Add a DescribeByCollect helper
Signed-off-by: beorn7 <beorn@soundcloud.com>
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@ -61,6 +61,37 @@ type Collector interface {
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Collect(chan<- Metric)
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}
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// DescribeByCollect is a helper to implement the Describe method of a custom
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// Collector. It collects the metrics from the provided Collector and sends
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// their descriptors to the provided channel.
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//
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// If a Collector collects the same metrics throughout its lifetime, its
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// Describe method can simply be implemented as:
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//
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// func (c customCollector) Describe(ch chan<- *Desc) {
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// DescribeByCollect(c, ch)
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// }
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//
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// However, this will not work if the metrics collected change dynamically over
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// the lifetime of the Collector in a way that their combined set of descriptors
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// changes as well. The shortcut implementation will then violate the contract
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// of the Describe method. If a Collector sometimes collects no metrics at all
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// (for example vectors like CounterVec, GaugeVec, etc., which only collect
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// metrics after a metric with a fully specified label set has been accessed),
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// it might even get registered as an unchecked Collecter (cf. the Register
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// method of the Registerer interface). Hence, only use this shortcut
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// implementation of Describe if you are certain to fulfill the contract.
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func DescribeByCollect(c Collector, descs chan<- *Desc) {
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metrics := make(chan Metric)
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go func() {
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c.Collect(metrics)
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close(metrics)
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}()
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for m := range metrics {
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descs <- m.Desc()
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}
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}
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// selfCollector implements Collector for a single Metric so that the Metric
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// collects itself. Add it as an anonymous field to a struct that implements
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// Metric, and call init with the Metric itself as an argument.
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@ -0,0 +1,62 @@
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// Copyright 2018 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package prometheus
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import "testing"
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type collectorDescribedByCollect struct {
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cnt Counter
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gge Gauge
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}
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func (c collectorDescribedByCollect) Collect(ch chan<- Metric) {
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ch <- c.cnt
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ch <- c.gge
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}
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func (c collectorDescribedByCollect) Describe(ch chan<- *Desc) {
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DescribeByCollect(c, ch)
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}
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func TestDescribeByCollect(t *testing.T) {
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goodCollector := collectorDescribedByCollect{
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cnt: NewCounter(CounterOpts{Name: "c1", Help: "help c1"}),
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gge: NewGauge(GaugeOpts{Name: "g1", Help: "help g1"}),
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}
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collidingCollector := collectorDescribedByCollect{
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cnt: NewCounter(CounterOpts{Name: "c2", Help: "help c2"}),
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gge: NewGauge(GaugeOpts{Name: "g1", Help: "help g1"}),
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}
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inconsistentCollector := collectorDescribedByCollect{
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cnt: NewCounter(CounterOpts{Name: "c3", Help: "help c3"}),
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gge: NewGauge(GaugeOpts{Name: "c3", Help: "help inconsistent"}),
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}
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reg := NewPedanticRegistry()
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if err := reg.Register(goodCollector); err != nil {
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t.Error("registration failed:", err)
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}
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if err := reg.Register(collidingCollector); err == nil {
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t.Error("registration unexpectedly succeeded")
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}
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if err := reg.Register(inconsistentCollector); err == nil {
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t.Error("registration unexpectedly succeeded")
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}
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if _, err := reg.Gather(); err != nil {
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t.Error("gathering failed:", err)
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}
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}
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