//! Module exposing the relay circuit reactor subsystem.

//!

//! See [`reactor`](crate::circuit::reactor) for a description of the overall architecture.

//!

//! All cells moving in the forward direction (i.e. away from the client)

//! are handled by the forward reactor, which deals with

//!

//!  * unrecognized RELAY* cells, by moving them in the forward direction (towards the exit)

//!  * recognized RELAY* cells, by splitting each cell into messages, and handling

//!    each message individually as described in the table below

//!    (Note: since prop340 is not yet implemented, in practice there is only 1 message per cell).

//!  * DESTROY cells, by tearing down the circuit, and causing a DESTROY to be sent forward,

//!    to the next hop, if there is one

//!  * PADDING_NEGOTIATE cells (**not yet implemented**)

//!

//! ```text

//!

//! Legend: `F` = "forward reactor", `B` = "backward reactor", `S` = "stream reactor"

//! `FH` = `ForwardHandler`

//!

//! | RELAY cmd  | Received in | Handled in            | Description                            |

//! |------------|-------------|-----------------------|----------------------------------------|

//! | DROP       | F           | FH::handle_meta_msg() | Passed to PaddingController for        |

//! |            |             |                       | validation                             |

//! |------------|-------------|-----------------------|----------------------------------------|

//! | EXTEND2    | F           | FH::handle_meta_msg() | Handled by the ExtendRequestHandler    |

//! |            |             |                       | See [forward::extend_handler].         |

//! |------------|-------------|-----------------------|----------------------------------------|

//! | TRUNCATE   | F           | FH::handle_meta_msg() | Not supported: TRUNCATE is considered  |

//! |            |             |                       | a protocol violation, because none of  |

//! |            |             |                       | of our implementations send it.        |

//! |------------|-------------|-----------------------|----------------------------------------|

//! | SENDME     | F           | B                     | Sent to BackwardReactor for handling.  |

//! | (sid = 0)  |             |                       | See the [crate::circuit::reactor] docs |

//! |------------|-------------|-----------------------|----------------------------------------|

//! | Other      | F           | FH::handle_meta_msg() | Rejected as unrecognized               |

//! | (sid = 0)  |             |                       |                                        |

//! |------------|-------------|-----------------------|----------------------------------------|

//! | Other      | F           | S                     | Handled in the `StreamReactor`         |

//! | (sid != 0) |             |                       |                                        |

//! ```

pub(crate) mod backward;

pub(crate) mod forward;

use std::sync::Arc;

use std::time::Duration;

use futures::StreamExt as _;

use futures::channel::mpsc;

use tor_cell::chancell::CircId;

use tor_cell::relaycell::RelayCmd;

use tor_linkspec::OwnedChanTarget;

use tor_memquota::mq_queue::{ChannelSpec, MpscSpec};

use tor_rtcompat::{DynTimeProvider, Runtime};

use crate::channel::Channel;

use crate::circuit::circhop::ReactorStreamComponents;

use crate::circuit::circhop::{CircHopOutbound, HopSettings};

use crate::circuit::reactor::Reactor as BaseReactor;

use crate::circuit::reactor::hop_mgr::HopMgr;

use crate::circuit::reactor::stream;

use crate::circuit::{CircuitRxReceiver, UniqId};

use crate::congestion::sendme::StreamRecvWindow;

use crate::crypto::cell::{InboundRelayLayer, OutboundRelayLayer};

use crate::memquota::{CircuitAccount, SpecificAccount};

use crate::relay::RelayCirc;

use crate::relay::channel_provider::ChannelProvider;

use crate::relay::reactor::backward::Backward;

use crate::relay::reactor::forward::Forward;

use crate::stream::flow_ctrl::state::WithSidechannelMitigations;

use crate::stream::flow_ctrl::xon_xoff::reader::XonXoffReaderCtrl;

use crate::stream::incoming::{

    IncomingCmdChecker, IncomingStream, IncomingStreamRequestFilter, IncomingStreamRequestHandler,

    StreamReqInfo,

};

use crate::stream::raw::StreamReceiver;

use crate::stream::{RECV_WINDOW_INIT, StreamComponents, StreamTarget, Tunnel};

// TODO(circpad): once padding is stabilized, the padding module will be moved out of client.

use crate::client::circuit::padding::{PaddingController, PaddingEventStream};

/// Type-alias for the relay base reactor type.

type RelayBaseReactor<R> = BaseReactor<R, Forward, Backward>;

/// The entry point of the circuit reactor subsystem.

#[must_use = "If you don't call run() on a reactor, the circuit won't work."]

pub(crate) struct Reactor<R: Runtime>(RelayBaseReactor<R>);

/// A handler customizing the relay stream reactor.

struct StreamHandler;

impl stream::StreamHandler for StreamHandler {

        // Note: if we have no measurements for the RTT, this will be set to 0,

        // so the stream will be removed from the stream map immediately,

        // and any subsequent messages arriving on it will trigger

        // a proto violation causing the circuit to close.

        //

        // TODO(relay-tuning): we should make sure that this doesn't cause us to

        // wrongly close legitimate circuits that still have in-flight stream data

            // TODO(relay): we should fallback to a non-zero default here

            // if we don't have any RTT measurements yet

        // We're a relay, so we don't want sidechannel mitigations for flow control.

}

impl<R: Runtime> Reactor<R> {

    /// Create a new circuit reactor.

    ///

    /// Returns the [`Reactor`], a [`RelayCirc`] handle to it,

    /// and a [`Stream`](futures::Stream) of `IncomingStream`s.

    ///

    /// The reactor will send outbound messages on `channel`, receive incoming

    /// messages on `input`, and identify this circuit by the channel-local

    /// [`CircId`] provided.

