1 <?php

     2 /**

     3  * Licensed to the Apache Software Foundation (ASF) under one or more

     4  * contributor license agreements. See the NOTICE file distributed with

     5  * this work for additional information regarding copyright ownership.

     6  * The ASF licenses this file to You under the Apache License, Version 2.0

     7  * (the "License"); you may not use this file except in compliance with

     8  * the License. You may obtain a copy of the License at

     9  *

    10  *       http://www.apache.org/licenses/LICENSE-2.0

    11  *

    12  * Unless required by applicable law or agreed to in writing, software

    13  * distributed under the License is distributed on an "AS IS" BASIS,

    14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

    15  * See the License for the specific language governing permissions and

    16  * limitations under the License.

    17  *

    18  * @package log4php

    19  */

    20 

    21 /**

    22  * The NDC class implements <i>nested diagnostic contexts</i>.

    23  *

    24  * NDC was defined by Neil Harrison in the article "Patterns for Logging

    25  * Diagnostic Messages" part of the book <i>"Pattern Languages of

    26  * Program Design 3"</i> edited by Martin et al.

    27  *

    28  * A Nested Diagnostic Context, or NDC in short, is an instrument

    29  * to distinguish interleaved log output from different sources. Log

    30  * output is typically interleaved when a server handles multiple

    31  * clients near-simultaneously.

    32  *

    33  * This class is similar to the {@link LoggerMDC} class except that it is

    34  * based on a stack instead of a map.

    35  *

    36  * Interleaved log output can still be meaningful if each log entry

    37  * from different contexts had a distinctive stamp. This is where NDCs

    38  * come into play.

    39  *

    40  * <b>Note that NDCs are managed on a per thread basis</b>.

    41  *

    42  * NDC operations such as {@link push()}, {@link pop()},

    43  * {@link clear()}, {@link getDepth()} and {@link setMaxDepth()}

    44  * affect the NDC of the <i>current</i> thread only. NDCs of other

    45  * threads remain unaffected.

    46  *

    47  * For example, a servlet can build a per client request NDC

    48  * consisting the clients host name and other information contained in

    49  * the the request. <i>Cookies</i> are another source of distinctive

    50  * information. To build an NDC one uses the {@link push()}

    51  * operation.

    52  *

    53  * Simply put,

    54  *

    55  * - Contexts can be nested.

    56  * - When entering a context, call <kbd>LoggerNDC::push()</kbd>

    57  *     As a side effect, if there is no nested diagnostic context for the

    58  *     current thread, this method will create it.

    59  * - When leaving a context, call <kbd>LoggerNDC::pop()</kbd>

    60  * - <b>When exiting a thread make sure to call {@link remove()}</b>

    61  *

    62  * There is no penalty for forgetting to match each

    63  * <kbd>push</kbd> operation with a corresponding <kbd>pop</kbd>,

    64  * except the obvious mismatch between the real application context

    65  * and the context set in the NDC.

    66  *

    67  * If configured to do so, {@link LoggerPatternLayout} and {@link LoggerLayoutTTCC}

    68  * instances automatically retrieve the nested diagnostic

    69  * context for the current thread without any user intervention.

    70  * Hence, even if a servlet is serving multiple clients

    71  * simultaneously, the logs emanating from the same code (belonging to

    72  * the same category) can still be distinguished because each client

    73  * request will have a different NDC tag.

