How to set the return value of gettag function

[chunyuliu106667777]

In this page，I understand the gettag function can fill the DNSQuestion.requestorId field, But in the logs obtained through the protobufServer function, the fields of DeviceId and DeviceName are N/A. What is the reason for this? It may be that I set them incorrectly. Can you provide me with a simple example of gettag?

function gettag(remote, ednssubnet, localip, qname, qtype, ednsoptions, tcp, proxyprotocolvalues)
    local device_id = ""
    local device_name = ""
    if ednsoptions ~= nil then
        if ednsoptions[CONFIG.device_code] ~= nil then
            device_id = ednsoptions[CONFIG.device_code]:getContent()
        end
        if ednsoptions[CONFIG.apikey_code] ~= nil then
            device_name = ednsoptions[CONFIG.apikey_code]:getContent()
        end
    end
    return 0, {}, {}, device_id, device_name, {}
end

[omoerbeek]

Do you have gettag-needs-edns-options set?

[chunyuliu106667777]

yes, Here are some of my configuration information.

dnssec=off
gettag-needs-edns-options=yes
hint-file=no
include-dir=/etc/pdns-recursor/recursor.d
lua-config-file=/etc/pdns-recursor/lua-config.lua
lua-dns-script=/etc/pdns-recursor/pdns-recursor.lua
pdns-distributes-queries=yes
setgid=pdns-recursor
setuid=pdns-recursor
threads=4
version-string=""

[omoerbeek]

OK, I'll try to reproduce later today.

[chunyuliu106667777]

Okay, Thanks a lot. I‘ll looking forward your reply.

[omoerbeek]

This script works for me:

function gettag(remote, ednssubnet, localip, qname, qtype, ednsoptions, tcp, proxyprotocolvalues)
    local req_id = "REQID"
    local device_id = "DEVID"
    local device_name = "DEVNAME"
    return 0, {}, {}, req_id, device_id, device_name
end

[2024-10-28 08:58:16.654196] Query of size 57: 127.0.0.1:58681 (N/A) -> 127.0.0.1:5301 (UDP) id: 13636 uuid: b'a92ae42eb6974dd6a03c6190871c7384' requestorid: REQID deviceid: b'4445564944' devicename: DEVNAME serverid: b'iMac.local' nod: N/A workerId: 1 pcCacheHit: N/A outgoingQueries: N/A
- Question: 1, 1, www.powerdns.com.
[2024-10-28 08:58:17.150896] Response of size 164: 127.0.0.1:58681 (N/A) -> 127.0.0.1:5301 (UDP) id: 13636 uuid: b'a92ae42eb6974dd6a03c6190871c7384' requestorid: REQID deviceid: b'4445564944' devicename: DEVNAME serverid: b'iMac.local' nod: N/A workerId: 1 pcCacheHit: False outgoingQueries: 14
- Question: 1, 1, www.powerdns.com.
- Query time: 2024-10-28 08:58:16.653266
- Response Code: 0, RRs: 4
	 - 1, 5, www.powerdns.com., 300, b'20334960.group10.sites.hubspot.net.', False
	 - 1, 5, 20334960.group10.sites.hubspot.net., 120, b'group10.sites.hscoscdn10.net.', False
	 - 1, 1, group10.sites.hscoscdn10.net., 300, 199.60.103.31, False
	 - 1, 1, group10.sites.hscoscdn10.net., 300, 199.60.103.225, False

Your script has a type error: the requestor id was missing, it comes before the device id. So the {} ended up being used as a string.

With your return 0, {}, {}, device_id, device_name, {} I was seeing an error message in the log:

Oct 28 09:00:49 msg="Error parsing a query packet for tag determination created an exception" error="Trying to cast a lua variable from \"number\" to \"NSt3__15tupleIJjN5boost8optionalINS_13unordered_mapIiNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEENS_4hashIiEENS_8equal_toIiEENS7_INS_4pairIKiS9_EEEEEEEENS2_IN10LuaContext9LuaObjectEEENS2_IS9_EESN_SN_SN_EEE\"" subsystem="in" level="0" prio="Error" tid="1" ts="1730102449.459" exception="std::exception" proto="udp" qname="www.powerdns.com" ratelimitingSkipped="0" remote="127.0.0.1:58996"

(Though older recursors might hide this errror)

[chunyuliu106667777]

Thanks a lot！

I have observed that the 'device id' field is not a real string. If I want to carry some specific strings or identifiers, is using the 'gettag' function to add them to the DNS log the optimal solution? I currently only know that the requestorId, DeviceId and DeviceName fields in DNSQuestion can be set in the gettag.

[omoerbeek]

Device id is a sequence of bytes (as defined in dnsmessage.proto) you should be able to put a string into it.
But if you want to set your strings I suggest to use the tags table. It can contain a number of values of type string:

function gettag(remote, ednssubnet, localip, qname, qtype, ednsoptions, tcp, proxyprotocolvalues)
    return 0, { 'value1', 'value2' }
end

[chunyuliu106667777]

Thank you for your suggestion！I'll make adjustments immediately