    ///

    /// The internal unique identifier for this circuit will be `unique_id`.

    ///

    /// The returned `IncomingStream`s are exit, dns, or directory streams.

    /// An incoming stream is automatically rejected by the reactor

    /// if the provided `IncomingStreamRequestFilter` rejects it.

    /// You can also explicitly reject a stream by calling [`IncomingStream::reject`].

    /// If the `Stream` is dropped, the next incoming stream request

    /// (`BEGIN`, `BEGIN_DIR`, or RESOLVE`)

    /// on this circuit will cause the stream reactor to shut down,

    /// which will trigger a shutdown of all the circuit reactors (FWD, BWD),

    /// which causing the circuit to close.

    ///

    /// The streams not rejected by the `IncomingStreamRequestFilter` will

    /// get an entry in the circuit's stream map.

    /// Rejecting such a stream using [`IncomingStream::reject`] will remove the entry.

    ///

    /// The `IncomingStreamRequestFilter` should only perform inexpensive checks

    /// that won't block the reactor.

    /// More expensive, or blocking checks, should be handled outside of the circuit reactor,

    /// when processing new `IncomingStream`s from the returned Rust stream.

    ///

    /// Data and directory streams can be accepted by calling [`IncomingStream::accept_data`].

    /// The caller is responsible for proxying data between the resulting `DataStream`

    /// and the local application stream.

    ///

    // TODO(relay): say how RESOLVE streams should be handled

    //

    // TODO: declare a type-alias for the impl futures::Stream return type

    // when support for impl in type aliases gets stabilized.

    //

    // See issue #63063 <https://github.com/rust-lang/rust/issues/63063>

    //

    // TODO(DEDUP): the incoming stream handling is *very* similar

    // to the impll from ServiceOnionServiceDataTunnel::allow_stream_requests.

    // We should dedupe these someday, when we rewrite the client reactor

    // to use the new multi-reactor architecture

    #[allow(clippy::too_many_arguments)] // TODO

        // NOTE: not registering this channel with the memquota subsystem is okay,

        // because it has no buffering (if ever decide to make the size of this buffer

        // non-zero for whatever reason, we must remember to register it with memquota

        // so that it counts towards the total memory usage for the circuit.

        #[allow(clippy::disallowed_methods)]

        /// The size of the channel receiving IncomingStreamRequestContexts.

        ///

        // TODO(relay-tuning): buffer size

        //

        // This is currently set to 2x the initial receive window,

        // the same as the buffer size we use for onion services.

        // This value was picked arbitrarily,

        // and is not necessarily tuned for relay needs.

        const INCOMING_BUFFER: usize = crate::stream::STREAM_READER_BUFFER;

        // Our IncomingCmdChecker does not reject BEGIN, BEGIN_DIR, RESOLVE cells,

        // but that doesn't necessarily mean the stream will be accepted.

        // An incoming stream can still be rejected at a later stage,

        // by the IncomingStreamRequestFilter, or directly by the consumer of the

        // futures::Stream<Item = IncomingStream> (by calling IncomingStream::reject()).

        );

        // On the relay side, we always have one "hop" (ourselves).

        //

        // Clients will need to call this function in response to CtrlMsg::Create

        // (TODO: for clients, we probably will need to store a bunch more state here)

        // TODO(relay): currently we don't need buffering on this channel,

        // but we might need it if we start using it for more than just EXTENDED2 events

        #[allow(clippy::disallowed_methods)]

        );

        // Note: tunnel is a bit of a misnomer for relays

        // TODO(relay): this is more or less copy-pasta from client code

            let StreamReqInfo {

                stream_components:

                    ReactorStreamComponents {

                    },

            // There is no originating hop if we're a relay

            // can be used to build a reader that supports XON/XOFF flow control

    /// Launch the reactor, and run until the circuit closes or we

    /// encounter an error.

    ///

    /// Once this method returns, the circuit is dead and cannot be

    /// used again.

}

#[cfg(test)]

pub(crate) mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_time_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    #![allow(clippy::string_slice)] // See arti#2571

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    use crate::channel::ChannelMode;

    use crate::channel::CtrlMsg;

    use crate::channel::circmap::CircIdRange;

    use crate::channel::test_utils::DummyChan;

    use crate::circuit::CircParameters;

    use crate::circuit::circ_sender;

    use crate::circuit::reactor::test::{AllowAllStreamsFilter, rmsg_to_ccmsg};

    use crate::circuit::test::new_circ_net_params;

    use crate::client::circuit::padding::new_padding;

    use crate::congestion::test_utils::params::build_cc_vegas_params;

    use crate::crypto::cell::RelayCellBody;

    use crate::crypto::cell::{InboundRelayLayer, OutboundRelayLayer};

    use crate::relay::CreateRequestHandler;

    use crate::relay::channel::test::DummyChanProvider;

    use crate::stream::flow_ctrl::params::FlowCtrlParameters;

    use crate::stream::incoming::{IncomingStream, IncomingStreamRequest, NoOpRequestFilter};

    use futures::AsyncReadExt as _;

    use futures::SinkExt as _;

    use oneshot_fused_workaround as oneshot;

    use tracing_test::traced_test;

    use tor_basic_utils::test_rng::{TestingRng, testing_rng};

    use tor_cell::chancell::{ChanCell, ChanCmd, msg as chanmsg};

    use tor_cell::relaycell::{AnyRelayMsgOuter, RelayCellFormat, StreamId, msg as relaymsg};

    use tor_key_forge::Keygen;

    use tor_linkspec::{EncodedLinkSpec, HasRelayIds, LinkSpec};

    use tor_llcrypto::pk::curve25519::StaticKeypair;

    use tor_llcrypto::pk::ed25519::Ed25519Identity;

    use tor_llcrypto::pk::rsa::RsaIdentity;

    use tor_llcrypto::rng::FakeEntropicRng;

    use tor_protover::{Protocols, named};

    use tor_relay_crypto::pk::RelayNtorKeys;

    use tor_rtcompat::SpawnExt;

    use tor_rtcompat::{DynTimeProvider, Runtime};

    use tor_rtmock::MockRuntime;

    use chanmsg::{AnyChanMsg, Destroy, DestroyReason, HandshakeType};

    use relaymsg::SendmeTag;

    use std::net::IpAddr;

    use std::sync::{Arc, Mutex, Weak, mpsc};

    use std::task::{Context, Poll, Waker};

