1// Copyright 2019 The OpenZipkin 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 zipkin 16 17import ( 18 "context" 19) 20 21var defaultNoopSpan = &noopSpan{} 22 23// SpanFromContext retrieves a Zipkin Span from Go's context propagation 24// mechanism if found. If not found, returns nil. 25func SpanFromContext(ctx context.Context) Span { 26 if s, ok := ctx.Value(spanKey).(Span); ok { 27 return s 28 } 29 return nil 30} 31 32// SpanOrNoopFromContext retrieves a Zipkin Span from Go's context propagation 33// mechanism if found. If not found, returns a noopSpan. 34// This function typically is used for modules that want to provide existing 35// Zipkin spans with additional data, but can't guarantee that spans are 36// properly propagated. It is preferred to use SpanFromContext() and test for 37// Nil instead of using this function. 38func SpanOrNoopFromContext(ctx context.Context) Span { 39 if s, ok := ctx.Value(spanKey).(Span); ok { 40 return s 41 } 42 return defaultNoopSpan 43} 44 45// NewContext stores a Zipkin Span into Go's context propagation mechanism. 46func NewContext(ctx context.Context, s Span) context.Context { 47 return context.WithValue(ctx, spanKey, s) 48} 49 50type ctxKey struct{} 51 52var spanKey = ctxKey{} 53