//! Type and code for handling a "half-closed" stream.

//!

//! A half-closed stream is one that we've sent an END on, but where

//! we might still receive some cells.

use crate::congestion::sendme::{cmd_counts_towards_windows, StreamRecvWindow};

use crate::stream::{AnyCmdChecker, StreamSendFlowControl, StreamStatus};

use crate::{Error, Result};

use tor_cell::relaycell::{RelayCmd, UnparsedRelayMsg};

/// Type to track state of half-closed streams.

///

/// A half-closed stream is one where we've sent an END cell, but where

/// the other side might still send us data.

///

/// We need to track these streams instead of forgetting about them entirely,

/// since otherwise we'd be vulnerable to a class of "DropMark" attacks;

/// see <https://gitlab.torproject.org/tpo/core/tor/-/issues/25573>.

#[derive(Debug)]

pub(super) struct HalfStream {

    /// Send flow control for this stream. Used to detect whether we get too

    /// many SENDME cells.

    send_flow_control: StreamSendFlowControl,

    /// Receive window for this stream. Used to detect whether we get too

    /// many data cells.

    recvw: StreamRecvWindow,

    /// Object to tell us which cells to accept on this stream.

    cmd_checker: AnyCmdChecker,

}

impl HalfStream {

    /// Create a new half-closed stream.

    /// Process an incoming message and adjust this HalfStream accordingly.

    /// Give an error if the protocol has been violated.

    ///

    /// The caller must handle END cells; it is an internal error to pass

    /// END cells to this method.

    /// no ends here.

        use tor_cell::relaycell::msg::Sendme;

        use StreamStatus::*;

            // We handle SENDME separately, and don't give it to the checker.

}

#[cfg(test)]

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_duration_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

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

    use super::*;

    use crate::{

        congestion::sendme::{StreamRecvWindow, StreamSendWindow},

        stream::DataCmdChecker,

    };

    use rand::{CryptoRng, Rng};

    use tor_basic_utils::test_rng::testing_rng;

    use tor_cell::relaycell::{

        msg::{self, AnyRelayMsg},

        AnyRelayMsgOuter, RelayCellFormat, StreamId,

    };

    fn to_unparsed<R: Rng + CryptoRng>(rng: &mut R, val: AnyRelayMsg) -> UnparsedRelayMsg {

        UnparsedRelayMsg::from_singleton_body(

            RelayCellFormat::V0,

            AnyRelayMsgOuter::new(StreamId::new(77), val)

                .encode(RelayCellFormat::V0, rng)

                .expect("encoding failed"),

        )

        .unwrap()

    }

    #[test]

    fn halfstream_sendme() {

        let mut rng = testing_rng();

        // Stream level SENDMEs are not authenticated and so the only way to make sure we were not

        // expecting one is if the window busts its maximum.

        //

        // Starting the window at 450, the first SENDME will increment it to 500 (the maximum)

        // meaning that the second SENDME will bust that and we'll noticed that it was unexpected.

        let sendw = StreamSendWindow::new(450);

        let mut hs = HalfStream::new(

            StreamSendFlowControl::new_window_based(sendw),

            StreamRecvWindow::new(20),

            DataCmdChecker::new_any(),

        );

        // one sendme is fine

        let m = msg::Sendme::new_empty();

        assert!(hs

            .handle_msg(to_unparsed(&mut rng, m.clone().into()))

            .is_ok());

        // but no more were expected!

        let e = hs

            .handle_msg(to_unparsed(&mut rng, m.into()))

            .err()

            .unwrap();

        assert_eq!(

            format!("{}", e),

            "Circuit protocol violation: Unexpected stream SENDME"

        );

    }

    fn hs_new() -> HalfStream {

        HalfStream::new(

            StreamSendFlowControl::new_window_based(StreamSendWindow::new(20)),

            StreamRecvWindow::new(20),

            DataCmdChecker::new_any(),

        )

    }

    #[test]

    fn halfstream_data() {

        let mut hs = hs_new();

        let mut rng = testing_rng();

        // we didn't give a connected cell during setup, so do it now.

        hs.handle_msg(to_unparsed(&mut rng, msg::Connected::new_empty().into()))

            .unwrap();

        // 20 data cells are okay.

        let m = msg::Data::new(&b"this offer is unrepeatable"[..]).unwrap();

        for _ in 0_u8..20 {

            assert!(hs

                .handle_msg(to_unparsed(&mut rng, m.clone().into()))

                .is_ok());

        }

        // But one more is a protocol violation.

        let e = hs

            .handle_msg(to_unparsed(&mut rng, m.into()))

            .err()

            .unwrap();

        assert_eq!(

            format!("{}", e),

            "Circuit protocol violation: Received a data cell in violation of a window"

        );

    }

    #[test]

    fn halfstream_connected() {

        let mut hs = hs_new();

        let mut rng = testing_rng();

        // We were told to accept a connected, so we'll accept one

        // and no more.

        let m = msg::Connected::new_empty();

        assert!(hs

            .handle_msg(to_unparsed(&mut rng, m.clone().into()))

            .is_ok());

        assert!(hs

            .handle_msg(to_unparsed(&mut rng, m.clone().into()))

            .is_err());

        // If we try that again _after getting a connected_,

        // accept any.

        let mut cmd_checker = DataCmdChecker::new_any();

        {

            cmd_checker

                .check_msg(&to_unparsed(&mut rng, msg::Connected::new_empty().into()))

                .unwrap();

        }

        let mut hs = HalfStream::new(

            StreamSendFlowControl::new_window_based(StreamSendWindow::new(20)),

            StreamRecvWindow::new(20),

            cmd_checker,

        );

        let e = hs

            .handle_msg(to_unparsed(&mut rng, m.into()))

            .err()

            .unwrap();

        assert_eq!(

            format!("{}", e),

            "Stream protocol violation: Received CONNECTED twice on a stream."

        );

    }

    #[test]

    fn halfstream_other() {

        let mut hs = hs_new();

        let mut rng = testing_rng();

        let m = msg::Extended2::new(Vec::new());

        let e = hs

            .handle_msg(to_unparsed(&mut rng, m.into()))

            .err()

            .unwrap();

        assert_eq!(

            format!("{}", e),

            "Stream protocol violation: Unexpected EXTENDED2 on a data stream!"

        );

    }

}