi_credit: Mutex<LocalOpenCredit>,
    local_uni_credit: Mutex<LocalOpenCredit>,
    bidi_queue_capacity: usize,
    uni_queue_capacity: usize,
    tracked_readers: Mutex<HashMap<StreamId, TrackedStreamReader>>,
    tracked_writers: Mutex<HashMap<StreamId, TrackedStreamWriter>>,
}

impl SessionState {
    #[allow(clippy::too_many_arguments)]
    fn new(
        session_id: WebTransportSessionId,
        registry: Registry,
        bidi_tx: mpsc::Sender<RoutedBiStream>,
        uni_tx: mpsc::Sender<RoutedUniStream>,
        bidi_credit: WebTransportStreamCount,
        uni_credit: WebTransportStreamCount,
        bidi_queue_capacity: usize,
        uni_queue_capacity: usize,
    ) -> Self {
        let (close_reason, _close_rx) = watch::channel(None);
        let (drain_status, _drain_rx) = watch::channel(None);
        let default_local_credit = default_initial_stream_credit();
        Self {
            session_id,
            registry,
            closed: AtomicBool::new(false),
            close_reason,
            drain_status,
            bidi_tx,
            uni_tx,
            bidi_credit: Mutex::new(IncomingStreamCredit::new(bidi_credit)),
            uni_credit: Mutex::new(IncomingStreamCredit::new(uni_credit)),
            local_bidi_credit: Mutex::new(LocalOpenCredit::new(default_local_credit)),
            local_uni_credit: Mutex::new(LocalOpenCredit::new(default_local_credit)),
            bidi_queue_capacity,
            uni_queue_capacity,
            tracked_readers: Mutex::new(HashMap::new()),
            tracked_writers: Mutex::new(HashMap::new()),
        }
    }

    pub(super) fn id(&self) -> WebTransportSessionId {
        self.session_id
    }

    pub(super) fn check_open(&self) -> Result<(), SessionClosed> {
        if self.closed.load(Ordering::Acquire) {
            Err(SessionClosed)
        } else {
            Ok(())
        }
    }

    pub(super) fn set_local_stream_credit(
        &self,
        peer_bidi_credit: WebTransportStreamCount,
        peer_uni_credit: WebTransportStreamCount,
    ) {
        if let Ok(mut credit) = self.local_bidi_credit.lock() {
            *credit = LocalOpenCredit::new(peer_bidi_credit);
        } else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session local bidi credit lock poisoned"
            );
            self.close();
        }
        if let Ok(mut credit) = self.local_uni_credit.lock() {
            *credit = LocalOpenCredit::new(peer_uni_credit);
        } else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session local uni credit lock poisoned"
            );
            self.close();
        }
    }

    pub(super) fn close(&self) {
        self.close_with_reason(CloseReason::Session(SessionCloseReason::ControlStreamError));
    }

    pub(super) fn close_with_reason(&self, reason: CloseReason) {
        if !self.closed.swap(true, Ordering::AcqRel) {
            let _ = self.close_reason.send(Some(reason.clone()));
            let _ = self.drain_status.send(Some(SessionDrain::Closed(reason)));
            self.registry.unregister(self.session_id);
            let (readers, writers) = self.take_tracked_streams();
            spawn_tracked_stream_cleanup(self.session_id, readers, writers);
        }
    }

    pub(super) fn drain_with_reason(&self, drain: SessionDrain) {
        if self.drain_status.borrow().is_none() {
            let _ = self.drain_status.send(Some(drain));
        }
    }

    pub(super) async fn closed(&self) -> CloseReason {
        let mut reason = self.close_reason.subscribe();
        loop {
            if let Some(reason) = reason.borrow().clone() {
                return reason;
            }
            if reason.changed().await.is_err() {
                return CloseReason::Session(SessionCloseReason::ControlStreamError);
            }
        }
    }

    pub(super) async fn drained(&self) -> SessionDrain {
        let mut drain = self.drain_status.subscribe();
        loop {
            if let Some(drain) = drain.borrow().clone() {
                return drain;
            }
            if drain.changed().await.is_err() {
                return SessionDrain::Closed(CloseReason::Session(
                    SessionCloseReason::ControlStreamError,
                ));
            }
        }
    }

    pub(super) fn insert_tracked_bi(
        &self,
        stream_id: StreamId,
        reader: TrackedStreamReader,
        writer: TrackedStreamWriter,
    ) -> Result<(), SessionClosed> {
        self.check_open()?;

