1package opentracing 2 3import "context" 4 5type contextKey struct{} 6 7var activeSpanKey = contextKey{} 8 9// ContextWithSpan returns a new `context.Context` that holds a reference to 10// the span. If span is nil, a new context without an active span is returned. 11func ContextWithSpan(ctx context.Context, span Span) context.Context { 12 if span != nil { 13 if tracerWithHook, ok := span.Tracer().(TracerContextWithSpanExtension); ok { 14 ctx = tracerWithHook.ContextWithSpanHook(ctx, span) 15 } 16 } 17 return context.WithValue(ctx, activeSpanKey, span) 18} 19 20// SpanFromContext returns the `Span` previously associated with `ctx`, or 21// `nil` if no such `Span` could be found. 22// 23// NOTE: context.Context != SpanContext: the former is Go's intra-process 24// context propagation mechanism, and the latter houses OpenTracing's per-Span 25// identity and baggage information. 26func SpanFromContext(ctx context.Context) Span { 27 val := ctx.Value(activeSpanKey) 28 if sp, ok := val.(Span); ok { 29 return sp 30 } 31 return nil 32} 33 34// StartSpanFromContext starts and returns a Span with `operationName`, using 35// any Span found within `ctx` as a ChildOfRef. If no such parent could be 36// found, StartSpanFromContext creates a root (parentless) Span. 37// 38// The second return value is a context.Context object built around the 39// returned Span. 40// 41// Example usage: 42// 43// SomeFunction(ctx context.Context, ...) { 44// sp, ctx := opentracing.StartSpanFromContext(ctx, "SomeFunction") 45// defer sp.Finish() 46// ... 47// } 48func StartSpanFromContext(ctx context.Context, operationName string, opts ...StartSpanOption) (Span, context.Context) { 49 return StartSpanFromContextWithTracer(ctx, GlobalTracer(), operationName, opts...) 50} 51 52// StartSpanFromContextWithTracer starts and returns a span with `operationName` 53// using a span found within the context as a ChildOfRef. If that doesn't exist 54// it creates a root span. It also returns a context.Context object built 55// around the returned span. 56// 57// It's behavior is identical to StartSpanFromContext except that it takes an explicit 58// tracer as opposed to using the global tracer. 59func StartSpanFromContextWithTracer(ctx context.Context, tracer Tracer, operationName string, opts ...StartSpanOption) (Span, context.Context) { 60 if parentSpan := SpanFromContext(ctx); parentSpan != nil { 61 opts = append(opts, ChildOf(parentSpan.Context())) 62 } 63 span := tracer.StartSpan(operationName, opts...) 64 return span, ContextWithSpan(ctx, span) 65} 66