You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: peer.rs
    path of file: ./repos/akula/src/sentry/devp2p
    
    the code of the file until where you have to start completion: use super::{ecies::ECIESStream, transport::Transport, types::*, util::pk2id};
use anyhow::{anyhow, bail, Context as _};
use bytes::{Buf, Bytes, BytesMut};
use derive_more::Display;
use enum_primitive_derive::Primitive;
use fastrlp::*;
use futures::{Sink, SinkExt};
use num_traits::*;
use secp256k1::{PublicKey, SecretKey, SECP256K1};
use std::{
    fmt::Debug,
    io,
    pin::Pin,
    task::{Context, Poll},
};
use tokio_stream::{Stream, StreamExt};
use tracing::*;

const MAX_PAYLOAD_SIZE: usize = 16 * 1024 * 1024;

/// RLPx disconnect reason.
#[derive(Clone, Copy, Debug, Display, Primitive)]
pub enum DisconnectReason {
    #[display(fmt = "disconnect requested")]
    DisconnectRequested = 0x00,
    #[display(fmt = "TCP sub-system error")]
    TcpSubsystemError = 0x01,
    #[display(fmt = "breach of protocol, e.g. a malformed message, bad RLP, ...")]
    ProtocolBreach = 0x02,
    #[display(fmt = "useless peer")]
    UselessPeer = 0x03,
    #[display(fmt = "too many peers")]
    TooManyPeers = 0x04,
    #[display(fmt = "already connected")]
    AlreadyConnected = 0x05,
    #[display(fmt = "incompatible P2P protocol version")]
    IncompatibleP2PProtocolVersion = 0x06,
    #[display(fmt = "null node identity received - this is automatically invalid")]
    NullNodeIdentity = 0x07,
    #[display(fmt = "client quitting")]
    ClientQuitting = 0x08,
    #[display(fmt = "unexpected identity in handshake")]
    UnexpectedHandshakeIdentity = 0x09,
    #[display(fmt = "identity is the same as this node (i.e. connected to itself)")]
    ConnectedToSelf = 0x0a,
    #[display(fmt = "ping timeout")]
    PingTimeout = 0x0b,
    #[display(fmt = "some other reason specific to a subprotocol")]
    SubprotocolSpecific = 0x10,
}

/// RLPx protocol versi
    
    fn start_send(self: Pin<&mut Self>, message: PeerMessage) -> Result<(), Self::Error> {
        let this = self.get_mut();

        if this.disconnected {
            return Err(io::Error::new(
                io::ErrorKind::BrokenPipe,
                "disconnection requested",
            ));
        }

        let (message_id, payload) = match message {
            PeerMessage::Disconnect(reason) => {
                this.disconnected = true;
                (
                    0x01,
                    fastrlp::encode_fixed_size(&reason.to_u8().unwrap())
                        .to_vec()
                        .into(),
                )
            }
            PeerMessage::Ping => {
                debug!("sending ping message");
                (0x02, Bytes::from_static(&[EMPTY_LIST_CODE]))
            }
            PeerMessage::Pong => {
                debug!("sending pong message");
                (0x03, Bytes::from_static(&[EMPTY_LIST_CODE]))
            }
            PeerMessage::Subprotocol(SubprotocolMessage { cap_name, message }) => {
                let Message { id, data } = message;
                let cap = *this
                    .shared_capabilities
                    .iter()
                    .find(|cap| cap.name == cap_name)
                    .unwrap_or_else(|| {
                        panic!(
                            "attempted to send payload of unsupported capability ({}/{}/{})",
                            cap_name.0,
                            id,
                            this.remote_id(),
                        )
                    });

                assert!(
                    id < cap.length,
                    "attempted to send payload with message id too big ({}/{}/{})",
                    cap_name.0,
                    id,
                    this.remote_id()
                );

                let mut message_id = 0x10;
                for scap in &this.shared_capabilities {
                    if scap == &cap {
                        break;
                    }

                    message_id += scap.length;
                }
                message_id += id;

                (message_id, data)
            }
        };

        let mut msg = BytesMut::with_capacity(2 + payload.len());
        message_id.encode(&mut msg);

        let mut buf = msg.split_off(msg.len());

        if payload.len() > MAX_PAYLOAD_SIZE {
            return Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                format!(
                    "payload size ({}) exceeds limit ({} bytes)",
                    payload.len(),
                    MAX_PAYLOAD_SIZE
                ),
            ));
        }

        buf.resize(snap::raw::max_compress_len(payload.len()), 0);

        let compressed_len = this.snappy.encoder.compress(&payload, &mut buf).unwrap();
        buf.truncate(compressed_len);

        msg.unsplit(buf);

        Pin::new(&mut this.stream).start_send(msg.freeze())?;

        Ok(())
    }