        let Ok(mut readers) = self.tracked_readers.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session reader tracking lock poisoned"
            );
            return Err(SessionClosed);
        };
        let Ok(mut writers) = self.tracked_writers.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session writer tracking lock poisoned"
            );
            return Err(SessionClosed);
        };

        if self.closed.load(Ordering::Acquire) {
            return Err(SessionClosed);
        }

        readers.insert(stream_id, reader);
        writers.insert(stream_id, writer);

        if self.closed.load(Ordering::Acquire) {
            readers.remove(&stream_id);
            writers.remove(&stream_id);
            Err(SessionClosed)
        } else {
            Ok(())
        }
    }

    pub(super) fn insert_tracked_reader(
        &self,
        stream_id: StreamId,
        reader: TrackedStreamReader,
    ) -> Result<(), SessionClosed> {
        self.check_open()?;

        let Ok(mut readers) = self.tracked_readers.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session reader tracking lock poisoned"
            );
            return Err(SessionClosed);
        };

        if self.closed.load(Ordering::Acquire) {
            return Err(SessionClosed);
        }

        readers.insert(stream_id, reader);

        if self.closed.load(Ordering::Acquire) {
            readers.remove(&stream_id);
            Err(SessionClosed)
        } else {
            Ok(())
        }
    }

    pub(super) fn insert_tracked_writer(
        &self,
        stream_id: StreamId,
        writer: TrackedStreamWriter,
    ) -> Result<(), SessionClosed> {
        self.check_open()?;

        let Ok(mut writers) = self.tracked_writers.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session writer tracking lock poisoned"
            );
            return Err(SessionClosed);
        };

        if self.closed.load(Ordering::Acquire) {
            return Err(SessionClosed);
        }

        writers.insert(stream_id, writer);

        if self.closed.load(Ordering::Acquire) {
            writers.remove(&stream_id);
            Err(SessionClosed)
        } else {
            Ok(())
        }
    }

    pub(super) fn route_incoming_bi(&self, stream: RoutedBiStream) -> Result<(), RouteBiError> {
        if self.check_open().is_err() {
            return Err(RouteBiError::Closed(stream));
        }

        let Ok(mut credit) = self.bidi_credit.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session bidi credit lock poisoned"
            );
            self.close();
            return Err(RouteBiError::Rejected(stream));
        };
        if let Err(error) = credit.reserve_incoming(self.bidi_queue_capacity) {
            let report = snafu::Report::from_error(&error);
            tracing::debug!(
                session_id = %self.session_id,
                error = %report,
                "webtransport session bidi stream credit exhausted"
            );
            drop(credit);
            self.close();
            return Err(RouteBiError::FlowControl(stream));
        }
        drop(credit);

        match self.bidi_tx.try_send(stream) {
            Ok(()) => Ok(()),
            Err(error) => {
                tracing::debug!(
                    session_id = %self.session_id,
                    "session bidi channel full or closed, rejecting stream"
                );
                self.close();
                Err(RouteBiError::Rejected(error.into_inner()))
            }
        }
    }

    pub(super) fn route_incoming_uni(&self, stream: RoutedUniStream) -> Result<(), RouteUniError> {
        if self.check_open().is_err() {
            return Err(RouteUniError::Closed(stream));
        }

        let Ok(mut credit) = self.uni_credit.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session uni credit lock poisoned"
            );
            self.close();
            return Err(RouteUniError::Rejected(stream));
        };
        if let Err(error) = credit.reserve_incoming(self.uni_queue_capacity) {
            let report = snafu::Report::from_error(&error);
            tracing::debug!(
                session_id = %self.session_id,
                error = %report,
                "webtransport session uni stream credit exhausted"
            );
            drop(credit);
            self.close();
            return Err(RouteUniError::FlowControl(stream));
        }
        drop(credit);

        match self.uni_tx.try_send(stream) {
            Ok(()) => Ok(()),
            Err(error) => {
                tracing::debug!(
                    session_id = %self.session_id,
                    "session uni channel full or closed, rejecting stream"
                );
                self.close();
                Err(RouteUniError::Rejected(error.into_inner()))
            }
        }
    }

    pub(super) fn accept_incoming_bi(
        &self,
    ) -> Result<WebTransportStreamCount, SessionFlowControlError> {
        let Ok(mut credit) = self.bidi_credit.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session bidi credit lock poisoned"
            );
            return Err(SessionFlowControlError::QueueCapacityInvariant);
        };
        credit.accept_one()
    }

