coredns/middleware/cache/handler.go

package cache

import (
	"github.com/miekg/coredns/middleware"

	"github.com/miekg/dns"
	"golang.org/x/net/context"
)

// ServeDNS implements the middleware.Handler interface.
func (c Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
	state := middleware.State{W: w, Req: r}

	qname := state.Name()
	qtype := state.QType()
	zone := middleware.Zones(c.Zones).Matches(qname)
	if zone == "" {
		return c.Next.ServeDNS(ctx, w, r)
	}

	do := state.Do() // might need more from OPT record?

	if i, ok := c.Get(qname, qtype, do); ok {
		resp := i.toMsg(r)
		state.SizeAndDo(resp)
		w.WriteMsg(resp)
		return dns.RcodeSuccess, nil
	}
	crr := NewCachingResponseWriter(w, c.cache, c.cap)
	return c.Next.ServeDNS(ctx, crr, r)
}

func (c Cache) Get(qname string, qtype uint16, do bool) (*item, bool) {
	nxdomain := nameErrorKey(qname, do)
	if i, ok := c.cache.Get(nxdomain); ok {
		return i.(*item), true
	}

	successOrNoData := successKey(qname, qtype, do)
	if i, ok := c.cache.Get(successOrNoData); ok {
		return i.(*item), true
	}
	return nil, false
}