From: Aaron Schulz <aschulz@wikimedia.org>
Date: Wed, 14 Sep 2016 03:57:54 +0000 (-0700)
Subject: Add MWExceptionRenderer class and decouple DBError
X-Git-Tag: 1.31.0-rc.0~5581^2
X-Git-Url: http://git.cyclocoop.org/%7B%24admin_url%7Dmes_infos.php?a=commitdiff_plain;h=00bee029718f3215396e984d04b9450bc3872503;p=lhc%2Fweb%2Fwiklou.git

Add MWExceptionRenderer class and decouple DBError

* This handles the work of showing exceptions so that
  MWException does not have too.
* Simplify the DBError classes to regular Exception
  classes. Lots of pointless prettification has been
  removed, but DBConnectionError still gets the usual
  special treatment of a fallback page and Google form.
* Remove hacky file cache fallback code that probably
  did not work.
* Make MWExceptionHandler::report() wrap
  MWExceptionExposer::output().
* Make MWException::runHooks() wrap
  MWExceptionExposer::runHooks().

Change-Id: I5dfdc84e94ddac65417226cf7c84513ebb9f9faa
---

diff --git a/autoload.php b/autoload.php
index a71d9432e7..5141c35c88 100644
--- a/autoload.php
+++ b/autoload.php
@@ -767,6 +767,7 @@ $wgAutoloadLocalClasses = [
 	'MWDocGen' => __DIR__ . '/maintenance/mwdocgen.php',
 	'MWException' => __DIR__ . '/includes/exception/MWException.php',
 	'MWExceptionHandler' => __DIR__ . '/includes/exception/MWExceptionHandler.php',
+	'MWExceptionRenderer' => __DIR__ . '/includes/exception/MWExceptionRenderer.php',
 	'MWGrants' => __DIR__ . '/includes/utils/MWGrants.php',
 	'MWHttpRequest' => __DIR__ . '/includes/HttpFunctions.php',
 	'MWMemcached' => __DIR__ . '/includes/compat/MemcachedClientCompat.php',
diff --git a/includes/db/DatabaseError.php b/includes/db/DatabaseError.php
index cfae74fdfd..2242c5af53 100644
--- a/includes/db/DatabaseError.php
+++ b/includes/db/DatabaseError.php
@@ -25,16 +25,16 @@
  * Database error base class
  * @ingroup Database
  */
-class DBError extends MWException {
-	/** @var DatabaseBase */
+class DBError extends Exception {
+	/** @var IDatabase */
 	public $db;
 
 	/**
 	 * Construct a database error
-	 * @param DatabaseBase $db Object which threw the error
+	 * @param IDatabase $db Object which threw the error
 	 * @param string $error A simple error message to be used for debugging
 	 */
-	function __construct( DatabaseBase $db = null, $error ) {
+	function __construct( IDatabase $db = null, $error ) {
 		$this->db = $db;
 		parent::__construct( $error );
 	}
@@ -48,274 +48,23 @@ class DBError extends MWException {
  * @since 1.23
  */
 class DBExpectedError extends DBError {
-	/**
-	 * @return string
-	 */
-	function getText() {
-		global $wgShowDBErrorBacktrace;
-
-		$s = $this->getTextContent() . "\n";
-
-		if ( $wgShowDBErrorBacktrace ) {
-			$s .= "Backtrace:\n" . $this->getTraceAsString() . "\n";
-		}
-
-		return $s;
-	}
-
-	/**
-	 * @return string
-	 */
-	function getHTML() {
-		global $wgShowDBErrorBacktrace;
-
-		$s = $this->getHTMLContent();
-
-		if ( $wgShowDBErrorBacktrace ) {
-			$s .= '<p>Backtrace:</p><pre>' . htmlspecialchars( $this->getTraceAsString() ) . '</pre>';
-		}
-
-		return $s;
-	}
-
-	function getPageTitle() {
-		return $this->msg( 'databaseerror', 'Database error' );
-	}
-
-	/**
-	 * @return string
-	 */
-	protected function getTextContent() {
-		return $this->getMessage();
-	}
-
-	/**
-	 * @return string
-	 */
-	protected function getHTMLContent() {
-		return '<p>' . nl2br( htmlspecialchars( $this->getTextContent() ) ) . '</p>';
-	}
 }
 
