HDDS-3638. Add a cat command to show the text of a file in the Ozone server

hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/shell/keys/CatKeyHandler.java

@@ -0,0 +1,60 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.ozone.shell.keys;
+
+import static org.apache.hadoop.hdds.scm.ScmConfigKeys.OZONE_SCM_CHUNK_SIZE_DEFAULT;
+import static org.apache.hadoop.hdds.scm.ScmConfigKeys.OZONE_SCM_CHUNK_SIZE_KEY;
+
+import org.apache.hadoop.conf.StorageUnit;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.ozone.client.OzoneBucket;
+import org.apache.hadoop.ozone.client.OzoneClient;
+import org.apache.hadoop.ozone.client.OzoneClientException;
+import org.apache.hadoop.ozone.client.OzoneVolume;
+import org.apache.hadoop.ozone.shell.OzoneAddress;
+import picocli.CommandLine.Command;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+/**
+ * Cat an existing key.
+ */
+@Command(name = "cat",
+    description = "Cat a specific key from ozone server")
+public class CatKeyHandler extends KeyHandler {
+
+  @Override
+  protected void execute(OzoneClient client, OzoneAddress address)
+      throws IOException, OzoneClientException {
+
+    String volumeName = address.getVolumeName();
+    String bucketName = address.getBucketName();
+    String keyName = address.getKeyName();
+
+    int chunkSize = (int) getConf().getStorageSize(OZONE_SCM_CHUNK_SIZE_KEY,
+        OZONE_SCM_CHUNK_SIZE_DEFAULT, StorageUnit.BYTES);
+
+    OzoneVolume vol = client.getObjectStore().getVolume(volumeName);
+    OzoneBucket bucket = vol.getBucket(bucketName);
+    try (InputStream input = bucket.readKey(keyName)) {
+      IOUtils.copyBytes(input, System.out, chunkSize);
+    }
+  }
+}

hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/shell/keys/KeyCommands.java

@@ -38,6 +38,7 @@
         InfoKeyHandler.class,
         ListKeyHandler.class,
         GetKeyHandler.class,
+        CatKeyHandler.class,
         PutKeyHandler.class,
         RenameKeyHandler.class,
         DeleteKeyHandler.class,