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 15 package global // import "go.opentelemetry.io/otel/internal/global" 16 17 import ( 18 "context" 19 "sync" 20 21 "go.opentelemetry.io/otel/propagation" 22 ) 23 24 // textMapPropagator is a default TextMapPropagator that delegates calls to a 25 // registered delegate if one is set, otherwise it defaults to delegating the 26 // calls to a the default no-op propagation.TextMapPropagator. 27 type textMapPropagator struct { 28 mtx sync.Mutex 29 once sync.Once 30 delegate propagation.TextMapPropagator 31 noop propagation.TextMapPropagator 32 } 33 34 // Compile-time guarantee that textMapPropagator implements the 35 // propagation.TextMapPropagator interface. 36 var _ propagation.TextMapPropagator = (*textMapPropagator)(nil) 37 38 func newTextMapPropagator() *textMapPropagator { 39 return &textMapPropagator{ 40 noop: propagation.NewCompositeTextMapPropagator(), 41 } 42 } 43 44 // SetDelegate sets a delegate propagation.TextMapPropagator that all calls are 45 // forwarded to. Delegation can only be performed once, all subsequent calls 46 // perform no delegation. 47 func (p *textMapPropagator) SetDelegate(delegate propagation.TextMapPropagator) { 48 if delegate == nil { 49 return 50 } 51 52 p.mtx.Lock() 53 p.once.Do(func() { p.delegate = delegate }) 54 p.mtx.Unlock() 55 } 56 57 // effectiveDelegate returns the current delegate of p if one is set, 58 // otherwise the default noop TextMapPropagator is returned. This method 59 // can be called concurrently. 60 func (p *textMapPropagator) effectiveDelegate() propagation.TextMapPropagator { 61 p.mtx.Lock() 62 defer p.mtx.Unlock() 63 if p.delegate != nil { 64 return p.delegate 65 } 66 return p.noop 67 } 68 69 // Inject set cross-cutting concerns from the Context into the carrier. 70 func (p *textMapPropagator) Inject(ctx context.Context, carrier propagation.TextMapCarrier) { 71 p.effectiveDelegate().Inject(ctx, carrier) 72 } 73 74 // Extract reads cross-cutting concerns from the carrier into a Context. 75 func (p *textMapPropagator) Extract(ctx context.Context, carrier propagation.TextMapCarrier) context.Context { 76 return p.effectiveDelegate().Extract(ctx, carrier) 77 } 78 79 // Fields returns the keys whose values are set with Inject. 80 func (p *textMapPropagator) Fields() []string { 81 return p.effectiveDelegate().Fields() 82 } 83