    // An inbound encryption layer that doesn't do any crypto.

    struct DummyInboundCrypto {}

    // An outbound encryption layer that doesn't do any crypto.

    struct DummyOutboundCrypto {

        /// Channel for controlling whether the current cell is meant for us or not.

        ///

        /// Useful for tests that check if recognized/unrecognized

        /// cells are handled/forwarded correctly.

        recognized_rx: mpsc::Receiver<Recognized>,

    }

    const DUMMY_TAG: [u8; 20] = [1; 20];

    impl InboundRelayLayer for DummyInboundCrypto {

        fn originate(&mut self, _cmd: ChanCmd, _cell: &mut RelayCellBody) -> SendmeTag {

            DUMMY_TAG.into()

        }

        fn encrypt_inbound(&mut self, _cmd: ChanCmd, _cell: &mut RelayCellBody) {}

    }

    impl OutboundRelayLayer for DummyOutboundCrypto {

        fn decrypt_outbound(

            &mut self,

            _cmd: ChanCmd,

            _cell: &mut RelayCellBody,

        ) -> Option<SendmeTag> {

            // Note: this should never block.

            let recognized = self.recognized_rx.recv().unwrap();

            match recognized {

                Recognized::Yes => Some(DUMMY_TAG.into()),

                Recognized::No => None,

            }

        }

    }

    /// A circuit reactor handle, for building circuits of the form

    /// A -> B, and A -> B -> C, where the circuit reactor under test

    /// "thinks" it is B.

    ///

    /// [`ReactorTestCtrl::new`] builds and spawns:

    ///

    ///   * a channel reactor for the A - B "Tor Channel"

    ///   * a circuit reactor for B's view of the circuit

    ///

    /// Some of the tests in this module extend the circuit by another dummy hop,

    /// to obtain an A -> B -> C circuit. This involves sending an EXTEND2

    /// cell over the A -> B channel, and calling [`ReactorTestCtrl::do_create2_handshake`]

    /// to finalize the handshake.

    struct ReactorTestCtrl {

        /// The relay circuit handle.

        relay_circ: Arc<RelayCirc>,

        /// The circuit id on our `inbound_chan`.

        circid: CircId,

        /// The inbound channel ("towards the client").

        ///

        /// This is the "Tor channel" between A and B in

        /// a circuit of the form A -> B or A -> B -> C.

        inbound_chan: DummyChan,

        /// The outbound channel ("away from the client"), if any.

        ///

        /// Shared with the DummyChanProvider, which initializes this

        /// when the relay reactor launches a channel to the next hop

        /// via `get_or_launch()`.

        ///

        /// This is the "Tor channel" between B and C,

        /// if our test circuit is of the form A -> B -> C

        /// (i.e. if we have extended the "base" circuit by another mock hop, to C).

        outbound_chan: Arc<Mutex<Option<DummyChan>>>,

        /// MPSC channel for telling the DummyOutboundCrypto that the next

        /// cell we're about to send to the reactor should be "recognized".

        recognized_tx: mpsc::Sender<Recognized>,

    }

    /// Whether a forward cell to send should be "recognized"

    /// or "unrecognized" by the relay under test.

    enum Recognized {

        /// Recognized

        Yes,

        /// Unrecognized

        No,

    }

    /// The direction we expect the reactor to have sent a DESTROY in

    #[allow(dead_code)] // we don't use all of these yet

    enum DestroyDirection {

        /// Forward ("towards the exit")

        Forward,

        /// Backward ("towards the client")

        Backward,

        /// Both forward and backward

        Both,

    }

    /// Decode a cell, extracting the underlying message of type `expect_msg`

    macro_rules! decode_relay_cell {

        ($cell:expr, $expect_msg:tt) => {{

            let rmsg = match $cell.msg() {

                chanmsg::AnyChanMsg::Relay(r) => AnyRelayMsgOuter::decode_singleton(

                    RelayCellFormat::V0,

                    r.clone().into_relay_body(),

                )

                .unwrap(),

                msg => panic!("unexpected forwarded {msg:?}"),

            };

            let msg = match rmsg.msg() {

                relaymsg::AnyRelayMsg::$expect_msg(inner) => inner.clone(),

                _ => panic!("unexpected relay message {rmsg:?}"),

            };

            (rmsg.stream_id(), msg)

        }};

    }

    const DUMMY_ED25519_KEY: [u8; 32] = *b"32 bytes pretending to be a key!";

    const DUMMY_RSA_KEY: [u8; 20] = *b"not really an RSA ky";

    /// Helper for building a [`ChannelMode::Relay`] for our test reactor

    fn build_channel_mode<R: Runtime>(

        chan_provider: Arc<DummyChanProvider<R>>,

        allowed_stream_cmds: &[RelayCmd],

    ) -> ChannelMode {

        let our_ed25519_id = Ed25519Identity::from_bytes(&DUMMY_ED25519_KEY).unwrap();

        let our_rsa_id = RsaIdentity::from_bytes(&DUMMY_RSA_KEY).unwrap();

        let mut rng = FakeEntropicRng::<TestingRng>(testing_rng());

        let relay_ntor_keys = StaticKeypair::generate(&mut rng).unwrap();

        // A handler that will process CREATE* requests on channels

        //

        // Note: in practice, this won't actually be used at all,

        // because for the purposes of these tests, the circuit reactor is spawned manually,

        // by ReactorTestCtrl::new(), which also hackily initializes the channel's circuit map

        // with a circuit entry for it.

