Empty tag value causes error on InfluxDB output

[lpic10]

Bug report

When a kubernetes label is empty, a empty tag is created and causes InfluxDB to complain:

unable to parse 'docker_container_cpu,cpu=cpu0,io.kubernetes.pod.namespace=xxxxx,io.kubernetes.container.name=POD,cluster=xxxxx,engine_host=xxxxx,io.kubernetes.container.terminationMessagePath=,container_version=v1.2.0,io.kubernetes.container.hash=4866dc9e,io.kubernetes.pod.name=xxxxx,io.kubernetes.pod.terminationGracePeriod=30,io.kubernetes.pod.uid=b3a1ef4e-ef6e-11e6-b4b8-005056835c46,io.kubernetes.container.restartCount=0,host=xxxxx,container_name=k8s_POD.4866dc9e_xxxxx_xxxxx_b3a1ef4e-ef6e-11e6-b4b8-005056835c46_6d9803e6,container_image=xxxxx usage_total=2122656i,container_id="76f7bc0453ffb0215bf9c776e9890e5e454c1ebaabd315074c646a1d0bb4956b" 1486717284000000000': missing tag value

This issue happens when using docker input and/or prometheus input reading metrics from kubelet.

I'm not sure how this needs to be fixed, possible solutions are:

1. Fix in the prometheus and docker input plugins checking if label value is empty, but there may be more plugins doing the same
2. Fix in the influxdb output plugin, but maybe it is a bad idea to allow the same in other outputs
3. Fix this in the metric/tag object, not allowing empty tags to happen

Additional info:

Telegraf built from master

[sparrc]

please fix it in (1)

[phemmer]

@sparrc I thought empty tags were already supposed to be skipped? #1927 (comment)

[sparrc]

it appears I must have been wrong about that

[sparrc]

looks like it's a TODO....classic 🤦‍♂️ https://github.com/influxdata/telegraf/blob/master/metric/metric.go#L47

@lpic10 sorry for the earlier misdirection, can you fix this by fixing the TODO in metric.go?

[lpic10]

@sparrc no problem, do you think this is ok?

for k, v := range tags {
    vsize := len(escape(v, "tagval"))
    if vsize > 0 {
        taglen += 2 + len(escape(k, "tagkey")) + vsize
    } else {
        delete(tags, k)
    }
}

[forestjohnsonpeoplenet]

I hit this bug too in telegraf 1.2.1 with a different input plugin (consul). It's actually a regression. Telegraf 1.0.0 would skip the empty tags.

The empty tag in line protocol is invalid in both influxdb 1.0.0 and in influxdb latest. So I'm glad to see this getting fixed.