//! 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::Result;
use crate::stream::cmdcheck::{AnyCmdChecker, StreamStatus};
use crate::stream::flow_ctrl::state::{HalfStreamFlowCtrl, HalfStreamFlowCtrlHooks};
use tor_cell::relaycell::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(crate) struct HalfStream {
    /// Flow control for this stream.
    ///
    /// Used to process incoming flow control messages (SENDME, XON, etc).
    flow_control: HalfStreamFlowCtrl,
    /// Object to tell us which cells to accept on this stream.
    cmd_checker: AnyCmdChecker,
}

impl HalfStream {
    /// Create a new half-closed stream.
    pub(crate) fn new(flow_control: HalfStreamFlowCtrl, cmd_checker: AnyCmdChecker) -> Self {
        HalfStream {
            flow_control,
            cmd_checker,
        }
    }

    /// 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.
    pub(crate) fn handle_msg(&mut self, msg: UnparsedRelayMsg) -> Result<StreamStatus> {
        use StreamStatus::*;

        let Some(msg) = self.flow_control.handle_incoming_msg(msg)? else {
            // The flow control code consumed the message,
            // which means that it was a flow control message.
            // We don't give flow control messages to the checker below.
            return Ok(Open);
        };

        let status = self.cmd_checker.check_msg(&msg)?;
        self.cmd_checker.consume_checked_msg(msg)?;
        Ok(status)
    }
}

#[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_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::stream::RECV_WINDOW_INIT;
    use crate::stream::flow_ctrl::state::StreamFlowCtrl;
    use crate::{client::stream::OutboundDataCmdChecker, congestion::sendme::StreamSendWindow};
    use rand::{CryptoRng, Rng};
    use tor_basic_utils::test_rng::testing_rng;
    use tor_cell::relaycell::{
        AnyRelayMsgOuter, RelayCellFormat, StreamId,
        msg::{self, AnyRelayMsg},
    };

    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(
            StreamFlowCtrl::new_window(sendw).half_stream(),
            OutboundDataCmdChecker::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(
            StreamFlowCtrl::new_window(StreamSendWindow::new(20)).half_stream(),
            OutboundDataCmdChecker::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();

        // `RECV_WINDOW_INIT` (500) data cells are okay.
        let m = msg::Data::new(&b"this offer is unrepeatable"[..]).unwrap();
        for _ in 0_u16..RECV_WINDOW_INIT {
            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 = OutboundDataCmdChecker::new_any();
        {
            cmd_checker
                .check_msg(&to_unparsed(&mut rng, msg::Connected::new_empty().into()))
                .unwrap();
        }
        let mut hs = HalfStream::new(
            StreamFlowCtrl::new_window(StreamSendWindow::new(20)).half_stream(),
            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!"
        );
    }
}
