1 package opentracing 2 3 import "context" 4 5 type contextKey struct{} 6 7 var 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. 11 func 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. 26 func 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 // } 48 func 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. 59 func 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