1// Copyright The OpenTelemetry Authors
 2// SPDX-License-Identifier: Apache-2.0
 3
 4package otelhttp // import "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 5
 6import (
 7	"context"
 8	"sync"
 9
10	"go.opentelemetry.io/otel/attribute"
11)
12
13// Labeler is used to allow instrumented HTTP handlers to add custom attributes to
14// the metrics recorded by the net/http instrumentation.
15type Labeler struct {
16	mu         sync.Mutex
17	attributes []attribute.KeyValue
18}
19
20// Add attributes to a Labeler.
21func (l *Labeler) Add(ls ...attribute.KeyValue) {
22	l.mu.Lock()
23	defer l.mu.Unlock()
24	l.attributes = append(l.attributes, ls...)
25}
26
27// Get returns a copy of the attributes added to the Labeler.
28func (l *Labeler) Get() []attribute.KeyValue {
29	l.mu.Lock()
30	defer l.mu.Unlock()
31	ret := make([]attribute.KeyValue, len(l.attributes))
32	copy(ret, l.attributes)
33	return ret
34}
35
36type labelerContextKeyType int
37
38const lablelerContextKey labelerContextKeyType = 0
39
40// ContextWithLabeler returns a new context with the provided Labeler instance.
41// Attributes added to the specified labeler will be injected into metrics
42// emitted by the instrumentation. Only one labeller can be injected into the
43// context. Injecting it multiple times will override the previous calls.
44func ContextWithLabeler(parent context.Context, l *Labeler) context.Context {
45	return context.WithValue(parent, lablelerContextKey, l)
46}
47
48// LabelerFromContext retrieves a Labeler instance from the provided context if
49// one is available.  If no Labeler was found in the provided context a new, empty
50// Labeler is returned and the second return value is false.  In this case it is
51// safe to use the Labeler but any attributes added to it will not be used.
52func LabelerFromContext(ctx context.Context) (*Labeler, bool) {
53	l, ok := ctx.Value(lablelerContextKey).(*Labeler)
54	if !ok {
55		l = &Labeler{}
56	}
57	return l, ok
58}