rusnel 0.5.0

use std::sync::atomic::{AtomicUsize, Ordering};

use anyhow::Result;
use quinn::{Connection, RecvStream, SendStream};
use tokio::{
    io::{AsyncWriteExt, BufReader},
    net::{TcpListener, TcpStream},
};
use tracing::{debug, debug_span, info, Instrument};

use crate::common::tunnel::client_send_remote_request;

use super::remote::RemoteRequest;

/// Per-direction copy buffer size. Larger than tokio::io::copy's default 8 KB
/// so each read/write through quinn batches ~32× more bytes per AEAD call and
/// per syscall, which is the dominant CPU cost on the data plane.
/// 256 KB is large enough to amortize the fixed overhead and small enough
/// to keep memory use bounded under many concurrent connections.
const TUNNEL_COPY_BUF: usize = 256 * 1024;

pub async fn tunnel_tcp_stream(
    tcp_stream: TcpStream,
    mut send_channel: SendStream,
    recv_channel: RecvStream,
) -> Result<()> {
    // Disable Nagle on the TCP leg of the tunnel. Tunneled traffic is opaque
    // to us, so coalescing small writes can deadlock for ~40ms against the
    // peer's delayed-ACK timer (classic Nagle/delayed-ACK interaction). All
    // tunneled TCP — forward, reverse, and SOCKS — flows through here, so
    // this single call covers every path.
    if let Err(e) = tcp_stream.set_nodelay(true) {
        debug!("set_nodelay failed: {}", e);
    }

    let (tcp_recv, mut tcp_send) = tcp_stream.into_split();

    // BufReader+copy_buf on both halves gives us a 256 KB transfer chunk
    // size end-to-end instead of the 8 KB hidden inside tokio::io::copy.
    // (We can't use copy_bidirectional here because quinn's bi-stream is
    // split into separate Send/Recv halves, not a single duplex.)
    //
    // We tried replacing the QUIC→TCP `BufReader` with `RecvStream::read_chunk`
    // + `write_all` to skip the intermediate copy ("single-copy data path").
    // On bulk WAN that's a small win, but on loopback the chunks quinn hands
    // back are often small (single QUIC frames) and the per-chunk syscall
    // overhead overwhelmed the savings — measured throughput dropped from
    // 763 MB/s to 458 MB/s in the iperf loopback profile. Keeping the
    // batched `BufReader` + `copy_buf` is strictly better today on every
    // workload we benchmark; revisit when quinn exposes a vectored read API
    // that returns several `Bytes` per await.
    let mut tcp_recv = BufReader::with_capacity(TUNNEL_COPY_BUF, tcp_recv);
    let mut quic_recv = BufReader::with_capacity(TUNNEL_COPY_BUF, recv_channel);

    let client_to_server = async {
        tokio::io::copy_buf(&mut tcp_recv, &mut send_channel).await?;
        send_channel.shutdown().await?;
        Ok::<(), anyhow::Error>(())
    };

    let server_to_client = async {
        tokio::io::copy_buf(&mut quic_recv, &mut tcp_send).await?;
        tcp_send.shutdown().await?;
        Ok::<(), anyhow::Error>(())
    };

    // tokio::join! (not try_join!) so that an error in one direction doesn't
    // cancel an in-flight copy in the other and silently lose buffered bytes
    // (#20 §3). The application has already half-closed appropriately.
    let (c2s, s2c) = tokio::join!(client_to_server, server_to_client);
    match (&c2s, &s2c) {
        (Ok(_), Ok(_)) => debug!("closed"),
        (Err(e), _) => debug!("client→server error: {}", e),
        (_, Err(e)) => debug!("server→client error: {}", e),
    }
    Ok(())
}

pub async fn tunnel_tcp_client(quic_connection: Connection, remote: RemoteRequest) -> Result<()> {
    // Use SocketAddr's Display so IPv6 literals come out bracketed
    // (`[::1]:8080`) — a manual `format!("{ip}:{port}")` on an IPv6
    // `IpAddr` produces `::1:8080`, which `TcpListener::bind` rejects.
    let local_addr = remote.local_socket_addr();
    let listener = TcpListener::bind(local_addr).await?;
    info!("listening on {}", local_addr);

    let conn_counter = AtomicUsize::new(0);

    loop {
        let (local_socket, addr) = listener.accept().await?;
        let conn_id = conn_counter.fetch_add(1, Ordering::Relaxed) + 1;
        let span = debug_span!("conn", id = conn_id, peer = %addr);

        let connection = quic_connection.clone();
        let remote = remote.clone();
        tokio::spawn(
            async move {
                debug!("open");
                let (mut send, mut recv) = connection.open_bi().await?;

                client_send_remote_request(&remote, &mut send, &mut recv).await?;

                tunnel_tcp_stream(local_socket, send, recv).await?;
                Ok::<(), anyhow::Error>(())
            }
            .instrument(span),
        );
    }
}

pub async fn tunnel_tcp_server(
    recv_channel: RecvStream,
    send_channel: SendStream,
    request: RemoteRequest,
) -> Result<()> {
    let remote_addr = request
        .remote_addr_string()
        .ok_or_else(|| anyhow::anyhow!("TCP server tunnel requires a host:port remote"))?;
    debug!("connecting to {}", remote_addr);
    let tcp_stream = TcpStream::connect(&remote_addr).await?;
    debug!("connected to {}", remote_addr);

    tunnel_tcp_stream(tcp_stream, send_channel, recv_channel).await?;

    Ok(())
}