Add interface for csi client (aws#3899)

* Add interface for csi client

* Add comments

* Add comments

ecs-agent/csiclient/csi_client.go

@@ -1,3 +1,16 @@
+// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"). You may
+// not use this file except in compliance with the License. A copy of the
+// License is located at
+//
+//	http://aws.amazon.com/apache2.0/
+//
+// or in the "license" file accompanying this file. This file 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 csiclient
 
 import (
@@ -18,13 +31,21 @@ const (
 	PROTOCOL = "unix"
 )
 
+// CSIClient is an interface that specifies all supported operations in the Container Storage Interface(CSI)
+// driver for Agent uses. The CSI driver provides many volume related operations to manage the lifecycle of
+// Amazon EBS volumes, including mounting, umounting, resizing and volume stats.
+type CSIClient interface {
+	GetVolumeMetrics(volumeId string, hostMountPath string) (*Metrics, error)
+}
+
 // csiClient encapsulates all CSI methods.
 type csiClient struct {
 	csiSocket string
 }
 
-func NewCSIClient(socketIn string) csiClient {
-	return csiClient{csiSocket: socketIn}
+// NewCSIClient creates a CSI client for the communication with CSI driver daemon.
+func NewCSIClient(socketIn string) CSIClient {
+	return &csiClient{csiSocket: socketIn}
 }
 
 // GetVolumeMetrics returns volume usage.

ecs-agent/csiclient/dummy_csiclient.go

@@ -0,0 +1,31 @@
+// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"). You may
+// not use this file except in compliance with the License. A copy of the
+// License is located at
+//
+//	http://aws.amazon.com/apache2.0/
+//
+// or in the "license" file accompanying this file. This file 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 csiclient
+
+const gibToBytes = 1024 * 1024 * 1024
+
+// dummyCSIClient can be used to test the behaviour of csi client.
+type dummyCSIClient struct {
+}
+
+func (c *dummyCSIClient) GetVolumeMetrics(volumeId string, hostMountPath string) (*Metrics, error) {
+	return &Metrics{
+		Used:     15 * gibToBytes,
+		Capacity: 20 * gibToBytes,
+	}, nil
+}
+
+func NewDummyCSIClient() CSIClient {
+	return &dummyCSIClient{}
+}

ecs-agent/csiclient/volume.go

@@ -1,10 +1,23 @@
+// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"). You may
+// not use this file except in compliance with the License. A copy of the
+// License is located at
+//
+//	http://aws.amazon.com/apache2.0/
+//
+// or in the "license" file accompanying this file. This file 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 csiclient
 
 // Metrics represents the used and capacity bytes of the Volume.
 type Metrics struct {
 	// Used represents the total bytes used by the Volume.
-	Used int64
+	Used int64 `json:"Used"`
 
 	// Capacity represents the total capacity (bytes) of the volume's underlying storage.
-	Capacity int64
+	Capacity int64 `json:"Capacity"`
 }