1 files changed, 63 insertions, 0 deletions
diff --git a/ntcp/dnat.go b/ntcp/dnat.go
new file mode 100644
index 0000000..1d47314
--- /dev/null
+++ b/ntcp/dnat.go
@@ -0,0 +1,63 @@
+// Copyright 2021 SNIX LLC sina@snix.ir
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License
+// version 2 as published by the Free Software Foundation.
+// This program 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.
+
+package ntcp
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+
+	"golang.org/x/sys/unix"
+)
+
+type sockOpt struct {
+	localAddr net.IP
+	localPort uint16
+}
+
+func newNfTab() *sockOpt { return &sockOpt{localAddr: make(net.IP, 16)} }
+
+func (p *sockOpt) HostString() string {
+	return fmt.Sprintf("%v:%d", p.localAddr.To4().String(), p.localPort)
+}
+
+func (p *sockOpt) PortNumber() uint16 {
+	return p.localPort
+}
+
+func (p *sockOpt) PortString() string {
+	return strconv.Itoa(int(p.localPort))
+}
+
+func (p *sockOpt) IPv4Address() net.IP {
+	return p.localAddr.To4()
+}
+
+func networkOpt(conn net.Conn) (*sockOpt, error) {
+	var nftab = newNfTab()
+	fd, err := conn.(*net.TCPConn).File()
+	if err != nil {
+		return nftab, err
+	}
+
+	defer fd.Close()
+
+	raddr, err := unix.GetsockoptIPv6Mreq(
+		int(fd.Fd()), unix.IPPROTO_IP, unix.SO_ORIGINAL_DST)
+	if err != nil {
+		return nftab, err
+	}
+
+	nftab.localAddr = net.IP(raddr.Multiaddr[4:8])
+	// convert big endian to little endian
+	nftab.localPort = uint16(raddr.Multiaddr[2])<<8 + uint16(raddr.Multiaddr[3])
+	return nftab, err
+}