Add support for kTLS

Reference: https://gitlab.com/go-extension/tls

common/ktls/ktls_close.go

@@ -0,0 +1,67 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && go1.25 && !without_badtls
+
+package ktls
+
+import (
+	"fmt"
+	"net"
+	"time"
+)
+
+func (c *Conn) Close() error {
+	if !c.kernelTx {
+		return c.Conn.Close()
+	}
+
+	// Interlock with Conn.Write above.
+	var x int32
+	for {
+		x = c.rawConn.ActiveCall.Load()
+		if x&1 != 0 {
+			return net.ErrClosed
+		}
+		if c.rawConn.ActiveCall.CompareAndSwap(x, x|1) {
+			break
+		}
+	}
+	if x != 0 {
+		// io.Writer and io.Closer should not be used concurrently.
+		// If Close is called while a Write is currently in-flight,
+		// interpret that as a sign that this Close is really just
+		// being used to break the Write and/or clean up resources and
+		// avoid sending the alertCloseNotify, which may block
+		// waiting on handshakeMutex or the c.out mutex.
+		return c.conn.Close()
+	}
+
+	var alertErr error
+	if c.rawConn.IsHandshakeComplete.Load() {
+		if err := c.closeNotify(); err != nil {
+			alertErr = fmt.Errorf("tls: failed to send closeNotify alert (but connection was closed anyway): %w", err)
+		}
+	}
+
+	if err := c.conn.Close(); err != nil {
+		return err
+	}
+	return alertErr
+}
+
+func (c *Conn) closeNotify() error {
+	c.rawConn.Out.Lock()
+	defer c.rawConn.Out.Unlock()
+
+	if !*c.rawConn.CloseNotifySent {
+		// Set a Write Deadline to prevent possibly blocking forever.
+		c.SetWriteDeadline(time.Now().Add(time.Second * 5))
+		*c.rawConn.CloseNotifyErr = c.sendAlertLocked(alertCloseNotify)
+		*c.rawConn.CloseNotifySent = true
+		// Any subsequent writes will fail.
+		c.SetWriteDeadline(time.Now())
+	}
+	return *c.rawConn.CloseNotifyErr
+}