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   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2015-2016 EfficiOS Inc.
   5  * Copyright (C) 2015-2016 Alexandre Montplaisir <alexmonthy@efficios.com>
   6  * Copyright (C) 2013 David Goulet <dgoulet@efficios.com>
   7  */
   8
   9 package org.lttng.ust.agent.client;
  10
  11 import java.nio.ByteBuffer;
  12 import java.nio.charset.Charset;
  13
  14 /**
  15  * Base class to represent all commands sent from the session daemon to the Java
  16  * agent. The agent is then expected to execute the command and provide a
  17  * response.
  18  *
  19  * @author Alexandre Montplaisir
  20  */
  21 abstract class SessiondCommand {
  22
  23         /**
  24          * Encoding that should be used for the strings in the sessiond agent
  25          * protocol on the socket.
  26          */
  27         protected static final Charset SESSIOND_PROTOCOL_CHARSET = Charset.forName("UTF-8");
  28
  29         enum CommandType {
  30                 /** List logger(s). */
  31                 CMD_LIST(1),
  32                 /** Enable logger by name. */
  33                 CMD_EVENT_ENABLE(2),
  34                 /** Disable logger by name. */
  35                 CMD_EVENT_DISABLE(3),
  36                 /** Registration done */
  37                 CMD_REG_DONE(4),
  38                 /** Enable application context */
  39                 CMD_APP_CTX_ENABLE(5),
  40                 /** Disable application context */
  41                 CMD_APP_CTX_DISABLE(6);
  42
  43                 private int code;
  44
  45                 private CommandType(int c) {
  46                         code = c;
  47                 }
  48
  49                 public int getCommandType() {
  50                         return code;
  51                 }
  52         }
  53
  54         /**
  55          * Execute the command handler's action on the specified tracing agent.
  56          *
  57          * @param agent
  58          *            The agent on which to execute the command
  59          * @return If the command completed successfully or not
  60          */
  61         public abstract LttngAgentResponse execute(ILttngTcpClientListener agent);
  62
  63         /**
  64          * Utility method to read agent-protocol strings passed on the socket. The
  65          * buffer will contain a 32-bit integer representing the length, immediately
  66          * followed by the string itself.
  67          *
  68          * @param buffer
  69          *            The ByteBuffer from which to read. It should already be setup
  70          *            and positioned where the read should begin.
  71          * @return The string that was read, or <code>null</code> if it was badly
  72          *         formatted.
  73          */
  74         protected static String readNextString(ByteBuffer buffer) {
  75                 int nbBytes = buffer.getInt();
  76                 if (nbBytes < 0) {
  77                         /* The string length should be positive */
  78                         return null;
  79                 }
  80                 if (nbBytes == 0) {
  81                         /* The string is explicitly an empty string */
  82                         return "";
  83                 }
  84
  85                 byte[] stringBytes = new byte[nbBytes];
  86                 buffer.get(stringBytes);
  87                 return new String(stringBytes, SESSIOND_PROTOCOL_CHARSET).trim();
  88         }
  89 }