83 lines
2.2 KiB
Go
83 lines
2.2 KiB
Go
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package alias
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import (
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"github.com/coredns/coredns/middleware"
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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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// Rewrite is middleware to rewrite requests internally before being handled.
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type Alias struct {
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Next middleware.Handler
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}
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// ServeDNS implements the middleware.Handler interface.
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func (al Alias) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
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mw := NewResponseModifier(w)
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return middleware.NextOrFailure(al.Name(), al.Next, ctx, mw, r)
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}
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// Name implements the Handler interface.
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func (al Alias) Name() string { return "alias" }
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type ResponseModifier struct {
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dns.ResponseWriter
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}
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// Returns a dns.Msg modifier that replaces CNAME on root zones with other records.
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func NewResponseModifier(w dns.ResponseWriter) *ResponseModifier {
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return &ResponseModifier{
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ResponseWriter: w,
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}
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}
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// WriteMsg records the status code and calls the
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// underlying ResponseWriter's WriteMsg method.
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func (r *ResponseModifier) WriteMsg(res *dns.Msg) error {
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// Guess zone based on authority section.
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var zone string
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for i := 0; i < len(res.Ns); i++ {
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rr := res.Ns[i]
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if rr.Header().Rrtype == dns.TypeNS {
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zone = rr.Header().Name
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}
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}
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// Find and delete CNAME record on that zone, storing the canonical name.
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var cname string
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for i := 0; i < len(res.Answer); i++ {
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rr := res.Answer[i]
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if rr.Header().Rrtype == dns.TypeCNAME && rr.Header().Name == zone {
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cname = rr.(*dns.CNAME).Target
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// Remove the CNAME record
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res.Answer = append(res.Answer[:i], res.Answer[i+1:]...)
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break
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}
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}
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// Rename all the records with the above canonical name to the zone name
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for i := 0; i < len(res.Answer); i++ {
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rr := res.Answer[i]
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if rr.Header().Name == cname {
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rr.Header().Name = zone
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}
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}
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return r.ResponseWriter.WriteMsg(res)
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}
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// Write is a wrapper that records the size of the message that gets written.
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func (r *ResponseModifier) Write(buf []byte) (int, error) {
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n, err := r.ResponseWriter.Write(buf)
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return n, err
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}
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// Hijack implements dns.Hijacker. It simply wraps the underlying
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// ResponseWriter's Hijack method if there is one, or returns an error.
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func (r *ResponseModifier) Hijack() {
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r.ResponseWriter.Hijack()
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return
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}
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