Add Tracing Header Context Name option for Jaeger

vendor/github.com/uber/jaeger-client-go/tracer.go

@@ -50,6 +50,7 @@ type Tracer struct {
 		gen128Bit            bool // whether to generate 128bit trace IDs
 		zipkinSharedRPCSpan  bool
 		highTraceIDGenerator func() uint64 // custom high trace ID generator
+		maxTagValueLength    int
 		// more options to come
 	}
 	// pool for Span objects
@@ -152,6 +153,9 @@ func NewTracer(
 		t.logger.Error("Overriding high trace ID generator but not generating " +
 			"128 bit trace IDs, consider enabling the \"Gen128Bit\" option")
 	}
+	if t.options.maxTagValueLength == 0 {
+		t.options.maxTagValueLength = DefaultMaxTagValueLength
+	}
 	t.process = Process{
 		Service: serviceName,
 		UUID:    strconv.FormatUint(t.randomNumber(), 16),
@@ -194,6 +198,12 @@ func (t *Tracer) startSpanWithOptions(
 		options.StartTime = t.timeNow()
 	}
 
+	// Predicate whether the given span context is a valid reference
+	// which may be used as parent / debug ID / baggage items source
+	isValidReference := func(ctx SpanContext) bool {
+		return ctx.IsValid() || ctx.isDebugIDContainerOnly() || len(ctx.baggage) != 0
+	}
+
 	var references []Reference
 	var parent SpanContext
 	var hasParent bool // need this because `parent` is a value, not reference
@@ -205,7 +215,7 @@ func (t *Tracer) startSpanWithOptions(
 				reflect.ValueOf(ref.ReferencedContext)))
 			continue
 		}
-		if !(ctx.IsValid() || ctx.isDebugIDContainerOnly() || len(ctx.baggage) != 0) {
+		if !isValidReference(ctx) {
 			continue
 		}
 		references = append(references, Reference{Type: ref.Type, Context: ctx})
@@ -214,7 +224,7 @@ func (t *Tracer) startSpanWithOptions(
 			hasParent = ref.Type == opentracing.ChildOfRef
 		}
 	}
-	if !hasParent && parent.IsValid() {
+	if !hasParent && isValidReference(parent) {
 		// If ChildOfRef wasn't found but a FollowFromRef exists, use the context from
 		// the FollowFromRef as the parent
 		hasParent = true