From 410986abf8157a3baed69a98afe90069d60c80a7 Mon Sep 17 00:00:00 2001
From: Tim Starling <tstarling@users.mediawiki.org>
Date: Tue, 6 Jun 2006 23:07:26 +0000
Subject: [PATCH] Some initial work on exceptions. More to follow.

---
 includes/Database.php           | 279 ++++++++++++++++++++++++++------
 includes/DatabaseOracle.php     |   8 +-
 includes/DatabasePostgreSQL.php |  18 +--
 includes/Exception.php          | 172 ++++++++++++++++++++
 includes/LoadBalancer.php       |   5 +-
 includes/Setup.php              |   6 +
 6 files changed, 423 insertions(+), 65 deletions(-)
 create mode 100644 includes/Exception.php

diff --git a/includes/Database.php b/includes/Database.php
index 2bdf610baa..173bc712bd 100644
--- a/includes/Database.php
+++ b/includes/Database.php
@@ -24,8 +24,12 @@ define( 'DEADLOCK_DELAY_MIN', 500000 );
 /** Maximum time to wait before retry */
 define( 'DEADLOCK_DELAY_MAX', 1500000 );
 
+/******************************************************************************
+ * Utility classes
+ *****************************************************************************/
+
 class DBObject {
-	var $mData;
+	public $mData;
 
 	function DBObject($data) {
 		$this->mData = $data;
@@ -40,6 +44,190 @@ class DBObject {
 	}
 };
 
