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// Package nsid implements NSID protocol
package nsid
import (
"context"
"encoding/hex"
"github.com/coredns/coredns/plugin"
"github.com/miekg/dns"
)
// Nsid plugin
type Nsid struct {
Next plugin.Handler
Data string
}
// ResponseWriter is a response writer that adds NSID response
type ResponseWriter struct {
dns.ResponseWriter
Data string
request *dns.Msg
}
// ServeDNS implements the plugin.Handler interface.
func (n Nsid) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
if option := r.IsEdns0(); option != nil {
for _, o := range option.Option {
if _, ok := o.(*dns.EDNS0_NSID); ok {
nw := &ResponseWriter{ResponseWriter: w, Data: n.Data, request: r}
return plugin.NextOrFailure(n.Name(), n.Next, ctx, nw, r)
}
}
}
return plugin.NextOrFailure(n.Name(), n.Next, ctx, w, r)
}
// WriteMsg implements the dns.ResponseWriter interface.
func (w *ResponseWriter) WriteMsg(res *dns.Msg) error {
if w.request.IsEdns0() != nil && res.IsEdns0() == nil {
res.SetEdns0(w.request.IsEdns0().UDPSize(), true)
}
if option := res.IsEdns0(); option != nil {
var exists bool
for _, o := range option.Option {
if e, ok := o.(*dns.EDNS0_NSID); ok {
e.Code = dns.EDNS0NSID
e.Nsid = hex.EncodeToString([]byte(w.Data))
exists = true
}
}
// Append the NSID if it doesn't exist in EDNS0 options
if !exists {
option.Option = append(option.Option, &dns.EDNS0_NSID{
Code: dns.EDNS0NSID,
Nsid: hex.EncodeToString([]byte(w.Data)),
})
}
}
return w.ResponseWriter.WriteMsg(res)
}
// Name implements the Handler interface.
func (n Nsid) Name() string { return "nsid" }
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