initial import

core/trace/carrier.go

@@ -0,0 +1,41 @@
+package trace
+
+import (
+	"errors"
+	"net/http"
+	"strings"
+)
+
+var ErrInvalidCarrier = errors.New("invalid carrier")
+
+type (
+	Carrier interface {
+		Get(key string) string
+		Set(key, value string)
+	}
+
+	httpCarrier http.Header
+	// grpc metadata takes keys as case insensitive
+	grpcCarrier map[string][]string
+)
+
+func (h httpCarrier) Get(key string) string {
+	return http.Header(h).Get(key)
+}
+
+func (h httpCarrier) Set(key, val string) {
+	http.Header(h).Set(key, val)
+}
+
+func (g grpcCarrier) Get(key string) string {
+	if vals, ok := g[strings.ToLower(key)]; ok && len(vals) > 0 {
+		return vals[0]
+	} else {
+		return ""
+	}
+}
+
+func (g grpcCarrier) Set(key, val string) {
+	key = strings.ToLower(key)
+	g[key] = append(g[key], val)
+}