        //

        // This should be fine for now, but we might want to rethink it in the future

        // (i.e. we might want to let the channel reactor spawn the circuit reactor under test,

        // in response to CREATE*).

        let (create_request_handler, _circuit_stream_rx) = CreateRequestHandler::new(

            Arc::downgrade(&chan_provider) as Weak<_>,

            new_circ_net_params(),

            RelayNtorKeys::new(relay_ntor_keys.into()),

            // Don't filter any stream requests.

            Box::new(|| Box::new(NoOpRequestFilter) as Box<_>),

            allowed_stream_cmds,

        );

        let create_request_handler = Arc::new(create_request_handler);

        ChannelMode::Relay {

            create_request_handler,

            our_ed25519_id,

            our_rsa_id,

            // This doesn't actually matter for these tests

            circ_id_range: CircIdRange::Low,

        }

    }

    /// Prepare our "inbound" channel,

    ///

    /// > Note: the concept of an "inbound" channel only really makes sense

    /// > if you think about it from a circuit perspective:

    /// > these tests essentially simulate circuits of the form A -> B

    /// > and A -> B -> C. The relay circuit reactor under test "thinks" it's relay B,

    /// > and its "inbound" and "outbound" channels are the A -> B and B -> C channels,

    /// > respectively.

    ///

    /// This spawns a channel reactor and creates a fake circuit entry in it,

    /// which is wired up to the circuit Reactor under test by [`ReactorTestCtrl::new`].

    async fn prepare_inbound_chan<R: Runtime>(

        rt: &R,

        mode: ChannelMode,

    ) -> (CircId, CircuitRxReceiver, DummyChan) {

        let mut inbound_chan = DummyChan::run(rt, mode);

        let memquota = CircuitAccount::new_noop();

        let time_provider = DynTimeProvider::new(rt.clone());

        let (sender, receiver) = MpscSpec::new(128)

            .new_mq(time_provider, memquota.as_raw_account())

            .unwrap();

        let (sender, receiver) = circ_sender::channel(sender, receiver);

        let (created_sender, created_receiver) = oneshot::channel();

        let (tx, rx) = oneshot::channel();

        // Note: we need to make sure the circuit is in the channel reactor's

        // circuit map, because otherwise we can't test the DESTROY behavior,

        // (the channel reactor conditionally sends DESTROY based on whether

        // the circuit entry is still in the circmap or not;

        // the presence of a circuit in the circmap is a proxy for

        // whether we have sent a DESTROY ourselves or not).

        inbound_chan

            .channel

            .send_control(CtrlMsg::AllocateCircuit {

                created_sender,

                sender,

                tx,

            })

            .unwrap();

        let (circid, _circ_unique_id, _padding_ctrl, _padding_stream) = rx.await.unwrap().unwrap();

        // Hack: AllocateCircuit puts the circuit in the "Opening" state,

        // but in order to actually be able to send anything on this channel,

        // we need to advance it to "Open". We do that by sending a CREATED2 cell on the channel,

        // which is nonsensical from the perspective of the relay-specific test setup

        // (it would make sense if this was a client channel, however).

        // Alas, it is the only way we can advance the circuit's state to "Open"

        // in the channel's circmap without introducing a test-only CtrlMsg for this,

        // or without surrendering the circuit Reactor setup to the channel impl

        // (the latter might not be so bad actually, because it would be closer to what

        // happens in reality).

        let handshake = vec![];

        let created2 = chanmsg::Created2::new(handshake.clone());

        let cell = ChanCell::new(Some(circid), created2.into());

        inbound_chan.tx.try_send(Ok(cell)).unwrap();

        // We **have** to read the CREATED2 (otherwise the channel reactor shuts down with an error)

        let _ = created_receiver.await;

        (circid, receiver, inbound_chan)

    }

    impl ReactorTestCtrl {

        /// Spawn a relay circuit reactor, returning a `ReactorTestCtrl` for

        /// controlling it.

        async fn spawn_reactor<R: Runtime>(

            rt: &R,

            allowed_stream_cmds: &[RelayCmd],

        ) -> (Self, impl futures::Stream<Item = IncomingStream>) {

            let outbound_chan = Arc::new(Mutex::new(None));

            let chan_provider = Arc::new(DummyChanProvider::new(

                rt.clone(),

                Arc::clone(&outbound_chan),

            ));

            let mode = build_channel_mode(Arc::clone(&chan_provider), allowed_stream_cmds);

            let (circid, receiver, inbound_chan) = prepare_inbound_chan(rt, mode).await;

            let unique_id = UniqId::new(8, 17);

            let (padding_ctrl, padding_stream) = new_padding(DynTimeProvider::new(rt.clone()));

            let params = CircParameters::new(

                true,

                build_cc_vegas_params(),

                FlowCtrlParameters::defaults_for_tests(),

            );

            let settings = HopSettings::from_params_and_caps(

                crate::circuit::circhop::HopNegotiationType::Full,

                &params,

                &[named::FLOWCTRL_CC].into_iter().collect::<Protocols>(),

            )

