Better exception handling in mysqli connect

lib/Doctrine/DBAL/Driver/Mysqli/MysqliConnection.php

@@ -67,15 +67,14 @@ class MysqliConnection implements Connection, PingableConnection, ServerInfoAwar
         $this->setDriverOptions($driverOptions);
 
         set_error_handler(function () {});
-
-        if ( ! $this->_conn->real_connect($params['host'], $username, $password, $dbname, $port, $socket, $flags)) {
+        try {
+            if ( ! $this->_conn->real_connect($params['host'], $username, $password, $dbname, $port, $socket, $flags)) {
+                throw new MysqliException($this->_conn->connect_error, $this->_conn->sqlstate ?? 'HY000', $this->_conn->connect_errno);
+            }
+        } finally {
             restore_error_handler();
-
-            throw new MysqliException($this->_conn->connect_error, @$this->_conn->sqlstate ?: 'HY000', $this->_conn->connect_errno);
         }
 
-        restore_error_handler();
-
         if (isset($params['charset'])) {
             $this->_conn->set_charset($params['charset']);
         }

tests/Doctrine/Tests/DBAL/Driver/Mysqli/MysqliConnectionTest.php

@@ -28,11 +28,33 @@ class MysqliConnectionTest extends DbalTestCase
             ->getMockForAbstractClass();
     }
 
+    protected function tearDown()
+    {
+        if ($this->getName() == "testRestoresErrorHandlerOnException") {
+            restore_error_handler();
+        }
+    }
+
     public function testDoesNotRequireQueryForServerVersion()
     {
         $this->assertFalse($this->connectionMock->requiresQueryForServerVersion());
     }
 
+    public function testRestoresErrorHandlerOnException()
+    {
+        $handler = function () { self::fail('Never expected this to be called'); };
+        $default_handler = set_error_handler($handler);
+
+        try {
+            new MysqliConnection(['host' => '255.255.255.255'], 'user', 'pass');
+            self::fail('An exception was supposed to be raised');
+        } catch (MysqliException $e) {
+            self::assertSame('Network is unreachable', $e->getMessage());
+        }
+
+        self::assertSame($handler, set_error_handler($default_handler), 'Restoring error handler failed.');
+    }
+
     /**
      * @dataProvider secureMissingParamsProvider
      */