    pub(super) fn accept_incoming_uni(
        &self,
    ) -> Result<WebTransportStreamCount, SessionFlowControlError> {
        let Ok(mut credit) = self.uni_credit.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session uni credit lock poisoned"
            );
            return Err(SessionFlowControlError::QueueCapacityInvariant);
        };
        credit.accept_one()
    }

    pub(super) fn reserve_local_bidi(&self) -> Result<LocalStreamCreditReservation, SessionClosed> {
        self.reserve_local_credit(&self.local_bidi_credit, "bidi")
    }

    pub(super) fn reserve_local_uni(&self) -> Result<LocalStreamCreditReservation, SessionClosed> {
        self.reserve_local_credit(&self.local_uni_credit, "uni")
    }

    fn reserve_local_credit(
        &self,
        credit: &Mutex<LocalOpenCredit>,
        direction: &'static str,
    ) -> Result<LocalStreamCreditReservation, SessionClosed> {
        self.check_open()?;
        let Ok(mut credit) = credit.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                direction,
                "webtransport session local stream credit lock poisoned"
            );
            self.close();
            return Err(SessionClosed);
        };
        match credit.try_reserve() {
            Ok(()) => Ok(LocalStreamCreditReservation::Reserved),
            Err(_) => Ok(LocalStreamCreditReservation::Blocked(credit.block())),
        }
    }

    pub(super) fn update_peer_bidi_max(
        &self,
        peer_max: WebTransportStreamCount,
    ) -> Result<(), SessionFlowControlError> {
        self.update_peer_max(&self.local_bidi_credit, peer_max, "bidi")
    }

    pub(super) fn update_peer_uni_max(
        &self,
        peer_max: WebTransportStreamCount,
    ) -> Result<(), SessionFlowControlError> {
        self.update_peer_max(&self.local_uni_credit, peer_max, "uni")
    }

    fn update_peer_max(
        &self,
        credit: &Mutex<LocalOpenCredit>,
        peer_max: WebTransportStreamCount,
        direction: &'static str,
    ) -> Result<(), SessionFlowControlError> {
        let Ok(mut credit) = credit.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                direction,
                "webtransport session local stream credit lock poisoned"
            );
            self.close();
            return Err(SessionFlowControlError::QueueCapacityInvariant);
        };
        credit.update_peer_max(peer_max)
    }

    pub(super) fn remove_tracked_reader(&self, stream_id: StreamId) {
        let Ok(mut readers) = self.tracked_readers.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session reader tracking lock poisoned"
            );
            return;
        };
        readers.remove(&stream_id);
    }

    pub(super) fn remove_tracked_writer(&self, stream_id: StreamId) {
        let Ok(mut writers) = self.tracked_writers.lock() else {
            tracing::debug!(
                session_id = %self.session_id,
                "webtransport session writer tracking lock poisoned"
            );
            return;
        };
        writers.remove(&stream_id);
    }

    fn take_tracked_streams(&self) -> (Vec<TrackedStreamReader>, Vec<TrackedStreamWriter>) {
        let readers = match self.tracked_readers.lock() {
            Ok(mut readers) => readers.drain().map(|(_stream_id, reader)| reader).collect(),
            Err(_) => {
                tracing::debug!(
                    session_id = %self.session_id,
                    "webtransport session reader tracking lock poisoned"
                );
                Vec::new()
            }
        };
        let writers = match self.tracked_writers.lock() {
            Ok(mut writers) => writers.drain().map(|(_stream_id, writer)| writer).collect(),
            Err(_) => {
                tracing::debug!(
                    session_id = %self.session_id,
                    "webtransport session writer tracking lock poisoned"
                );
                Vec::new()
            }
        };
        (readers, writers)
    }
}

fn spawn_tracked_stream_cleanup(
    session_id: WebTransportSessionId,
    readers: Vec<TrackedStreamReader>,
    writers: Vec<TrackedStreamWriter>,
) {
    if readers.is_empty() && writers.is_empty() {
        return;
    }

    let cleanup = cleanup_tracked_streams(session_id, readers, writers);
    match tokio::runtime::Handle::try_current() {
        Ok(handle) => {
            // Inherent termination: the task owns the taken tracked halves and
            // exits after every STOP/RESET future resolves or returns an error.
            let _cleanup_task = handle.spawn(cleanup.in_current_span());
        }
        Err(error) => {
            let report = snafu::Report::from_error(&error);
            tracing::debug!(
                session_id = %session_id,
                error = %report,
                "failed to spawn webtransport session stream cleanup"
            );
        }
    }
}

