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    480

    use super::*;

    use std::task::{Context, Waker};
    use std::time::Instant;
    use std::usize;

    /// Tracks Stream related state
    ///
    /// # Reference counting
    ///
    /// There can be a number of outstanding handles to a single Stream. These are
    /// tracked using reference counting. The `ref_count` field represents the
    /// number of outstanding userspace handles that can reach this stream.
    ///
    /// It's important to note that when the stream is placed in an internal queue
    /// (such as an accept queue), this is **not** tracked by a reference count.
    /// Thus, `ref_count` can be zero and the stream still has to be kept around.
    #[derive(Debug)]
    pub(super) struct Stream {
        /// The h2 stream identifier
        pub id: StreamId,

        /// Current state of the stream
        pub state: State,

        /// Set to `true` when the stream is counted against the connection's max
        /// concurrent streams.
        pub is_counted: bool,

        /// Number of outstanding handles pointing to this stream
        pub ref_count: usize,

        // ===== Fields related to sending =====
        /// Next node in the accept linked list
        pub next_pending_send: Option<store::Key>,

        /// Set to true when the stream is pending accept
        pub is_pending_send: bool,

        /// Send data flow control
        pub send_flow: FlowControl,

        /// Amount of send capacity that has been requested, but not yet allocated.
        pub requested_send_capacity: WindowSize,

        /// Amount of data buffered at the prioritization layer.
        /// TODO: Technically this could be greater than the window size...
        pub buffered_send_data: WindowSize,

        /// Task tracking additional send capacity (i.e. window updates).
        send_task: Option<Waker>,

        /// Frames pending for this stream being sent to the socket
        pub pending_send: buffer::Deque,

        /// Next node in the linked list of streams waiting for additional
        /// connection level capacity.
        pub next_pending_send_capacity: Option<store::Key>,

        /// True if the stream is waiting for outbound connection capacity
        pub is_pending_send_capacity: bool,

        /// Set to true when the send capacity has been incremented
        pub send_capacity_inc: bool,

        /// Next node in the open linked list
        pub next_open: Option<store::Key>,

        /// Set to true when the stream is pending to be opened
        pub is_pending_open: bool,

        /// Set to true when a push is pending for this stream
        pub is_pending_push: bool,

        // ===== Fields related to receiving =====
        /// Next node in the accept linked list
        pub next_pending_accept: Option<store::Key>,

        /// Set to true when the stream is pending accept
        pub is_pending_accept: bool,

        /// Receive data flow control
        pub recv_flow: FlowControl,

        pub in_flight_recv_data: WindowSize,

        /// Next node in the linked list of streams waiting to send window updates.
        pub next_window_update: Option<store::Key>,

        /// True if the stream is waiting to send a window update
        pub is_pending_window_update: bool,

        /// The time when this stream may have been locally reset.
        pub reset_at: Option<Instant>,

        /// Next node in list of reset streams that should expire eventually
        pub next_reset_expire: Option<store::Key>,

        /// Frames pending for this stream to read
        pub pending_recv: buffer::Deque,

        /// Task tracking receiving frames
        pub recv_task: Option<Waker>,

        /// The stream's pending push promises
        pub pending_push_promises: store::Queue<NextAccept>,

        /// Validate content-length headers
        pub content_length: ContentLength,
    }

    /// State related to validating a stream's content-length
    #[derive(Debug)]
    pub enum ContentLength {
        Omitted,
        Head,
        Remaining(u64),
    }

    #[derive(Debug)]
    pub(super) struct NextAccept;

    #[derive(Debug)]
    pub(super) struct NextSend;

    #[derive(Debug)]
    pub(super) struct NextSendCapacity;

    #[derive(Debug)]
    pub(super) struct NextWindowUpdate;

    #[derive(Debug)]
    pub(super) struct NextOpen;

    #[derive(Debug)]
    pub(super) struct NextResetExpire;

    impl Stream {
        pub fn new(id: StreamId, init_send_window: WindowSize, init_recv_window: WindowSize) -> Stream {
            let mut send_flow = FlowControl::new();
            let mut recv_flow = FlowControl::new();

            recv_flow
                .inc_window(init_recv_window)
                .expect("invalid initial receive window");
            recv_flow.assign_capacity(init_recv_window);

            send_flow
                .inc_window(init_send_window)
                .expect("invalid initial send window size");

            Stream {
                id,
                state: State::default(),
                ref_count: 0,
                is_counted: false,

