From 6a5d0e2bcd1fe64b48ac462ffff0a31154f1050f Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Mon, 11 Jun 2018 19:04:38 +0200
Subject: Support IPv6-less kernels

---
 conn_default.go | 89 ++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 60 insertions(+), 29 deletions(-)

(limited to 'conn_default.go')

diff --git a/conn_default.go b/conn_default.go
index 14ed56c..92135cb 100644
--- a/conn_default.go
+++ b/conn_default.go
@@ -11,7 +11,9 @@ package main
 import (
 	"golang.org/x/sys/unix"
 	"net"
+	"os"
 	"runtime"
+	"syscall"
 )
 
 /* This code is meant to be a temporary solution
@@ -87,6 +89,18 @@ func listenNet(network string, port int) (*net.UDPConn, int, error) {
 	return conn, uaddr.Port, nil
 }
 
+func extractErrno(err error) error {
+	opErr, ok := err.(*net.OpError)
+	if !ok {
+		return nil
+	}
+	syscallErr, ok := opErr.Err.(*os.SyscallError)
+	if !ok {
+		return nil
+	}
+	return syscallErr.Err
+}
+
 func CreateBind(uport uint16, device *Device) (Bind, uint16, error) {
 	var err error
 	var bind NativeBind
@@ -94,13 +108,15 @@ func CreateBind(uport uint16, device *Device) (Bind, uint16, error) {
 	port := int(uport)
 
 	bind.ipv4, port, err = listenNet("udp4", port)
-	if err != nil {
+	if err != nil && extractErrno(err) != syscall.EAFNOSUPPORT {
 		return nil, 0, err
 	}
 
 	bind.ipv6, port, err = listenNet("udp6", port)
-	if err != nil {
+	if err != nil && extractErrno(err) != syscall.EAFNOSUPPORT {
+		return nil, 0, err
 		bind.ipv4.Close()
+		bind.ipv4 = nil
 		return nil, 0, err
 	}
 
@@ -108,8 +124,13 @@ func CreateBind(uport uint16, device *Device) (Bind, uint16, error) {
 }
 
 func (bind *NativeBind) Close() error {
-	err1 := bind.ipv4.Close()
-	err2 := bind.ipv6.Close()
+	var err1, err2 error
+	if bind.ipv4 != nil {
+		err1 = bind.ipv4.Close()
+	}
+	if bind.ipv6 != nil {
+		err2 = bind.ipv6.Close()
+	}
 	if err1 != nil {
 		return err1
 	}
@@ -117,6 +138,9 @@ func (bind *NativeBind) Close() error {
 }
 
 func (bind *NativeBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
+	if bind.ipv4 == nil {
+		return 0, nil, syscall.EAFNOSUPPORT
+	}
 	n, endpoint, err := bind.ipv4.ReadFromUDP(buff)
 	if endpoint != nil {
 		endpoint.IP = endpoint.IP.To4()
@@ -125,6 +149,9 @@ func (bind *NativeBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
 }
 
 func (bind *NativeBind) ReceiveIPv6(buff []byte) (int, Endpoint, error) {
+	if bind.ipv6 == nil {
+		return 0, nil, syscall.EAFNOSUPPORT
+	}
 	n, endpoint, err := bind.ipv6.ReadFromUDP(buff)
 	return n, (*NativeEndpoint)(endpoint), err
 }
@@ -133,8 +160,14 @@ func (bind *NativeBind) Send(buff []byte, endpoint Endpoint) error {
 	var err error
 	nend := endpoint.(*NativeEndpoint)
 	if nend.IP.To4() != nil {
+		if bind.ipv4 == nil {
+			return syscall.EAFNOSUPPORT
+		}
 		_, err = bind.ipv4.WriteToUDP(buff, (*net.UDPAddr)(nend))
 	} else {
+		if bind.ipv6 == nil {
+			return syscall.EAFNOSUPPORT
+		}
 		_, err = bind.ipv6.WriteToUDP(buff, (*net.UDPAddr)(nend))
 	}
 	return err
@@ -157,31 +190,29 @@ func (bind *NativeBind) SetMark(mark uint32) error {
 	if fwmarkIoctl == 0 {
 		return nil
 	}
-	fd4, err1 := bind.ipv4.SyscallConn()
-	fd6, err2 := bind.ipv6.SyscallConn()
-	if err1 != nil {
-		return err1
-	}
-	if err2 != nil {
-		return err2
-	}
-	err3 := fd4.Control(func(fd uintptr) {
-		err1 = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, fwmarkIoctl, int(mark))
-	})
-	err4 := fd6.Control(func(fd uintptr) {
-		err2 = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, fwmarkIoctl, int(mark))
-	})
-	if err1 != nil {
-		return err1
-	}
-	if err2 != nil {
-		return err2
-	}
-	if err3 != nil {
-		return err3
-	}
-	if err4 != nil {
-		return err4
+	if bind.ipv4 != nil {
+		fd, err := bind.ipv4.SyscallConn()
+		if err != nil {
+			return err
+		}
+		err = fd.Control(func(fd uintptr) {
+			err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, fwmarkIoctl, int(mark))
+		})
+		if err != nil {
+			return err
+		}
+	}
+	if bind.ipv6 != nil {
+		fd, err := bind.ipv6.SyscallConn()
+		if err != nil {
+			return err
+		}
+		err = fd.Control(func(fd uintptr) {
+			err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, fwmarkIoctl, int(mark))
+		})
+		if err != nil {
+			return err
+		}
 	}
 	return nil
 }
-- 
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