Added integration support for DataDog APM Tracing

vendor/gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer/propagator.go

@@ -0,0 +1,52 @@
+package tracer
+
+import (
+	"errors"
+
+	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
+)
+
+// Propagator implementations should be able to inject and extract
+// SpanContexts into an implementation specific carrier.
+type Propagator interface {
+	// Inject takes the SpanContext and injects it into the carrier.
+	Inject(context ddtrace.SpanContext, carrier interface{}) error
+
+	// Extract returns the SpanContext from the given carrier.
+	Extract(carrier interface{}) (ddtrace.SpanContext, error)
+}
+
+// TextMapWriter allows setting key/value pairs of strings on the underlying
+// data structure. Carriers implementing TextMapWriter are compatible to be
+// used with Datadog's TextMapPropagator.
+type TextMapWriter interface {
+	// Set sets the given key/value pair.
+	Set(key, val string)
+}
+
+// TextMapReader allows iterating over sets of key/value pairs. Carriers implementing
+// TextMapReader are compatible to be used with Datadog's TextMapPropagator.
+type TextMapReader interface {
+	// ForeachKey iterates over all keys that exist in the underlying
+	// carrier. It takes a callback function which will be called
+	// using all key/value pairs as arguments. ForeachKey will return
+	// the first error returned by the handler.
+	ForeachKey(handler func(key, val string) error) error
+}
+
+var (
+	// ErrInvalidCarrier is returned when the carrier provided to the propagator
+	// does not implemented the correct interfaces.
+	ErrInvalidCarrier = errors.New("invalid carrier")
+
+	// ErrInvalidSpanContext is returned when the span context found in the
+	// carrier is not of the expected type.
+	ErrInvalidSpanContext = errors.New("invalid span context")
+
+	// ErrSpanContextCorrupted is returned when there was a problem parsing
+	// the information found in the carrier.
+	ErrSpanContextCorrupted = errors.New("span context corrupted")
+
+	// ErrSpanContextNotFound represents missing information in the given carrier.
+	ErrSpanContextNotFound = errors.New("span context not found")
+)