initial import

core/trace/propagator.go

@@ -0,0 +1,85 @@
+package trace
+
+import (
+	"net/http"
+
+	"google.golang.org/grpc/metadata"
+)
+
+const (
+	HttpFormat = iota
+	GrpcFormat
+)
+
+var (
+	emptyHttpPropagator httpPropagator
+	emptyGrpcPropagator grpcPropagator
+)
+
+type (
+	Propagator interface {
+		Extract(carrier interface{}) (Carrier, error)
+		Inject(carrier interface{}) (Carrier, error)
+	}
+
+	httpPropagator struct{}
+	grpcPropagator struct{}
+)
+
+func (h httpPropagator) Extract(carrier interface{}) (Carrier, error) {
+	if c, ok := carrier.(http.Header); !ok {
+		return nil, ErrInvalidCarrier
+	} else {
+		return httpCarrier(c), nil
+	}
+}
+
+func (h httpPropagator) Inject(carrier interface{}) (Carrier, error) {
+	if c, ok := carrier.(http.Header); ok {
+		return httpCarrier(c), nil
+	} else {
+		return nil, ErrInvalidCarrier
+	}
+}
+
+func (g grpcPropagator) Extract(carrier interface{}) (Carrier, error) {
+	if c, ok := carrier.(metadata.MD); ok {
+		return grpcCarrier(c), nil
+	} else {
+		return nil, ErrInvalidCarrier
+	}
+}
+
+func (g grpcPropagator) Inject(carrier interface{}) (Carrier, error) {
+	if c, ok := carrier.(metadata.MD); ok {
+		return grpcCarrier(c), nil
+	} else {
+		return nil, ErrInvalidCarrier
+	}
+}
+
+func Extract(format, carrier interface{}) (Carrier, error) {
+	switch v := format.(type) {
+	case int:
+		if v == HttpFormat {
+			return emptyHttpPropagator.Extract(carrier)
+		} else if v == GrpcFormat {
+			return emptyGrpcPropagator.Extract(carrier)
+		}
+	}
+
+	return nil, ErrInvalidCarrier
+}
+
+func Inject(format, carrier interface{}) (Carrier, error) {
+	switch v := format.(type) {
+	case int:
+		if v == HttpFormat {
+			return emptyHttpPropagator.Inject(carrier)
+		} else if v == GrpcFormat {
+			return emptyGrpcPropagator.Inject(carrier)
+		}
+	}
+
+	return nil, ErrInvalidCarrier
+}