    74  *

    75  * Example:

    76  *

    77  * {@example ../../examples/php/ndc.php 19}<br>

    78  *

    79  * With the properties file:

    80  *

    81  * {@example ../../examples/resources/ndc.properties 18}<br>

    82  *

    83  * Will result in the following (notice the conn and client ids):

    84  *

    85  * <pre>

    86  * 2009-09-13 19:04:27 DEBUG root conn=1234: just received a new connection in src/examples/php/ndc.php at 23

    87  * 2009-09-13 19:04:27 DEBUG root conn=1234 client=ab23: some more messages that can in src/examples/php/ndc.php at 25

    88  * 2009-09-13 19:04:27 DEBUG root conn=1234 client=ab23: now related to a client in src/examples/php/ndc.php at 26

    89  * 2009-09-13 19:04:27 DEBUG root : back and waiting for new connections in src/examples/php/ndc.php at 29

    90  * </pre>

    91  *

    92  * @version $Revision: 1350602 $

    93  * @package log4php

    94  * @since 0.3

    95  */

    96 class LoggerNDC {

    97 

    98     /** This is the repository of NDC stack */

    99     private static $stack = array();

   100 

   101     /**

   102      * Clear any nested diagnostic information if any. This method is

   103      * useful in cases where the same thread can be potentially used

   104      * over and over in different unrelated contexts.

   105      *

   106      * <p>This method is equivalent to calling the {@link setMaxDepth()}

   107      * method with a zero <var>maxDepth</var> argument.

   108      */

   109     public static function clear() {

   110         self::$stack = array();

   111     }

   112 

   113     /**

   114      * Never use this method directly, use the {@link LoggerLoggingEvent::getNDC()} method instead.

   115      * @return array

   116      */

   117     public static function get() {

   118         return implode(' ', self::$stack);

   119     }

   120 

   121     /**

   122      * Get the current nesting depth of this diagnostic context.

   123      *

   124      * @see setMaxDepth()

   125      * @return integer

   126      */

   127     public static function getDepth() {

   128         return count(self::$stack);

   129     }

   130 

   131     /**

   132      * Clients should call this method before leaving a diagnostic

   133      * context.

   134      *

   135      * <p>The returned value is the value that was pushed last. If no

   136      * context is available, then the empty string "" is returned.</p>

   137      *

   138      * @return string The innermost diagnostic context.

   139      */

   140     public static function pop() {

   141         if (count(self::$stack) > 0) {

   142             return array_pop(self::$stack);

   143         } else {

   144             return '';

   145         }

   146     }

   147 

   148     /**

   149      * Looks at the last diagnostic context at the top of this NDC

   150      * without removing it.

   151      *

   152      * <p>The returned value is the value that was pushed last. If no

   153      * context is available, then the empty string "" is returned.</p>

   154      * @return string The innermost diagnostic context.

   155      */

   156     public static function peek() {

   157         if (count(self::$stack) > 0) {

   158             return end(self::$stack);

   159         } else {

   160             return '';

   161         }

   162     }

   163 

   164     /**

   165      * Push new diagnostic context information for the current thread.

   166      *

   167      * <p>The contents of the <var>message</var> parameter is

   168      * determined solely by the client.

   169      *

   170      * @param string $message The new diagnostic context information.

   171      */

   172     public static function push($message) {

   173         array_push(self::$stack, (string)$message);

   174     }

   175 

   176     /**

   177      * Remove the diagnostic context for this thread.

   178      */

   179     public static function remove() {

   180         LoggerNDC::clear();

   181     }

   182 

   183     /**

   184      * Set maximum depth of this diagnostic context. If the current

   185      * depth is smaller or equal to <var>maxDepth</var>, then no

   186      * action is taken.

   187      *

   188      * <p>This method is a convenient alternative to multiple

   189      * {@link pop()} calls. Moreover, it is often the case that at

   190      * the end of complex call sequences, the depth of the NDC is

   191      * unpredictable. The {@link setMaxDepth()} method circumvents

   192      * this problem.

   193      *

   194      * @param integer $maxDepth

   195      * @see getDepth()

   196      */

   197     public static function setMaxDepth($maxDepth) {

   198         $maxDepth = (int)$maxDepth;

   199         if (LoggerNDC::getDepth() > $maxDepth) {

   200             self::$stack = array_slice(self::$stack, 0, $maxDepth);

   201         }

   202     }

   203 }