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cache.go
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cache.go
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package recursive
import (
"math"
"net/netip"
"sync"
"sync/atomic"
"time"
"github.com/miekg/dns"
)
const DefaultMinTTL = 10
const DefaultMaxTTL = 3600
type Cache struct {
MinTTL int // always cache items for at least this long
MaxTTL int // never cache items for longer than this
count uint64 // atomic
hits uint64 // atomic
mu sync.RWMutex
wilds int
cache map[cacheKey]cacheValue
}
func NewCache() *Cache {
return &Cache{
MinTTL: DefaultMinTTL,
MaxTTL: DefaultMaxTTL,
cache: make(map[cacheKey]cacheValue),
}
}
// HitRatio returns the hit ratio as a percentage.
func (cache *Cache) HitRatio() float64 {
if cache != nil {
if count := atomic.LoadUint64(&cache.count); count > 0 {
hits := atomic.LoadUint64(&cache.hits)
return float64(hits*100) / float64(count)
}
}
return 0
}
// Size returns the number of entries in the cache.
func (cache *Cache) Size() (n int) {
if cache != nil {
cache.mu.RLock()
n = len(cache.cache)
cache.mu.RUnlock()
}
return
}
func (cache *Cache) Set(nsaddr netip.Addr, msg *dns.Msg) {
if cache != nil && msg != nil && !msg.Zero && len(msg.Question) == 1 {
ttl := max(cache.MinTTL, min(cache.MaxTTL, MinTTL(msg)))
msg = msg.Copy()
msg.Zero = true
ck := cacheKey{
nsaddr: nsaddr,
qname: msg.Question[0].Name,
qtype: msg.Question[0].Qtype,
}
cv := cacheValue{
Msg: msg,
expires: time.Now().Add(time.Duration(ttl) * time.Second),
}
cache.mu.Lock()
if !nsaddr.IsValid() {
if _, ok := cache.cache[ck]; !ok {
cache.wilds++
}
}
cache.cache[ck] = cv
cache.mu.Unlock()
}
}
func (cache *Cache) Get(nsaddr netip.Addr, qname string, qtype uint16) *dns.Msg {
if cache != nil {
ck := cacheKey{
nsaddr: nsaddr,
qname: qname,
qtype: qtype,
}
atomic.AddUint64(&cache.count, 1)
cache.mu.RLock()
cv, ok := cache.cache[ck]
if !ok && !nsaddr.IsValid() {
for k, v := range cache.cache {
if k.qtype == qtype && k.qname == qname {
if v.expires.After(cv.expires) {
ck = k
cv = v
ok = true
}
}
}
}
if !ok && cache.wilds > 0 {
ck.nsaddr = netip.Addr{}
cv, ok = cache.cache[ck]
}
cache.mu.RUnlock()
if ok {
if time.Since(cv.expires) < 0 {
atomic.AddUint64(&cache.hits, 1)
return cv.Msg
}
cache.mu.Lock()
if cv, ok := cache.cache[ck]; ok {
cache.deleteLocked(ck, cv)
}
cache.mu.Unlock()
}
}
return nil
}
func (cache *Cache) deleteLocked(ck cacheKey, cv cacheValue) {
if !ck.nsaddr.IsValid() {
cache.wilds--
}
clear(cv.Msg.Question)
clear(cv.Msg.Answer)
clear(cv.Msg.Ns)
clear(cv.Msg.Extra)
delete(cache.cache, ck)
}
func (cache *Cache) Clear() {
cache.mu.Lock()
defer cache.mu.Unlock()
for ck, cv := range cache.cache {
cache.deleteLocked(ck, cv)
}
}
func (cache *Cache) Clean() {
if cache != nil {
now := time.Now()
cache.mu.Lock()
defer cache.mu.Unlock()
for ck, cv := range cache.cache {
if now.After(cv.expires) {
cache.deleteLocked(ck, cv)
}
}
}
}
// MinTTL returns the lowest resource record TTL in the message, or -1 if there are no records.
func MinTTL(msg *dns.Msg) int {
minTTL := math.MaxInt
for _, rr := range msg.Answer {
minTTL = min(minTTL, int(rr.Header().Ttl))
}
for _, rr := range msg.Ns {
minTTL = min(minTTL, int(rr.Header().Ttl))
}
for _, rr := range msg.Extra {
if rr.Header().Rrtype != dns.TypeOPT {
minTTL = min(minTTL, int(rr.Header().Ttl))
}
}
if minTTL == math.MaxInt {
minTTL = -1
}
return minTTL
}