+/******************************************************************************
+ * Error classes
+ *****************************************************************************/
+
+/**
+ * Database error base class
+ */
+class DBError extends MWException {
+	public $db;
+
+	/**
+	 * Construct a database error
+	 * @param Database $db The database object which threw the error
+	 * @param string $error A simple error message to be used for debugging
+	 */
+	function __construct( Database &$db, $error ) {
+		$this->db =& $db;
+		parent::__construct( $error );
+	}
+}
+
+class DBConnectionError extends DBError {
+	public $error;
+	
+	function __construct( Database &$db, $error = 'unknown error' ) {
+		$msg = 'DB connection error';
+		if ( trim( $error ) != '' ) {
+			$msg .= ": $error";
+		}
+		$this->error = $error;
+		parent::__construct( $db, $msg );
+	}
+
+	function useOutputPage() {
+		// Not likely to work
+		return false;
+	}
+
+	function useMessageCache() {
+		// Not likely to work
+		return false;
+	}
+	
+	function getText() {
+		return $this->getMessage() . "\n";
+	}
+
+	function getPageTitle() {
+		global $wgSitename;
+		return "$wgSitename has a problem";
+	}
+
+	function getHTML() {
+		global $wgTitle, $wgUseFileCache, $title, $wgInputEncoding, $wgOutputEncoding;
+		global $wgSitename, $wgServer, $wgMessageCache, $wgLogo;
+
+		# I give up, Brion is right. Getting the message cache to work when there is no DB is tricky.
+		# Hard coding strings instead.
+
+		$noconnect = "<p><strong>Sorry! This site is experiencing technical difficulties.</strong></p><p>Try waiting a few minutes and reloading.</p><p><small>(Can't contact the database server: $1)</small></p>";
+		$mainpage = 'Main Page';
+		$searchdisabled = <<<EOT
+<p style="margin: 1.5em 2em 1em">$wgSitename search is disabled for performance reasons. You can search via Google in the meantime.
+<span style="font-size: 89%; display: block; margin-left: .2em">Note that their indexes of $wgSitename content may be out of date.</span></p>',
+EOT;
+
+		$googlesearch = "
+<!-- SiteSearch Google -->
+<FORM method=GET action=\"http://www.google.com/search\">
+<TABLE bgcolor=\"#FFFFFF\"><tr><td>
+<A HREF=\"http://www.google.com/\">
+<IMG SRC=\"http://www.google.com/logos/Logo_40wht.gif\"
+border=\"0\" ALT=\"Google\"></A>
+</td>
+<td>
+<INPUT TYPE=text name=q size=31 maxlength=255 value=\"$1\">
+<INPUT type=submit name=btnG VALUE=\"Google Search\">
+<font size=-1>
+<input type=hidden name=domains value=\"$wgServer\"><br /><input type=radio name=sitesearch value=\"\"> WWW <input type=radio name=sitesearch value=\"$wgServer\" checked> $wgServer <br />
+<input type='hidden' name='ie' value='$2'>
+<input type='hidden' name='oe' value='$2'>
+</font>
+</td></tr></TABLE>
+</FORM>
+<!-- SiteSearch Google -->";
+		$cachederror = "The following is a cached copy of the requested page, and may not be up to date. ";
+
+		# No database access
+		if ( is_object( $wgMessageCache ) ) {
+			$wgMessageCache->disable();
+		}
+
+		if ( trim( $this->error ) == '' ) {
+			$this->error = $this->db->getProperty('mServer');
+		}
+
+		$text = str_replace( '$1', $this->error, $noconnect );
+		$text .= wfGetSiteNotice();
+
+		if($wgUseFileCache) {
+			if($wgTitle) {
+				$t =& $wgTitle;
+			} else {
+				if($title) {
+					$t = Title::newFromURL( $title );
+				} elseif (@/**/$_REQUEST['search']) {
+					$search = $_REQUEST['search'];
+					return $searchdisabled .
+					  str_replace( array( '$1', '$2' ), array( htmlspecialchars( $search ),
+					  $wgInputEncoding ), $googlesearch );
+				} else {
+					$t = Title::newFromText( $mainpage );
+				}
+			}
+
+			$cache = new CacheManager( $t );
+			if( $cache->isFileCached() ) {
+				$msg = '<p style="color: red"><b>'.$msg."<br />\n" .
+					$cachederror . "</b></p>\n";
+
+				$tag = '<div id="article">';
+				$text = str_replace(
+					$tag,
+					$tag . $msg,
+					$cache->fetchPageText() );
+			}
+		}
+
+		return $text;
+	}
+}
+
+class DBQueryError extends DBError {
+	public $error, $errno, $sql, $fname;
+	
+	function __construct( Database &$db, $error, $errno, $sql, $fname ) {
+		$message = "A database error has occurred\n" .
+		  "Query: $sql\n" .
+		  "Function: $fname\n" .
+		  "Error: $errno $error\n";
+
+		parent::__construct( $db, $message );
+		$this->error = $error;
+		$this->errno = $errno;
+		$this->sql = $sql;
+		$this->fname = $fname;
+	}
+
+	function getText() {
+		if ( $this->useMessageCache() ) {
+			return wfMsg( 'dberrortextcl', htmlspecialchars( $this->getSQL() ),
+			  htmlspecialchars( $this->fname ), $this->errno, htmlspecialchars( $this->error ) ) . "\n";
+		} else {
+			return $this->getMessage();
+		}
+	}
+	
+	function getSQL() {
+		global $wgShowSQLErrors;
+		if( !$wgShowSQLErrors ) {
+			return $this->msg( 'sqlhidden', 'SQL hidden' );
+		} else {
+			return $this->sql;
+		}
+	}
+	
+	function getPageTitle() {
+		return $this->msg( 'databaseerror', 'Database error' );
+	}
+
+	function getHTML() {
+		if ( $this->useMessageCache() ) {
+			return wfMsgNoDB( 'dberrortext', htmlspecialchars( $this->getSQL() ),
+			  htmlspecialchars( $this->fname ), $this->errno, htmlspecialchars( $this->error ) );
+		} else {
+			return nl2br( htmlspecialchars( $this->getMessage() ) );
+		}
+	}
+}
+
+class DBUnexpectedError extends DBError {}
+
+/******************************************************************************/
+
 /**
  * Database abstraction object
  * @package MediaWiki
@@ -49,21 +237,18 @@ class Database {
 #------------------------------------------------------------------------------
 # Variables
 #------------------------------------------------------------------------------
-	/**#@+
-	 * @private
-	 */
-	var $mLastQuery = '';
 
