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- // Copyright 2014 The Prometheus Authors
- // Licensed under the Apache License, Version 2.0 (the "License");
- // you may not use this file except in compliance with the License.
- // You may obtain a copy of the License at
- //
- // http://www.apache.org/licenses/LICENSE-2.0
- //
- // Unless required by applicable law or agreed to in writing, software
- // distributed under the License is distributed on an "AS IS" BASIS,
- // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- // See the License for the specific language governing permissions and
- // limitations under the License.
- package prometheus
- import (
- "encoding/json"
- "expvar"
- )
- type expvarCollector struct {
- exports map[string]*Desc
- }
- // NewExpvarCollector returns a newly allocated expvar Collector that still has
- // to be registered with a Prometheus registry.
- //
- // An expvar Collector collects metrics from the expvar interface. It provides a
- // quick way to expose numeric values that are already exported via expvar as
- // Prometheus metrics. Note that the data models of expvar and Prometheus are
- // fundamentally different, and that the expvar Collector is inherently slower
- // than native Prometheus metrics. Thus, the expvar Collector is probably great
- // for experiments and prototying, but you should seriously consider a more
- // direct implementation of Prometheus metrics for monitoring production
- // systems.
- //
- // The exports map has the following meaning:
- //
- // The keys in the map correspond to expvar keys, i.e. for every expvar key you
- // want to export as Prometheus metric, you need an entry in the exports
- // map. The descriptor mapped to each key describes how to export the expvar
- // value. It defines the name and the help string of the Prometheus metric
- // proxying the expvar value. The type will always be Untyped.
- //
- // For descriptors without variable labels, the expvar value must be a number or
- // a bool. The number is then directly exported as the Prometheus sample
- // value. (For a bool, 'false' translates to 0 and 'true' to 1). Expvar values
- // that are not numbers or bools are silently ignored.
- //
- // If the descriptor has one variable label, the expvar value must be an expvar
- // map. The keys in the expvar map become the various values of the one
- // Prometheus label. The values in the expvar map must be numbers or bools again
- // as above.
- //
- // For descriptors with more than one variable label, the expvar must be a
- // nested expvar map, i.e. where the values of the topmost map are maps again
- // etc. until a depth is reached that corresponds to the number of labels. The
- // leaves of that structure must be numbers or bools as above to serve as the
- // sample values.
- //
- // Anything that does not fit into the scheme above is silently ignored.
- func NewExpvarCollector(exports map[string]*Desc) Collector {
- return &expvarCollector{
- exports: exports,
- }
- }
- // Describe implements Collector.
- func (e *expvarCollector) Describe(ch chan<- *Desc) {
- for _, desc := range e.exports {
- ch <- desc
- }
- }
- // Collect implements Collector.
- func (e *expvarCollector) Collect(ch chan<- Metric) {
- for name, desc := range e.exports {
- var m Metric
- expVar := expvar.Get(name)
- if expVar == nil {
- continue
- }
- var v interface{}
- labels := make([]string, len(desc.variableLabels))
- if err := json.Unmarshal([]byte(expVar.String()), &v); err != nil {
- ch <- NewInvalidMetric(desc, err)
- continue
- }
- var processValue func(v interface{}, i int)
- processValue = func(v interface{}, i int) {
- if i >= len(labels) {
- copiedLabels := append(make([]string, 0, len(labels)), labels...)
- switch v := v.(type) {
- case float64:
- m = MustNewConstMetric(desc, UntypedValue, v, copiedLabels...)
- case bool:
- if v {
- m = MustNewConstMetric(desc, UntypedValue, 1, copiedLabels...)
- } else {
- m = MustNewConstMetric(desc, UntypedValue, 0, copiedLabels...)
- }
- default:
- return
- }
- ch <- m
- return
- }
- vm, ok := v.(map[string]interface{})
- if !ok {
- return
- }
- for lv, val := range vm {
- labels[i] = lv
- processValue(val, i+1)
- }
- }
- processValue(v, 0)
- }
- }
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