async fn cleanup_tracked_streams(
    session_id: WebTransportSessionId,
    readers: Vec<TrackedStreamReader>,
    writers: Vec<TrackedStreamWriter>,
) {
    let mut cleanup = FuturesUnordered::<BoxFuture<'static, ()>>::new();

    for mut reader in readers {
        cleanup.push(Box::pin(async move {
            if let Err(error) = reader.stop(Code::WT_SESSION_GONE.into_inner()).await {
                let report = snafu::Report::from_error(&error);
                tracing::debug!(
                    session_id = %session_id,
                    error = %report,
                    "failed to stop webtransport session stream reader"
                );
            }
        }));
    }

    for mut writer in writers {
        cleanup.push(Box::pin(async move {
            if let Err(error) = writer.reset(Code::WT_SESSION_GONE.into_inner()).await {
                let report = snafu::Report::from_error(&error);
                tracing::debug!(
                    session_id = %session_id,
                    error = %report,
                    "failed to reset webtransport session stream writer"
                );
            }
        }));
    }

    while cleanup.next().await.is_some() {}
}

impl Drop for SessionState {
    fn drop(&mut self) {
        self.close();
    }
}

fn default_initial_stream_credit() -> WebTransportStreamCount {
    WebTransportStreamCount::try_from(VarInt::from_u32(SESSION_STREAM_CHANNEL_SIZE as u32))
        .expect("default webtransport stream credit is valid")
}

fn incoming_stream_queue_capacity(credit: WebTransportStreamCount) -> usize {
    usize::try_from(credit.into_varint().into_inner())
        .unwrap_or(SESSION_STREAM_CHANNEL_SIZE)
        .clamp(1, SESSION_STREAM_CHANNEL_SIZE)
}

#[cfg(test)]
mod tests {
    use std::{
        collections::VecDeque,
        panic::{AssertUnwindSafe, catch_unwind},
        pin::Pin,
        sync::{Arc, Mutex},
        task::{Context, Poll},
    };

    use bytes::Bytes;
    use futures::{Sink, SinkExt, Stream, StreamExt};

    use super::*;
    use crate::{
        quic::{
            self, BoxQuicStreamReader, BoxQuicStreamWriter, GetStreamIdExt, ResetStreamExt,
            StopStreamExt,
        },
        varint::VarInt,
        webtransport::WebTransportStreamCount,
    };

    #[derive(Debug, Default)]
    struct StreamState {
        written: Mutex<Vec<u8>>,
    }

    #[derive(Debug)]
    struct TestReadStream {
        chunks: VecDeque<Bytes>,
        stream_id: VarInt,
    }

    impl Stream for TestReadStream {
        type Item = Result<Bytes, quic::StreamError>;

        fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
            Poll::Ready(self.chunks.pop_front().map(Ok))
        }
    }

    impl quic::GetStreamId for TestReadStream {
        fn poll_stream_id(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
        ) -> Poll<Result<VarInt, quic::StreamError>> {
            Poll::Ready(Ok(self.stream_id))
        }
    }

    impl quic::StopStream for TestReadStream {
        fn poll_stop(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
            _code: VarInt,
        ) -> Poll<Result<(), quic::StreamError>> {
            Poll::Ready(Ok(()))
        }
    }

    #[derive(Debug)]
    struct TestWriteStream {
        state: Arc<StreamState>,
        stream_id: VarInt,
    }

    impl Sink<Bytes> for TestWriteStream {
        type Error = quic::StreamError;

        fn poll_ready(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
        ) -> Poll<Result<(), Self::Error>> {
            Poll::Ready(Ok(()))
        }

        fn start_send(self: Pin<&mut Self>, item: Bytes) -> Result<(), Self::Error> {
            self.state
                .written
                .lock()
                .expect("written lock poisoned")
                .extend_from_slice(&item);
            Ok(())
        }

        fn poll_flush(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
        ) -> Poll<Result<(), Self::Error>> {
            Poll::Ready(Ok(()))
        }

        fn poll_close(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
        ) -> Poll<Result<(), Self::Error>> {
            Poll::Ready(Ok(()))
        }
    }

    impl quic::GetStreamId for TestWriteStream {
        fn poll_stream_id(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
        ) -> Poll<Result<VarInt, quic::StreamError>> {
            Poll::Ready(Ok(self.stream_id))
        }
    }

    impl quic::ResetStream for TestWriteStream {
        fn poll_reset(
            self: Pin<&mut Self>,
            _cx: &mut Context<'_>,
            _code: VarInt,
        ) -> Poll<Result<(), quic::StreamError>> {
            Poll::Ready(Ok(()))
        }
    }