 /**
  * @ingroup Database
  */
 class DBConnectionError extends DBExpectedError {
-	/** @var string Error text */
-	public $error;
-
 	/**
-	 * @param DatabaseBase $db Object throwing the error
+	 * @param IDatabase $db Object throwing the error
 	 * @param string $error Error text
 	 */
-	function __construct( DatabaseBase $db = null, $error = 'unknown error' ) {
-		$msg = 'DB connection error';
-
+	function __construct( IDatabase $db = null, $error = 'unknown error' ) {
+		$msg = 'Cannot access the database';
 		if ( trim( $error ) != '' ) {
 			$msg .= ": $error";
-		} elseif ( $db ) {
-			$error = $this->db->getServer();
 		}
 
 		parent::__construct( $db, $msg );
-		$this->error = $error;
-	}
-
-	/**
-	 * @return bool
-	 */
-	function useOutputPage() {
-		// Not likely to work
-		return false;
-	}
-
-	/**
-	 * @param string $key
-	 * @param string $fallback Unescaped alternative error text in case the
-	 *   message cache cannot be used. Can contain parameters as in regular
-	 *   messages, that should be passed as additional parameters.
-	 * @return string Unprocessed plain error text with parameters replaced
-	 */
-	function msg( $key, $fallback /*[, params...] */ ) {
-		$args = array_slice( func_get_args(), 2 );
-
-		if ( $this->useMessageCache() ) {
-			return wfMessage( $key, $args )->useDatabase( false )->text();
-		} else {
-			return wfMsgReplaceArgs( $fallback, $args );
-		}
-	}
-
-	/**
-	 * @return bool
-	 */
-	function isLoggable() {
-		// Don't send to the exception log, already in dberror log
-		return false;
-	}
-
-	/**
-	 * @return string Safe HTML
-	 */
-	function getHTML() {
-		global $wgShowDBErrorBacktrace, $wgShowHostnames, $wgShowSQLErrors;
-
-		$sorry = htmlspecialchars( $this->msg(
-			'dberr-problems',
-			'Sorry! This site is experiencing technical difficulties.'
-		) );
-		$again = htmlspecialchars( $this->msg(
-			'dberr-again',
-			'Try waiting a few minutes and reloading.'
-		) );
-
-		if ( $wgShowHostnames || $wgShowSQLErrors ) {
-			$info = str_replace(
-				'$1', Html::element( 'span', [ 'dir' => 'ltr' ], $this->error ),
-				htmlspecialchars( $this->msg( 'dberr-info', '(Cannot access the database: $1)' ) )
-			);
-		} else {
-			$info = htmlspecialchars( $this->msg(
-				'dberr-info-hidden',
-				'(Cannot access the database)'
-			) );
-		}
-
-		# No database access
-		MessageCache::singleton()->disable();
-
-		$html = "<h1>$sorry</h1><p>$again</p><p><small>$info</small></p>";
-
-		if ( $wgShowDBErrorBacktrace ) {
-			$html .= '<p>Backtrace:</p><pre>' . htmlspecialchars( $this->getTraceAsString() ) . '</pre>';
-		}
-
-		$html .= '<hr />';
-		$html .= $this->searchForm();
-
-		return $html;
-	}
-
-	protected function getTextContent() {
-		global $wgShowHostnames, $wgShowSQLErrors;
-
-		if ( $wgShowHostnames || $wgShowSQLErrors ) {
-			return $this->getMessage();
-		} else {
-			return 'DB connection error';
-		}
-	}
-
-	/**
-	 * Output the exception report using HTML.
-	 *
-	 * @return void
-	 */
-	public function reportHTML() {
-		global $wgUseFileCache;
-
-		// Check whether we can serve a file-cached copy of the page with the error underneath
-		if ( $wgUseFileCache ) {
