Add tls fragment support

common/tlsfragment/wait_linux.go

@@ -0,0 +1,36 @@
+package tf
+
+import (
+	"context"
+	"syscall"
+	"time"
+
+	"github.com/sagernet/sing/common/control"
+
+	"golang.org/x/sys/unix"
+)
+
+func waitAck(ctx context.Context, conn syscall.Conn, fallbackDelay time.Duration) error {
+	return control.Conn(conn, func(fd uintptr) error {
+		start := time.Now()
+		for {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
+			tcpInfo, err := unix.GetsockoptTCPInfo(int(fd), unix.IPPROTO_TCP, unix.TCP_INFO)
+			if err != nil {
+				return err
+			}
+			if tcpInfo.Unacked == 0 {
+				if time.Since(start) <= 20*time.Millisecond {
+					// under transparent proxy
+					time.Sleep(fallbackDelay)
+				}
+				return nil
+			}
+			time.Sleep(10 * time.Millisecond)
+		}
+	})
+}