Enum Tunnel 

pub enum Tunnel {
    Bidi {
        client: Box<dyn AsyncReadWrite + Send>,
        upstream: Box<dyn AsyncReadWrite + Send>,
        close_reason_tx: Option<Sender<CloseReason>>,
    },
    SpliceBidi {
        client: TcpStream,
        upstream: TcpStream,
        close_reason_tx: Option<Sender<CloseReason>>,
    },
    Udp(UdpTunnel),
}

Bridge between the executor’s ByteTunnel arm and a fetch’s chosen transport. Bidi is the stream-pair shape that tokio::io::copy_bidirectional consumes — covers TCP forward, TLS passthrough, and the H1 WebSocket post-upgrade path. Udp is the session-driven shape: the fetch has already spawned the per-5-tuple forwarder task; the executor’s role degenerates to awaiting join so ConnContext cleanup runs at the right moment.

See spec/crates/engine.md § udp_dispatch for the UDP session lifecycle and spec/crates/engine.md § Concrete fetches for the TCP arm.

Variants

Bidi

Fields

client: Box<dyn AsyncReadWrite + Send>

upstream: Box<dyn AsyncReadWrite + Send>

close_reason_tx: Option<Sender<CloseReason>>

SpliceBidi

Zero-copy TCP↔TCP forward suitable for splice(2) on Linux. Both halves are bare tokio::net::TcpStreams — no TLS, no peek prelude, no virtual sockets — so the kernel can move bytes through a pipe without entering user space. The engine emits this variant from L4ForwardFetch when the inbound L4Conn::Tcp and the dialed upstream are both raw TCP, and drive_byte_tunnel routes Linux platforms through tokio-splice2; non-Linux platforms fall back to the same tokio::io::copy_bidirectional driver as Self::Bidi.

Fields

client: TcpStream

upstream: TcpStream

close_reason_tx: Option<Sender<CloseReason>>

Udp(UdpTunnel)