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[mediawiki.git] / includes / exception / MWExceptionHandler.php

<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

/**
 * Handler class for MWExceptions
 * @ingroup Exception
 */
class MWExceptionHandler {
        /**
         * Install an exception handler for MediaWiki exception types.
         */
        public static function installHandler() {
                set_exception_handler( array( 'MWExceptionHandler', 'handle' ) );
        }

        /**
         * Report an exception to the user
         * @param Exception $e
         */
        protected static function report( Exception $e ) {
                global $wgShowExceptionDetails;

                $cmdLine = MWException::isCommandLine();

                if ( $e instanceof MWException ) {
                        try {
                                // Try and show the exception prettily, with the normal skin infrastructure
                                $e->report();
                        } catch ( Exception $e2 ) {
                                // Exception occurred from within exception handler
                                // Show a simpler error message for the original exception,
                                // don't try to invoke report()
                                $message = "MediaWiki internal error.\n\n";

                                if ( $wgShowExceptionDetails ) {
                                        $message .= 'Original exception: ' . self::getLogMessage( $e ) .
                                                "\nBacktrace:\n" . self::getRedactedTraceAsString( $e ) .
                                                "\n\nException caught inside exception handler: " . self::getLogMessage( $e2 ) .
                                                "\nBacktrace:\n" . self::getRedactedTraceAsString( $e2 );
                                } else {
                                        $message .= "Exception caught inside exception handler.\n\n" .
                                                "Set \$wgShowExceptionDetails = true; at the bottom of LocalSettings.php " .
                                                "to show detailed debugging information.";
                                }

                                $message .= "\n";

                                if ( $cmdLine ) {
                                        self::printError( $message );
                                } else {
                                        echo nl2br( htmlspecialchars( $message ) ) . "\n";
                                }
                        }
                } else {
                        $message = "Unexpected non-MediaWiki exception encountered, of type \"" .
                                get_class( $e ) . "\"";

                        if ( $wgShowExceptionDetails ) {
                                $message .= "\n" . MWExceptionHandler::getLogMessage( $e ) . "\nBacktrace:\n" .
                                        self::getRedactedTraceAsString( $e ) . "\n";
                        }

                        if ( $cmdLine ) {
                                self::printError( $message );
                        } else {
                                echo nl2br( htmlspecialchars( $message ) ) . "\n";
                        }

                        self::logException( $e );
                }
        }

        /**
         * Print a message, if possible to STDERR.
         * Use this in command line mode only (see isCommandLine)
         *
         * @param string $message Failure text
         */
        public static function printError( $message ) {
                # NOTE: STDERR may not be available, especially if php-cgi is used from the
                # command line (bug #15602). Try to produce meaningful output anyway. Using
                # echo may corrupt output to STDOUT though.
                if ( defined( 'STDERR' ) ) {
                        fwrite( STDERR, $message );
                } else {
                        echo $message;
                }
        }

        /**
         * If there are any open database transactions, roll them back and log
         * the stack trace of the exception that should have been caught so the
         * transaction could be aborted properly.
         * @since 1.23
         * @param Exception $e
         */
        public static function rollbackMasterChangesAndLog( Exception $e ) {
                $factory = wfGetLBFactory();
                if ( $factory->hasMasterChanges() ) {
                        wfDebugLog( 'Bug56269',
                                'Exception thrown with an uncommited database transaction: ' .
                                        MWExceptionHandler::getLogMessage( $e ) . "\n" .
                                        $e->getTraceAsString()
                        );
                        $factory->rollbackMasterChanges();
                }
        }

        /**
         * Exception handler which simulates the appropriate catch() handling:
         *
         *   try {
         *       ...
         *   } catch ( MWException $e ) {
         *       $e->report();
         *   } catch ( Exception $e ) {
         *       echo $e->__toString();
         *   }
         * @param Exception $e
         */
        public static function handle( $e ) {
                global $wgFullyInitialised;

                self::rollbackMasterChangesAndLog( $e );

                self::report( $e );

                // Final cleanup
                if ( $wgFullyInitialised ) {
                        try {
                                // uses $wgRequest, hence the $wgFullyInitialised condition
                                wfLogProfilingData();
                        } catch ( Exception $e ) {
                        }
                }

                // Exit value should be nonzero for the benefit of shell jobs
                exit( 1 );
        }

        /**
         * Generate a string representation of an exception's stack trace
         *
         * Like Exception::getTraceAsString, but replaces argument values with
         * argument type or class name.
         *
         * @param Exception $e
         * @return string
         */
        public static function getRedactedTraceAsString( Exception $e ) {
                $text = '';

                foreach ( self::getRedactedTrace( $e ) as $level => $frame ) {
                        if ( isset( $frame['file'] ) && isset( $frame['line'] ) ) {
                                $text .= "#{$level} {$frame['file']}({$frame['line']}): ";
                        } else {
                                // 'file' and 'line' are unset for calls via call_user_func (bug 55634)
                                // This matches behaviour of Exception::getTraceAsString to instead
                                // display "[internal function]".
                                $text .= "#{$level} [internal function]: ";
                        }

                        if ( isset( $frame['class'] ) ) {
                                $text .= $frame['class'] . $frame['type'] . $frame['function'];
                        } else {
                                $text .= $frame['function'];
                        }

                        if ( isset( $frame['args'] ) ) {
                                $text .= '(' . implode( ', ', $frame['args'] ) . ")\n";
                        } else {
                                $text .= "()\n";
                        }
                }