    fn test_read_stream(id: u32, bytes: Vec<u8>) -> BoxQuicStreamReader {
        Box::pin(TestReadStream {
            chunks: VecDeque::from([Bytes::from(bytes)]),
            stream_id: VarInt::from_u32(id),
        }) as BoxQuicStreamReader
    }

    fn test_write_stream(id: u32, state: Arc<StreamState>) -> BoxQuicStreamWriter {
        Box::pin(TestWriteStream {
            state,
            stream_id: VarInt::from_u32(id),
        }) as BoxQuicStreamWriter
    }

    fn bidi_stream(id: u32) -> RoutedBiStream {
        let state = Arc::new(StreamState::default());
        (
            test_read_stream(id, vec![id as u8]),
            test_write_stream(id, Arc::clone(&state)),
        )
    }

    fn uni_stream(id: u32) -> RoutedUniStream {
        test_read_stream(id, vec![id as u8])
    }

    fn wt_session_id(id: u32) -> WebTransportSessionId {
        WebTransportSessionId::try_from(StreamId::from(VarInt::from_u32(id)))
            .expect("test id must be a valid webtransport session id")
    }

    fn poison_registry(registry: &Registry) {
        let registry = registry.clone();
        let _ = catch_unwind(AssertUnwindSafe(move || {
            let _guard = registry.inner.lock().expect("registry lock should succeed");
            panic!("poison registry mutex");
        }));
    }

    fn route_bi_error_stream(error: RouteBiError) -> RoutedBiStream {
        match error {
            RouteBiError::Unknown(stream)
            | RouteBiError::Closed(stream)
            | RouteBiError::FlowControl(stream)
            | RouteBiError::Rejected(stream) => stream,
        }
    }

    fn route_uni_error_stream(error: RouteUniError) -> RoutedUniStream {
        match error {
            RouteUniError::Unknown(stream)
            | RouteUniError::Closed(stream)
            | RouteUniError::FlowControl(stream)
            | RouteUniError::Rejected(stream) => stream,
        }
    }

    #[tokio::test]
    async fn test_read_stream_reads_chunks_and_stops() {
        let mut stream = test_read_stream(40, b"chunk".to_vec());

        assert_eq!(
            stream
                .next()
                .await
                .expect("read stream should yield one chunk")
                .expect("read chunk should succeed"),
            Bytes::from_static(b"chunk")
        );
        assert!(
            stream.next().await.is_none(),
            "read stream should be exhausted"
        );
        stream
            .stop(VarInt::from_u32(41))
            .await
            .expect("read stream stop should succeed");
    }

    #[tokio::test]
    async fn test_write_stream_writes_flushes_closes_and_resets() {
        let state = Arc::new(StreamState::default());
        let mut stream = test_write_stream(42, Arc::clone(&state));

        assert_eq!(
            stream
                .stream_id()
                .await
                .expect("write stream id should be readable"),
            VarInt::from_u32(42)
        );
        stream
            .send(Bytes::from_static(b"payload"))
            .await
            .expect("write stream send should succeed");
        stream
            .close()
            .await
            .expect("write stream close should succeed");
        stream
            .reset(VarInt::from_u32(43))
            .await
            .expect("write stream reset should succeed");

        assert_eq!(
            *state
                .written
                .lock()
                .expect("written lock should not poison"),
            b"payload".to_vec()
        );
    }

    #[test]
    fn register_len_duplicate_and_close_unregister() {
        let registry = Registry::default();
        let session_id = wt_session_id(4);

        let registered = registry
            .register(session_id)
            .expect("first registration should succeed");
        assert_eq!(registry.len(), 1);
        assert_eq!(registered.state.id(), session_id);
        assert!(registered.state.check_open().is_ok());

        let error = registry
            .register(session_id)
            .expect_err("duplicate session should be rejected");
        assert!(matches!(
            error,
            RegisterSessionError::AlreadyRegistered { session_id: duplicate } if duplicate == session_id
        ));

        registered.state.close();
        assert_eq!(registry.len(), 0);
        assert!(registered.state.check_open().is_err());

        registered.state.close();
        assert_eq!(registry.len(), 0);
    }

    #[test]
    fn dropping_registered_session_unregisters_it() {
        let registry = Registry::default();
        let session_id = wt_session_id(8);

        let registered = registry
            .register(session_id)
            .expect("registration should succeed");
        assert_eq!(registry.len(), 1);