-			try {
-				$cache = $this->fileCachedPage();
-				// Cached version on file system?
-				if ( $cache !== null ) {
-					// Hack: extend the body for error messages
-					$cache = str_replace( [ '</html>', '</body>' ], '', $cache );
-					// Add cache notice...
-					$cache .= '<div style="border:1px solid #ffd0d0;padding:1em;">' .
-						htmlspecialchars( $this->msg( 'dberr-cachederror',
-							'This is a cached copy of the requested page, and may not be up to date.' ) ) .
-						'</div>';
-
-					// Output cached page with notices on bottom and re-close body
-					echo "{$cache}<hr />{$this->getHTML()}</body></html>";
-
-					return;
-				}
-			} catch ( Exception $e ) {
-				// Do nothing, just use the default page
-			}
-		}
-
-		// We can't, cough and die in the usual fashion
-		parent::reportHTML();
-	}
-
-	/**
-	 * @return string
-	 */
-	function searchForm() {
-		global $wgSitename, $wgCanonicalServer, $wgRequest;
-
-		$usegoogle = htmlspecialchars( $this->msg(
-			'dberr-usegoogle',
-			'You can try searching via Google in the meantime.'
-		) );
-		$outofdate = htmlspecialchars( $this->msg(
-			'dberr-outofdate',
-			'Note that their indexes of our content may be out of date.'
-		) );
-		$googlesearch = htmlspecialchars( $this->msg( 'searchbutton', 'Search' ) );
-
-		$search = htmlspecialchars( $wgRequest->getVal( 'search' ) );
-
-		$server = htmlspecialchars( $wgCanonicalServer );
-		$sitename = htmlspecialchars( $wgSitename );
-
-		$trygoogle = <<<EOT
-<div style="margin: 1.5em">$usegoogle<br />
-<small>$outofdate</small>
-</div>
-<form method="get" action="//www.google.com/search" id="googlesearch">
-	<input type="hidden" name="domains" value="$server" />
-	<input type="hidden" name="num" value="50" />
-	<input type="hidden" name="ie" value="UTF-8" />
-	<input type="hidden" name="oe" value="UTF-8" />
-
-	<input type="text" name="q" size="31" maxlength="255" value="$search" />
-	<input type="submit" name="btnG" value="$googlesearch" />
-	<p>
-		<label><input type="radio" name="sitesearch" value="$server" checked="checked" />$sitename</label>
-		<label><input type="radio" name="sitesearch" value="" />WWW</label>
-	</p>
-</form>
-EOT;
-
-		return $trygoogle;
-	}
-
-	/**
-	 * @return string
-	 */
-	private function fileCachedPage() {
-		$context = RequestContext::getMain();
-
-		if ( $context->getOutput()->isDisabled() ) {
-			// Done already?
-			return '';
-		}
-
-		if ( $context->getTitle() ) {
-			// Use the main context's title if we managed to set it
-			$t = $context->getTitle()->getPrefixedDBkey();
-		} else {
-			// Fallback to the raw title URL param. We can't use the Title
-			// class is it may hit the interwiki table and give a DB error.
-			// We may get a cache miss due to not sanitizing the title though.
-			$t = str_replace( ' ', '_', $context->getRequest()->getVal( 'title' ) );
-			if ( $t == '' ) { // fallback to main page
-				$t = Title::newFromText(
-					$this->msg( 'mainpage', 'Main Page' ) )->getPrefixedDBkey();
-			}
-		}
-
-		$cache = new HTMLFileCache( $t, 'view' );
-		if ( $cache->isCached() ) {
-			return $cache->fetchText();
-		} else {
-			return '';
-		}
 	}
 }
 
