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// Copyright 2019 The Go Cloud Development Kit 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
//
// https://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 oc
import (
"context"
"fmt"
"reflect"
"time"
"go.opencensus.io/stats"
"go.opencensus.io/tag"
"go.opencensus.io/trace"
"gocloud.dev/gcerrors"
)
// A Tracer supports OpenCensus tracing and latency metrics.
type Tracer struct {
Package string
Provider string
LatencyMeasure *stats.Float64Measure
}
// ProviderName returns the name of the provider associated with the driver value.
// It is intended to be used to set Tracer.Provider.
// It actually returns the package path of the driver's type.
func ProviderName(driver interface{}) string {
// Return the last component of the package path.
if driver == nil {
return ""
}
t := reflect.TypeOf(driver)
if t.Kind() == reflect.Ptr {
t = t.Elem()
}
return t.PkgPath()
}
// Context key for starting time of a method call.
type startTimeKey struct{}
// Start adds a span to the trace, and prepares for recording a latency measurement.
func (t *Tracer) Start(ctx context.Context, methodName string) context.Context {
fullName := t.Package + "." + methodName
ctx, _ = trace.StartSpan(ctx, fullName)
ctx, err := tag.New(ctx,
tag.Upsert(MethodKey, fullName),
tag.Upsert(ProviderKey, t.Provider))
if err != nil {
// The only possible errors are from invalid key or value names, and those are programming
// errors that will be found during testing.
panic(fmt.Sprintf("fullName=%q, provider=%q: %v", fullName, t.Provider, err))
}
return context.WithValue(ctx, startTimeKey{}, time.Now())
}
// End ends a span with the given error, and records a latency measurement.
func (t *Tracer) End(ctx context.Context, err error) {
startTime := ctx.Value(startTimeKey{}).(time.Time)
elapsed := time.Since(startTime)
code := gcerrors.Code(err)
span := trace.FromContext(ctx)
if err != nil {
span.SetStatus(trace.Status{Code: int32(code), Message: err.Error()})
}
span.End()
stats.RecordWithTags(ctx, []tag.Mutator{tag.Upsert(StatusKey, fmt.Sprint(code))},
t.LatencyMeasure.M(float64(elapsed.Nanoseconds())/1e6)) // milliseconds
}
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