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package opentracing
import "golang.org/x/net/context"
type contextKey struct{}
var activeSpanKey = contextKey{}
// ContextWithSpan returns a new `context.Context` that holds a reference to
// `span`'s SpanContext.
func ContextWithSpan(ctx context.Context, span Span) context.Context {
return context.WithValue(ctx, activeSpanKey, span)
}
// SpanFromContext returns the `Span` previously associated with `ctx`, or
// `nil` if no such `Span` could be found.
//
// NOTE: context.Context != SpanContext: the former is Go's intra-process
// context propagation mechanism, and the latter houses OpenTracing's per-Span
// identity and baggage information.
func SpanFromContext(ctx context.Context) Span {
val := ctx.Value(activeSpanKey)
if sp, ok := val.(Span); ok {
return sp
}
return nil
}
// StartSpanFromContext starts and returns a Span with `operationName`, using
// any Span found within `ctx` as a ChildOfRef. If no such parent could be
// found, StartSpanFromContext creates a root (parentless) Span.
//
// The second return value is a context.Context object built around the
// returned Span.
//
// Example usage:
//
// SomeFunction(ctx context.Context, ...) {
// sp, ctx := opentracing.StartSpanFromContext(ctx, "SomeFunction")
// defer sp.Finish()
// ...
// }
func StartSpanFromContext(ctx context.Context, operationName string, opts ...StartSpanOption) (Span, context.Context) {
return startSpanFromContextWithTracer(ctx, GlobalTracer(), operationName, opts...)
}
// startSpanFromContextWithTracer is factored out for testing purposes.
func startSpanFromContextWithTracer(ctx context.Context, tracer Tracer, operationName string, opts ...StartSpanOption) (Span, context.Context) {
var span Span
if parentSpan := SpanFromContext(ctx); parentSpan != nil {
opts = append(opts, ChildOf(parentSpan.Context()))
span = tracer.StartSpan(operationName, opts...)
} else {
span = tracer.StartSpan(operationName, opts...)
}
return span, ContextWithSpan(ctx, span)
}