@@ -323,17 +72,24 @@ EOT;
  * @ingroup Database
  */
 class DBQueryError extends DBExpectedError {
-	public $error, $errno, $sql, $fname;
+	/** @var string */
+	public $error;
+	/** @var integer */
+	public $errno;
+	/** @var string */
+	public $sql;
+	/** @var string */
+	public $fname;
 
 	/**
-	 * @param DatabaseBase $db
+	 * @param IDatabase $db
 	 * @param string $error
 	 * @param int|string $errno
 	 * @param string $sql
 	 * @param string $fname
 	 */
-	function __construct( DatabaseBase $db, $error, $errno, $sql, $fname ) {
-		if ( $db->wasConnectionError( $errno ) ) {
+	function __construct( IDatabase $db, $error, $errno, $sql, $fname ) {
+		if ( $db instanceof DatabaseBase && $db->wasConnectionError( $errno ) ) {
 			$message = "A connection error occured. \n" .
 				"Query: $sql\n" .
 				"Function: $fname\n" .
@@ -353,122 +109,31 @@ class DBQueryError extends DBExpectedError {
 		$this->sql = $sql;
 		$this->fname = $fname;
 	}
+}
 
-	/**
-	 * @return string
-	 */
-	function getPageTitle() {
-		return $this->msg( 'databaseerror', 'Database error' );
-	}
-
-	/**
-	 * @return string
-	 */
-	protected function getHTMLContent() {
-		$key = 'databaseerror-text';
-		$s = Html::element( 'p', [], $this->msg( $key, $this->getFallbackMessage( $key ) ) );
-
-		$details = $this->getTechnicalDetails();
-		if ( $details ) {
-			$s .= '<ul>';
-			foreach ( $details as $key => $detail ) {
-				$s .= str_replace(
-					'$1', call_user_func_array( 'Html::element', $detail ),
-					Html::element( 'li', [],
-						$this->msg( $key, $this->getFallbackMessage( $key ) )
-					)
-				);
-			}
-			$s .= '</ul>';
-		}
-
-		return $s;
-	}
-
-	/**
-	 * @return string
-	 */
-	protected function getTextContent() {
-		$key = 'databaseerror-textcl';
-		$s = $this->msg( $key, $this->getFallbackMessage( $key ) ) . "\n";
-
-		foreach ( $this->getTechnicalDetails() as $key => $detail ) {
-			$s .= $this->msg( $key, $this->getFallbackMessage( $key ), $detail[2] ) . "\n";
-		}
-
-		return $s;
-	}
-
-	/**
-	 * Make a list of technical details that can be shown to the user. This information can
-	 * aid in debugging yet may be useful to an attacker trying to exploit a security weakness
-	 * in the software or server configuration.
-	 *
-	 * Thus no such details are shown by default, though if $wgShowHostnames is true, only the
-	 * full SQL query is hidden; in fact, the error message often does contain a hostname, and
-	 * sites using this option probably don't care much about "security by obscurity". Of course,
-	 * if $wgShowSQLErrors is true, the SQL query *is* shown.
-	 *
-	 * @return array Keys are message keys; values are arrays of arguments for Html::element().
-	 *   Array will be empty if users are not allowed to see any of these details at all.
-	 */
-	protected function getTechnicalDetails() {
-		global $wgShowHostnames, $wgShowSQLErrors;
-
-		$attribs = [ 'dir' => 'ltr' ];
-		$details = [];
-
-		if ( $wgShowSQLErrors ) {
-			$details['databaseerror-query'] = [
-				'div', [ 'class' => 'mw-code' ] + $attribs, $this->sql ];
-		}
-
-		if ( $wgShowHostnames || $wgShowSQLErrors ) {
-			$errorMessage = $this->errno . ' ' . $this->error;
-			$details['databaseerror-function'] = [ 'code', $attribs, $this->fname ];
-			$details['databaseerror-error'] = [ 'samp', $attribs, $errorMessage ];
-		}
-
-		return $details;
-	}
-
-	/**
-	 * @param string $key Message key
-	 * @return string English message text
-	 */
-	private function getFallbackMessage( $key ) {
-		$messages = [
-			'databaseerror-text' => 'A database query error has occurred.
-This may indicate a bug in the software.',
-			'databaseerror-textcl' => 'A database query error has occurred.',
-			'databaseerror-query' => 'Query: $1',
-			'databaseerror-function' => 'Function: $1',
-			'databaseerror-error' => 'Error: $1',
-		];
-
-		return $messages[$key];
-	}
+/**
+ * @ingroup Database
+ */
+class DBReadOnlyError extends DBExpectedError {
 }
 
 /**
  * @ingroup Database
  */
-class DBUnexpectedError extends DBError {
+class DBTransactionError extends DBExpectedError {
 }
 
 /**
+ * Exception class for replica DB wait timeouts
  * @ingroup Database
  */
-class DBReadOnlyError extends DBExpectedError {
-	function getPageTitle() {
-		return $this->msg( 'readonly', 'Database is locked' );
-	}
+class DBReplicationWaitError extends DBExpectedError {
 }
 
 /**
  * @ingroup Database
  */
-class DBTransactionError extends DBExpectedError {
+class DBUnexpectedError extends DBError {
 }
 
