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unbound做mosdns前置的时候会重新查询域名返回的dns cname记录，这样mosdns做dns域名分流的时候还要额外添加cname域名规则，写了一个mosdns插件删除cname信息直接返回a记录避免二次查询。

//dispatcher/plugin/executable/dcname/dcname.go
package dcname

import (
  "context"
  "github.com/IrineSistiana/mosdns/v3/dispatcher/handler"
  "github.com/IrineSistiana/mosdns/v3/dispatcher/pkg/dnsutils"
  "github.com/miekg/dns"
)

const (
  PluginType = "dcname"
)

func init() {
  handler.RegInitFunc(PluginType, Init, func() interface{} { return new(Args) })
}

var _ handler.ExecutablePlugin = (*dcname)(nil)

type Args struct {
}

type dcname struct {
  *handler.BP
  args *Args
}

func Init(bp *handler.BP, args interface{}) (p handler.Plugin, err error) {
  return newDcname(bp, args.(*Args)), nil
}

func newDcname(bp *handler.BP, args *Args) handler.Plugin {
  return &dcname{
    BP:   bp,
    args: args,
  }
}

func (t *dcname) Exec(ctx context.Context, qCtx *handler.Context, next handler.ExecutableChainNode) error {
  if r := qCtx.R(); r != nil {
    q := qCtx.Q()
    if (len(q.Question) == 1 && len(r.Answer) >= 1) {
      qname := q.Question[0].Name
      qtype := q.Question[0].Qtype
      rname := r.Answer[0].Header().Name
      rtype := r.Answer[0].Header().Rrtype
      if ((qtype == dns.TypeA || qtype == dns.TypeAAAA) && qname == rname && rtype == dns.TypeCNAME) {
        var Answer2 []dns.RR
        for i := range r.Answer {
          var rr2 dns.RR
          switch rr := r.Answer[i].(type) {
          case *dns.A:
            rr2 = &dns.A{
              Hdr: dns.RR_Header{
                Name:   qname,
                Rrtype: dns.TypeA,
                Class:  dns.ClassINET,
                Ttl:    r.Answer[i].Header().Ttl,
              },
              A: rr.A,
            }
          case *dns.AAAA:
            rr2 = &dns.AAAA{
              Hdr: dns.RR_Header{
                Name:   qname,
                Rrtype: dns.TypeAAAA,
                Class:  dns.ClassINET,
                Ttl:    r.Answer[i].Header().Ttl,
              },
              AAAA: rr.AAAA,
            }
          default:
            continue
          }
          Answer2 = append(Answer2, rr2)
        }
        r.Answer = Answer2
      }
    }
  }
  return handler.ExecChainNode(ctx, qCtx, next)
}

开启插件：

dispatcher/plugin/enabled_plugin.go 
_ "github.com/IrineSistiana/mosdns/v3/dispatcher/plugin/executable/dcname"

qCtx.Q()和qCtx.R()分别获取查询和返回的信息，*dns.Msg定义在：
https://github.com/miekg/dns/blob/master/msg.go#L109
查询信息Question []Question定义在：
https://github.com/miekg/dns/blob/master/types.go#L228
返回信息Answer RR[]定义在：
https://github.com/miekg/dns/blob/master/dns.go#L31
Answer Header：
https://github.com/miekg/dns/blob/master/dns.go#L67
DNS TYPE:
https://github.com/miekg/dns/blob/master/types.go#L25

标签：dns, mosdns, cname