From 0af87f7461a3f5caefe3f2bfd9dba136aa060892 Mon Sep 17 00:00:00 2001
From: gVisor bot <gvisor-bot@google.com>
Date: Thu, 13 Dec 2018 19:30:43 -0800
Subject: [PATCH] Feature: FreeBSD compatibility patch (#63)

---
 proxy/redir/tcp_freebsd.go | 52 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 proxy/redir/tcp_freebsd.go

diff --git a/proxy/redir/tcp_freebsd.go b/proxy/redir/tcp_freebsd.go
new file mode 100644
index 00000000..f0ceb36c
--- /dev/null
+++ b/proxy/redir/tcp_freebsd.go
@@ -0,0 +1,52 @@
+package redir
+
+import (
+	"errors"
+	"net"
+	"syscall"
+	"unsafe"
+
+	"github.com/Dreamacro/go-shadowsocks2/socks"
+)
+
+const (
+	SO_ORIGINAL_DST      = 80 // from linux/include/uapi/linux/netfilter_ipv4.h
+	IP6T_SO_ORIGINAL_DST = 80 // from linux/include/uapi/linux/netfilter_ipv6/ip6_tables.h
+)
+
+func parserPacket(conn net.Conn) (socks.Addr, error) {
+	c, ok := conn.(*net.TCPConn)
+	if !ok {
+		return nil, errors.New("only work with TCP connection")
+	}
+
+	rc, err := c.SyscallConn()
+	if err != nil {
+		return nil, err
+	}
+
+	var addr socks.Addr
+
+	rc.Control(func(fd uintptr) {
+		addr, err = getorigdst(fd)
+	})
+
+	return addr, err
+}
+
+// Call getorigdst() from linux/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
+func getorigdst(fd uintptr) (socks.Addr, error) {
+	raw := syscall.RawSockaddrInet4{}
+	siz := unsafe.Sizeof(raw)
+	_, _, err := syscall.Syscall6(syscall.SYS_GETSOCKOPT, fd, syscall.IPPROTO_IP, SO_ORIGINAL_DST, uintptr(unsafe.Pointer(&raw)), uintptr(unsafe.Pointer(&siz)), 0);
+	if err != 0 {
+		return nil, err
+	}
+
+	addr := make([]byte, 1+net.IPv4len+2)
+	addr[0] = socks.AtypIPv4
+	copy(addr[1:1+net.IPv4len], raw.Addr[:])
+	port := (*[2]byte)(unsafe.Pointer(&raw.Port)) // big-endian
+	addr[1+net.IPv4len], addr[1+net.IPv4len+1] = port[0], port[1]
+	return addr, nil
+}