 /**
@@ -482,9 +147,3 @@ class DBAccessError extends DBUnexpectedError {
 	}
 }
 
-/**
- * Exception class for replica DB wait timeouts
- * @ingroup Database
- */
-class DBReplicationWaitError extends DBUnexpectedError {
-}
diff --git a/includes/db/IDatabase.php b/includes/db/IDatabase.php
index f312357fe3..e2d743617e 100644
--- a/includes/db/IDatabase.php
+++ b/includes/db/IDatabase.php
@@ -28,7 +28,6 @@
 /**
  * Basic database interface for live and lazy-loaded DB handles
  *
- * @todo: loosen up DB classes from MWException
  * @note: IDatabase and DBConnRef should be updated to reflect any changes
  * @ingroup Database
  */
diff --git a/includes/db/loadbalancer/ILoadBalancer.php b/includes/db/loadbalancer/ILoadBalancer.php
index 9313ccd37c..94e0f2be53 100644
--- a/includes/db/loadbalancer/ILoadBalancer.php
+++ b/includes/db/loadbalancer/ILoadBalancer.php
@@ -25,7 +25,6 @@
 /**
  * Interface for database load balancing object that manages IDatabase handles
  *
- * @todo: loosen up DB classes from MWException
  * @since 1.28
  * @ingroup Database
  */
diff --git a/includes/exception/MWException.php b/includes/exception/MWException.php
index 0a174fe471..5496cb63d0 100644
--- a/includes/exception/MWException.php
+++ b/includes/exception/MWException.php
@@ -71,37 +71,7 @@ class MWException extends Exception {
 	 * @return string|null String to output or null if any hook has been called
 	 */
 	public function runHooks( $name, $args = [] ) {
-		global $wgExceptionHooks;
-
-		if ( !isset( $wgExceptionHooks ) || !is_array( $wgExceptionHooks ) ) {
-			return null; // Just silently ignore
-		}
-
-		if ( !array_key_exists( $name, $wgExceptionHooks ) ||
-			!is_array( $wgExceptionHooks[$name] )
-		) {
-			return null;
-		}
-
-		$hooks = $wgExceptionHooks[$name];
-		$callargs = array_merge( [ $this ], $args );
-
-		foreach ( $hooks as $hook ) {
-			if (
-				is_string( $hook ) ||
-				( is_array( $hook ) && count( $hook ) >= 2 && is_string( $hook[0] ) )
-			) {
-				// 'function' or [ 'class', 'hook' ]
-				$result = call_user_func_array( $hook, $callargs );
-			} else {
-				$result = null;
-			}
-
-			if ( is_string( $result ) ) {
-				return $result;
-			}
-		}
-		return null;
+		return MWExceptionRenderer::runHooks( $this, $name, $args );
 	}
 
 	/**
@@ -229,20 +199,7 @@ class MWException extends Exception {
 	 * It will be either HTML or plain text based on isCommandLine().
 	 */
 	public function report() {
-		global $wgMimeType;
-
-		if ( defined( 'MW_API' ) ) {
-			// Unhandled API exception, we can't be sure that format printer is alive
-			self::header( 'MediaWiki-API-Error: internal_api_error_' . get_class( $this ) );
-			wfHttpError( 500, 'Internal Server Error', $this->getText() );
-		} elseif ( self::isCommandLine() ) {
-			MWExceptionHandler::printError( $this->getText() );
-		} else {
-			self::statusHeader( 500 );
-			self::header( "Content-Type: $wgMimeType; charset=utf-8" );
-
-			$this->reportHTML();
-		}
+		MWExceptionRenderer::output( $this, MWExceptionRenderer::AS_PRETTY );
 	}
 
 	/**
diff --git a/includes/exception/MWExceptionHandler.php b/includes/exception/MWExceptionHandler.php
index 9c83d3c365..8359846a42 100644
--- a/includes/exception/MWExceptionHandler.php
+++ b/includes/exception/MWExceptionHandler.php
@@ -60,71 +60,14 @@ class MWExceptionHandler {
 	 * @param Exception|Throwable $e
 	 */
 	protected static function report( $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 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( $message ) ) . "\n";
-				}
-			}
-		} else {
-			if ( !$wgShowExceptionDetails ) {
-				$message = self::getPublicLogMessage( $e );
-			} else {
-				$message = self::getLogMessage( $e ) .
-					"\nBacktrace:\n" .
-					self::getRedactedTraceAsString( $e ) . "\n";
-			}
-
-			if ( $cmdLine ) {
-				self::printError( $message );
-			} else {
-				echo nl2br( htmlspecialchars( $message ) ) . "\n";
-			}
-
-		}
-	}
-
-	/**
-	 * 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;
+		try {
+			// Try and show the exception prettily, with the normal skin infrastructure
+			MWExceptionRenderer::output( $e, MWExceptionRenderer::AS_PRETTY );
+		} catch ( Exception $e2 ) {
+			// Exception occurred from within exception handler
+			// Show a simpler message for the original exception,
+			// don't try to invoke report()
+			MWExceptionRenderer::output( $e, MWExceptionRenderer::AS_PRETTY, $e2 );
 		}
 	}
 
