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// Copyright (c) 2017 Uber Technologies, Inc.
//
// 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 metrics
import (
"fmt"
"reflect"
"strings"
)
// Init initializes the passed in metrics and initializes its fields using the passed in factory.
func Init(metrics interface{}, factory Factory, globalTags map[string]string) {
if err := initMetrics(metrics, factory, globalTags); err != nil {
panic(err.Error())
}
}
// initMetrics uses reflection to initialize a struct containing metrics fields
// by assigning new Counter/Gauge/Timer values with the metric name retrieved
// from the `metric` tag and stats tags retrieved from the `tags` tag.
//
// Note: all fields of the struct must be exported, have a `metric` tag, and be
// of type Counter or Gauge or Timer.
func initMetrics(m interface{}, factory Factory, globalTags map[string]string) error {
// Allow user to opt out of reporting metrics by passing in nil.
if factory == nil {
factory = NullFactory
}
counterPtrType := reflect.TypeOf((*Counter)(nil)).Elem()
gaugePtrType := reflect.TypeOf((*Gauge)(nil)).Elem()
timerPtrType := reflect.TypeOf((*Timer)(nil)).Elem()
v := reflect.ValueOf(m).Elem()
t := v.Type()
for i := 0; i < t.NumField(); i++ {
tags := make(map[string]string)
for k, v := range globalTags {
tags[k] = v
}
field := t.Field(i)
metric := field.Tag.Get("metric")
if metric == "" {
return fmt.Errorf("Field %s is missing a tag 'metric'", field.Name)
}
if tagString := field.Tag.Get("tags"); tagString != "" {
tagPairs := strings.Split(tagString, ",")
for _, tagPair := range tagPairs {
tag := strings.Split(tagPair, "=")
if len(tag) != 2 {
return fmt.Errorf(
"Field [%s]: Tag [%s] is not of the form key=value in 'tags' string [%s]",
field.Name, tagPair, tagString)
}
tags[tag[0]] = tag[1]
}
}
var obj interface{}
if field.Type.AssignableTo(counterPtrType) {
obj = factory.Counter(metric, tags)
} else if field.Type.AssignableTo(gaugePtrType) {
obj = factory.Gauge(metric, tags)
} else if field.Type.AssignableTo(timerPtrType) {
obj = factory.Timer(metric, tags)
} else {
return fmt.Errorf(
"Field %s is not a pointer to timer, gauge, or counter",
field.Name)
}
v.Field(i).Set(reflect.ValueOf(obj))
}
return nil
}
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