-	var $mServer, $mUser, $mPassword, $mConn = null, $mDBname;
-	var $mOut, $mOpened = false;
+	protected $mLastQuery = '';
 
-	var $mFailFunction;
-	var $mTablePrefix;
-	var $mFlags;
-	var $mTrxLevel = 0;
-	var $mErrorCount = 0;
-	var $mLBInfo = array();
-	/**#@-*/
+	protected $mServer, $mUser, $mPassword, $mConn = null, $mDBname;
+	protected $mOut, $mOpened = false;
+
+	protected $mFailFunction;
+	protected $mTablePrefix;
+	protected $mFlags;
+	protected $mTrxLevel = 0;
+	protected $mErrorCount = 0;
+	protected $mLBInfo = array();
 
 #------------------------------------------------------------------------------
 # Accessors
@@ -173,6 +358,13 @@ class Database {
 		return !!($this->mFlags & $flag);
 	}
 
+	/**
+	 * General read-only accessor
+	 */
+	function getProperty( $name ) {
+		return $this->$name;
+	}
+
 #------------------------------------------------------------------------------
 # Other functions
 #------------------------------------------------------------------------------
@@ -189,7 +381,7 @@ class Database {
 	 * @param $flags
 	 * @param $tablePrefix String: database table prefixes. By default use the prefix gave in LocalSettings.php
 	 */
-	function Database( $server = false, $user = false, $password = false, $dbName = false,
+	function __construct( $server = false, $user = false, $password = false, $dbName = false,
 		$failFunction = false, $flags = 0, $tablePrefix = 'get from global' ) {
 
 		global $wgOut, $wgDBprefix, $wgCommandLineMode;
@@ -234,7 +426,7 @@ class Database {
 	 * @param failFunction
 	 * @param $flags
 	 */
-	function newFromParams( $server, $user, $password, $dbName,
+	static function newFromParams( $server, $user, $password, $dbName,
 		$failFunction = false, $flags = 0 )
 	{
 		return new Database( $server, $user, $password, $dbName, $failFunction, $flags );
@@ -253,9 +445,10 @@ class Database {
 			@dl('mysql.so');
 		}
 
+		# Fail now
 		# Otherwise we get a suppressed fatal error, which is very hard to track down
 		if ( !function_exists( 'mysql_connect' ) ) {
-			wfDie( "MySQL functions missing, have you compiled PHP with the --with-mysql option?\n" );
+			throw new DBConnectionError( $this, "MySQL functions missing, have you compiled PHP with the --with-mysql option?\n" );
 		}
 
 		$this->close();
@@ -328,7 +521,6 @@ class Database {
 	}
 
 	/**
-	 * @private
 	 * @param string $error fallback error message, used if none is given by MySQL
 	 */
 	function reportConnectionError( $error = 'Unknown error' ) {
@@ -338,12 +530,15 @@ class Database {
 		}
 
 		if ( $this->mFailFunction ) {
+			# Legacy error handling method
 			if ( !is_int( $this->mFailFunction ) ) {
 				$ff = $this->mFailFunction;
 				$ff( $this, $error );
 			}
 		} else {
-			wfEmergencyAbort( $this, $error );
+			# New method
+			wfLogDBError( "Connection error: $error\n" );
+			throw new DBConnectionError( $this, $error );
 		}
 	}
 