                $level = $level + 1;
                $text .= "#{$level} {main}";

                return $text;
        }

        /**
         * Return a copy of an exception's backtrace as an array.
         *
         * Like Exception::getTrace, but replaces each element in each frame's
         * argument array with the name of its class (if the element is an object)
         * or its type (if the element is a PHP primitive).
         *
         * @since 1.22
         * @param Exception $e
         * @return array
         */
        public static function getRedactedTrace( Exception $e ) {
                return array_map( function ( $frame ) {
                        if ( isset( $frame['args'] ) ) {
                                $frame['args'] = array_map( function ( $arg ) {
                                        return is_object( $arg ) ? get_class( $arg ) : gettype( $arg );
                                }, $frame['args'] );
                        }
                        return $frame;
                }, $e->getTrace() );
        }

        /**
         * Get the ID for this error.
         *
         * The ID is saved so that one can match the one output to the user (when
         * $wgShowExceptionDetails is set to false), to the entry in the debug log.
         *
         * @since 1.22
         * @param Exception $e
         * @return string
         */
        public static function getLogId( Exception $e ) {
                if ( !isset( $e->_mwLogId ) ) {
                        $e->_mwLogId = wfRandomString( 8 );
                }
                return $e->_mwLogId;
        }

        /**
         * If the exception occurred in the course of responding to a request,
         * returns the requested URL. Otherwise, returns false.
         *
         * @since 1.23
         * @return string|bool
         */
        public static function getURL() {
                global $wgRequest;
                if ( !isset( $wgRequest ) || $wgRequest instanceof FauxRequest ) {
                        return false;
                }
                return $wgRequest->getRequestURL();
        }

        /**
         * Return the requested URL and point to file and line number from which the
         * exception occurred.
         *
         * @since 1.22
         * @param Exception $e
         * @return string
         */
        public static function getLogMessage( Exception $e ) {
                $id = self::getLogId( $e );
                $file = $e->getFile();
                $line = $e->getLine();
                $message = $e->getMessage();
                $url = self::getURL() ?: '[no req]';

                return "[$id] $url   Exception from line $line of $file: $message";
        }

        /**
         * Serialize an Exception object to JSON.
         *
         * The JSON object will have keys 'id', 'file', 'line', 'message', and
         * 'url'. These keys map to string values, with the exception of 'line',
         * which is a number, and 'url', which may be either a string URL or or
         * null if the exception did not occur in the context of serving a web
         * request.
         *
         * If $wgLogExceptionBacktrace is true, it will also have a 'backtrace'
         * key, mapped to the array return value of Exception::getTrace, but with
         * each element in each frame's "args" array (if set) replaced with the
         * argument's class name (if the argument is an object) or type name (if
         * the argument is a PHP primitive).
         *
         * @par Sample JSON record ($wgLogExceptionBacktrace = false):
         * @code
         *  {
         *    "id": "c41fb419",
         *    "file": "/var/www/mediawiki/includes/cache/MessageCache.php",
         *    "line": 704,
         *    "message": "Non-string key given",
         *    "url": "/wiki/Main_Page"
         *  }
         * @endcode
         *
         * @par Sample JSON record ($wgLogExceptionBacktrace = true):
         * @code
         *  {
         *    "id": "dc457938",
         *    "file": "/vagrant/mediawiki/includes/cache/MessageCache.php",
         *    "line": 704,
         *    "message": "Non-string key given",
         *    "url": "/wiki/Main_Page",
         *    "backtrace": [{
         *      "file": "/vagrant/mediawiki/extensions/VisualEditor/VisualEditor.hooks.php",
         *      "line": 80,
         *      "function": "get",
         *      "class": "MessageCache",
         *      "type": "->",
         *      "args": ["array"]
         *    }]
         *  }
         * @endcode
         *
         * @since 1.23
         * @param Exception $e
         * @param bool $pretty Add non-significant whitespace to improve readability (default: false).
         * @param int $escaping Bitfield consisting of FormatJson::.*_OK class constants.
         * @return string|bool JSON string if successful; false upon failure
         */
        public static function jsonSerializeException( Exception $e, $pretty = false, $escaping = 0 ) {
                global $wgLogExceptionBacktrace;

                $exceptionData = array(
                        'id' => self::getLogId( $e ),
                        'file' => $e->getFile(),
                        'line' => $e->getLine(),
                        'message' => $e->getMessage(),
                );

                // Because MediaWiki is first and foremost a web application, we set a
                // 'url' key unconditionally, but set it to null if the exception does
                // not occur in the context of a web request, as a way of making that
                // fact visible and explicit.
                $exceptionData['url'] = self::getURL() ?: null;

                if ( $wgLogExceptionBacktrace ) {
                        // Argument values may not be serializable, so redact them.
                        $exceptionData['backtrace'] = self::getRedactedTrace( $e );
                }

                return FormatJson::encode( $exceptionData, $pretty, $escaping );
        }

        /**
         * Log an exception to the exception log (if enabled).
         *
         * This method must not assume the exception is an MWException,
         * it is also used to handle PHP errors or errors from other libraries.
         *
         * @since 1.22
         * @param Exception $e
         */
        public static function logException( Exception $e ) {
                global $wgLogExceptionBacktrace;

                if ( !( $e instanceof MWException ) || $e->isLoggable() ) {
                        $log = self::getLogMessage( $e );
                        if ( $wgLogExceptionBacktrace ) {
                                wfDebugLog( 'exception', $log . "\n" . $e->getTraceAsString() );
                        } else {
                                wfDebugLog( 'exception', $log );
                        }

                        $json = self::jsonSerializeException( $e, false, FormatJson::ALL_OK );
                        if ( $json !== false ) {
                                wfDebugLog( 'exception-json', $json, 'private' );
                        }
                }

        }

}