feat: initial tracing support (#1623)

vendor/google.golang.org/grpc/internal/balancerload/load.go

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2019 gRPC authors.
+ *
+ * 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 balancerload defines APIs to parse server loads in trailers. The
+// parsed loads are sent to balancers in DoneInfo.
+package balancerload
+
+import (
+	"google.golang.org/grpc/metadata"
+)
+
+// Parser converts loads from metadata into a concrete type.
+type Parser interface {
+	// Parse parses loads from metadata.
+	Parse(md metadata.MD) interface{}
+}
+
+var parser Parser
+
+// SetParser sets the load parser.
+//
+// Not mutex-protected, should be called before any gRPC functions.
+func SetParser(lr Parser) {
+	parser = lr
+}
+
+// Parse calls parser.Read().
+func Parse(md metadata.MD) interface{} {
+	if parser == nil {
+		return nil
+	}
+	return parser.Parse(md)
+}