add cluster support for realtime bucket stats (#11963)

implementation in #11949 only catered from single
node, but we need cluster metrics by capturing
from all peers. introduce bucket stats API that
will be used for capturing in-line bucket usage
as well eventually

cmd/bucket-stats.go

@@ -0,0 +1,41 @@
+/*
+ * MinIO Cloud Storage, (C) 2021 MinIO, Inc.
+ *
+ * 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 cmd
+
+//go:generate msgp -file $GOFILE
+
+// BucketStats bucket statistics
+type BucketStats struct {
+	ReplicationStats BucketReplicationStats
+}
+
+// BucketReplicationStats represents inline replication statistics
+// such as pending, failed and completed bytes in total for a bucket
+type BucketReplicationStats struct {
+	// Pending size in bytes
+	PendingSize uint64 `json:"pendingReplicationSize"`
+	// Completed size in bytes
+	ReplicatedSize uint64 `json:"completedReplicationSize"`
+	// Total Replica size in bytes
+	ReplicaSize uint64 `json:"replicaSize"`
+	// Failed size in bytes
+	FailedSize uint64 `json:"failedReplicationSize"`
+	// Total number of pending operations including metadata updates
+	PendingCount uint64 `json:"pendingReplicationCount"`
+	// Total number of failed operations including metadata updates
+	FailedCount uint64 `json:"failedReplicationCount"`
+}