1 files changed, 51 insertions, 0 deletions
diff --git a/l4s/unix.go b/l4s/unix.go
new file mode 100644
index 0000000..cfaf43c
--- /dev/null
+++ b/l4s/unix.go
@@ -0,0 +1,51 @@
+//go:build linux
+// +build linux
+
+/*
+ * This file is part of Go Responsiveness.
+ *
+ * Go Responsiveness is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software Foundation,
+ * either version 2 of the License, or (at your option) any later version.
+ * Go Responsiveness is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE. See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with Go Responsiveness. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package l4s
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net"
+	"syscall"
+)
+
+func SetL4S(conn net.Conn, algorithm *string) error {
+	if algorithm == nil {
+		panic("Attempting to set L4S congestion control without specifying a congestion control algorithm.")
+	}
+	tlsConn, ok := conn.(*tls.Conn)
+	if !ok {
+		return fmt.Errorf("when setting L4S congestion control algorithm, outermost connection is not a TLS connection")
+	}
+	tcpConn, ok := tlsConn.NetConn().(*net.TCPConn)
+	if !ok {
+		return fmt.Errorf("when setting L4S congestion control algorithm, could not get the underlying IP connection")
+	}
+	rawConn, err := tcpConn.SyscallConn()
+	if err != nil {
+		return fmt.Errorf("when setting L4S congestion control algorithm, could not get the underlying raw connection")
+	}
+	var sockoptError error = nil
+	rawConn.Control(func(fd uintptr) {
+		sockoptError = syscall.SetsockoptString(int(fd), syscall.IPPROTO_TCP, syscall.TCP_CONGESTION, *algorithm)
+	})
+	if sockoptError != nil {
+		return fmt.Errorf("when setting L4S congestion control algorithm, could not set the algorithm to %v: %v", *algorithm, sockoptError.Error())
+	}
+	return nil
+}