liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/client/SessiondCommand.java

   1 /*
   2  * Copyright (C) 2015-2016 - EfficiOS Inc., Alexandre Montplaisir <alexmonthy@efficios.com>
   3  * Copyright (C) 2013 - David Goulet <dgoulet@efficios.com>
   4  *
   5  * This library is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU Lesser General Public License, version 2.1 only,
   7  * as published by the Free Software Foundation.
   8  *
   9  * This library is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
  12  * for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public License
  15  * along with this library; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  17  */
  18
  19 package org.lttng.ust.agent.client;
  20
  21 import java.nio.ByteBuffer;
  22
  23 /**
  24  * Base class to represent all commands sent from the session daemon to the Java
  25  * agent. The agent is then expected to execute the command and provide a
  26  * response.
  27  *
  28  * @author Alexandre Montplaisir
  29  */
  30 abstract class SessiondCommand {
  31
  32         enum CommandType {
  33                 /** List logger(s). */
  34                 CMD_LIST(1),
  35                 /** Enable logger by name. */
  36                 CMD_EVENT_ENABLE(2),
  37                 /** Disable logger by name. */
  38                 CMD_EVENT_DISABLE(3),
  39                 /** Registration done */
  40                 CMD_REG_DONE(4),
  41                 /** Enable application context */
  42                 CMD_APP_CTX_ENABLE(5),
  43                 /** Disable application context */
  44                 CMD_APP_CTX_DISABLE(6);
  45
  46                 private int code;
  47
  48                 private CommandType(int c) {
  49                         code = c;
  50                 }
  51
  52                 public int getCommandType() {
  53                         return code;
  54                 }
  55         }
  56
  57         /**
  58          * Execute the command handler's action on the specified tracing agent.
  59          *
  60          * @param agent
  61          *            The agent on which to execute the command
  62          * @return If the command completed successfully or not
  63          */
  64         public abstract LttngAgentResponse execute(ILttngTcpClientListener agent);
  65
  66         /**
  67          * Utility method to read agent-protocol strings passed on the socket. The
  68          * buffer will contain a 32-bit integer representing the length, immediately
  69          * followed by the string itself.
  70          *
  71          * @param buffer
  72          *            The ByteBuffer from which to read. It should already be setup
  73          *            and positioned where the read should begin.
  74          * @return The string that was read, or <code>null</code> if it was badly
  75          *         formatted.
  76          */
  77         protected static String readNextString(ByteBuffer buffer) {
  78                 int length = buffer.getInt();
  79                 if (length < 0) {
  80                         /* The string length should be positive */
  81                         return null;
  82                 }
  83                 if (length == 0) {
  84                         /* The string is explicitly an empty string */
  85                         return "";
  86                 }
  87
  88                 byte[] stringBytes = new byte[length];
  89                 buffer.get(stringBytes);
  90                 return new String(stringBytes).trim();
  91         }
  92 }