                // ===== Fields related to sending =====
                next_pending_send: None,
                is_pending_send: false,
                send_flow,
                requested_send_capacity: 0,
                buffered_send_data: 0,
                send_task: None,
                pending_send: buffer::Deque::new(),
                is_pending_send_capacity: false,
                next_pending_send_capacity: None,
                send_capacity_inc: false,
                is_pending_open: false,
                next_open: None,
                is_pending_push: false,

                // ===== Fields related to receiving =====
                next_pending_accept: None,
                is_pending_accept: false,
                recv_flow,
                in_flight_recv_data: 0,
                next_window_update: None,
                is_pending_window_update: false,
                reset_at: None,
                next_reset_expire: None,
                pending_recv: buffer::Deque::new(),
                recv_task: None,
                pending_push_promises: store::Queue::new(),
                content_length: ContentLength::Omitted,
            }
        }

        /// Increment the stream's ref count
        pub fn ref_inc(&mut self) {
            assert!(self.ref_count < usize::MAX);
            self.ref_count += 1;
        }

        /// Decrements the stream's ref count
        pub fn ref_dec(&mut self) {
            assert!(self.ref_count > 0);
            self.ref_count -= 1;
        }

        /// Returns true if stream is currently being held for some time because of
        /// a local reset.
        pub fn is_pending_reset_expiration(&self) -> bool {
            self.reset_at.is_some()
        }

        /// Returns true if frames for this stream are ready to be sent over the wire
        pub fn is_send_ready(&self) -> bool {
            // Why do we check pending_open?
            //
            // We allow users to call send_request() which schedules a stream to be pending_open
            // if there is no room according to the concurrency limit (max_send_streams), and we
            // also allow data to be buffered for send with send_data() if there is no capacity for
            // the stream to send the data, which attempts to place the stream in pending_send.
            // If the stream is not open, we don't want the stream to be scheduled for
            // execution (pending_send). Note that if the stream is in pending_open, it will be
            // pushed to pending_send when there is room for an open stream.
            //
            // In pending_push we track whether a PushPromise still needs to be sent
            // from a different stream before we can start sending frames on this one.
            // This is different from the "open" check because reserved streams don't count
            // toward the concurrency limit.
            // See https://httpwg.org/specs/rfc7540.html#rfc.section.5.1.2
            !self.is_pending_open && !self.is_pending_push
        }

        /// Returns true if the stream is closed
        pub fn is_closed(&self) -> bool {
            // The state has fully transitioned to closed.
            self.state.is_closed() &&
                // Because outbound frames transition the stream state before being
                // buffered, we have to ensure that all frames have been flushed.
                self.pending_send.is_empty() &&
                // Sometimes large data frames are sent out in chunks. After a chunk
                // of the frame is sent, the remainder is pushed back onto the send
                // queue to be rescheduled.
                //
                // Checking for additional buffered data lets us catch this case.
                self.buffered_send_data == 0
        }

        /// Returns true if the stream is no longer in use
        pub fn is_released(&self) -> bool {
            // The stream is closed and fully flushed
            self.is_closed() &&
                // There are no more outstanding references to the stream
                self.ref_count == 0 &&
                // The stream is not in any queue
                !self.is_pending_send && !self.is_pending_send_capacity &&
                !self.is_pending_accept && !self.is_pending_window_update &&
                !self.is_pending_open && !self.reset_at.is_some()
        }

        /// Returns true when the consumer of the stream has dropped all handles
        /// (indicating no further interest in the stream) and the stream state is
        /// not actually closed.
        ///
        /// In this case, a reset should be sent.
        pub fn is_canceled_interest(&self) -> bool {
            self.ref_count == 0 && !self.state.is_closed()
        }

        pub fn assign_capacity(&mut self, capacity: WindowSize) {
            debug_assert!(capacity > 0);
            self.send_capacity_inc = true;
            self.send_flow.assign_capacity(capacity);

            tracing::trace!(
                "  assigned capacity to stream; available={}; buffered={}; id={:?}",
                self.send_flow.available(),
                self.buffered_send_data,
                self.id
            );

            // Only notify if the capacity exceeds the amount of buffered data
            if self.send_flow.available() > self.buffered_send_data {
                tracing::trace!("  notifying task");
                self.notify_send();
            }
        }

        /// Returns `Err` when the decrement cannot be completed due to overflow.
        pub fn dec_content_length(&mut self, len: usize) -> Result<(), ()> {
            match self.content_length {
                ContentLength::Remaining(ref mut rem) => match rem.checked_sub(len as u64) {
                    Some(val) => *rem = val,
                    None => return Err(()),
                },
                ContentLength::Head => {
                    if len != 0 {
                        return Err(());
                    }
                }
                _ => {}
            }

