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package dns
import (
"fmt"
"log"
"net"
"strings"
"sync"
"github.com/miekg/dns"
"github.com/mpolden/zdns/cache"
"github.com/mpolden/zdns/dns/dnsutil"
)
const (
// TypeA represents th resource record type A, an IPv4 address.
TypeA = dns.TypeA
// TypeAAAA represents the resource record type AAAA, an IPv6 address.
TypeAAAA = dns.TypeAAAA
)
// Request represents a simplified DNS request.
type Request struct {
Type uint16
Name string
}
// Reply represents a simplifed DNS reply.
type Reply struct{ rr []dns.RR }
// Handler represents the handler for a DNS request.
type Handler func(*Request) *Reply
// Proxy represents a DNS proxy.
type Proxy struct {
Handler Handler
cache *cache.Cache
logger *log.Logger
dnsLogger logger
server *dns.Server
client *dnsutil.Client
mu sync.RWMutex
}
type logger interface {
Record(net.IP, bool, uint16, string, ...string)
Close() error
}
// NewProxy creates a new DNS proxy.
func NewProxy(cache *cache.Cache, client *dnsutil.Client, logger *log.Logger, dnsLogger logger) (*Proxy, error) {
return &Proxy{
logger: logger,
dnsLogger: dnsLogger,
cache: cache,
client: client,
}, nil
}
// ReplyA creates a resource record of type A.
func ReplyA(name string, ipAddr ...net.IP) *Reply {
rr := make([]dns.RR, 0, len(ipAddr))
for _, ip := range ipAddr {
rr = append(rr, &dns.A{
A: ip,
Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 3600},
})
}
return &Reply{rr}
}
// ReplyAAAA creates a resource record of type AAAA.
func ReplyAAAA(name string, ipAddr ...net.IP) *Reply {
rr := make([]dns.RR, 0, len(ipAddr))
for _, ip := range ipAddr {
rr = append(rr, &dns.AAAA{
AAAA: ip,
Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: 3600},
})
}
return &Reply{rr}
}
func (r *Reply) String() string {
b := strings.Builder{}
for i, rr := range r.rr {
b.WriteString(rr.String())
if i < len(r.rr)-1 {
b.WriteRune('\n')
}
}
return b.String()
}
func (p *Proxy) reply(r *dns.Msg) *dns.Msg {
if p.Handler == nil || len(r.Question) != 1 {
return nil
}
reply := p.Handler(&Request{
Name: r.Question[0].Name,
Type: r.Question[0].Qtype,
})
if reply == nil {
return nil
}
m := dns.Msg{Answer: reply.rr}
// Pretend this is an recursive answer
m.RecursionAvailable = true
m.SetReply(r)
return &m
}
// Close closes the proxy.
func (p *Proxy) Close() error {
p.mu.RLock()
defer p.mu.RUnlock()
if p.server != nil {
return p.server.Shutdown()
}
return nil
}
func (p *Proxy) writeMsg(w dns.ResponseWriter, msg *dns.Msg, hijacked bool) {
var ip net.IP
switch v := w.RemoteAddr().(type) {
case *net.UDPAddr:
ip = v.IP
case *net.TCPAddr:
ip = v.IP
default:
panic(fmt.Sprintf("unexpected remote address type %T", v))
}
if p.dnsLogger != nil {
p.dnsLogger.Record(ip, hijacked, msg.Question[0].Qtype, msg.Question[0].Name, dnsutil.Answers(msg)...)
}
w.WriteMsg(msg)
}
// ServeDNS implements the dns.Handler interface.
func (p *Proxy) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
if reply := p.reply(r); reply != nil {
p.writeMsg(w, reply, true)
return
}
q := r.Question[0]
key := cache.NewKey(q.Name, q.Qtype, q.Qclass)
if msg, ok := p.cache.Get(key); ok {
msg.SetReply(r)
p.writeMsg(w, msg, false)
return
}
rr, err := p.client.Exchange(r)
if err == nil {
p.writeMsg(w, rr, false)
p.cache.Set(key, rr)
} else {
p.logger.Print(err)
dns.HandleFailed(w, r)
}
}
// ListenAndServe listens on the network address addr and uses the server to process requests.
func (p *Proxy) ListenAndServe(addr string, network string) error {
p.mu.Lock()
p.server = &dns.Server{Addr: addr, Net: network, Handler: p}
p.mu.Unlock()
return p.server.ListenAndServe()
}
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