How to add EDNS Client Subnet option as a client?

[sajal]

Hi, I am trying to issue query to a server that supports ECS. I see example code for creating the option, but how to attach it to an outgoing message?

I see there is ways to read using Msg.IsEdns0 when acting as server, but how do I set it as a client?

Example code:-

package main

import (
    "github.com/miekg/dns"
    "log"
    "net"
    "strings"
)

func main() {
    c := new(dns.Client)

    m := new(dns.Msg)
    m.SetQuestion("something.example.org.", dns.TypeCNAME)

    o := new(dns.OPT)
    o.Hdr.Name = "."
    o.Hdr.Rrtype = dns.TypeOPT
    e := new(dns.EDNS0_SUBNET)
    e.Code = dns.EDNS0SUBNET
    e.Family = 1         // 1 for IPv4 source address, 2 for IPv6
    e.SourceNetmask = 32 // 32 for IPV4, 128 for IPv6
    e.SourceScope = 0
    e.Address = net.ParseIP("1.2.3.4").To4()
    o.Option = append(o.Option, e)

    //QUESTION: How do I attach o to m?

    //log.Println(o)
    //m.SetEdns0(4096, false)
    //log.Println(m.IsEdns0())
    //log.Println(m)
    in, rtt, err := c.Exchange(m, "ns1.example.org:53")
    if err != nil {
        log.Fatal(err)
    }
    log.Println(in)
    log.Println(rtt)
    if t, ok := in.Answer[0].(*dns.CNAME); ok {
        log.Println(strings.ToUpper(strings.Split(t.Target, ".")[0]))
    } else {
        log.Fatal("should not reach here...")
    }
}

[miekg]

[ Quoting notifications@github.com in "[miekg/dns] How to add EDNS Client ..." ]

m := new(dns.Msg)
m.SetQuestion("something.example.org.", dns.TypeCNAME)

o := new(dns.OPT)
o.Hdr.Name = "."
o.Hdr.Rrtype = dns.TypeOPT
e := new(dns.EDNS0_SUBNET)
e.Code = dns.EDNS0SUBNET
e.Family = 1 // 1 for IPv4 source address, 2 for IPv6
e.SourceNetmask = 32 // 32 for IPV4, 128 for IPv6
e.SourceScope = 0
e.Address = net.ParseIP("1.2.3.4").To4()
o.Option = append(o.Option, e)

//QUESTION: How do I attach o to m?

m.Extra = append(m.Extra, o)

[sajal]

Thanks a lot. Works as intended.