func serve(w dns.ResponseWriter, r *dns.Msg, c *Cache) {
switch {
case r.IsNotify():
if *flaglog {
log.Printf("fks-shield: notify/update")
}
fallthrough
case r.IsUpdate():
client := new(dns.Client)
if p, e := client.Exchange(r, *server); e == nil {
w.WriteMsg(p)
}
return
}
if p := c.Find(r); p != nil {
b := []byte{byte(r.MsgHdr.Id >> 8), byte(r.MsgHdr.Id)}
p = append(b, p...)
w.Write(p)
return
}
// Cache miss
client := new(dns.Client)
if p, e := client.Exchange(r, *server); e == nil {
// TODO(mg): If r has edns0 and p has not we create a mismatch here
w.WriteMsg(p)
c.Insert(p)
return
} else {
log.Printf("fks-shield: failed to get answer " + e.Error())
m := new(dns.Msg)
m.SetRcode(r, dns.RcodeServerFailure)
w.WriteMsg(m)
}
}