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 import java.nio.charset.Charset;
  23
  24 /**
  25  * Base class to represent all commands sent from the session daemon to the Java
  26  * agent. The agent is then expected to execute the command and provide a
  27  * response.
  28  *
  29  * @author Alexandre Montplaisir
  30  */
  31 abstract class SessiondCommand {
  32
  33         /**
  34          * Encoding that should be used for the strings in the sessiond agent
  35          * protocol on the socket.
  36          */
  37         protected static final Charset SESSIOND_PROTOCOL_CHARSET = Charset.forName("UTF-8");
  38
  39         enum CommandType {
  40                 /** List logger(s). */
  41                 CMD_LIST(1),
  42                 /** Enable logger by name. */
  43                 CMD_EVENT_ENABLE(2),
  44                 /** Disable logger by name. */
  45                 CMD_EVENT_DISABLE(3),
  46                 /** Registration done */
  47                 CMD_REG_DONE(4),
  48                 /** Enable application context */
  49                 CMD_APP_CTX_ENABLE(5),
  50                 /** Disable application context */
  51                 CMD_APP_CTX_DISABLE(6);
  52
  53                 private int code;
  54
  55                 private CommandType(int c) {
  56                         code = c;
  57                 }
  58
  59                 public int getCommandType() {
  60                         return code;
  61                 }
  62         }
  63
  64         /**
  65          * Execute the command handler's action on the specified tracing agent.
  66          *
  67          * @param agent
  68          *            The agent on which to execute the command
  69          * @return If the command completed successfully or not
  70          */
  71         public abstract LttngAgentResponse execute(ILttngTcpClientListener agent);
  72
  73         /**
  74          * Utility method to read agent-protocol strings passed on the socket. The
  75          * buffer will contain a 32-bit integer representing the length, immediately
  76          * followed by the string itself.
  77          *
  78          * @param buffer
  79          *            The ByteBuffer from which to read. It should already be setup
  80          *            and positioned where the read should begin.
  81          * @return The string that was read, or <code>null</code> if it was badly
  82          *         formatted.
  83          */
  84         protected static String readNextString(ByteBuffer buffer) {
  85                 int nbBytes = buffer.getInt();
  86                 if (nbBytes < 0) {
  87                         /* The string length should be positive */
  88                         return null;
  89                 }
  90                 if (nbBytes == 0) {
  91                         /* The string is explicitly an empty string */
  92                         return "";
  93                 }
  94
  95                 byte[] stringBytes = new byte[nbBytes];
  96                 buffer.get(stringBytes);
  97                 return new String(stringBytes, SESSIOND_PROTOCOL_CHARSET).trim();
  98         }
  99 }