Add skipping to nth page option/ability for dump importing process

Usage: php importDump.php --skip-to 271500 /path_to/dumpfile.xml.gz

When importing a database dump and the import process crashes
(for random reasons) after a certain number of pages, the
"--skip-to" parameter allows restarting the import process at
a certain page instead of starting the import from scratch.

Change-Id: Ib36063b69d6846fc197800bba44287493b0632c0

includes/import/WikiImporter.php

@@ -39,6 +39,7 @@ class WikiImporter {
 	private $mNoticeCallback, $mDebug;
 	private $mImportUploads, $mImageBasePath;
 	private $mNoUpdates = false;
+	private $pageOffset = 0;
 	/** @var Config */
 	private $config;
 	/** @var ImportTitleFactory */
@@ -146,6 +147,16 @@ function setNoUpdates( $noupdates ) {
 		$this->mNoUpdates = $noupdates;
 	}
 
+	/**
+	 * Sets 'pageOffset' value. So it will skip the first n-1 pages
+	 * and start from the nth page. It's 1-based indexing.
+	 * @param int $nthPage
+	 * @since 1.29
+	 */
+	function setPageOffset( $nthPage ) {
+		$this->pageOffset = $nthPage;
+	}
+
 	/**
 	 * Set a callback that displays notice messages
 	 *
@@ -562,9 +573,19 @@ public function doImport() {
 		$keepReading = $this->reader->read();
 		$skip = false;
 		$rethrow = null;
+		$pageCount = 0;
 		try {
 			while ( $keepReading ) {
 				$tag = $this->reader->localName;
+				if ( $this->pageOffset ) {
+					if ( $tag === 'page' ) {
+						$pageCount++;
+					}
+					if ( $pageCount < $this->pageOffset ) {
+						$keepReading = $this->reader->next();
+						continue;
+					}
+				}
 				$type = $this->reader->nodeType;
 
 				if ( !Hooks::run( 'ImportHandleToplevelXMLTag', [ $this ] ) ) {

maintenance/importDump.php

@@ -80,6 +80,7 @@ function __construct() {
 			'Disable link table updates. Is faster but leaves the wiki in an inconsistent state'
 		);
 		$this->addOption( 'image-base-path', 'Import files from a specified path', false, true );
+		$this->addOption( 'skip-to', 'Start from nth page by skipping first n-1 pages', false, true );
 		$this->addArg( 'file', 'Dump file to import [else use stdin]', false );
 	}
 
@@ -301,6 +302,11 @@ function importFromHandle( $handle ) {
 				return false;
 			}
 		}
+		if ( $this->hasOption( 'skip-to' ) ) {
+			$nthPage = (int)$this->getOption( 'skip-to' );
+			$importer->setPageOffset( $nthPage );
+			$this->pageCount = $nthPage - 1;
+		}
 		$importer->setPageCallback( [ $this, 'reportPage' ] );
 		$this->importCallback = $importer->setRevisionCallback(
 			[ $this, 'handleRevision' ] );