NAPTR lookup only appears to support 9 records in the msg.Answer

[miekg]

NAPTR lookup only appears to support 9 records in the msg.Answer

[andrewtj]

Are you querying over TCP or UDP? If the later, are you checking that the response isn't truncated and is within the UDP payload size you have (or haven't) set? Might help to post your code and the response in a gist.

[jsgoecke]

In this case I am using UDP:

func queryDns(query string, dnsMaster string, queryType uint16) (*dns.Msg, error) {
    m := new(dns.Msg)
    m.SetQuestion(query, queryType)
    msg, err := dns.Exchange(m, dnsMaster)
    if err != nil {
        return nil, err
    }
    return msg, nil
}

Where the query is a token, dnsMaster is the private DNS server, and queryType is set to TypeNATPR. So, simple defaults. Not clear how I might set the UDP payload size on the client side in the lib.

[andrewtj]

You can set the UDP size with SetEdns0 (something like m.SetEdns0(1440, false) is probably what you're after) and check if the response has been truncated by looking at the Truncated field of the message header.

[jsgoecke]

Yes, it is indeed being truncated. Does not like the UDP size (dns: bad rdlength), but I will figure that out. Thank you.

[jsgoecke]

Maybe not a re-open, but instead of changing the size (as in my case the returns vary in size) would it be good to fallback to TCP as the default Go library doe? Or, at least, how does one force a TCP query over a UDP one?

https://code.google.com/p/go/issues/detail?id=5686

[andrewtj]

The UDP payload size you set in the client should be the largest size the client can get on and off the wire. That is it should be set based on network conditions as opposed to the query.

A TCP query can be done with something like:

tcpConn, err := Net.Dial("tcp", "example.com:53")
if err != nil {
    // appropriate action
}
dnsConn := &dns.Conn{Conn: tcpConn}
if err := dnsConn.WriteMsg(qm); err != nil {
    // appropriate action
}
rm, err := dnsConn.ReadMsg()
if err != nil {
    // appropriate action
}

[jsgoecke]

I did force TCP this way:

func queryDns(query string, dnsMaster string, queryType uint16) (*dns.Msg, error) {
    c := new(dns.Client)
    c.Net = "tcp"
    m := new(dns.Msg)
    m.SetQuestion(query, queryType)
    msg, _, err := c.Exchange(m, dnsMaster)
    if err != nil {
        return nil, err
    }
    return msg, nil
}

But thought, like the Go standard library, that if UDP fails it should default to TCP unless you tell it not to.

[miekg]

No this package does not implement TCP fallback, nor retries. I may make
the current docs reflect this better.
On Dec 27, 2013 4:23 AM, "Jason Goecke" [email protected] wrote:

I did force TCP this way:

func queryDns(query string, dnsMaster string, queryType uint16) (*dns.Msg, error) {
c := new(dns.Client)
c.Net = "tcp"
m := new(dns.Msg)
m.SetQuestion(query, queryType)
msg, _, err := c.Exchange(m, dnsMaster)
if err != nil {
return nil, err
}
return msg, nil}

But thought, like the Go standard library, that if UDP fails it should
default to TCP unless you tell it not to.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/65#issuecomment-31246676
.

[miekg]

'dns: bad rdlength' looks to be a bug...? Can you open another issue or send some example code my way?