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    use crate::codec::RecvError;
    use crate::error::Reason;
    use crate::frame::{Pseudo, StreamId};
    use crate::proto::Open;

    use http::{HeaderMap, Request, Response};

    use std::fmt;

    /// Either a Client or a Server
    pub(crate) trait Peer {
        /// Message type polled from the transport
        type Poll: fmt::Debug;
        const NAME: &'static str;

        fn r#dyn() -> Dyn;

        fn is_server() -> bool;

        fn convert_poll_message(
            pseudo: Pseudo,
            fields: HeaderMap,
            stream_id: StreamId,
        ) -> Result<Self::Poll, RecvError>;

        fn is_local_init(id: StreamId) -> bool {
            assert!(!id.is_zero());
            Self::is_server() == id.is_server_initiated()
        }
    }

    /// A dynamic representation of `Peer`.
    ///
    /// This is used internally to avoid incurring a generic on all internal types.
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub(crate) enum Dyn {
        Client,
        Server,
    }

    #[derive(Debug)]
    pub enum PollMessage {
        Client(Response<()>),
        Server(Request<()>),
    }

    // ===== impl Dyn =====

    impl Dyn {
        pub fn is_server(&self) -> bool {
            *self == Dyn::Server
        }

        pub fn is_local_init(&self, id: StreamId) -> bool {
            assert!(!id.is_zero());
            self.is_server() == id.is_server_initiated()
        }

        pub fn convert_poll_message(
            &self,
            pseudo: Pseudo,
            fields: HeaderMap,
            stream_id: StreamId,
        ) -> Result<PollMessage, RecvError> {
            if self.is_server() {
                crate::server::Peer::convert_poll_message(pseudo, fields, stream_id)
                    .map(PollMessage::Server)
            } else {
                crate::client::Peer::convert_poll_message(pseudo, fields, stream_id)
                    .map(PollMessage::Client)
            }
        }

        /// Returns true if the remote peer can initiate a stream with the given ID.
        pub fn ensure_can_open(&self, id: StreamId, mode: Open) -> Result<(), RecvError> {
            if self.is_server() {
                // Ensure that the ID is a valid client initiated ID
                if mode.is_push_promise() || !id.is_client_initiated() {
                    proto_err!(conn: "cannot open stream {:?} - not client initiated", id);
                    return Err(RecvError::Connection(Reason::PROTOCOL_ERROR));
                }

                Ok(())
            } else {
                // Ensure that the ID is a valid server initiated ID
                if !mode.is_push_promise() || !id.is_server_initiated() {
                    proto_err!(conn: "cannot open stream {:?} - not server initiated", id);
                    return Err(RecvError::Connection(Reason::PROTOCOL_ERROR));
                }

                Ok(())
            }
        }
    }