restic/vendor/github.com/Azure/go-autorest/tracing/tracing.go

package tracing

// Copyright 2018 Microsoft Corporation
//
//  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.

import (
	"context"
	"net/http"
)

// Tracer represents an HTTP tracing facility.
type Tracer interface {
	NewTransport(base *http.Transport) http.RoundTripper
	StartSpan(ctx context.Context, name string) context.Context
	EndSpan(ctx context.Context, httpStatusCode int, err error)
}

var (
	tracer Tracer
)

// Register will register the provided Tracer.  Pass nil to unregister a Tracer.
func Register(t Tracer) {
	tracer = t
}

// IsEnabled returns true if a Tracer has been registered.
func IsEnabled() bool {
	return tracer != nil
}

// NewTransport creates a new instrumenting http.RoundTripper for the
// registered Tracer.  If no Tracer has been registered it returns nil.
func NewTransport(base *http.Transport) http.RoundTripper {
	if tracer != nil {
		return tracer.NewTransport(base)
	}
	return nil
}

// StartSpan starts a trace span with the specified name, associating it with the
// provided context.  Has no effect if a Tracer has not been registered.
func StartSpan(ctx context.Context, name string) context.Context {
	if tracer != nil {
		return tracer.StartSpan(ctx, name)
	}
	return ctx
}

// EndSpan ends a previously started span stored in the context.
// Has no effect if a Tracer has not been registered.
func EndSpan(ctx context.Context, httpStatusCode int, err error) {
	if tracer != nil {
		tracer.EndSpan(ctx, httpStatusCode, err)
	}
}