        drop(registered);
        assert_eq!(registry.len(), 0);
    }

    #[tokio::test]
    async fn route_unknown_sessions_return_original_streams() {
        let registry = Registry::default();
        let session_id = wt_session_id(4);

        let bidi = bidi_stream(1);
        let error = registry
            .route_bi(session_id, bidi)
            .expect_err("unknown bidi session should reject stream");
        assert!(matches!(&error, RouteBiError::Unknown(_)));
        let mut returned_bidi = route_bi_error_stream(error);
        assert_eq!(
            returned_bidi
                .0
                .stream_id()
                .await
                .expect("returned bidi stream id should be readable"),
            VarInt::from_u32(1)
        );

        let uni = uni_stream(2);
        let error = registry
            .route_uni(session_id, uni)
            .expect_err("unknown uni session should reject stream");
        assert!(matches!(&error, RouteUniError::Unknown(_)));
        let mut returned_uni = route_uni_error_stream(error);
        assert_eq!(
            returned_uni
                .stream_id()
                .await
                .expect("returned uni stream id should be readable"),
            VarInt::from_u32(2)
        );
    }

    #[tokio::test]
    async fn route_known_sessions_deliver_streams_to_receivers() {
        let registry = Registry::default();
        let session_id = wt_session_id(4);
        let mut registered = registry
            .register(session_id)
            .expect("registration should succeed");

        assert!(registry.route_bi(session_id, bidi_stream(3)).is_ok());
        assert!(registry.route_uni(session_id, uni_stream(4)).is_ok());

        let (mut bidi_reader, _bidi_writer) = registered
            .bidi_rx
            .recv()
            .await
            .expect("bidi receiver should get a stream");
        let mut uni_reader = registered
            .uni_rx
            .recv()
            .await
            .expect("uni receiver should get a stream");

        assert_eq!(
            bidi_reader
                .stream_id()
                .await
                .expect("bidi stream id should be readable"),
            VarInt::from_u32(3)
        );
        assert_eq!(
            uni_reader
                .stream_id()
                .await
                .expect("uni stream id should be readable"),
            VarInt::from_u32(4)
        );
    }

    #[tokio::test]
    async fn route_incoming_bidi_closes_session_when_peer_exceeds_advertised_credit() {
        let registry = Registry::default();
        let session_id = wt_session_id(4);
        let mut registered = registry
            .register_with_credit(
                session_id,
                WebTransportStreamCount::try_from(VarInt::from_u32(1)).expect("bidi credit"),
                WebTransportStreamCount::try_from(VarInt::from_u32(0)).expect("uni credit"),
            )
            .expect("registration should succeed");

        assert!(
            registry.route_bi(session_id, bidi_stream(8)).is_ok(),
            "first stream should be allowed"
        );
        let error = registry
            .route_bi(session_id, bidi_stream(12))
            .expect_err("second stream exceeds credit");

        assert!(matches!(error, RouteBiError::FlowControl(_)));
        assert!(registered.state.check_open().is_err());
        let (_reader, _writer) = registered
            .bidi_rx
            .recv()
            .await
            .expect("first stream remains queued");
    }

    #[tokio::test]
    async fn route_incoming_uni_closes_session_when_peer_exceeds_advertised_credit() {
        let registry = Registry::default();
        let session_id = wt_session_id(4);
        let mut registered = registry
            .register_with_credit(
                session_id,
                WebTransportStreamCount::try_from(VarInt::from_u32(0)).expect("bidi credit"),
                WebTransportStreamCount::try_from(VarInt::from_u32(1)).expect("uni credit"),
            )
            .expect("registration should succeed");

        assert!(
            registry.route_uni(session_id, uni_stream(10)).is_ok(),
            "first stream should be allowed"
        );
        let error = registry
            .route_uni(session_id, uni_stream(14))
            .expect_err("second stream exceeds credit");

        assert!(matches!(error, RouteUniError::FlowControl(_)));
        assert!(registered.state.check_open().is_err());
        let _reader = registered
            .uni_rx
            .recv()
            .await
            .expect("first stream remains queued");
    }