            .unwrap();

            let (recognized_tx, recognized_rx) = mpsc::channel();

            let (reactor, relay_circ, incoming_streams) = Reactor::new(

                rt.clone(),

                &Arc::clone(&inbound_chan.channel),

                circid,

                unique_id,

                receiver,

                Box::new(DummyInboundCrypto {}),

                Box::new(DummyOutboundCrypto { recognized_rx }),

                &settings,

                chan_provider,

                padding_ctrl,

                padding_stream,

                Box::new(AllowAllStreamsFilter),

                allowed_stream_cmds,

                &CircuitAccount::new_noop(),

            )

            .unwrap();

            rt.spawn(async {

                let _ = reactor.run().await;

            })

            .unwrap();

            let ctrl = Self {

                relay_circ,

                circid,

                recognized_tx,

                inbound_chan,

                outbound_chan,

            };

            (ctrl, incoming_streams)

        }

        /// Simulate the sending of a forward relay message through our relay.

        async fn send_fwd(

            &mut self,

            id: Option<StreamId>,

            msg: relaymsg::AnyRelayMsg,

            recognized: Recognized,

            early: bool,

        ) {

            // This a bit janky, but for each forward cell we send to the reactor

            // we need to send a bit of metadata to the DummyOutboundLayer

            // specifying whether the cell should be treated as recognized

            // or unrecognized

            self.recognized_tx.send(recognized).unwrap();

            self.send_fwd_cmsg(rmsg_to_ccmsg(id, msg, early)).await;

        }

        /// Simulate the sending of a forward channel message through our relay.

        async fn send_fwd_cmsg(&mut self, msg: chanmsg::AnyChanMsg) {

            let cell = ChanCell::new(Some(self.circid), msg);

            self.inbound_chan.tx.send(Ok(cell)).await.unwrap();

        }

        /// Whether the reactor opened an outbound channel

        /// (i.e. a channel to the next relay in the circuit).

        fn outbound_chan_launched(&self) -> bool {

            self.outbound_chan.lock().unwrap().is_some()

        }

        /// Perform the CREATE2 handshake.

        async fn do_create2_handshake(

            &mut self,

            rt: &MockRuntime,

            expected_hs_type: HandshakeType,

        ) -> Option<CircId> {

            // First, check that the reactor actually sent a CREATE2 to the next hop...

            let (circid, msg) = self.read_outbound().into_circid_and_msg();

            let _create2 = match msg {

                chanmsg::AnyChanMsg::Create2(c) => {

                    assert_eq!(c.handshake_type(), expected_hs_type);

                    c

                }

                _ => panic!("unexpected forwarded {msg:?}"),

            };

            let handshake = vec![];

            let created2 = chanmsg::Created2::new(handshake.clone());

            // ...and then finalize the handshake by pretending to be

            // the responding relay

            self.write_outbound(circid, chanmsg::AnyChanMsg::Created2(created2));

            rt.advance_until_stalled().await;

            // Make sure we actually did send an EXTENDED2 towards the client

            let msg = self.read_inbound();

            let (_sid, e) = decode_relay_cell!(msg, Extended2);

            assert_eq!(e.clone().into_body(), handshake);

            circid

        }

        /// Whether the circuit is closing (e.g. due to a proto violation).

        fn is_closing(&self) -> bool {

            self.relay_circ.is_closing()

        }

        /// Read a cell from the inbound channel

        /// (moving towards the client).

        ///

        /// See [`try_read_inbound`](Self::try_read_inbound).

        ///

        /// Panics if there are no ready cells on the inbound MPSC channel.

        fn read_inbound(&mut self) -> ChanCell<AnyChanMsg> {

            self.try_read_inbound().unwrap()

        }

        /// Try to read a cell from the inbound channel

        /// (moving towards the client).

        ///

        /// For example, for a circuit of the form A -> B -> C,

        /// where B is the relay whose circuit reactor we're testing,

        /// this function reads a channel message on the A <-> B channel,

        /// from the perspective of A (i.e. it reads a channel message sent by B).

        ///

        /// Returns None if there are no ready cells on the inbound MPSC channel.

        fn try_read_inbound(&mut self) -> Option<ChanCell<AnyChanMsg>> {

            #[allow(deprecated)] // TODO(#2386)

            self.inbound_chan.rx.try_next().ok().flatten()

        }

        /// Read a cell from the outbound channel

        /// (moving towards the next hop).

        ///

        /// See [`try_read_outbound`](Self::try_read_outbound).

        ///

        /// Panics if there are no ready cells on the outbound MPSC channel,

        /// or if there is no outbound channel.

        fn read_outbound(&mut self) -> ChanCell<AnyChanMsg> {

            self.try_read_outbound().unwrap()

        }

        /// Read a cell from the outbound channel

        /// (moving towards the next hop).

        ///

        /// For example, for a circuit of the form A -> B -> C,

        /// where B is the relay whose circuit reactor we're testing,

        /// this function reads a channel message on the B <-> C channel,

        /// from the perspective of C (i.e. it reads a channel message sent by B).

        ///

        /// Returns None if there are no ready cells on the outbound MPSC channel,

        /// or if there is no outbound channel.

        fn try_read_outbound(&mut self) -> Option<ChanCell<AnyChanMsg>> {

            let mut lock = self.outbound_chan.lock().unwrap();

            let chan = lock.as_mut()?;

            #[allow(deprecated)] // TODO(#2386)

            chan.rx.try_next().ok().flatten()

        }

        /// Write to the sending end of the outbound Tor channel.

        ///

        /// Simulates the receipt of a cell from the next hop.

