//! Socket-level options for TCP streams (keepalive, etc.).
//!
//! Uses `socket2::SockRef::from()` to borrow the raw fd without ownership transfer.

use std::io;
use std::time::Duration;
use tokio::net::TcpStream;

/// Apply TCP keepalive to a connected socket.
///
/// Enables SO_KEEPALIVE and sets the initial probe delay.
/// On Linux, also sets the interval between probes to the same value.
pub fn apply_keepalive(stream: &TcpStream, delay: Duration) -> io::Result<()> {
    let sock_ref = socket2::SockRef::from(stream);
    let ka = socket2::TcpKeepalive::new().with_time(delay);
    #[cfg(target_os = "linux")]
    let ka = ka.with_interval(delay);
    sock_ref.set_tcp_keepalive(&ka)
}