godns/resolver/resolver.go

package resolver

import (
	"bufio"
	"errors"
	"fmt"
	log "github.com/sirupsen/logrus"
	"meow.tf/joker/godns/utils"
	"net"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"

	"crypto/tls"
	"github.com/miekg/dns"
)

type ResolvError struct {
	qname, net  string
	nameservers []*Nameserver
}

func (e ResolvError) Error() string {
	nameservers := make([]string, len(e.nameservers))

	for i, nameserver := range e.nameservers {
		nameservers[i] = nameserver.address
	}

	return fmt.Sprintf("%s resolv failed on %s (%s)", e.qname, strings.Join(nameservers, "; "), e.net)
}

type RResp struct {
	msg        *dns.Msg
	nameserver *Nameserver
	rtt        time.Duration
}

type Resolver struct {
	servers      []*Nameserver
	domainServer *suffixTreeNode
	config       *Settings

	clients map[string]*dns.Client
	clientLock sync.RWMutex
}

func NewResolver(c Settings) *Resolver {
	r := &Resolver{
		servers:      make([]*Nameserver, 0),
		domainServer: newSuffixTreeRoot(),
		config:       &c,
	}

	if len(c.ServerListFile) > 0 {
		r.ReadServerListFile(c.ServerListFile)
	}

	if len(c.ResolvFile) > 0 {
		clientConfig, err := dns.ClientConfigFromFile(c.ResolvFile)

		if err != nil {
			log.Error(":%s is not a valid resolv.conf file\n", c.ResolvFile)
			log.Error("%s", err)
			panic(err)
		}

		for _, server := range clientConfig.Servers {
			r.servers = append(r.servers, &Nameserver{net: "udp", address: net.JoinHostPort(server, clientConfig.Port)})
		}
	}

	return r
}

func (r *Resolver) parseServerListFile(buf *os.File) {
	scanner := bufio.NewScanner(buf)

	var line string
	var idx int

	for scanner.Scan() {
		line = strings.TrimSpace(scanner.Text())

		if !strings.HasPrefix(line, "server") {
			continue
		}

		idx = strings.Index(line, "=")

		if idx == -1 {
			continue
		}

		line = strings.TrimSpace(line[idx+1:])

		if strings.HasPrefix(line, "https://") {
			r.servers = append(r.servers, &Nameserver{net: "https", address: line})
			continue
		}

		tokens := strings.Split(line, "/")
		switch len(tokens) {
		case 3:
			domain := tokens[1]
			ip := tokens[2]

			if !utils.IsDomain(domain) || !utils.IsIP(ip) {
				continue
			}

			r.domainServer.sinsert(strings.Split(domain, "."), ip)
		case 1:
			srvPort := strings.Split(line, "#")

			if len(srvPort) > 2 {
				continue
			}

			ip := ""

			if ip = srvPort[0]; !utils.IsIP(ip) {
				continue
			}

			port := "53"

			if len(srvPort) == 2 {
				if _, err := strconv.Atoi(srvPort[1]); err != nil {
					continue
				}

				port = srvPort[1]
			}

			r.servers = append(r.servers, &Nameserver{address: net.JoinHostPort(ip, port)})
		}
	}

}

func (r *Resolver) ReadServerListFile(files []string) {
	for _, file := range files {
		buf, err := os.Open(file)
		if err != nil {
			panic("Can't open " + file)
		}
		r.parseServerListFile(buf)
		buf.Close()
	}
}

// Lookup will ask each nameserver in top-to-bottom fashion, starting a new request
// in every second, and return as early as possbile (have an answer).
// It returns an error if no request has succeeded.
func (r *Resolver) Lookup(net string, req *dns.Msg) (message *dns.Msg, err error) {
	if net == "udp" && r.config.SetEDNS0 {
		req = req.SetEdns0(65535, true)
	}

	qname := req.Question[0].Name

	res := make(chan *RResp, 1)
	var wg sync.WaitGroup
	L := func(resolver *Resolver, nameserver *Nameserver) {
		defer wg.Done()

		c, err := resolver.resolverFor(net, nameserver)

		if err != nil {
			log.Warn("error:%s", err.Error())
			return
		}

		r, rtt, err := c.Exchange(req, nameserver.address)

		if err != nil {
			log.Warn("%s socket error on %s", qname, nameserver)
			log.Warn("error:%s", err.Error())
			return
		}
		// If SERVFAIL happen, should return immediately and try another upstream resolver.
		// However, other Error code like NXDOMAIN is an clear response stating
		// that it has been verified no such domain existas and ask other resolvers
		// would make no sense. See more about #20
		if r != nil && r.Rcode != dns.RcodeSuccess {
			log.Warn("%s failed to get an valid answer on %s", qname, nameserver)
			if r.Rcode == dns.RcodeServerFailure {
				return
			}
		}
		re := &RResp{r, nameserver, rtt}
		select {
		case res <- re:
		default:
		}
	}

	ticker := time.NewTicker(time.Duration(r.config.Interval) * time.Millisecond)
	defer ticker.Stop()
	// Start lookup on each nameserver top-down, in every second
	nameservers := r.Nameservers(qname)
	for _, nameserver := range nameservers {
		wg.Add(1)
		go L(r, nameserver)
		// but exit early, if we have an answer
		select {
		case re := <-res:
			log.Debug("%s resolv on %s rtt: %v", utils.UnFqdn(qname), re.nameserver, re.rtt)
			return re.msg, nil
		case <-ticker.C:
			continue
		}
	}
	// wait for all the namservers to finish
	wg.Wait()
	select {
	case re := <-res:
		log.Debug("%s resolv on %s rtt: %v", utils.UnFqdn(qname), re.nameserver.address, re.rtt)
		return re.msg, nil
	default:
		return nil, ResolvError{qname, net, nameservers}
	}
}

func (r *Resolver) resolverFor(network string, n *Nameserver) (*dns.Client, error) {
	key := network

	// Use HTTPS if network is https, or TLS to force secure connections
	if n.net == "https" {
		key = n.net
	} else if n.net == "tcp-tls" {
		key = n.net + ":" + n.address
	}

	r.clientLock.RLock()
	client, exists := r.clients[key]
	r.clientLock.RUnlock()

	if exists {
		return client, nil
	}

	if n.net != "tcp" && n.net != "tcp-tls" && n.net != "https" && n.net != "udp" {
		return nil, errors.New("unknown network type")
	}

	timeout := r.Timeout()

	client = &dns.Client{
		Net: n.net,
		ReadTimeout: timeout,
		WriteTimeout: timeout,
	}

	if n.net == "tcp-tls" {
		host, _, err := net.SplitHostPort(n.address)

		if err != nil {
			host = n.address
		}

		client.TLSConfig = &tls.Config{
			ServerName: host,
		}
	}

	r.clientLock.Lock()
	r.clients[key] = client
	r.clientLock.Lock()

	return client, nil
}

// Nameservers return the array of nameservers, with port number appended.
// '#' in the name is treated as port separator, as with dnsmasq.

func (r *Resolver) Nameservers(qname string) []*Nameserver {
	queryKeys := strings.Split(qname, ".")
	queryKeys = queryKeys[:len(queryKeys)-1] // ignore last '.'

	if v, found := r.domainServer.search(queryKeys); found {
		log.Debug("%s found in domain server list, upstream: %v", qname, v)

		//Ensure query the specific upstream nameserver in async Lookup() function.
		return []*Nameserver{
			{net: "udp", address: net.JoinHostPort(v, "53")},
		}
	}

	return r.servers
}

func (r *Resolver) Timeout() time.Duration {
	return time.Duration(r.config.Timeout) * time.Second
}