        ///

        /// Panics if the outbound chan sender is full.

        fn write_outbound(&mut self, circid: Option<CircId>, msg: chanmsg::AnyChanMsg) {

            let mut lock = self.outbound_chan.lock().unwrap();

            let chan = lock.as_mut().unwrap();

            let cell = ChanCell::new(circid, msg);

            chan.tx.try_send(Ok(cell)).unwrap();

        }

    }

    fn dummy_linkspecs() -> Vec<EncodedLinkSpec> {

        vec![

            LinkSpec::Ed25519Id([43; 32].into()).encode().unwrap(),

            LinkSpec::RsaId([45; 20].into()).encode().unwrap(),

            LinkSpec::OrPort("127.0.0.1".parse::<IpAddr>().unwrap(), 999)

                .encode()

                .unwrap(),

        ]

    }

    macro_rules! assert_cell_is_destroy {

        ($cell:expr, $reason:expr) => {{

            match $cell.msg() {

                chanmsg::AnyChanMsg::Destroy(d) => {

                    assert_eq!(d.reason(), $reason);

                }

                _ => panic!("unexpected ending {:?}", $cell),

            }

        }};

    }

    /// Assert that we have sent a DESTROY cell with the specified `reason`

    /// towards the "client" and/or the "next hop".

    ///

    /// The test is expected to drain the inbound Tor "channel"

    /// of any non-ending cells it might be expecting before calling this function.

    fn assert_destroy_sent(

        ctrl: &mut ReactorTestCtrl,

        reason: DestroyReason,

        direction: DestroyDirection,

    ) {

        assert!(ctrl.is_closing());

        match direction {

            DestroyDirection::Backward => {

                assert_cell_is_destroy!(ctrl.read_inbound(), reason);

                assert!(ctrl.try_read_outbound().is_none());

            }

            DestroyDirection::Forward => {

                assert_cell_is_destroy!(ctrl.read_outbound(), reason);

                assert!(ctrl.try_read_inbound().is_none());

            }

            DestroyDirection::Both => {

                assert_cell_is_destroy!(ctrl.read_inbound(), reason);

                assert_cell_is_destroy!(ctrl.read_outbound(), reason);

            }

        }

    }

    macro_rules! expect_cell {

        ($cell:expr, $chanmsg:tt, $relaymsg:tt) => {{

            let msg = match $cell.msg() {

                chanmsg::AnyChanMsg::$chanmsg(m) => {

                    let body = m.clone().into_relay_body();

                    AnyRelayMsgOuter::decode_singleton(RelayCellFormat::V0, body).unwrap()

                }

                _ => panic!("unexpected forwarded {:?}", $cell),

            };

            match msg.msg() {

                relaymsg::AnyRelayMsg::$relaymsg(m) => m.clone(),

                _ => panic!("unexpected cell {msg:?}"),

            }

        }};

    }

    #[traced_test]

    #[test]

    fn reject_extend2_relay() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            let linkspecs = dummy_linkspecs();

            let extend2 = relaymsg::Extend2::new(linkspecs, HandshakeType::NTOR_V3, vec![]).into();

            ctrl.send_fwd(None, extend2, Recognized::Yes, false).await;

            rt.advance_until_stalled().await;

            assert!(logs_contain("got EXTEND2 in a RELAY cell?!"));

            assert!(!ctrl.outbound_chan_launched());

            // There is no next hop because we haven't extended the circuit,

            // so only expect the DESTROY to be sent toward the client (Backward).

            assert_destroy_sent(&mut ctrl, DestroyReason::NONE, DestroyDirection::Backward);

        });

    }

    #[traced_test]

    #[test]

    fn reject_extend2_previous_hop() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            // No outbound circuits yet

            assert!(!ctrl.outbound_chan_launched());

            // Build a linkspec with the identities of the dummy channel

            let mut linkspecs = ctrl

                .inbound_chan

                .channel

                .target()

                .identities()

                .map(|id| LinkSpec::from(id.to_owned()).encode())

                .collect::<Result<Vec<_>, _>>()

                .unwrap();

            // Make sure this channel actually has some identities

            // (i.e. that it's not a client channel or something)

            assert_eq!(linkspecs.len(), 2);

            // There must be at least one IPv4 OR port address

            linkspecs.push(

                LinkSpec::OrPort("127.0.0.1".parse::<IpAddr>().unwrap(), 999)

                    .encode()

                    .unwrap(),

            );

            let handshake_type = HandshakeType::NTOR_V3;

            let extend2 = relaymsg::Extend2::new(linkspecs, handshake_type, vec![]).into();

            ctrl.send_fwd(None, extend2, Recognized::Yes, true).await;

            rt.advance_until_stalled().await;

            // The reactor handled the EXTEND2 and launched an outbound channel

            assert!(logs_contain("Cannot extend circuit to previous hop"));

            assert!(!ctrl.outbound_chan_launched());

            assert!(ctrl.is_closing());

        });

    }

    #[traced_test]

    #[test]

    fn extend_and_forward() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            // No outbound circuits yet

            assert!(!ctrl.outbound_chan_launched());

            let linkspecs = dummy_linkspecs();

            let handshake_type = HandshakeType::NTOR_V3;

            let extend2 = relaymsg::Extend2::new(linkspecs, handshake_type, vec![]).into();

            ctrl.send_fwd(None, extend2, Recognized::Yes, true).await;

            rt.advance_until_stalled().await;

            // The reactor handled the EXTEND2 and launched an outbound channel

            assert!(logs_contain(

                "Launched channel to the next hop circ_uniq_id=Circ 8.17"

            ));

            assert!(ctrl.outbound_chan_launched());

            assert!(!ctrl.is_closing());

            let _circid = ctrl.do_create2_handshake(&rt, handshake_type).await;

            assert!(logs_contain("Got CREATED2 response from next hop"));

            assert!(logs_contain("Extended circuit to the next hop"));

