content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.cli.fs.command;
  
  import alluxio.AlluxioURI;
  import alluxio.Constants;
  import alluxio.annotation.PublicApi;
  import alluxio.cli.CommandUtils;
  import alluxio.client.file.FileInStream;
  import alluxio.client.file.FileSystemContext;
  import alluxio.client.file.URIStatus;
  import alluxio.exception.AlluxioException;
  import alluxio.exception.ExceptionMessage;
  import alluxio.exception.status.InvalidArgumentException;
  import alluxio.util.FormatUtils;
  
  import com.google.common.base.Preconditions;
  import com.google.common.io.ByteStreams;
  import org.apache.commons.cli.CommandLine;
  import org.apache.commons.cli.Option;
  import org.apache.commons.cli.Options;
  
  import java.io.IOException;
  import javax.annotation.concurrent.ThreadSafe;
  
  /**
   * Prints the file's last n bytes (by default, 1KB) to the console.
   */
  @ThreadSafe
  @PublicApi
  public final class TailCommand extends AbstractFileSystemCommand {
    private static final Option BYTES_OPTION = Option.builder("c")
        .required(false)
        .numberOfArgs(1)
        .desc("number of bytes (e.g., 1024, 4KB)")
        .build();
  
    /**
     * @param fsContext the filesystem of Alluxio
     */
    public TailCommand(FileSystemContext fsContext) {
      super(fsContext);
    }
  
    @Override
    public String getCommandName() {
      return "tail";
    }
  
    @Override
    protected void runPlainPath(AlluxioURI path, CommandLine cl)
        throws AlluxioException, IOException {
      URIStatus status = mFileSystem.getStatus(path);
      int numOfBytes = Constants.KB;
      if (cl.hasOption('c')) {
        numOfBytes = (int) FormatUtils.parseSpaceSize(cl.getOptionValue('c'));
        Preconditions.checkArgument(numOfBytes > 0, "specified bytes must be > 0");
      }
  
      if (status.isFolder()) {
        throw new IOException(ExceptionMessage.PATH_MUST_BE_FILE.getMessage(path));
      }
      try (FileInStream is = mFileSystem.openFile(path)) {
        final long bytesToRead = Math.min(status.getLength(), numOfBytes);
        ByteStreams.skipFully(is, status.getLength() - bytesToRead);
        ByteStreams.copy(ByteStreams.limit(is, bytesToRead), System.out);
      }
    }
  
    @Override
    public int run(CommandLine cl) throws AlluxioException, IOException {
      String[] args = cl.getArgs();
      AlluxioURI path = new AlluxioURI(args[0]);
      runWildCardCmd(path, cl);
      return 0;
    }
  
    @Override
    public String getUsage() {
      return "tail [-c <bytes>] <path>";
    }
  
    @Override
    public String getDescription() {
      return "Prints the file's last n bytes (by default, 1KB) to the console.";
    }
  
    @Override
    public void validateArgs(CommandLine cl) throws InvalidArgumentException {
      CommandUtils.checkNumOfArgsEquals(this, cl, 1);
    }
  
    @Override
    public Options getOptions() {
      return new Options().addOption(BYTES_OPTION);
    }
  }
  