netbird/client/internal/dns/upstream_ios.go

//go:build ios

package dns

import (
	"net"
	"syscall"

	"github.com/miekg/dns"
	log "github.com/sirupsen/logrus"
	"golang.org/x/sys/unix"
)

// getClientPrivate returns a new DNS client bound to the local IP address of the Netbird interface
// This method is needed for iOS
func (u *upstreamResolver) getClientPrivate() *dns.Client {
	dialer := &net.Dialer{
		LocalAddr: &net.UDPAddr{
			IP:   u.lIP,
			Port: 0, // Let the OS pick a free port
		},
		Timeout: upstreamTimeout,
		Control: func(network, address string, c syscall.RawConn) error {
			var operr error
			fn := func(s uintptr) {
				operr = unix.SetsockoptInt(int(s), unix.IPPROTO_IP, unix.IP_BOUND_IF, u.iIndex)
			}

			if err := c.Control(fn); err != nil {
				return err
			}

			if operr != nil {
				log.Errorf("error while setting socket option: %s", operr)
			}

			return operr
		},
	}
	client := &dns.Client{
		Dialer: dialer,
	}
	return client
}