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This middleware allows playing with responses. Only one type is implemented: it allows you to drop queries. I.e. withhold the response from the client.
75 lines
1.5 KiB
Go
75 lines
1.5 KiB
Go
// Package erratic implements a middleware that returns erratic answers (delayed, dropped).
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package erratic
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import (
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"sync/atomic"
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"github.com/miekg/coredns/request"
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"github.com/miekg/dns"
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"golang.org/x/net/context"
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)
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// Erratic is a middleware that returns erratic repsonses to each client.
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type Erratic struct {
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amount uint64
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q uint64 // counter of queries
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}
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// ServeDNS implements the middleware.Handler interface.
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func (e *Erratic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
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state := request.Request{W: w, Req: r}
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drop := false
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if e.amount > 0 {
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queryNr := atomic.LoadUint64(&e.q)
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if queryNr%e.amount == 0 {
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drop = true
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}
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atomic.AddUint64(&e.q, 1)
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}
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m := new(dns.Msg)
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m.SetReply(r)
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m.Compress = true
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m.Authoritative = true
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// small dance to copy rrA or rrAAAA into a non-pointer var that allows us to overwrite the ownername
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// in a non-racy manor.
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switch state.QType() {
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case dns.TypeA:
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rr := *(rrA.(*dns.A))
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rr.Header().Name = state.QName()
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m.Answer = append(m.Answer, &rr)
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case dns.TypeAAAA:
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rr := *(rrAAAA.(*dns.AAAA))
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rr.Header().Name = state.QName()
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m.Answer = append(m.Answer, &rr)
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default:
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if !drop {
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// coredns will return error.
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return dns.RcodeServerFailure, nil
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}
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}
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if drop {
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return 0, nil
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}
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state.SizeAndDo(m)
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w.WriteMsg(m)
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return 0, nil
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}
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// Name implements the Handler interface.
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func (e *Erratic) Name() string { return "erratic" }
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var (
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rrA, _ = dns.NewRR(". IN 0 A 192.0.2.53")
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rrAAAA, _ = dns.NewRR(". IN 0 AAAA 2001:DB8::53")
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)
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