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package cache
import (
"context"
"math"
"time"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/metadata"
"github.com/coredns/coredns/plugin/metrics"
"github.com/coredns/coredns/request"
"github.com/miekg/dns"
)
// ServeDNS implements the plugin.Handler interface.
func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
rc := r.Copy() // We potentially modify r, to prevent other plugins from seeing this (r is a pointer), copy r into rc.
state := request.Request{W: w, Req: rc}
do := state.Do()
ad := r.AuthenticatedData
zone := plugin.Zones(c.Zones).Matches(state.Name())
if zone == "" {
return plugin.NextOrFailure(c.Name(), c.Next, ctx, w, rc)
}
now := c.now().UTC()
server := metrics.WithServer(ctx)
// On cache refresh, we will just use the DO bit from the incoming query for the refresh since we key our cache
// with the query DO bit. That means two separate cache items for the query DO bit true or false. In the situation
// in which upstream doesn't support DNSSEC, the two cache items will effectively be the same. Regardless, any
// DNSSEC RRs in the response are written to cache with the response.
ttl := 0
i := c.getIgnoreTTL(now, state, server)
if i == nil {
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server, do: do, ad: ad,
nexcept: c.nexcept, pexcept: c.pexcept, wildcardFunc: wildcardFunc(ctx)}
return c.doRefresh(ctx, state, crr)
}
ttl = i.ttl(now)
if ttl < 0 {
// serve stale behavior
if c.verifyStale {
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server, do: do}
cw := newVerifyStaleResponseWriter(crr)
ret, err := c.doRefresh(ctx, state, cw)
if cw.refreshed {
return ret, err
}
}
// Adjust the time to get a 0 TTL in the reply built from a stale item.
now = now.Add(time.Duration(ttl) * time.Second)
if !c.verifyStale {
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
}
servedStale.WithLabelValues(server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
} else if c.shouldPrefetch(i, now) {
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
}
if i.wildcard != "" {
// Set wildcard source record name to metadata
metadata.SetValueFunc(ctx, "zone/wildcard", func() string {
return i.wildcard
})
}
resp := i.toMsg(r, now, do, ad)
w.WriteMsg(resp)
return dns.RcodeSuccess, nil
}
func wildcardFunc(ctx context.Context) func() string {
return func() string {
// Get wildcard source record name from metadata
if f := metadata.ValueFunc(ctx, "zone/wildcard"); f != nil {
return f()
}
return ""
}
}
func (c *Cache) doPrefetch(ctx context.Context, state request.Request, cw *ResponseWriter, i *item, now time.Time) {
cachePrefetches.WithLabelValues(cw.server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
c.doRefresh(ctx, state, cw)
// 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) doRefresh(ctx context.Context, state request.Request, cw dns.ResponseWriter) (int, error) {
return plugin.NextOrFailure(c.Name(), c.Next, ctx, cw, state.Req)
}
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" }
// 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())
cacheRequests.WithLabelValues(server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
if i, ok := c.ncache.Get(k); ok {
itm := i.(*item)
ttl := itm.ttl(now)
if itm.matches(state) && (ttl > 0 || (c.staleUpTo > 0 && -ttl < int(c.staleUpTo.Seconds()))) {
cacheHits.WithLabelValues(server, Denial, c.zonesMetricLabel, c.viewMetricLabel).Inc()
return i.(*item)
}
}
if i, ok := c.pcache.Get(k); ok {
itm := i.(*item)
ttl := itm.ttl(now)
if itm.matches(state) && (ttl > 0 || (c.staleUpTo > 0 && -ttl < int(c.staleUpTo.Seconds()))) {
cacheHits.WithLabelValues(server, Success, c.zonesMetricLabel, c.viewMetricLabel).Inc()
return i.(*item)
}
}
cacheMisses.WithLabelValues(server, c.zonesMetricLabel, c.viewMetricLabel).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
}
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