feat: initial tracing support (#1623)

vendor/google.golang.org/grpc/balancer/base/base.go

@@ -0,0 +1,71 @@
+/*
+ *
+ * Copyright 2017 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 base defines a balancer base that can be used to build balancers with
+// different picking algorithms.
+//
+// The base balancer creates a new SubConn for each resolved address. The
+// provided picker will only be notified about READY SubConns.
+//
+// This package is the base of round_robin balancer, its purpose is to be used
+// to build round_robin like balancers with complex picking algorithms.
+// Balancers with more complicated logic should try to implement a balancer
+// builder from scratch.
+//
+// All APIs in this package are experimental.
+package base
+
+import (
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/resolver"
+)
+
+// PickerBuilder creates balancer.Picker.
+type PickerBuilder interface {
+	// Build returns a picker that will be used by gRPC to pick a SubConn.
+	Build(info PickerBuildInfo) balancer.Picker
+}
+
+// PickerBuildInfo contains information needed by the picker builder to
+// construct a picker.
+type PickerBuildInfo struct {
+	// ReadySCs is a map from all ready SubConns to the Addresses used to
+	// create them.
+	ReadySCs map[balancer.SubConn]SubConnInfo
+}
+
+// SubConnInfo contains information about a SubConn created by the base
+// balancer.
+type SubConnInfo struct {
+	Address resolver.Address // the address used to create this SubConn
+}
+
+// Config contains the config info about the base balancer builder.
+type Config struct {
+	// HealthCheck indicates whether health checking should be enabled for this specific balancer.
+	HealthCheck bool
+}
+
+// NewBalancerBuilder returns a base balancer builder configured by the provided config.
+func NewBalancerBuilder(name string, pb PickerBuilder, config Config) balancer.Builder {
+	return &baseBuilder{
+		name:          name,
+		pickerBuilder: pb,
+		config:        config,
+	}
+}