1// Copyright The OpenTelemetry Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package propagation // import "go.opentelemetry.io/otel/propagation"
16
17import (
18	"context"
19	"net/http"
20)
21
22// TextMapCarrier is the storage medium used by a TextMapPropagator.
23type TextMapCarrier interface {
24	// Get returns the value associated with the passed key.
25	Get(key string) string
26	// Set stores the key-value pair.
27	Set(key string, value string)
28	// Keys lists the keys stored in this carrier.
29	Keys() []string
30}
31
32// HeaderCarrier adapts http.Header to satisfy the TextMapCarrier interface.
33type HeaderCarrier http.Header
34
35// Get returns the value associated with the passed key.
36func (hc HeaderCarrier) Get(key string) string {
37	return http.Header(hc).Get(key)
38}
39
40// Set stores the key-value pair.
41func (hc HeaderCarrier) Set(key string, value string) {
42	http.Header(hc).Set(key, value)
43}
44
45// Keys lists the keys stored in this carrier.
46func (hc HeaderCarrier) Keys() []string {
47	keys := make([]string, 0, len(hc))
48	for k := range hc {
49		keys = append(keys, k)
50	}
51	return keys
52}
53
54// TextMapPropagator propagates cross-cutting concerns as key-value text
55// pairs within a carrier that travels in-band across process boundaries.
56type TextMapPropagator interface {
57	// Inject set cross-cutting concerns from the Context into the carrier.
58	Inject(ctx context.Context, carrier TextMapCarrier)
59	// Extract reads cross-cutting concerns from the carrier into a Context.
60	Extract(ctx context.Context, carrier TextMapCarrier) context.Context
61	// Fields returns the keys who's values are set with Inject.
62	Fields() []string
63}
64
65type compositeTextMapPropagator []TextMapPropagator
66
67func (p compositeTextMapPropagator) Inject(ctx context.Context, carrier TextMapCarrier) {
68	for _, i := range p {
69		i.Inject(ctx, carrier)
70	}
71}
72
73func (p compositeTextMapPropagator) Extract(ctx context.Context, carrier TextMapCarrier) context.Context {
74	for _, i := range p {
75		ctx = i.Extract(ctx, carrier)
76	}
77	return ctx
78}
79
80func (p compositeTextMapPropagator) Fields() []string {
81	unique := make(map[string]struct{})
82	for _, i := range p {
83		for _, k := range i.Fields() {
84			unique[k] = struct{}{}
85		}
86	}
87
88	fields := make([]string, 0, len(unique))
89	for k := range unique {
90		fields = append(fields, k)
91	}
92	return fields
93}
94
95// NewCompositeTextMapPropagator returns a unified TextMapPropagator from the
96// group of passed TextMapPropagator. This allows different cross-cutting
97// concerns to be propagates in a unified manner.
98//
99// The returned TextMapPropagator will inject and extract cross-cutting
100// concerns in the order the TextMapPropagators were provided. Additionally,
101// the Fields method will return a de-duplicated slice of the keys that are
102// set with the Inject method.
103func NewCompositeTextMapPropagator(p ...TextMapPropagator) TextMapPropagator {
104	return compositeTextMapPropagator(p)
105}
106