Opentracing support

vendor/github.com/opentracing/opentracing-go/noop.go

@@ -0,0 +1,64 @@
+package opentracing
+
+import "github.com/opentracing/opentracing-go/log"
+
+// A NoopTracer is a trivial, minimum overhead implementation of Tracer
+// for which all operations are no-ops.
+//
+// The primary use of this implementation is in libraries, such as RPC
+// frameworks, that make tracing an optional feature controlled by the
+// end user. A no-op implementation allows said libraries to use it
+// as the default Tracer and to write instrumentation that does
+// not need to keep checking if the tracer instance is nil.
+//
+// For the same reason, the NoopTracer is the default "global" tracer
+// (see GlobalTracer and SetGlobalTracer functions).
+//
+// WARNING: NoopTracer does not support baggage propagation.
+type NoopTracer struct{}
+
+type noopSpan struct{}
+type noopSpanContext struct{}
+
+var (
+	defaultNoopSpanContext = noopSpanContext{}
+	defaultNoopSpan        = noopSpan{}
+	defaultNoopTracer      = NoopTracer{}
+)
+
+const (
+	emptyString = ""
+)
+
+// noopSpanContext:
+func (n noopSpanContext) ForeachBaggageItem(handler func(k, v string) bool) {}
+
+// noopSpan:
+func (n noopSpan) Context() SpanContext                                  { return defaultNoopSpanContext }
+func (n noopSpan) SetBaggageItem(key, val string) Span                   { return defaultNoopSpan }
+func (n noopSpan) BaggageItem(key string) string                         { return emptyString }
+func (n noopSpan) SetTag(key string, value interface{}) Span             { return n }
+func (n noopSpan) LogFields(fields ...log.Field)                         {}
+func (n noopSpan) LogKV(keyVals ...interface{})                          {}
+func (n noopSpan) Finish()                                               {}
+func (n noopSpan) FinishWithOptions(opts FinishOptions)                  {}
+func (n noopSpan) SetOperationName(operationName string) Span            { return n }
+func (n noopSpan) Tracer() Tracer                                        { return defaultNoopTracer }
+func (n noopSpan) LogEvent(event string)                                 {}
+func (n noopSpan) LogEventWithPayload(event string, payload interface{}) {}
+func (n noopSpan) Log(data LogData)                                      {}
+
+// StartSpan belongs to the Tracer interface.
+func (n NoopTracer) StartSpan(operationName string, opts ...StartSpanOption) Span {
+	return defaultNoopSpan
+}
+
+// Inject belongs to the Tracer interface.
+func (n NoopTracer) Inject(sp SpanContext, format interface{}, carrier interface{}) error {
+	return nil
+}
+
+// Extract belongs to the Tracer interface.
+func (n NoopTracer) Extract(format interface{}, carrier interface{}) (SpanContext, error) {
+	return nil, ErrSpanContextNotFound
+}