diff --git a/includes/exception/MWExceptionRenderer.php b/includes/exception/MWExceptionRenderer.php
new file mode 100644
index 0000000000..f455191c48
--- /dev/null
+++ b/includes/exception/MWExceptionRenderer.php
@@ -0,0 +1,402 @@
+<?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
+ * @author Aaron Schulz
+ */
+
+/**
+ * Class to expose exceptions to the client (API bots, users, admins using CLI scripts)
+ * @since 1.28
+ */
+class MWExceptionRenderer {
+	const AS_RAW = 1; // show as text
+	const AS_PRETTY = 2; // show as HTML
+
+	/**
+	 * @param Exception $e Original exception
+	 * @param integer $mode MWExceptionExposer::AS_* constant
+	 * @param Exception|null $eNew New exception from attempting to show the first
+	 */
+	public static function output( Exception $e, $mode, Exception $eNew = null ) {
+		global $wgMimeType;
+
+		if ( $e instanceof DBConnectionError ) {
+			self::reportOutageHTML( $e );
+			return;
+		}
+
+		if ( defined( 'MW_API' ) ) {
+			// Unhandled API exception, we can't be sure that format printer is alive
+			self::header( 'MediaWiki-API-Error: internal_api_error_' . get_class( $e ) );
+			wfHttpError( 500, 'Internal Server Error', self::getText( $e ) );
+		} elseif ( self::isCommandLine() ) {
+			self::printError( self::getText( $e ) );
+		} elseif ( $mode === self::AS_PRETTY ) {
+			self::statusHeader( 500 );
+			self::header( "Content-Type: $wgMimeType; charset=utf-8" );
+			self::reportHTML( $e );
+		} else {
+			if ( $eNew ) {
+				$message = "MediaWiki internal error.\n\n";
+				if ( self::showBackTrace( $e ) ) {
+					$message .= 'Original exception: ' .
+						MWExceptionHandler::getLogMessage( $e ) .
+						"\nBacktrace:\n" . MWExceptionHandler::getRedactedTraceAsString( $e ) .
+						"\n\nException caught inside exception handler: " .
+							MWExceptionHandler::getLogMessage( $eNew ) .
+						"\nBacktrace:\n" . MWExceptionHandler::getRedactedTraceAsString( $eNew );
+				} 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";
+			} else {
+				if ( self::showBackTrace( $e ) ) {
+					$message = MWExceptionHandler::getLogMessage( $e ) .
+						"\nBacktrace:\n" .
+						MWExceptionHandler::getRedactedTraceAsString( $e ) . "\n";
+				} else {
+					$message = MWExceptionHandler::getPublicLogMessage( $e );
+				}
+			}
+			if ( self::isCommandLine() ) {
+				self::printError( $message );
+			} else {
+				echo nl2br( htmlspecialchars( $message ) ) . "\n";
+			}
+		}
+	}
+
+	/**
+	 * Run hook to allow extensions to modify the text of the exception
+	 *
+	 * Called by MWException for b/c
+	 *
+	 * @param Exception $e
+	 * @param string $name Class name of the exception
+	 * @param array $args Arguments to pass to the callback functions
+	 * @return string|null String to output or null if any hook has been called
+	 */
+	public static function runHooks( Exception $e, $name, $args = [] ) {
+		global $wgExceptionHooks;
+
+		if ( !isset( $wgExceptionHooks ) || !is_array( $wgExceptionHooks ) ) {
+			return null; // Just silently ignore
+		}
+
+		if ( !array_key_exists( $name, $wgExceptionHooks ) ||
+			!is_array( $wgExceptionHooks[$name] )
+		) {
+			return null;
+		}
+
+		$hooks = $wgExceptionHooks[$name];
+		$callargs = array_merge( [ $e ], $args );
+
+		foreach ( $hooks as $hook ) {
+			if (
+				is_string( $hook ) ||
+				( is_array( $hook ) && count( $hook ) >= 2 && is_string( $hook[0] ) )
+			) {
+				// 'function' or [ 'class', 'hook' ]
+				$result = call_user_func_array( $hook, $callargs );
+			} else {
+				$result = null;
+			}
+
+			if ( is_string( $result ) ) {
+				return $result;
+			}
+		}
+
+		return null;
+	}
+
+	/**
+	 * @param Exception $e
+	 * @return bool Should the exception use $wgOut to output the error?
+	 */
+	private static function useOutputPage( Exception $e ) {