            Ok(())
        }

        pub fn ensure_content_length_zero(&self) -> Result<(), ()> {
            match self.content_length {
                ContentLength::Remaining(0) => Ok(()),
                ContentLength::Remaining(_) => Err(()),
                _ => Ok(()),
            }
        }

        pub fn notify_send(&mut self) {
            if let Some(task) = self.send_task.take() {
                task.wake();
            }
        }

        pub fn wait_send(&mut self, cx: &Context) {
            self.send_task = Some(cx.waker().clone());
        }

        pub fn notify_recv(&mut self) {
            if let Some(task) = self.recv_task.take() {
                task.wake();
            }
        }
    }

    impl store::Next for NextAccept {
        fn next(stream: &Stream) -> Option<store::Key> {
            stream.next_pending_accept
        }

        fn set_next(stream: &mut Stream, key: Option<store::Key>) {
            stream.next_pending_accept = key;
        }

        fn take_next(stream: &mut Stream) -> Option<store::Key> {
            stream.next_pending_accept.take()
        }

        fn is_queued(stream: &Stream) -> bool {
            stream.is_pending_accept
        }

        fn set_queued(stream: &mut Stream, val: bool) {
            stream.is_pending_accept = val;
        }
    }

    impl store::Next for NextSend {
        fn next(stream: &Stream) -> Option<store::Key> {
            stream.next_pending_send
        }

        fn set_next(stream: &mut Stream, key: Option<store::Key>) {
            stream.next_pending_send = key;
        }

        fn take_next(stream: &mut Stream) -> Option<store::Key> {
            stream.next_pending_send.take()
        }

        fn is_queued(stream: &Stream) -> bool {
            stream.is_pending_send
        }

        fn set_queued(stream: &mut Stream, val: bool) {
            if val {
                // ensure that stream is not queued for being opened
                // if it's being put into queue for sending data
                debug_assert_eq!(stream.is_pending_open, false);
            }
            stream.is_pending_send = val;
        }
    }

    impl store::Next for NextSendCapacity {
        fn next(stream: &Stream) -> Option<store::Key> {
            stream.next_pending_send_capacity
        }

        fn set_next(stream: &mut Stream, key: Option<store::Key>) {
            stream.next_pending_send_capacity = key;
        }

        fn take_next(stream: &mut Stream) -> Option<store::Key> {
            stream.next_pending_send_capacity.take()
        }

        fn is_queued(stream: &Stream) -> bool {
            stream.is_pending_send_capacity
        }

        fn set_queued(stream: &mut Stream, val: bool) {
            stream.is_pending_send_capacity = val;
        }
    }

    impl store::Next for NextWindowUpdate {
        fn next(stream: &Stream) -> Option<store::Key> {
            stream.next_window_update
        }

        fn set_next(stream: &mut Stream, key: Option<store::Key>) {
            stream.next_window_update = key;
        }

        fn take_next(stream: &mut Stream) -> Option<store::Key> {
            stream.next_window_update.take()
        }

        fn is_queued(stream: &Stream) -> bool {
            stream.is_pending_window_update
        }

        fn set_queued(stream: &mut Stream, val: bool) {
            stream.is_pending_window_update = val;
        }
    }

    impl store::Next for NextOpen {
        fn next(stream: &Stream) -> Option<store::Key> {
            stream.next_open
        }

        fn set_next(stream: &mut Stream, key: Option<store::Key>) {
            stream.next_open = key;
        }

        fn take_next(stream: &mut Stream) -> Option<store::Key> {
            stream.next_open.take()
        }

        fn is_queued(stream: &Stream) -> bool {
            stream.is_pending_open
        }

        fn set_queued(stream: &mut Stream, val: bool) {
            if val {
                // ensure that stream is not queued for being sent
                // if it's being put into queue for opening the stream
                debug_assert_eq!(stream.is_pending_send, false);
            }
            stream.is_pending_open = val;
        }
    }

    impl store::Next for NextResetExpire {
        fn next(stream: &Stream) -> Option<store::Key> {
            stream.next_reset_expire
        }

        fn set_next(stream: &mut Stream, key: Option<store::Key>) {
            stream.next_reset_expire = key;
        }

        fn take_next(stream: &mut Stream) -> Option<store::Key> {
            stream.next_reset_expire.take()
        }

        fn is_queued(stream: &Stream) -> bool {
            stream.reset_at.is_some()
        }

        fn set_queued(stream: &mut Stream, val: bool) {
            if val {
                stream.reset_at = Some(Instant::now());
            } else {
                stream.reset_at = None;
            }
        }
    }

    // ===== impl ContentLength =====

    impl ContentLength {
        pub fn is_head(&self) -> bool {
            match *self {
                ContentLength::Head => true,
                _ => false,
            }
        }
    }