TCP fast open server side support.

Provide default and non_exhaustive for TcpSocketOptions to future proof
its changes.

Also fix an issue that TcpScoketOptions can't be used for IPv4 sockets
at all.

.bleep

@@ -1 +1 @@
-6047acc79584d167765d8a3a557df7d4d3ceac88
+2c9d4c55853235e908a1acd20454ebe7b979d246

pingora-core/src/listeners/l4.rs

@@ -25,6 +25,7 @@ use std::os::unix::net::UnixListener as StdUnixListener;
 use std::time::Duration;
 use tokio::net::TcpSocket;
 
+use crate::protocols::l4::ext::set_tcp_fastopen_backlog;
 use crate::protocols::l4::listener::Listener;
 pub use crate::protocols::l4::stream::Stream;
 use crate::server::ListenFds;
@@ -51,12 +52,16 @@ impl AsRef<str> for ServerAddress {
 }
 
 /// TCP socket configuration options.
-#[derive(Clone, Debug)]
+#[non_exhaustive]
+#[derive(Clone, Debug, Default)]
 pub struct TcpSocketOptions {
     /// IPV6_V6ONLY flag (if true, limit socket to IPv6 communication only).
     /// This is mostly useful when binding to `[::]`, which on most Unix distributions
     /// will bind to both IPv4 and IPv6 addresses by default.
     pub ipv6_only: bool,
+    /// Enable TCP fast open and set the backlog size of it.
+    /// See the [man page](https://man7.org/linux/man-pages/man7/tcp.7.html) for more information.
+    pub tcp_fastopen: Option<usize>,
     // TODO: allow configuring reuseaddr, backlog, etc. from here?
 }
 
@@ -121,10 +126,17 @@ fn apply_tcp_socket_options(sock: &TcpSocket, opt: Option<&TcpSocketOptions>) ->
     let Some(opt) = opt else {
         return Ok(());
     };
-    let socket_ref = socket2::SockRef::from(sock);
-    socket_ref
-        .set_only_v6(opt.ipv6_only)
-        .or_err(BindError, "failed to set IPV6_V6ONLY")
+    if opt.ipv6_only {
+        let socket_ref = socket2::SockRef::from(sock);
+        socket_ref
+            .set_only_v6(opt.ipv6_only)
+            .or_err(BindError, "failed to set IPV6_V6ONLY")?;
+    }
+
+    if let Some(backlog) = opt.tcp_fastopen {
+        set_tcp_fastopen_backlog(sock.as_raw_fd(), backlog)?;
+    }
+    Ok(())
 }
 
 fn from_raw_fd(address: &ServerAddress, fd: i32) -> Result<Listener> {
@@ -279,7 +291,10 @@ mod test {
 
     #[tokio::test]
     async fn test_listen_tcp_ipv6_only() {
-        let sock_opt = Some(TcpSocketOptions { ipv6_only: true });
+        let sock_opt = Some(TcpSocketOptions {
+            ipv6_only: true,
+            ..Default::default()
+        });
         let mut listener = ListenerEndpoint::new(ServerAddress::Tcp("[::]:7101".into(), sock_opt));
         listener.listen(None).await.unwrap();
         tokio::spawn(async move {

pingora-core/src/protocols/l4/ext.rs

@@ -240,6 +240,18 @@ pub fn set_tcp_fastopen_connect(_fd: RawFd) -> Result<()> {
     Ok(())
 }
 
+/// Enable server side TCP fast open.
+#[cfg(target_os = "linux")]
+pub fn set_tcp_fastopen_backlog(fd: RawFd, backlog: usize) -> Result<()> {
+    set_opt(fd, libc::IPPROTO_TCP, libc::TCP_FASTOPEN, backlog as c_int)
+        .or_err(ConnectError, "failed to set TCP_FASTOPEN")
+}
+
+#[cfg(not(target_os = "linux"))]
+pub fn set_tcp_fastopen_backlog(_fd: RawFd, _backlog: usize) -> Result<()> {
+    Ok(())
+}
+
 /// connect() to the given address while optionally binding to the specific source address.
 ///
 /// The `set_socket` callback can be used to tune the socket before `connect()` is called.

pingora/examples/server.rs

@@ -119,7 +119,9 @@ pub fn main() {
         .unwrap();
 
     let mut echo_service_http = service::echo::echo_service_http();
-    echo_service_http.add_tcp("0.0.0.0:6145");
+    let mut options = pingora::listeners::TcpSocketOptions::default();
+    options.tcp_fastopen = Some(10);
+    echo_service_http.add_tcp_with_settings("0.0.0.0:6145", options);
     echo_service_http.add_uds("/tmp/echo.sock", None);
 
     let dynamic_cert = DynamicCert::new(&cert_path, &key_path);