@@ -447,29 +642,13 @@ class Database {
 
 		if( $ignore || $tempIgnore ) {
 			wfDebug("SQL ERROR (ignored): $error\n");
+			$this->ignoreErrors( $ignore );
 		} else {
 			$sql1line = str_replace( "\n", "\\n", $sql );
 			wfLogDBError("$fname\t{$this->mServer}\t$errno\t$error\t$sql1line\n");
 			wfDebug("SQL ERROR: " . $error . "\n");
-			if ( $wgCommandLineMode || !$this->mOut || empty( $wgFullyInitialised ) ) {
-				$message = "A database error has occurred\n" .
-				  "Query: $sql\n" .
-				  "Function: $fname\n" .
-				  "Error: $errno $error\n";
-				if ( !$wgCommandLineMode ) {
-					$message = nl2br( $message );
-				}
-				if( $wgCommandLineMode && $wgColorErrors && !wfIsWindows() && posix_isatty(1) ) {
-					$color = 31; // bright red!
-					$message = "\x1b[1;{$color}m{$message}\x1b[0m";
-				}
-				wfDebugDieBacktrace( $message );
-			} else {
-				// this calls wfAbruptExit()
-				$this->mOut->databaseError( $fname, $sql, $error, $errno );
-			}
+			throw new DBQueryError( $this, $error, $errno, $sql, $fname );
 		}
-		$this->ignoreErrors( $ignore );
 	}
 
 
@@ -561,9 +740,9 @@ class Database {
 			case '!': return $arg;
 			case '&':
 				# return $this->addQuotes( file_get_contents( $arg ) );
-				wfDebugDieBacktrace( '& mode is not implemented. If it\'s really needed, uncomment the line above.' );
+				throw new DBUnexpectedError( $this, '& mode is not implemented. If it\'s really needed, uncomment the line above.' );
 			default:
-				wfDebugDieBacktrace( 'Received invalid match. This should never happen!' );
+				throw new DBUnexpectedError( $this, 'Received invalid match. This should never happen!' );
 		}
 	}
 
@@ -575,7 +754,7 @@ class Database {
 	 */
 	function freeResult( $res ) {
 		if ( !@/**/mysql_free_result( $res ) ) {
-			wfDebugDieBacktrace( "Unable to free MySQL result\n" );
+			throw new DBUnexpectedError( $this, "Unable to free MySQL result" );
 		}
 	}
 
@@ -585,7 +764,7 @@ class Database {
 	function fetchObject( $res ) {
 		@/**/$row = mysql_fetch_object( $res );
 		if( mysql_errno() ) {
-			wfDebugDieBacktrace( 'Error in fetchObject(): ' . htmlspecialchars( mysql_error() ) );
+			throw new DBUnexpectedError( $this, 'Error in fetchObject(): ' . htmlspecialchars( mysql_error() ) );
 		}
 		return $row;
 	}
@@ -597,7 +776,7 @@ class Database {
  	function fetchRow( $res ) {
 		@/**/$row = mysql_fetch_array( $res );
 		if (mysql_errno() ) {
-			wfDebugDieBacktrace( 'Error in fetchRow(): ' . htmlspecialchars( mysql_error() ) );
+			throw new DBUnexpectedError( $this, 'Error in fetchRow(): ' . htmlspecialchars( mysql_error() ) );
 		}
 		return $row;
 	}
@@ -608,7 +787,7 @@ class Database {
 	function numRows( $res ) {
 		@/**/$n = mysql_num_rows( $res );
 		if( mysql_errno() ) {
-			wfDebugDieBacktrace( 'Error in numRows(): ' . htmlspecialchars( mysql_error() ) );
+			throw new DBUnexpectedError( $this, 'Error in numRows(): ' . htmlspecialchars( mysql_error() ) );
 		}
 		return $n;
 	}
@@ -847,7 +1026,7 @@ class Database {
 	 * @param string $sql A SQL Query
 	 * @static
 	 */
-	function generalizeSQL( $sql ) {
+	static function generalizeSQL( $sql ) {
 		# This does the same as the regexp below would do, but in such a way
 		# as to avoid crashing php on some large strings.
 		# $sql = preg_replace ( "/'([^\\\\']|\\\\.)*'|\"([^\\\\\"]|\\\\.)*\"/", "'X'", $sql);
@@ -1079,7 +1258,7 @@ class Database {
 	 */
 	function makeList( $a, $mode = LIST_COMMA ) {
 		if ( !is_array( $a ) ) {
-			wfDebugDieBacktrace( 'Database::makeList called with incorrect parameters' );
+			throw new DBUnexpectedError( $this, 'Database::makeList called with incorrect parameters' );
 		}
 