    #[test]
    fn route_rejects_closed_or_full_channels() {
        let registry = Registry::default();
        let bidi_session_id = wt_session_id(4);
        let bidi_registered = registry
            .register(bidi_session_id)
            .expect("registration should succeed");

        drop(bidi_registered.bidi_rx);
        assert!(matches!(
            registry.route_bi(bidi_session_id, bidi_stream(5)),
            Err(RouteBiError::Rejected(_))
        ));

        let uni_session_id = wt_session_id(8);
        let uni_registered = registry
            .register(uni_session_id)
            .expect("registration should succeed");

        drop(uni_registered.uni_rx);
        assert!(matches!(
            registry.route_uni(uni_session_id, uni_stream(6)),
            Err(RouteUniError::Rejected(_))
        ));
    }

    #[tokio::test]
    async fn route_closed_channels_return_original_streams() {
        let registry = Registry::default();
        let bidi_session_id = wt_session_id(16);
        let bidi_registered = registry
            .register(bidi_session_id)
            .expect("registration should succeed");

        drop(bidi_registered.bidi_rx);

        let error = registry
            .route_bi(bidi_session_id, bidi_stream(17))
            .expect_err("closed bidi receiver should reject stream");
        assert!(matches!(&error, RouteBiError::Rejected(_)));
        let mut returned_bidi = route_bi_error_stream(error);
        assert_eq!(
            returned_bidi
                .0
                .stream_id()
                .await
                .expect("returned bidi stream id should be readable"),
            VarInt::from_u32(17)
        );

        let uni_session_id = wt_session_id(20);
        let uni_registered = registry
            .register(uni_session_id)
            .expect("registration should succeed");

        drop(uni_registered.uni_rx);

        let error = registry
            .route_uni(uni_session_id, uni_stream(18))
            .expect_err("closed uni receiver should reject stream");
        assert!(matches!(&error, RouteUniError::Rejected(_)));
        let mut returned_uni = route_uni_error_stream(error);
        assert_eq!(
            returned_uni
                .stream_id()
                .await
                .expect("returned uni stream id should be readable"),
            VarInt::from_u32(18)
        );
    }

    #[test]
    fn route_flow_control_when_initial_credit_is_exhausted() {
        let registry = Registry::default();
        let bidi_session_id = wt_session_id(24);
        let _bidi_registered = registry
            .register(bidi_session_id)
            .expect("registration should succeed");

        for id in 0..SESSION_STREAM_CHANNEL_SIZE {
            assert!(
                registry
                    .route_bi(bidi_session_id, bidi_stream(id as u32))
                    .is_ok()
            );
        }

        assert!(matches!(
            registry.route_bi(bidi_session_id, bidi_stream(99)),
            Err(RouteBiError::FlowControl(_))
        ));

        let uni_session_id = wt_session_id(28);
        let _uni_registered = registry
            .register(uni_session_id)
            .expect("registration should succeed");

        for id in 0..SESSION_STREAM_CHANNEL_SIZE {
            assert!(
                registry
                    .route_uni(uni_session_id, uni_stream(id as u32))
                    .is_ok()
            );
        }

        assert!(matches!(
            registry.route_uni(uni_session_id, uni_stream(100)),
            Err(RouteUniError::FlowControl(_))
        ));
    }

    #[tokio::test]
    async fn route_uses_exact_registered_session_id() {
        let registry = Registry::default();
        let first_session_id = wt_session_id(32);
        let second_session_id = wt_session_id(36);
        let mut first = registry
            .register(first_session_id)
            .expect("first registration should succeed");
        let mut second = registry
            .register(second_session_id)
            .expect("second registration should succeed");

        assert!(
            registry
                .route_bi(second_session_id, bidi_stream(37))
                .is_ok()
        );
        assert!(
            registry
                .route_uni(second_session_id, uni_stream(38))
                .is_ok()
        );

        assert!(matches!(
            first.bidi_rx.try_recv(),
            Err(mpsc::error::TryRecvError::Empty)
        ));
        assert!(matches!(
            first.uni_rx.try_recv(),
            Err(mpsc::error::TryRecvError::Empty)
        ));

        let (mut second_bidi_reader, _second_bidi_writer) = second
            .bidi_rx
            .recv()
            .await
            .expect("second session should receive routed bidi stream");
        assert_eq!(
            second_bidi_reader
                .stream_id()
                .await
                .expect("second bidi stream id should be readable"),
            VarInt::from_u32(37)
        );

        let mut second_uni_reader = second
            .uni_rx
            .recv()
            .await
            .expect("second session should receive routed uni stream");
        assert_eq!(
            second_uni_reader
                .stream_id()
                .await
                .expect("second uni stream id should be readable"),
            VarInt::from_u32(38)
        );
    }