            // Time to forward a message to the next hop!

            let early = false;

            let begin = relaymsg::Begin::new("127.0.0.1", 1111, 0).unwrap();

            ctrl.send_fwd(None, begin.clone().into(), Recognized::No, early)

                .await;

            rt.advance_until_stalled().await;

            // Ensure the other end received the BEGIN cell

            let cell = ctrl.read_outbound();

            let recvd_begin = expect_cell!(cell, Relay, Begin);

            assert_eq!(begin, recvd_begin);

            // Now send the same message again, but this time in a RELAY_EARLY

            let early = true;

            let begin = relaymsg::Begin::new("127.0.0.1", 1111, 0).unwrap();

            ctrl.send_fwd(None, begin.clone().into(), Recognized::No, early)

                .await;

            rt.advance_until_stalled().await;

            let cell = ctrl.read_outbound();

            let recvd_begin = expect_cell!(cell, RelayEarly, Begin);

            assert_eq!(begin, recvd_begin);

        });

    }

    #[traced_test]

    #[test]

    fn forward_before_extend() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            // Send an arbitrary unrecognized cell. The reactor should flag this as

            // a protocol violation, because we don't have an outbound channel to forward it on.

            let end = relaymsg::End::new_misc().into();

            ctrl.send_fwd(None, end, Recognized::No, true).await;

            rt.advance_until_stalled().await;

            assert!(logs_contain(

                "Asked to forward cell before the circuit was extended?!"

            ));

            // There is no next hop because we haven't extended the circuit,

            // so only expect the DESTROY to be sent toward the client (Backward).

            assert_destroy_sent(&mut ctrl, DestroyReason::NONE, DestroyDirection::Backward);

        });

    }

    #[traced_test]

    #[test]

    fn reject_invalid_begin() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            let begin = relaymsg::Begin::new("127.0.0.1", 1111, 0).unwrap().into();

            // BEGIN cells *must* have a stream ID, so expect the reactor to reject this

            // and close the circuit

            ctrl.send_fwd(None, begin, Recognized::Yes, false).await;

            rt.advance_until_stalled().await;

            assert!(logs_contain(

                "Invalid stream ID [scrubbed] for relay command BEGIN"

            ));

            // There is no next hop because we haven't extended the circuit,

            // so only expect the DESTROY to be sent toward the client (Backward).

            assert_destroy_sent(&mut ctrl, DestroyReason::NONE, DestroyDirection::Backward);

        });

    }

    #[traced_test]

    #[test]

    fn destroy_from_client() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            // Extend the circuit by another hop

            let linkspecs = dummy_linkspecs();

            let handshake_type = HandshakeType::NTOR_V3;

            let extend2 = relaymsg::Extend2::new(linkspecs, handshake_type, vec![]).into();

            ctrl.send_fwd(None, extend2, Recognized::Yes, true).await;

            rt.advance_until_stalled().await;

            let _circid = ctrl.do_create2_handshake(&rt, handshake_type).await;

            assert!(logs_contain("Extended circuit to the next hop"));

            assert!(ctrl.outbound_chan_launched());

            // Simulate the client sending us a DESTROY cell

            let destroy = Destroy::new(DestroyReason::PROTOCOL);

            ctrl.send_fwd_cmsg(destroy.into()).await;

            rt.advance_until_stalled().await;

            assert!(logs_contain(

                "Received outbound DESTROY, circuit shutting down"

            ));

            // Since this is a circuit of the form A -> B -> C,

            // and A sent us a DESTROY, we expect our relay (B) to forward

            // the DESTROY to C.

            assert_destroy_sent(&mut ctrl, DestroyReason::NONE, DestroyDirection::Forward);

        });

    }

    #[traced_test]

    #[test]

    fn destroy_from_next_hop() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            // Extend the circuit by another hop

            let linkspecs = dummy_linkspecs();

            let handshake_type = HandshakeType::NTOR_V3;

            let extend2 = relaymsg::Extend2::new(linkspecs, handshake_type, vec![]).into();

            ctrl.send_fwd(None, extend2, Recognized::Yes, true).await;

            rt.advance_until_stalled().await;

            let circid = ctrl.do_create2_handshake(&rt, handshake_type).await;

            assert!(logs_contain("Extended circuit to the next hop"));

            assert!(ctrl.outbound_chan_launched());

            // Simulate the next hop sending us a DESTROY cell

            let destroy = Destroy::new(DestroyReason::PROTOCOL);

            ctrl.write_outbound(circid, destroy.into());

            rt.advance_until_stalled().await;

            // We have *not* received an outbound destroy

            assert!(!logs_contain(

                "Received outbound DESTROY, circuit shutting down"

            ));

            // We received an inbound one (from the next hop)

            assert!(logs_contain(

                "Received inbound DESTROY, circuit shutting down"

            ));

            // There is no next hop because we haven't extended the circuit,

            // so only expect the DESTROY to be sent toward the client (Backward).