 		$first = true;
@@ -1282,7 +1461,7 @@ class Database {
 	 */
 	function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname = 'Database::deleteJoin' ) {
 		if ( !$conds ) {
-			wfDebugDieBacktrace( 'Database::deleteJoin() called with empty $conds' );
+			throw new DBUnexpectedError( $this, 'Database::deleteJoin() called with empty $conds' );
 		}
 
 		$delTable = $this->tableName( $delTable );
@@ -1327,7 +1506,7 @@ class Database {
 	 */
 	function delete( $table, $conds, $fname = 'Database::delete' ) {
 		if ( !$conds ) {
-			wfDebugDieBacktrace( 'Database::delete() called with no conditions' );
+			throw new DBUnexpectedError( $this, 'Database::delete() called with no conditions' );
 		}
 		$table = $this->tableName( $table );
 		$sql = "DELETE FROM $table";
@@ -1379,7 +1558,7 @@ class Database {
 	 */
 	function limitResult($sql, $limit, $offset=false) {
 		if( !is_numeric($limit) ) {
-			wfDie( "Invalid non-numeric limit passed to limitResult()\n" );
+			throw new DBUnexpectedError( $this, "Invalid non-numeric limit passed to limitResult()\n" );
 		}
 		return " $sql LIMIT "
 				. ( (is_numeric($offset) && $offset != 0) ? "{$offset}," : "" )
@@ -1737,7 +1916,7 @@ class Database {
 	/**
 	 * Replace variables in sourced SQL
 	 */
-	function replaceVars( $ins ) {
+	protected function replaceVars( $ins ) {
 		$varnames = array(
 			'wgDBserver', 'wgDBname', 'wgDBintlname', 'wgDBuser',
 			'wgDBpassword', 'wgDBsqluser', 'wgDBsqlpassword',
@@ -1764,7 +1943,7 @@ class Database {
 	 * Table name callback
 	 * @private
 	 */
-	function tableNameCallback( $matches ) {
+	protected function tableNameCallback( $matches ) {
 		return $this->tableName( $matches[1] );
 	}
 
diff --git a/includes/DatabaseOracle.php b/includes/DatabaseOracle.php
index 226bb4d6bd..d5d7379dc6 100644
--- a/includes/DatabaseOracle.php
+++ b/includes/DatabaseOracle.php
@@ -52,7 +52,7 @@ class DatabaseOracle extends Database {
 	 */
 	function open( $server, $user, $password, $dbName ) {
 		if ( !function_exists( 'oci_connect' ) ) {
-			wfDie( "Oracle functions missing, have you compiled PHP with the --with-oci8 option?\n" );
+			throw new DBConnectionError( $this, "Oracle functions missing, have you compiled PHP with the --with-oci8 option?\n" );
 		}
 		$this->close();
 		$this->mServer = $server;
@@ -137,7 +137,7 @@ class DatabaseOracle extends Database {
 
 	function freeResult( $res ) {
 		if (!oci_free_statement($res)) {
-			wfDebugDieBacktrace( "Unable to free Oracle result\n" );
+			throw new DBUnexpectedError( $this, "Unable to free Oracle result\n" );
 		}
 		unset($this->mFetchID[$res]);
 		unset($this->mFetchCache[$res]);
@@ -385,7 +385,7 @@ class DatabaseOracle extends Database {
 	# DELETE where the condition is a join
 	function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname = "Database::deleteJoin" ) {
 		if ( !$conds ) {
-			wfDebugDieBacktrace( 'Database::deleteJoin() called with empty $conds' );
+			throw new DBUnexpectedError( $this, 'Database::deleteJoin() called with empty $conds' );
 		}
 
