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106 lines
2.8 KiB
Go
106 lines
2.8 KiB
Go
// +build linux,!appengine
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package dns
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// See:
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// * http://stackoverflow.com/questions/3062205/setting-the-source-ip-for-a-udp-socket and
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// * http://blog.powerdns.com/2012/10/08/on-binding-datagram-udp-sockets-to-the-any-addresses/
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//
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// Why do we need this: When listening on 0.0.0.0 with UDP so kernel decides what is the outgoing
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// interface, this might not always be the correct one. This code will make sure the egress
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// packet's interface matched the ingress' one.
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import (
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"net"
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"syscall"
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)
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// setUDPSocketOptions sets the UDP socket options.
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// This function is implemented on a per platform basis. See udp_*.go for more details
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func setUDPSocketOptions(conn *net.UDPConn) error {
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sa, err := getUDPSocketName(conn)
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if err != nil {
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return err
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}
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switch sa.(type) {
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case *syscall.SockaddrInet6:
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v6only, err := getUDPSocketOptions6Only(conn)
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if err != nil {
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return err
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}
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setUDPSocketOptions6(conn)
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if !v6only {
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setUDPSocketOptions4(conn)
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}
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case *syscall.SockaddrInet4:
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setUDPSocketOptions4(conn)
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}
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return nil
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}
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// setUDPSocketOptions4 prepares the v4 socket for sessions.
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func setUDPSocketOptions4(conn *net.UDPConn) error {
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file, err := conn.File()
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if err != nil {
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return err
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}
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if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IP, syscall.IP_PKTINFO, 1); err != nil {
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file.Close()
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return err
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}
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// Calling File() above results in the connection becoming blocking, we must fix that.
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// See https://github.com/miekg/dns/issues/279
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err = syscall.SetNonblock(int(file.Fd()), true)
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if err != nil {
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file.Close()
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return err
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}
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file.Close()
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return nil
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}
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// setUDPSocketOptions6 prepares the v6 socket for sessions.
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func setUDPSocketOptions6(conn *net.UDPConn) error {
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file, err := conn.File()
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if err != nil {
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return err
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}
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if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_RECVPKTINFO, 1); err != nil {
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file.Close()
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return err
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}
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err = syscall.SetNonblock(int(file.Fd()), true)
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if err != nil {
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file.Close()
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return err
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}
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file.Close()
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return nil
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}
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// getUDPSocketOption6Only return true if the socket is v6 only and false when it is v4/v6 combined
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// (dualstack).
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func getUDPSocketOptions6Only(conn *net.UDPConn) (bool, error) {
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file, err := conn.File()
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if err != nil {
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return false, err
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}
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// dual stack. See http://stackoverflow.com/questions/1618240/how-to-support-both-ipv4-and-ipv6-connections
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v6only, err := syscall.GetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY)
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if err != nil {
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file.Close()
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return false, err
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}
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file.Close()
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return v6only == 1, nil
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}
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func getUDPSocketName(conn *net.UDPConn) (syscall.Sockaddr, error) {
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file, err := conn.File()
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if err != nil {
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return nil, err
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}
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defer file.Close()
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return syscall.Getsockname(int(file.Fd()))
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}
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