            // This also ensures the destroy reason (PROTOCOL) is not propagated.

            assert_destroy_sent(&mut ctrl, DestroyReason::NONE, DestroyDirection::Backward);

        });

    }

    #[traced_test]

    #[test]

    fn truncate() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, _incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            // Simulate the client sending us a TRUNCATE cell

            let truncate = relaymsg::Truncate::default().into();

            ctrl.send_fwd(None, truncate, Recognized::Yes, false).await;

            rt.advance_until_stalled().await;

            assert!(logs_contain(

                "Circuit protocol violation: TRUNCATE not allowed"

            ));

            // There is no next hop because we haven't extended the circuit,

            // so only expect the DESTROY to be sent toward the client (Backward).

            assert_destroy_sent(&mut ctrl, DestroyReason::NONE, DestroyDirection::Backward);

        });

    }

    #[traced_test]

    #[test]

    fn data_stream() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            const TO_SEND: &[u8] = b"The bells were musical in the silvery sun";

            let (mut ctrl, mut incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            let begin = relaymsg::Begin::new("127.0.0.1", 1111, 0).unwrap().into();

            ctrl.send_fwd(StreamId::new(1), begin, Recognized::Yes, false)

                .await;

            rt.advance_until_stalled().await;

            let data = relaymsg::Data::new(TO_SEND).unwrap().into();

            ctrl.send_fwd(StreamId::new(1), data, Recognized::Yes, false)

                .await;

            // We should have a pending incoming stream

            let pending = incoming_streams.next().await.unwrap();

            // Accept it, and let's see what we have!

            let mut stream = pending

                .accept_data(relaymsg::Connected::new_empty())

                .await

                .unwrap();

            let mut recv_buf = [0_u8; TO_SEND.len()];

            stream.read_exact(&mut recv_buf).await.unwrap();

            assert_eq!(recv_buf, TO_SEND);

        });

    }

    #[traced_test]

    #[test]

    fn reject_stream() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, mut incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::BEGIN]).await;

            rt.advance_until_stalled().await;

            let begin = relaymsg::Begin::new("127.0.0.1", 1111, 0).unwrap().into();

            ctrl.send_fwd(StreamId::new(1), begin, Recognized::Yes, false)

                .await;

            rt.advance_until_stalled().await;

            // We should have a pending incoming stream

            let pending = incoming_streams.next().await.unwrap();

            // Reject the stream, and wait for the reactor to finish sending the END

            let end = relaymsg::End::new_misc();

            pending.reject(end.clone()).await.unwrap();

            rt.advance_until_stalled().await;

            // The END cell written to the Tor channel should be the same as

            // the one we sent above, in reject().

            let cell = ctrl.read_inbound();

            let actual_end = expect_cell!(cell, Relay, End);

            assert_eq!(end.reason(), actual_end.reason());

            // Sending another message on this stream results is flagged

            // as a proto violation

            let data = relaymsg::Data::new(b"no dice").unwrap().into();

            ctrl.send_fwd(StreamId::new(1), data, Recognized::Yes, false)

                .await;

            rt.advance_until_stalled().await;

            assert!(logs_contain("Stream protocol violation"));

            assert!(logs_contain(

                "Unexpected RelayCmd(DATA) message on unknown stream 1"

            ));

        });

    }

    #[traced_test]

    #[test]

    fn only_allow_begin_dir() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, mut incoming_streams) = ReactorTestCtrl::spawn_reactor(

                &rt,

                // The stream reactor will only accept BEGIN_DIR streams

                &[RelayCmd::BEGIN_DIR],

            )

            .await;

            rt.advance_until_stalled().await;

            // Directory streams should be allowed (because BEGIN_DIR is allowed)...

            let begin_dir = relaymsg::BeginDir::default().into();

            ctrl.send_fwd(StreamId::new(1), begin_dir, Recognized::Yes, false)

                .await;

            rt.advance_until_stalled().await;

            let pending_dir_stream = incoming_streams.next().await.unwrap();

            assert!(matches!(

                pending_dir_stream.request(),

                IncomingStreamRequest::BeginDir(_)

            ));

            let begin = relaymsg::Begin::new("127.0.0.1", 1111, 0).unwrap().into();

            ctrl.send_fwd(StreamId::new(2), begin, Recognized::Yes, false)

                .await;

            rt.advance_until_stalled().await;

            // ... but the exit stream is not

            assert!(logs_contain("stream reactor shut down"));

            assert!(logs_contain(

                "Stream protocol violation: Unexpected BEGIN on incoming stream circ_uniq_id=Circ 8.17"

            ));

            // The reactor won't create an IncomingStream,

            // because the stream request is rejected right away

            let mut noop_cx = Context::from_waker(Waker::noop());

            assert_eq!(

                incoming_streams.poll_next_unpin(&mut noop_cx).map(|_| ()),

                Poll::Pending

            );

        });

    }

    #[traced_test]

    #[test]

    fn resolve_stream() {

        tor_rtmock::MockRuntime::test_with_various(|rt| async move {

            let (mut ctrl, mut incoming_streams) =

                ReactorTestCtrl::spawn_reactor(&rt, &[RelayCmd::RESOLVE]).await;

            rt.advance_until_stalled().await;

            let resolve = relaymsg::Resolve::new("example.com");

            let resolve_sid = StreamId::new(1337);

            ctrl.send_fwd(resolve_sid, resolve.into(), Recognized::Yes, false)

                .await;

            rt.advance_until_stalled().await;

            // We should have a pending incoming stream

            let pending = incoming_streams.next().await.unwrap();

            let mut resolved = relaymsg::Resolved::new_empty();

            let resolved_val = relaymsg::ResolvedVal::Ip(IpAddr::from([1, 2, 3, 4]));

            resolved.add_answer(resolved_val.clone(), 1337);

            // We expect the client to receive this cell

            let expected_resolved = resolved.clone();

            // Respond with RESOLVED

            pending.resolve(resolved).await.unwrap();

            rt.advance_until_stalled().await;

            let (sid, resolved) = decode_relay_cell!(ctrl.read_inbound(), Resolved);

            // Make sure the RESOLVED cell sent towards the client

            // matches what we sent via the IncomingStream::resolve() call above

            assert_eq!(resolved.into_answers(), expected_resolved.into_answers());

            assert_eq!(sid, resolve_sid);

            assert!(logs_contain("Ending stream"));

        });

    }

}