 		$delTable = $this->tableName( $delTable );
@@ -467,7 +467,7 @@ class DatabaseOracle extends Database {
 			"Query: $sql\n" .
 			"Function: $fname\n" .
 			"Error: $errno $error\n";
-		wfDebugDieBacktrace($message);
+		throw new DBUnexpectedError($this, $message);
 	}
 
 	/**
diff --git a/includes/DatabasePostgreSQL.php b/includes/DatabasePostgreSQL.php
index 130a247a85..23f82c25ae 100644
--- a/includes/DatabasePostgreSQL.php
+++ b/includes/DatabasePostgreSQL.php
@@ -45,7 +45,7 @@ class DatabasePgsql extends Database {
 	function open( $server, $user, $password, $dbName ) {
 		# Test for PostgreSQL support, to avoid suppressed fatal error
 		if ( !function_exists( 'pg_connect' ) ) {
-			wfDie( "PostgreSQL functions missing, have you compiled PHP with the --with-pgsql option?\n" );
+			throw new DBConnectionError( $this, "PostgreSQL functions missing, have you compiled PHP with the --with-pgsql option?\n" );
 		}
 
 		global $wgDBschema;
@@ -101,7 +101,7 @@ class DatabasePgsql extends Database {
 
 	function freeResult( $res ) {
 		if ( !@pg_free_result( $res ) ) {
-			wfDebugDieBacktrace( "Unable to free PostgreSQL result\n" );
+			throw new DBUnexpectedError($this,  "Unable to free PostgreSQL result\n" );
 		}
 	}
 
@@ -113,7 +113,7 @@ class DatabasePgsql extends Database {
 		# hashar : not sure if the following test really trigger if the object
 		#          fetching failled.
 		if( pg_last_error($this->mConn) ) {
-			wfDebugDieBacktrace( 'SQL error: ' . htmlspecialchars( pg_last_error($this->mConn) ) );
+			throw new DBUnexpectedError($this,  'SQL error: ' . htmlspecialchars( pg_last_error($this->mConn) ) );
 		}
 		return $row;
 	}
@@ -121,7 +121,7 @@ class DatabasePgsql extends Database {
 	function fetchRow( $res ) {
 		@$row = pg_fetch_array( $res );
 		if( pg_last_error($this->mConn) ) {
-			wfDebugDieBacktrace( 'SQL error: ' . htmlspecialchars( pg_last_error($this->mConn) ) );
+			throw new DBUnexpectedError($this,  'SQL error: ' . htmlspecialchars( pg_last_error($this->mConn) ) );
 		}
 		return $row;
 	}
@@ -129,7 +129,7 @@ class DatabasePgsql extends Database {
 	function numRows( $res ) {
 		@$n = pg_num_rows( $res );
 		if( pg_last_error($this->mConn) ) {
-			wfDebugDieBacktrace( 'SQL error: ' . htmlspecialchars( pg_last_error($this->mConn) ) );
+			throw new DBUnexpectedError($this,  'SQL error: ' . htmlspecialchars( pg_last_error($this->mConn) ) );
 		}
 		return $n;
 	}
@@ -183,13 +183,13 @@ class DatabasePgsql extends Database {
 	}
 
