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rdns.go
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rdns.go
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package home
import (
"encoding/binary"
"net/netip"
"sync/atomic"
"time"
"github.com/AdguardTeam/AdGuardHome/internal/dnsforward"
"github.com/AdguardTeam/golibs/cache"
"github.com/AdguardTeam/golibs/errors"
"github.com/AdguardTeam/golibs/log"
)
// RDNS resolves clients' addresses to enrich their metadata.
type RDNS struct {
exchanger dnsforward.RDNSExchanger
clients *clientsContainer
// ipCh used to pass client's IP to rDNS workerLoop.
ipCh chan netip.Addr
// ipCache caches the IP addresses to be resolved by rDNS. The resolved
// address stays here while it's inside clients. After leaving clients the
// address will be resolved once again. If the address couldn't be
// resolved, cache prevents further attempts to resolve it for some time.
ipCache cache.Cache
// usePrivate stores the state of current private reverse-DNS resolving
// settings.
usePrivate atomic.Bool
}
// Default AdGuard Home reverse DNS values.
const (
revDNSCacheSize = 10000
// TODO(e.burkov): Make these values configurable.
revDNSCacheTTL = 24 * 60 * 60
revDNSFailureCacheTTL = 1 * 60 * 60
revDNSQueueSize = 256
)
// NewRDNS creates and returns initialized RDNS.
func NewRDNS(
exchanger dnsforward.RDNSExchanger,
clients *clientsContainer,
usePrivate bool,
) (rDNS *RDNS) {
rDNS = &RDNS{
exchanger: exchanger,
clients: clients,
ipCache: cache.New(cache.Config{
EnableLRU: true,
MaxCount: revDNSCacheSize,
}),
ipCh: make(chan netip.Addr, revDNSQueueSize),
}
rDNS.usePrivate.Store(usePrivate)
go rDNS.workerLoop()
return rDNS
}
// ensurePrivateCache ensures that the state of the RDNS cache is consistent
// with the current private client RDNS resolving settings.
//
// TODO(e.burkov): Clearing cache each time this value changed is not a perfect
// approach since only unresolved locally-served addresses should be removed.
// Implement when improving the cache.
func (r *RDNS) ensurePrivateCache() {
usePrivate := r.exchanger.ResolvesPrivatePTR()
if r.usePrivate.CompareAndSwap(!usePrivate, usePrivate) {
r.ipCache.Clear()
}
}
// isCached returns true if ip is already cached and not expired yet. It also
// caches it otherwise.
func (r *RDNS) isCached(ip netip.Addr) (ok bool) {
ipBytes := ip.AsSlice()
now := uint64(time.Now().Unix())
if expire := r.ipCache.Get(ipBytes); len(expire) != 0 {
return binary.BigEndian.Uint64(expire) > now
}
return false
}
// cache caches the ip address for ttl seconds.
func (r *RDNS) cache(ip netip.Addr, ttl uint64) {
ipData := ip.AsSlice()
ttlData := [8]byte{}
binary.BigEndian.PutUint64(ttlData[:], uint64(time.Now().Unix())+ttl)
r.ipCache.Set(ipData, ttlData[:])
}
// Begin adds the ip to the resolving queue if it is not cached or already
// resolved.
func (r *RDNS) Begin(ip netip.Addr) {
r.ensurePrivateCache()
if r.isCached(ip) || r.clients.clientSource(ip) > ClientSourceRDNS {
return
}
select {
case r.ipCh <- ip:
log.Debug("rdns: %q added to queue", ip)
default:
log.Debug("rdns: queue is full")
}
}
// workerLoop handles incoming IP addresses from ipChan and adds it into
// clients.
func (r *RDNS) workerLoop() {
defer log.OnPanic("rdns")
for ip := range r.ipCh {
ttl := uint64(revDNSCacheTTL)
host, err := r.exchanger.Exchange(ip.AsSlice())
if err != nil {
log.Debug("rdns: resolving %q: %s", ip, err)
if errors.Is(err, dnsforward.ErrRDNSFailed) {
// Cache failure for a less time.
ttl = revDNSFailureCacheTTL
}
}
r.cache(ip, ttl)
if host != "" {
_ = r.clients.AddHost(ip, host, ClientSourceRDNS)
}
}
}