Cleanup the pull request somewhat

udp.go

@@ -18,70 +18,56 @@ func (session *UDPSession) RemoteAddr() net.Addr {
 	return session.raddr
 }
 
+// UDPConn wrap a net.UDPConn with dns.UDPConn struct
 type UDPConn struct {
 	*net.UDPConn
 }
 
-// Wrap a net.UDPConn with dns.UDPConn struct
+// NewUDPConn return a new UDPConn.
 // Initialize the underlying net.UDPConn for supporting "sessions"
 // Sessions solve https://github.com/miekg/dns/issues/95
-func NewUDPConn(conn *net.UDPConn) (newconn *UDPConn, err error) {
+func NewUDPConn(conn *net.UDPConn) (*UDPConn, error) {
 	// this function is implemented on a per platform basis. See udp_*.go for more details
-	err = udpPatchSocket(conn)
-
-	if err != nil {
-		return
-	}
-
-	return &UDPConn{conn}, nil
-}
-
-// Just like net.UDPConn.ReadFrom(), but returns a session object instead of net.UDPAddr
-// (RemoteAddr() is available from the UDPSession object)
-func (conn *UDPConn) ReadFromSessionUDP(b []byte) (n int, session *UDPSession, err error) {
-	oob := make([]byte, 40)
-
-	n, oobn, _, raddr, err := conn.ReadMsgUDP(b, oob)
-	if err != nil {
-		return
-	}
-
-	session = &UDPSession{raddr, oob[:oobn]}
-
-	return
-}
-
-// Just like net.UDPConn.WritetTo(), but uses a session object instead of net.Addr
-func (conn *UDPConn) WriteToSessionUDP(b []byte, session *UDPSession) (n int, err error) {
-	n, _, err = conn.WriteMsgUDP(b, session.context, session.raddr)
-	return
-}
-
-func udpPatchSocket(conn *net.UDPConn) (err error) {
+	conn := new(net.UDPConn)
 	file, err := conn.File()
 	if err != nil {
 		return
 	}
 
 	sa, err := syscall.Getsockname(int(file.Fd()))
-
-	ipv4, ipv6 := false, false
 	switch sa.(type) {
 	case *syscall.SockaddrInet6:
-		ipv6 = true
-
 		// dual stack. See http://stackoverflow.com/questions/1618240/how-to-support-both-ipv4-and-ipv6-connections
 		v6only, err := syscall.GetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY)
 		if err != nil {
 			return err
 		}
+		SetUDPSocketOptions6(conn)
 
 		if v6only == 0 {
-			ipv4 = true
+			SetUDPSocketOptions4(conn)
 		}
 	case *syscall.SockaddrInet4:
-		ipv4 = true
+		SetUDPSocketOptions4(conn)
+	}
+	return &UDPConn{conn}, nil
+}
+
+// ReadFromSessionUDP ... Just like net.UDPConn.ReadFrom(), but returns a session object instead of net.UDPAddr
+// (RemoteAddr() is available from the UDPSession object)
+func (conn *UDPConn) ReadFromSessionUDP(b []byte) (int, *UDPSession, error) {
+	oob := make([]byte, 40)
+	n, oobn, _, raddr, err := conn.ReadMsgUDP(b, oob)
+	if err != nil {
+		return
 	}
 
-	return udpPatchSocketTypes(conn, ipv4, ipv6)
+	session := &UDPSession{raddr, oob[:oobn]}
+	return n, session, err
+}
+
+// WriteToSessionUDP Just like net.UDPConn.WritetTo(), but uses a session object instead of net.Addr
+func (conn *UDPConn) WriteToSessionUDP(b []byte, session *UDPSession) (int, error) {
+	n, _, err = conn.WriteMsgUDP(b, session.context, session.raddr)
+	return n, err
 }

udp_linux.go

@@ -1,43 +1,42 @@
-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2011 Miek Gieben. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
-// Extensions of the original work are copyright (c) 2011 Miek Gieben
 
 // +build linux
 
 package dns
 
+// See:
+// * http://stackoverflow.com/questions/3062205/setting-the-source-ip-for-a-udp-socket and
+// * http://blog.powerdns.com/2012/10/08/on-binding-datagram-udp-sockets-to-the-any-addresses/
+//
+// Why do we need this: When listening on 0.0.0.0 with UDP so kernel decides what is the outoging
+// interface, this might not always be the correct one. This code will make sure the egress
+// packet's interface matched the ingress' one.
+
 import (
 	"net"
 	"syscall"
 )
 
-// Linux implementation for preparing the socket for sessions
-// Based on http://stackoverflow.com/questions/3062205/setting-the-source-ip-for-a-udp-socket
-// and http://blog.powerdns.com/2012/10/08/on-binding-datagram-udp-sockets-to-the-any-addresses/
-func udpPatchSocketTypes(conn *net.UDPConn, ipv4, ipv6 bool) (err error) {
-	file, err := conn.File()
+// SetUDPSocketOptions4 prepares the v4 socket for sessions.
+func SetUDPSocketOptions4(conn *net.UDPConn) error {
+	// We got the .File() in NewUDPConn, this this will work
+	file, _ := conn.File()
+	err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IP, syscall.IP_PKTINFO, 1)
 	if err != nil {
-		return
+		return err
+	}
+	return nil
+}
+
+// SetUDPSocketOptions6 prepares the v6 socket for sessions.
+func SetUDPSocketOptions6(conn *net.UDPConn) error {
+	// We got the .File() in NewUDPConn, this this will work
+	file, _ := conn.File()
+	err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_RECVPKTINFO, 1)
+	if err != nil {
+		return err
 	}
-
-	if ipv4 {
-		// socket supports IPv4
-
-		err = syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IP, syscall.IP_PKTINFO, 1)
-		if err != nil {
-			return err
-		}
-	}
-
-	if ipv6 {
-		// socket supports IPv6
-
-		err = syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_RECVPKTINFO, 1)
-		if err != nil {
-			return err
-		}
-	}
-
 	return nil
 }

udp_other.go

@@ -1,7 +1,6 @@
-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2011 Miek Gieben. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
-// Extensions of the original work are copyright (c) 2011 Miek Gieben
 
 // +build !linux
 
@@ -11,9 +10,7 @@ import (
 	"net"
 )
 
-// Default implementation for preparing the socket for sessions
-// This actually does nothing. See udp_linux.go for an example of how to implement this.
-// Make sure you edit the comment on the top of this file accordingly when adding implementations
-func udpPatchSocketTypes(conn *net.UDPConn, ipv4, ipv6 bool) (err error) {
-	return nil
-}
+// These actually do nothing. See udp_linux.go for an example of how to implement this.
+
+func SetUDPSocketOptions4(conn *net.UDPConn) error { return nil }
+func SetUDPSocketOptions6(conn *net.UDPConn) error { return nil }