DNS against local resolvers with ResultSet respojse does not recognise rtt correctly

[warmfusion]

While testing the exporter against some of my ongoing DNS test I noticed that the rtt value isn't recognised when the response contains multiple results in a resultset.

According to the ripe documentation;

resultset - [optional] an array of objects containing all the fields of a DNS result object, except for the fields: fw, from, msm_id, prb_id, and type. Available for queries sent to each local resolver.

This was added in version 4750.

Test ID as a reference: 16878571

Here's a lazy workaround that's super ugly, but i can't get the nicer version working (See later).

diff --git a/dns/exporter.go b/dns/exporter.go
index d7819ed..55e7bf5 100644
--- a/dns/exporter.go
+++ b/dns/exporter.go
@@ -41,8 +41,18 @@ func (m *dnsExporter) Export(res *measurement.Result, probe *probe.Probe, ch cha
        var rtt float64
        if res.DnsResult() != nil {
                rtt = res.DnsResult().Rt()
+               recordRtt(rtt, labelValues, ch)
+       } else if res.DnsResultsets() != nil {
+               for _, s := range res.DnsResultsets() {
+                       if s.Result() != nil {
+                               rtt = s.Result().Rt()
+                               recordRtt(rtt, labelValues, ch)
+                       }
+               }
        }
+}

+func recordRtt(rtt float64, labelValues []string, ch chan<- prometheus.Metric) {
        if rtt > 0 {
                ch <- prometheus.MustNewConstMetric(successDesc, prometheus.GaugeValue, 1, labelValues...)
                ch <- prometheus.MustNewConstMetric(rttDesc, prometheus.GaugeValue, rtt, labelValues...)

Non Working Workaround

I'd much prefer to do something like this, but I can't quite get my head around golangs slices/arrays pointers/references etc to make the popping of the first element off the DNSResultSets() array response not cause a segfault.

diff --git a/dns/exporter.go b/dns/exporter.go
index d7819ed..b6706d4 100644
--- a/dns/exporter.go
+++ b/dns/exporter.go
@@ -41,6 +41,8 @@ func (m *dnsExporter) Export(res *measurement.Result, probe *probe.Probe, ch cha
        var rtt float64
        if res.DnsResult() != nil {
                rtt = res.DnsResult().Rt()
+       } else if res.DnsResultsets() != nil {
+               rtt = res.DnsResultsets()[0].Result().Rt()
        }

        if rtt > 0 {