 	function fieldInfo( $table, $field ) {
-		wfDebugDieBacktrace( 'Database::fieldInfo() error : mysql_fetch_field() not implemented for postgre' );
+		throw new DBUnexpectedError($this,  'Database::fieldInfo() error : mysql_fetch_field() not implemented for postgre' );
 		/*
 		$res = $this->query( "SELECT * FROM '$table' LIMIT 1" );
 		$n = pg_num_fields( $res );
 		for( $i = 0; $i < $n; $i++ ) {
 			// FIXME
-			wfDebugDieBacktrace( "Database::fieldInfo() error : mysql_fetch_field() not implemented for postgre" );
+			throw new DBUnexpectedError($this,  "Database::fieldInfo() error : mysql_fetch_field() not implemented for postgre" );
 			$meta = mysql_fetch_field( $res, $i );
 			if( $field == $meta->name ) {
 				return $meta;
@@ -328,7 +328,7 @@ class DatabasePgsql extends Database {
 	# DELETE where the condition is a join
 	function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname = "Database::deleteJoin" ) {
 		if ( !$conds ) {
-			wfDebugDieBacktrace( 'Database::deleteJoin() called with empty $conds' );
+			throw new DBUnexpectedError($this,  'Database::deleteJoin() called with empty $conds' );
 		}
 
 		$delTable = $this->tableName( $delTable );
@@ -404,7 +404,7 @@ class DatabasePgsql extends Database {
 			"Query: $sql\n" .
 			"Function: $fname\n" .
 			"Error: $errno $error\n";
-		wfDebugDieBacktrace($message);
+		throw new DBUnexpectedError($this, $message);
 	}
 
