Opentracing support

vendor/github.com/opentracing-contrib/go-observer/observer.go

@@ -0,0 +1,39 @@
+// This project is licensed under the Apache License 2.0, see LICENSE.
+
+package otobserver
+
+import opentracing "github.com/opentracing/opentracing-go"
+
+// Observer can be registered with a Tracer to recieve notifications
+// about new Spans. Tracers are not required to support the Observer API.
+// The actual registration depends on the implementation, which might look
+// like the below e.g :
+// observer := myobserver.NewObserver()
+// tracer := client.NewTracer(..., client.WithObserver(observer))
+//
+type Observer interface {
+	// Create and return a span observer. Called when a span starts.
+	// If the Observer is not interested in the given span, it must return (nil, false).
+	// E.g :
+	//     func StartSpan(opName string, opts ...opentracing.StartSpanOption) {
+	//         var sp opentracing.Span
+	//         sso := opentracing.StartSpanOptions{}
+	//         spanObserver, ok := observer.OnStartSpan(span, opName, sso);
+	//         if ok {
+	//             // we have a valid SpanObserver
+	//         }
+	//         ...
+	//     }
+	OnStartSpan(sp opentracing.Span, operationName string, options opentracing.StartSpanOptions) (SpanObserver, bool)
+}
+
+// SpanObserver is created by the Observer and receives notifications about
+// other Span events.
+type SpanObserver interface {
+	// Callback called from opentracing.Span.SetOperationName()
+	OnSetOperationName(operationName string)
+	// Callback called from opentracing.Span.SetTag()
+	OnSetTag(key string, value interface{})
+	// Callback called from opentracing.Span.Finish()
+	OnFinish(options opentracing.FinishOptions)
+}