Added support for Haystack tracing

vendor/github.com/ExpediaDotCom/haystack-client-go/span_context.go

@@ -0,0 +1,80 @@
+/*
+ *  Copyright 2018 Expedia Group.
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ *
+ */
+
+package haystack
+
+import (
+	"fmt"
+)
+
+/*SpanContext implements opentracing.spanContext*/
+type SpanContext struct {
+	// traceID represents globally unique ID of the trace.
+	TraceID string
+
+	// spanID represents span ID that must be unique within its trace
+	SpanID string
+
+	// parentID refers to the ID of the parent span.
+	// Should be empty if the current span is a root span.
+	ParentID string
+
+	//Context baggage. The is a snapshot in time.
+	Baggage map[string]string
+
+	// set to true if extracted using a extractor in tracer
+	IsExtractedContext bool
+}
+
+// IsValid indicates whether this context actually represents a valid trace.
+func (context SpanContext) IsValid() bool {
+	return context.TraceID != "" && context.SpanID != ""
+}
+
+/*ForeachBaggageItem implements opentracing.spancontext*/
+func (context SpanContext) ForeachBaggageItem(handler func(k, v string) bool) {
+	for k, v := range context.Baggage {
+		if !handler(k, v) {
+			break
+		}
+	}
+}
+
+// WithBaggageItem creates a new context with an extra baggage item.
+func (context SpanContext) WithBaggageItem(key, value string) *SpanContext {
+	var newBaggage map[string]string
+	if context.Baggage == nil {
+		newBaggage = map[string]string{key: value}
+	} else {
+		newBaggage = make(map[string]string, len(context.Baggage)+1)
+		for k, v := range context.Baggage {
+			newBaggage[k] = v
+		}
+		newBaggage[key] = value
+	}
+	return &SpanContext{
+		TraceID:  context.TraceID,
+		SpanID:   context.SpanID,
+		ParentID: context.ParentID,
+		Baggage:  newBaggage,
+	}
+}
+
+/*ToString represents the string*/
+func (context SpanContext) ToString() string {
+	return fmt.Sprintf("%+v", context)
+}