 	/**
diff --git a/includes/Exception.php b/includes/Exception.php
new file mode 100644
index 0000000000..11bb5971d5
--- /dev/null
+++ b/includes/Exception.php
@@ -0,0 +1,172 @@
+<?php
+
+class MWException extends Exception
+{
+	function useOutputPage() {
+		return !empty( $GLOBALS['wgFullyInitialised'] );
+	}
+
+	function useMessageCache() {
+		global $wgLang;
+		return is_object( $wgLang );
+	}
+
+	function msg( $key, $fallback /*[, params...] */ ) {
+		$args = array_slice( func_get_args(), 2 );
+		if ( $this->useMessageCache() ) {
+			return wfMsgReal( $key, $args );
+		} else {
+			return wfMsgReplaceArgs( $fallback, $args );
+		}
+	}
+			
+	function getHTML() {
+		return '<p>' . htmlspecialchars( $this->getMessage() ) . 
+			'</p><p>Backtrace:</p><p>' . nl2br( htmlspecialchars( $this->getTraceAsString() ) ) .
+			"</p>\n";
+	}
+
+	function getText() {
+		return $this->getMessage() .  
+			"\nBacktrace:\n" . $this->getTraceAsString() . "\n";
+	}
+	
+	function getPageTitle() {
+		if ( $this->useMessageCache() ) {
+			return wfMsg( 'internalerror' );
+		} else {
+			global $wgSitename;
+			return "$wgSitename error";
+		}
+	}
+	
+	function reportHTML() {
+		global $wgOut;
+		if ( $this->useOutputPage() ) {
+			$wgOut->setPageTitle( $this->getPageTitle() );
+			$wgOut->setRobotpolicy( "noindex,nofollow" );
+			$wgOut->setArticleRelated( false );
+			$wgOut->enableClientCache( false );
+			$wgOut->redirect( '' );
+			$wgOut->clearHTML();
+			$wgOut->addHTML( $this->getHTML() );
+			$wgOut->output();
+		} else {
+			echo $this->htmlHeader();
+			echo $this->getHTML();
+			echo $this->htmlFooter();
+		}
+	}
+	
+	function reportText() {
+		echo $this->getText();
+	}
+
+	function report() {
+		global $wgCommandLineMode;
+		if ( $wgCommandLineMode ) {
+			$this->reportText();
+		} else {
+			$this->reportHTML();
+		}
+	}
+
+	function htmlHeader() {
+		global $wgLogo, $wgSitename, $wgOutputEncoding;
+
+		if ( !headers_sent() ) {
+			header( 'HTTP/1.0 500 Internal Server Error' );
+			header( 'Content-type: text/html; charset='.$wgOutputEncoding );
+			/* Don't cache error pages!  They cause no end of trouble... */
+			header( 'Cache-control: none' );
+			header( 'Pragma: nocache' );
+		}
+		$title = $this->getPageTitle();
+		echo "<html>
+		<head>
+		<title>$title</title>
+		</head>
+		<body>
+		<h1><img src='$wgLogo' style='float:left;margin-right:1em' alt=''>$title</h1>
+		";
+	}
+
+	function htmlFooter() {
+		echo "</body></html>";
+	}		
+}
+
+/**
+ * Exception class which takes an HTML error message, and does not 
+ * produce a backtrace. Replacement for OutputPage::fatalError().
+ */
+class FatalError extends MWException {
+	function getHTML() {
+		return $this->getMessage();
+	}
+
+	function getText() {
+		return $this->getMessage();
+	}
+}
+
+/**
+ * Install an exception handler for MediaWiki exception types.
+ */
+function wfInstallExceptionHandler() {
+	set_exception_handler( 'wfExceptionHandler' );
+}
+
+/**
+ * Report an exception to the user
+ */
+function wfReportException( Exception $e ) {
+	 if ( is_a( $e, 'MWException' ) ) {
+		 try {
+			 $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" .
+			 "Original exception: " . $e->__toString() . 
+			 "\n\nException caught inside exception handler: " . 
+			 $e2->__toString() . "\n";
+
+			 if ( !empty( $GLOBALS['wgCommandLineMode'] ) ) {
+				 echo $message;
+			 } else {
+				 echo nl2br( htmlspecialchars( $message ) ). "\n";
+			 }
+		 }
+	 } else {
+		 echo $e->__toString();
+	 }
+}
+
+/**
+ * Exception handler which simulates the appropriate catch() handling:
+ * 
+ *   try {
+ *       ...
+ *   } catch ( MWException $e ) {
+ * 
+ *       $e->report();
+ *   } catch ( Exception $e ) {
+ *       echo $e->__toString();
+ *   }
+ */
+function wfExceptionHandler( $e ) {
+	wfReportException( $e );
+	
+	// Final cleanup, similar to wfErrorExit()
+	try {
+		wfProfileClose();
+		logProfilingData();
+	} catch ( Exception $e ) {}
+
+	// Exit value should be nonzero for the benefit of shell jobs
+	exit( 1 );
+}
+
+?>
diff --git a/includes/LoadBalancer.php b/includes/LoadBalancer.php
index d77cf3f66a..dada8d44fa 100644
--- a/includes/LoadBalancer.php
+++ b/includes/LoadBalancer.php
@@ -436,7 +436,7 @@ class LoadBalancer {
 	 */
 	function reallyOpenConnection( &$server ) {
 		if( !is_array( $server ) ) {
-			wfDebugDieBacktrace( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
+			throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 		}
 
 		extract( $server );
@@ -477,7 +477,8 @@ class LoadBalancer {
 				} else {
 					$conn->failFunction( false );
 				}
-				$conn->reportConnectionError( "{$this->mLastError} ({$conn->mServer})" );
+				$server = $conn->getProperty( 'mServer' );
+				$conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 			}
 			$reporting = false;
 		}
diff --git a/includes/Setup.php b/includes/Setup.php
index 423022698b..b5480d65f2 100644
--- a/includes/Setup.php
+++ b/includes/Setup.php
@@ -43,6 +43,12 @@ if ( function_exists( 'wfProfileIn' ) ) {
 
 $fname = 'Setup.php';
 wfProfileIn( $fname );
+
+wfProfileIn( $fname.'-exception' );
+require_once( 'Exception.php' );
+wfInstallExceptionHandler();
+wfProfileOut( $fname.'-exception' );
+
 wfProfileIn( $fname.'-includes' );
 
 require_once( 'AutoLoader.php' );
-- 
2.20.1