Vendor main dependencies.

vendor/github.com/miekg/dns/udp_linux.go

@@ -0,0 +1,82 @@
+// +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 outgoing
+// 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"
+)
+
+// setUDPSocketOptions4 prepares the v4 socket for sessions.
+func setUDPSocketOptions4(conn *net.UDPConn) error {
+	file, err := conn.File()
+	if err != nil {
+		return err
+	}
+	if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IP, syscall.IP_PKTINFO, 1); err != nil {
+		file.Close()
+		return err
+	}
+	// Calling File() above results in the connection becoming blocking, we must fix that.
+	// See https://github.com/miekg/dns/issues/279
+	err = syscall.SetNonblock(int(file.Fd()), true)
+	if err != nil {
+		file.Close()
+		return err
+	}
+	file.Close()
+	return nil
+}
+
+// setUDPSocketOptions6 prepares the v6 socket for sessions.
+func setUDPSocketOptions6(conn *net.UDPConn) error {
+	file, err := conn.File()
+	if err != nil {
+		return err
+	}
+	if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_RECVPKTINFO, 1); err != nil {
+		file.Close()
+		return err
+	}
+	err = syscall.SetNonblock(int(file.Fd()), true)
+	if err != nil {
+		file.Close()
+		return err
+	}
+	file.Close()
+	return nil
+}
+
+// getUDPSocketOption6Only return true if the socket is v6 only and false when it is v4/v6 combined
+// (dualstack).
+func getUDPSocketOptions6Only(conn *net.UDPConn) (bool, error) {
+	file, err := conn.File()
+	if err != nil {
+		return false, err
+	}
+	// 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 {
+		file.Close()
+		return false, err
+	}
+	file.Close()
+	return v6only == 1, nil
+}
+
+func getUDPSocketName(conn *net.UDPConn) (syscall.Sockaddr, error) {
+	file, err := conn.File()
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	return syscall.Getsockname(int(file.Fd()))
+}