+		// Can the extension use the Message class/wfMessage to get i18n-ed messages?
+		$useMessageCache = ( $GLOBALS['wgLang'] instanceof Language );
+		foreach ( $e->getTrace() as $frame ) {
+			if ( isset( $frame['class'] ) && $frame['class'] === 'LocalisationCache' ) {
+				$useMessageCache = false;
+			}
+		}
+
+		return (
+			$useMessageCache &&
+			!empty( $GLOBALS['wgFullyInitialised'] ) &&
+			!empty( $GLOBALS['wgOut'] ) &&
+			!defined( 'MEDIAWIKI_INSTALL' )
+		);
+	}
+
+	/**
+	 * Output the exception report using HTML
+	 *
+	 * @param Exception $e
+	 */
+	private static function reportHTML( Exception $e ) {
+		global $wgOut, $wgSitename;
+
+		if ( self::useOutputPage( $e ) ) {
+			if ( $e instanceof MWException ) {
+				$wgOut->prepareErrorPage( $e->getPageTitle() );
+			} elseif ( $e instanceof DBReadOnlyError ) {
+				$wgOut->prepareErrorPage( self::msg( 'readonly', 'Database is locked' ) );
+			} elseif ( $e instanceof DBExpectedError ) {
+				$wgOut->prepareErrorPage( self::msg( 'databaseerror', 'Database error' ) );
+			} else {
+				$wgOut->prepareErrorPage( self::msg( 'internalerror', 'Internal error' ) );
+			}
+
+			$hookResult = self::runHooks( $e, get_class( $e ) );
+			if ( $hookResult ) {
+				$wgOut->addHTML( $hookResult );
+			} else {
+				$wgOut->addHTML( self::getHTML( $e ) );
+			}
+
+			$wgOut->output();
+		} else {
+			self::header( 'Content-Type: text/html; charset=utf-8' );
+			$pageTitle = self::msg( 'internalerror', 'Internal error' );
+			echo "<!DOCTYPE html>\n" .
+				'<html><head>' .
+				// Mimick OutputPage::setPageTitle behaviour
+				'<title>' .
+				htmlspecialchars( self::msg( 'pagetitle', "$1 - $wgSitename", $pageTitle ) ) .
+				'</title>' .
+				'<style>body { font-family: sans-serif; margin: 0; padding: 0.5em 2em; }</style>' .
+				"</head><body>\n";
+
+			$hookResult = self::runHooks( $e, get_class( $e ) . 'Raw' );
+			if ( $hookResult ) {
+				echo $hookResult;
+			} else {
+				echo self::getHTML( $e );
+			}
+
+			echo "</body></html>\n";
+		}
+	}
+
+	/**
+	 * If $wgShowExceptionDetails is true, return a HTML message with a
+	 * backtrace to the error, otherwise show a message to ask to set it to true
+	 * to show that information.
+	 *
+	 * @param Exception $e
+	 * @return string Html to output
+	 */
+	private static function getHTML( Exception $e ) {
+		if ( self::showBackTrace( $e ) ) {
+			return '<p>' .
+				nl2br( htmlspecialchars( MWExceptionHandler::getLogMessage( $e ) ) ) .
+				'</p><p>Backtrace:</p><p>' .
+				nl2br( htmlspecialchars( MWExceptionHandler::getRedactedTraceAsString( $e ) ) ) .
+				"</p>\n";
+		} else {
+			$logId = WebRequest::getRequestId();
+			return "<div class=\"errorbox\">" .
+				'[' . $logId . '] ' .
+				gmdate( 'Y-m-d H:i:s' ) . ": " .
+				self::msg( "internalerror-fatal-exception",
+					"Fatal exception of type $1",
+					get_class( $e ),
+					$logId,
+					MWExceptionHandler::getURL()
+				) . "</div>\n" .
+			"<!-- Set \$wgShowExceptionDetails = true; " .
+			"at the bottom of LocalSettings.php to show detailed " .
+			"debugging information. -->";
+		}
+	}
+
+	/**
+	 * Get a message from i18n
+	 *
+	 * @param string $key Message name
+	 * @param string $fallback Default message if the message cache can't be
+	 *                  called by the exception
+	 * The function also has other parameters that are arguments for the message
+	 * @return string Message with arguments replaced
+	 */
+	private static function msg( $key, $fallback /*[, params...] */ ) {
+		$args = array_slice( func_get_args(), 2 );
+		try {
+			return wfMessage( $key, $args )->text();
+		} catch ( Exception $e ) {
+			return wfMsgReplaceArgs( $fallback, $args );
+		}
+	}
+
+	/**
+	 * @param Exception $e
+	 * @return string
+	 */
+	private function getText( Exception $e ) {
+		if ( self::showBackTrace( $e ) ) {
