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package cache
import (
"context"
"math"
"time"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/metrics"
"github.com/coredns/coredns/request"
"github.com/miekg/dns"
"github.com/prometheus/client_golang/prometheus"
)
// ServeDNS implements the plugin.Handler interface.
func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
state := request.Request{W: w, Req: r}
zone := plugin.Zones(c.Zones).Matches(state.Name())
if zone == "" {
return plugin.NextOrFailure(c.Name(), c.Next, ctx, w, r)
}
now := c.now().UTC()
server := metrics.WithServer(ctx)
ttl := 0
i := c.getIgnoreTTL(now, state, server)
if i != nil {
ttl = i.ttl(now)
}
if i == nil || -ttl >= int(c.staleUpTo.Seconds()) {
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server}
return plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, r)
}
if ttl < 0 {
servedStale.WithLabelValues(server).Inc()
// Adjust the time to get a 0 TTL in the reply built from a stale item.
now = now.Add(time.Duration(ttl) * time.Second)
go func() {
r := r.Copy()
crr := &ResponseWriter{Cache: c, state: state, server: server, prefetch: true, remoteAddr: w.LocalAddr()}
plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, r)
}()
}
resp := i.toMsg(r, now)
w.WriteMsg(resp)
if c.shouldPrefetch(i, now) {
go c.doPrefetch(ctx, state, server, i, now)
}
return dns.RcodeSuccess, nil
}
func (c *Cache) doPrefetch(ctx context.Context, state request.Request, server string, i *item, now time.Time) {
cw := newPrefetchResponseWriter(server, state, c)
cachePrefetches.WithLabelValues(server).Inc()
plugin.NextOrFailure(c.Name(), c.Next, ctx, cw, state.Req)
// When prefetching we loose the item i, and with it the frequency
// that we've gathered sofar. See we copy the frequencies info back
// into the new item that was stored in the cache.
if i1 := c.exists(state); i1 != nil {
i1.Freq.Reset(now, i.Freq.Hits())
}
}
func (c *Cache) shouldPrefetch(i *item, now time.Time) bool {
if c.prefetch <= 0 {
return false
}
i.Freq.Update(c.duration, now)
threshold := int(math.Ceil(float64(c.percentage) / 100 * float64(i.origTTL)))
return i.Freq.Hits() >= c.prefetch && i.ttl(now) <= threshold
}
// Name implements the Handler interface.
func (c *Cache) Name() string { return "cache" }
func (c *Cache) get(now time.Time, state request.Request, server string) (*item, bool) {
k := hash(state.Name(), state.QType(), state.Do())
if i, ok := c.ncache.Get(k); ok && i.(*item).ttl(now) > 0 {
cacheHits.WithLabelValues(server, Denial).Inc()
return i.(*item), true
}
if i, ok := c.pcache.Get(k); ok && i.(*item).ttl(now) > 0 {
cacheHits.WithLabelValues(server, Success).Inc()
return i.(*item), true
}
cacheMisses.WithLabelValues(server).Inc()
return nil, false
}
// getIgnoreTTL unconditionally returns an item if it exists in the cache.
func (c *Cache) getIgnoreTTL(now time.Time, state request.Request, server string) *item {
k := hash(state.Name(), state.QType(), state.Do())
if i, ok := c.ncache.Get(k); ok {
ttl := i.(*item).ttl(now)
if ttl > 0 || (c.staleUpTo > 0 && -ttl < int(c.staleUpTo.Seconds())) {
cacheHits.WithLabelValues(server, Denial).Inc()
}
return i.(*item)
}
if i, ok := c.pcache.Get(k); ok {
ttl := i.(*item).ttl(now)
if ttl > 0 || (c.staleUpTo > 0 && -ttl < int(c.staleUpTo.Seconds())) {
cacheHits.WithLabelValues(server, Success).Inc()
}
return i.(*item)
}
cacheMisses.WithLabelValues(server).Inc()
return nil
}
func (c *Cache) exists(state request.Request) *item {
k := hash(state.Name(), state.QType(), state.Do())
if i, ok := c.ncache.Get(k); ok {
return i.(*item)
}
if i, ok := c.pcache.Get(k); ok {
return i.(*item)
}
return nil
}
var (
cacheSize = prometheus.NewGaugeVec(prometheus.GaugeOpts{
Namespace: plugin.Namespace,
Subsystem: "cache",
Name: "size",
Help: "The number of elements in the cache.",
}, []string{"server", "type"})
cacheHits = prometheus.NewCounterVec(prometheus.CounterOpts{
Namespace: plugin.Namespace,
Subsystem: "cache",
Name: "hits_total",
Help: "The count of cache hits.",
}, []string{"server", "type"})
cacheMisses = prometheus.NewCounterVec(prometheus.CounterOpts{
Namespace: plugin.Namespace,
Subsystem: "cache",
Name: "misses_total",
Help: "The count of cache misses.",
}, []string{"server"})
cachePrefetches = prometheus.NewCounterVec(prometheus.CounterOpts{
Namespace: plugin.Namespace,
Subsystem: "cache",
Name: "prefetch_total",
Help: "The number of time the cache has prefetched a cached item.",
}, []string{"server"})
cacheDrops = prometheus.NewCounterVec(prometheus.CounterOpts{
Namespace: plugin.Namespace,
Subsystem: "cache",
Name: "drops_total",
Help: "The number responses that are not cached, because the reply is malformed.",
}, []string{"server"})
servedStale = prometheus.NewCounterVec(prometheus.CounterOpts{
Namespace: plugin.Namespace,
Subsystem: "cache",
Name: "served_stale_total",
Help: "The number of requests served from stale cache entries.",
}, []string{"server"})
)
|
