104 lines
2.9 KiB
Go
104 lines
2.9 KiB
Go
//go:build !windows
|
|
// +build !windows
|
|
|
|
package dns
|
|
|
|
import (
|
|
"net"
|
|
|
|
"golang.org/x/net/ipv4"
|
|
"golang.org/x/net/ipv6"
|
|
)
|
|
|
|
// This is the required size of the OOB buffer to pass to ReadMsgUDP.
|
|
var udpOOBSize = func() int {
|
|
// We can't know whether we'll get an IPv4 control message or an
|
|
// IPv6 control message ahead of time. To get around this, we size
|
|
// the buffer equal to the largest of the two.
|
|
|
|
oob4 := ipv4.NewControlMessage(ipv4.FlagDst | ipv4.FlagInterface)
|
|
oob6 := ipv6.NewControlMessage(ipv6.FlagDst | ipv6.FlagInterface)
|
|
|
|
if len(oob4) > len(oob6) {
|
|
return len(oob4)
|
|
}
|
|
|
|
return len(oob6)
|
|
}()
|
|
|
|
// SessionUDP holds the remote address and the associated
|
|
// out-of-band data.
|
|
type SessionUDP struct {
|
|
raddr *net.UDPAddr
|
|
context []byte
|
|
}
|
|
|
|
// RemoteAddr returns the remote network address.
|
|
func (s *SessionUDP) RemoteAddr() net.Addr { return s.raddr }
|
|
|
|
// ReadFromSessionUDP acts just like net.UDPConn.ReadFrom(), but returns a session object instead of a
|
|
// net.UDPAddr.
|
|
func ReadFromSessionUDP(conn *net.UDPConn, b []byte) (int, *SessionUDP, error) {
|
|
oob := make([]byte, udpOOBSize)
|
|
n, oobn, _, raddr, err := conn.ReadMsgUDP(b, oob)
|
|
if err != nil {
|
|
return n, nil, err
|
|
}
|
|
return n, &SessionUDP{raddr, oob[:oobn]}, err
|
|
}
|
|
|
|
// WriteToSessionUDP acts just like net.UDPConn.WriteTo(), but uses a *SessionUDP instead of a net.Addr.
|
|
func WriteToSessionUDP(conn *net.UDPConn, b []byte, session *SessionUDP) (int, error) {
|
|
oob := correctSource(session.context)
|
|
n, _, err := conn.WriteMsgUDP(b, oob, session.raddr)
|
|
return n, err
|
|
}
|
|
|
|
func setUDPSocketOptions(conn *net.UDPConn) error {
|
|
// Try setting the flags for both families and ignore the errors unless they
|
|
// both error.
|
|
err6 := ipv6.NewPacketConn(conn).SetControlMessage(ipv6.FlagDst|ipv6.FlagInterface, true)
|
|
err4 := ipv4.NewPacketConn(conn).SetControlMessage(ipv4.FlagDst|ipv4.FlagInterface, true)
|
|
if err6 != nil && err4 != nil {
|
|
return err4
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// parseDstFromOOB takes oob data and returns the destination IP.
|
|
func parseDstFromOOB(oob []byte) net.IP {
|
|
// Start with IPv6 and then fallback to IPv4
|
|
// TODO(fastest963): Figure out a way to prefer one or the other. Looking at
|
|
// the lvl of the header for a 0 or 41 isn't cross-platform.
|
|
cm6 := new(ipv6.ControlMessage)
|
|
if cm6.Parse(oob) == nil && cm6.Dst != nil {
|
|
return cm6.Dst
|
|
}
|
|
cm4 := new(ipv4.ControlMessage)
|
|
if cm4.Parse(oob) == nil && cm4.Dst != nil {
|
|
return cm4.Dst
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// correctSource takes oob data and returns new oob data with the Src equal to the Dst
|
|
func correctSource(oob []byte) []byte {
|
|
dst := parseDstFromOOB(oob)
|
|
if dst == nil {
|
|
return nil
|
|
}
|
|
// If the dst is definitely an IPv6, then use ipv6's ControlMessage to
|
|
// respond otherwise use ipv4's because ipv6's marshal ignores ipv4
|
|
// addresses.
|
|
if dst.To4() == nil {
|
|
cm := new(ipv6.ControlMessage)
|
|
cm.Src = dst
|
|
oob = cm.Marshal()
|
|
} else {
|
|
cm := new(ipv4.ControlMessage)
|
|
cm.Src = dst
|
|
oob = cm.Marshal()
|
|
}
|
|
return oob
|
|
}
|