ctrld/cmd/ctrld/prog.go

package main

import (
	"errors"
	"net"
	"os"
	"strconv"
	"sync"
	"syscall"

	"github.com/kardianos/service"
	"github.com/miekg/dns"

	"github.com/Control-D-Inc/ctrld"
)

var errWindowsAddrInUse = syscall.Errno(0x2740)

var svcConfig = &service.Config{
	Name:        "ctrld",
	DisplayName: "Control-D Helper Service",
}

type prog struct {
	cfg *ctrld.Config
}

func (p *prog) Start(s service.Service) error {
	p.cfg = &cfg
	go p.run()
	return nil
}

func (p *prog) run() {
	var wg sync.WaitGroup
	wg.Add(len(p.cfg.Listener))

	for _, nc := range p.cfg.Network {
		for _, cidr := range nc.Cidrs {
			_, ipNet, err := net.ParseCIDR(cidr)
			if err != nil {
				proxyLog.Error().Err(err).Str("network", nc.Name).Str("cidr", cidr).Msg("invalid cidr")
				continue
			}
			nc.IPNets = append(nc.IPNets, ipNet)
		}
	}
	for n := range p.cfg.Upstream {
		uc := p.cfg.Upstream[n]
		uc.Init()

		if uc.BootstrapIP == "" {
			// resolve it manually and set the bootstrap ip
			c := new(dns.Client)
			m := new(dns.Msg)
			m.SetQuestion(uc.Domain+".", dns.TypeA)
			m.RecursionDesired = true
			r, _, err := c.Exchange(m, net.JoinHostPort(bootstrapDNS, "53"))
			if err != nil {
				proxyLog.Error().Err(err).Msgf("could not resolve domain %s for upstream.%s", uc.Domain, n)
			} else {
				if r.Rcode != dns.RcodeSuccess {
					proxyLog.Error().Msgf("could not resolve domain return code: %d, upstream.%s", r.Rcode, n)
				} else {
					for _, a := range r.Answer {
						if ar, ok := a.(*dns.A); ok {
							uc.BootstrapIP = ar.A.String()
							proxyLog.Info().Str("bootstrap_ip", uc.BootstrapIP).Msgf("Setting bootstrap IP for upstream.%s", n)
						}
					}
				}
			}
		}
	}

	for listenerNum := range p.cfg.Listener {
		go func(listenerNum string) {
			defer wg.Done()
			listenerConfig := p.cfg.Listener[listenerNum]
			upstreamConfig := p.cfg.Upstream[listenerNum]
			if upstreamConfig == nil {
				proxyLog.Error().Msgf("missing upstream config for: [listener.%s]", listenerNum)
				return
			}
			addr := net.JoinHostPort(listenerConfig.IP, strconv.Itoa(listenerConfig.Port))
			proxyLog.Info().Msgf("Starting DNS server on listener.%s: %s", listenerNum, addr)
			err := p.serveUDP(listenerNum)
			if err != nil && !defaultConfigWritten {
				proxyLog.Error().Err(err).Msgf("Unable to start dns proxy on listener.%s", listenerNum)
				return
			}

			if opErr, ok := err.(*net.OpError); ok {
				if sErr, ok := opErr.Err.(*os.SyscallError); ok && errors.Is(opErr.Err, syscall.EADDRINUSE) || errors.Is(sErr.Err, errWindowsAddrInUse) {
					proxyLog.Warn().Msgf("Address %s already in used, pick a random one", addr)
					pc, err := net.ListenPacket("udp", net.JoinHostPort(listenerConfig.IP, "0"))
					if err != nil {
						proxyLog.Error().Err(err).Msg("failed to listen packet")
						return
					}
					_, portStr, _ := net.SplitHostPort(pc.LocalAddr().String())
					port, err := strconv.Atoi(portStr)
					if err != nil {
						proxyLog.Error().Err(err).Msg("malformed port")
						return
					}
					listenerConfig.Port = port
					v.Set("listener", map[string]*ctrld.ListenerConfig{
						"0": {
							IP:   "127.0.0.1",
							Port: port,
						},
					})
					writeConfigFile()
					proxyLog.Info().Msgf("Starting DNS server on listener.%s: %s", listenerNum, pc.LocalAddr())
					// There can be a race between closing the listener and start our own UDP server, but it's
					// rare, and we only do this once, so let conservative here.
					if err := pc.Close(); err != nil {
						proxyLog.Error().Err(err).Msg("failed to close packet conn")
						return
					}
					if err := p.serveUDP(listenerNum); err != nil {
						proxyLog.Error().Err(err).Msgf("Unable to start dns proxy on listener.%s", listenerNum)
						return
					}
				}
			}
		}(listenerNum)
	}

	wg.Wait()
}

func (p *prog) Stop(s service.Service) error {
	if err := p.deAllocateIP(); err != nil {
		mainLog.Error().Err(err).Msg("de-allocate ip failed")
		return err
	}
	return nil
}

func (p *prog) allocateIP(ip string) error {
	if !p.cfg.Service.AllocateIP {
		return nil
	}
	return allocateIP(ip)
}

func (p *prog) deAllocateIP() error {
	if !p.cfg.Service.AllocateIP {
		return nil
	}
	for _, lc := range p.cfg.Listener {
		if err := deAllocateIP(lc.IP); err != nil {
			return err
		}
	}
	return nil
}