xds/google_default_creds: handshake based on cluster name in address attributes (#4310)

internal/credentials/xds/handshake_cluster.go

@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2021 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 xds
+
+import (
+	"google.golang.org/grpc/attributes"
+	"google.golang.org/grpc/resolver"
+)
+
+// handshakeClusterNameKey is the type used as the key to store cluster name in
+// the Attributes field of resolver.Address.
+type handshakeClusterNameKey struct{}
+
+// SetHandshakeClusterName returns a copy of addr in which the Attributes field
+// is updated with the cluster name.
+func SetHandshakeClusterName(addr resolver.Address, clusterName string) resolver.Address {
+	addr.Attributes = addr.Attributes.WithValues(handshakeClusterNameKey{}, clusterName)
+	return addr
+}
+
+// GetHandshakeClusterName returns cluster name stored in attr.
+func GetHandshakeClusterName(attr *attributes.Attributes) (string, bool) {
+	v := attr.Value(handshakeClusterNameKey{})
+	name, ok := v.(string)
+	return name, ok
+}