    #[tokio::test]
    async fn route_full_channels_return_original_streams() {
        let registry = Registry::default();
        let bidi_session_id = wt_session_id(40);
        let _bidi_registered = registry
            .register(bidi_session_id)
            .expect("registration should succeed");

        for id in 0..SESSION_STREAM_CHANNEL_SIZE {
            assert!(
                registry
                    .route_bi(bidi_session_id, bidi_stream(id as u32))
                    .is_ok()
            );
        }

        let error = registry
            .route_bi(bidi_session_id, bidi_stream(21))
            .expect_err("exhausted bidi credit should reject stream");
        assert!(matches!(&error, RouteBiError::FlowControl(_)));
        let mut returned_bidi = route_bi_error_stream(error);
        assert_eq!(
            returned_bidi
                .0
                .stream_id()
                .await
                .expect("returned bidi stream id should be readable"),
            VarInt::from_u32(21)
        );

        let uni_session_id = wt_session_id(44);
        let _uni_registered = registry
            .register(uni_session_id)
            .expect("registration should succeed");

        for id in 0..SESSION_STREAM_CHANNEL_SIZE {
            assert!(
                registry
                    .route_uni(uni_session_id, uni_stream(id as u32))
                    .is_ok()
            );
        }

        let error = registry
            .route_uni(uni_session_id, uni_stream(22))
            .expect_err("exhausted uni credit should reject stream");
        assert!(matches!(&error, RouteUniError::FlowControl(_)));
        let mut returned_uni = route_uni_error_stream(error);
        assert_eq!(
            returned_uni
                .stream_id()
                .await
                .expect("returned uni stream id should be readable"),
            VarInt::from_u32(22)
        );
    }

    #[tokio::test]
    async fn closed_session_tombstone_is_preserved_for_connection_lifetime() {
        let registry = Registry::default();
        let session_id = wt_session_id(24);
        let registered = registry
            .register(session_id)
            .expect("initial registration should succeed");

        registered.state.close();
        assert_eq!(registry.len(), 0);

        let error = registry
            .route_uni(session_id, uni_stream(25))
            .expect_err("closed session should no longer route streams");
        assert!(matches!(&error, RouteUniError::Closed(_)));
        let mut returned = route_uni_error_stream(error);
        assert_eq!(
            returned
                .stream_id()
                .await
                .expect("returned uni stream id should be readable"),
            VarInt::from_u32(25)
        );

        let error = registry
            .register(session_id)
            .expect_err("closed session id must not be re-registered");
        assert!(matches!(
            error,
            RegisterSessionError::AlreadyRegistered {
                session_id: duplicate
            } if duplicate == session_id
        ));
    }

    #[test]
    fn cloned_session_state_keeps_registration_until_last_state_drop() {
        let registry = Registry::default();
        let session_id = wt_session_id(28);
        let registered = registry
            .register(session_id)
            .expect("registration should succeed");
        let state = Arc::clone(&registered.state);

        drop(registered);
        assert_eq!(registry.len(), 1);
        assert!(matches!(
            registry.route_uni(session_id, uni_stream(29)),
            Err(RouteUniError::Rejected(_))
        ));
        assert!(state.check_open().is_err());
        assert_eq!(registry.len(), 0);

        drop(state);
        assert_eq!(registry.len(), 0);
    }

    #[tokio::test]
    async fn poisoned_registry_surfaces_errors_and_preserves_streams() {
        let registry = Registry::default();
        let session_id = wt_session_id(12);
        poison_registry(&registry);

        let error = registry
            .register(session_id)
            .expect_err("poisoned registry should reject new registrations");
        assert!(matches!(error, RegisterSessionError::RegistryPoisoned));
        assert_eq!(registry.len(), 0);

        registry.unregister(session_id);

        let error = registry
            .route_bi(session_id, bidi_stream(13))
            .expect_err("poisoned registry should return routed bidi stream");
        assert!(matches!(&error, RouteBiError::Rejected(_)));
        let mut returned_bidi = route_bi_error_stream(error);
        assert_eq!(
            returned_bidi
                .0
                .stream_id()
                .await
                .expect("returned bidi stream id should be readable"),
            VarInt::from_u32(13)
        );

        let error = registry
            .route_uni(session_id, uni_stream(14))
            .expect_err("poisoned registry should return routed uni stream");
        assert!(matches!(&error, RouteUniError::Rejected(_)));
        let mut returned_uni = route_uni_error_stream(error);
        assert_eq!(
            returned_uni
                .stream_id()
                .await
                .expect("returned uni stream id should be readable"),
            VarInt::from_u32(14)
        );
    }
}