+			return MWExceptionHandler::getLogMessage( $e ) .
+				"\nBacktrace:\n" .
+				MWExceptionHandler::getRedactedTraceAsString( $e ) . "\n";
+		} else {
+			return "Set \$wgShowExceptionDetails = true; " .
+				"in LocalSettings.php to show detailed debugging information.\n";
+		}
+	}
+
+	/**
+	 * @param Exception $e
+	 * @return bool
+	 */
+	private static function showBackTrace( Exception $e ) {
+		global $wgShowExceptionDetails, $wgShowDBErrorBacktrace;
+
+		return (
+			$wgShowExceptionDetails &&
+			( !( $e instanceof DBError ) || $wgShowDBErrorBacktrace )
+		);
+	}
+
+	/**
+	 * @return bool
+	 */
+	private static function isCommandLine() {
+		return !empty( $GLOBALS['wgCommandLineMode'] );
+	}
+
+	/**
+	 * @param string $header
+	 */
+	private static function header( $header ) {
+		if ( !headers_sent() ) {
+			header( $header );
+		}
+	}
+
+	/**
+	 * @param integer $code
+	 */
+	private static function statusHeader( $code ) {
+		if ( !headers_sent() ) {
+			HttpStatus::header( $code );
+		}
+	}
+
+	/**
+	 * Print a message, if possible to STDERR.
+	 * Use this in command line mode only (see isCommandLine)
+	 *
+	 * @param string $message Failure text
+	 */
+	private 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;
+		}
+	}
+
+	/**
+	 * @param Exception $e
+	 */
+	private static function reportOutageHTML( Exception $e ) {
+		global $wgShowDBErrorBacktrace, $wgShowHostnames, $wgShowSQLErrors;
+
+		$sorry = htmlspecialchars( self::msg(
+			'dberr-problems',
+			'Sorry! This site is experiencing technical difficulties.'
+		) );
+		$again = htmlspecialchars( self::msg(
+			'dberr-again',
+			'Try waiting a few minutes and reloading.'
+		) );
+
+		if ( $wgShowHostnames || $wgShowSQLErrors ) {
+			$info = str_replace(
+				'$1',
+				Html::element( 'span', [ 'dir' => 'ltr' ], htmlspecialchars( $e->getMessage() ) ),
+				htmlspecialchars( self::msg( 'dberr-info', '($1)' ) )
+			);
+		} else {
+			$info = htmlspecialchars( self::msg(
+				'dberr-info-hidden',
+				'(Cannot access the database)'
+			) );
+		}
+
+		MessageCache::singleton()->disable(); // no DB access
+
+		$html = "<h1>$sorry</h1><p>$again</p><p><small>$info</small></p>";
+
+		if ( $wgShowDBErrorBacktrace ) {
+			$html .= '<p>Backtrace:</p><pre>' .
+				htmlspecialchars( $e->getTraceAsString() ) . '</pre>';
+		}
+
+		$html .= '<hr />';
+		$html .= self::googleSearchForm();
+
+		echo $html;
+	}
+
+	/**
+	 * @return string
+	 */
+	private static function googleSearchForm() {
+		global $wgSitename, $wgCanonicalServer, $wgRequest;
+
+		$usegoogle = htmlspecialchars( self::msg(
+			'dberr-usegoogle',
+			'You can try searching via Google in the meantime.'
+		) );
+		$outofdate = htmlspecialchars( self::msg(
+			'dberr-outofdate',
+			'Note that their indexes of our content may be out of date.'
+		) );
+		$googlesearch = htmlspecialchars( self::msg( 'searchbutton', 'Search' ) );
+		$search = htmlspecialchars( $wgRequest->getVal( 'search' ) );
+		$server = htmlspecialchars( $wgCanonicalServer );
+		$sitename = htmlspecialchars( $wgSitename );
+		$trygoogle = <<<EOT
+<div style="margin: 1.5em">$usegoogle<br />
+<small>$outofdate</small>
+</div>
+<form method="get" action="//www.google.com/search" id="googlesearch">
+	<input type="hidden" name="domains" value="$server" />
+	<input type="hidden" name="num" value="50" />
+	<input type="hidden" name="ie" value="UTF-8" />
+	<input type="hidden" name="oe" value="UTF-8" />
+	<input type="text" name="q" size="31" maxlength="255" value="$search" />
+	<input type="submit" name="btnG" value="$googlesearch" />
+	<p>
+		<label><input type="radio" name="sitesearch" value="$server" checked="checked" />$sitename</label>
+		<label><input type="radio" name="sitesearch" value="" />WWW</label>
+	</p>
+</form>
+EOT;
+		return $trygoogle;
+	}
+}