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diff --git a/includes/externalstore/ExternalStore.php b/includes/externalstore/ExternalStore.php
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+<?php
+/**
+ * @defgroup ExternalStorage ExternalStorage
+ */
+
+/**
+ * Interface for data storage in external repositories.
+ *
+ * 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
+ */
+
+/**
+ * Constructor class for key/value blob data kept in external repositories.
+ *
+ * Objects in external stores are defined by a special URL. The URL is of
+ * the form "<store protocol>://<location>/<object name>". The protocol is used
+ * to determine what ExternalStoreMedium class is used. The location identifies
+ * particular storage instances or database clusters for store class to use.
+ *
+ * When an object is inserted into a store, the calling code uses a partial URL of
+ * the form "<store protocol>://<location>" and receives the full object URL on success.
+ * This is useful since object names can be sequential IDs, UUIDs, or hashes.
+ * Callers are not responsible for unique name generation.
+ *
+ * External repositories might be populated by maintenance/async
+ * scripts, thus partial moving of data may be possible, as well
+ * as the possibility to have any storage format (i.e. for archives).
+ *
+ * @ingroup ExternalStorage
+ */
+class ExternalStore {
+	/**
+	 * Get an external store object of the given type, with the given parameters
+	 *
+	 * @param string $proto Type of external storage, should be a value in $wgExternalStores
+	 * @param array $params Associative array of ExternalStoreMedium parameters
+	 * @return ExternalStoreMedium|bool The store class or false on error
+	 */
+	public static function getStoreObject( $proto, array $params = array() ) {
+		global $wgExternalStores;
+
+		if ( !$wgExternalStores || !in_array( $proto, $wgExternalStores ) ) {
+			return false; // protocol not enabled
+		}
+
+		$class = 'ExternalStore' . ucfirst( $proto );
+		// Any custom modules should be added to $wgAutoLoadClasses for on-demand loading
+		return MWInit::classExists( $class ) ? new $class( $params ) : false;
+	}
+
+	/**
+	 * Fetch data from given URL
+	 *
+	 * @param string $url The URL of the text to get
+	 * @param array $params Associative array of ExternalStoreMedium parameters
+	 * @return string|bool The text stored or false on error
+	 * @throws MWException
+	 */
+	public static function fetchFromURL( $url, array $params = array() ) {
+		$parts = explode( '://', $url, 2 );
+		if ( count( $parts ) != 2 ) {
+			return false; // invalid URL
+		}
+
+		list( $proto, $path ) = $parts;
+		if ( $path == '' ) { // bad URL
+			return false;
+		}
+
+		$store = self::getStoreObject( $proto, $params );
+		if ( $store === false ) {
+			return false;
+		}
+
+		return $store->fetchFromURL( $url );
+	}
+
+	/**
+	 * Store a data item to an external store, identified by a partial URL
+	 * The protocol part is used to identify the class, the rest is passed to the
+	 * class itself as a parameter.
+	 *
+	 * @param string $url A partial external store URL ("<store type>://<location>")
+	 * @param $data string
+	 * @param array $params Associative array of ExternalStoreMedium parameters
+	 * @return string|bool The URL of the stored data item, or false on error
+	 * @throws MWException
+	 */
+	public static function insert( $url, $data, array $params = array() ) {
+		$parts = explode( '://', $url, 2 );
+		if ( count( $parts ) != 2 ) {
+			return false; // invalid URL
+		}
+
+		list( $proto, $path ) = $parts;
+		if ( $path == '' ) { // bad URL
+			return false;
+		}
+
+		$store = self::getStoreObject( $proto, $params );
+		if ( $store === false ) {
+			return false;
+		} else {
+			return $store->store( $path, $data );
+		}
+	}
+
+	/**
+	 * Like insert() above, but does more of the work for us.
+	 * This function does not need a url param, it builds it by
+	 * itself. It also fails-over to the next possible clusters.
+	 *
+	 * @param $data string
+	 * @param array $params Associative array of ExternalStoreMedium parameters
+	 * @return string|bool The URL of the stored data item, or false on error
+	 * @throws MWException
+	 */
+	public static function insertToDefault( $data, array $params = array() ) {
+		global $wgDefaultExternalStore;
+
+		$error = false;
+		$tryStores = (array)$wgDefaultExternalStore;
+		while ( count( $tryStores ) > 0 ) {
+			$index = mt_rand( 0, count( $tryStores ) - 1 );
+			$storeUrl = $tryStores[$index];
+			wfDebug( __METHOD__ . ": trying $storeUrl\n" );
+			list( $proto, $path ) = explode( '://', $storeUrl, 2 );
+			$store = self::getStoreObject( $proto, $params );
+			if ( $store === false ) {
+				throw new MWException( "Invalid external storage protocol - $storeUrl" );
+			}
+			try {
+				$url = $store->store( $path, $data ); // Try to save the object
+			} catch ( MWException $error ) {
+				$url = false;
+			}
+			if ( strlen( $url ) ) {
+				return $url; // Done!
+			} else {
+				unset( $tryStores[$index] ); // Don't try this one again!
+				$tryStores = array_values( $tryStores ); // Must have consecutive keys
+				wfDebugLog( 'ExternalStorage',
+					"Unable to store text to external storage $storeUrl" );
+			}
+		}
+		// All stores failed
+		if ( $error ) {
+			throw $error; // rethrow the last error
+		} else {
+			throw new MWException( "Unable to store text to external storage" );
+		}
+	}
+
+	/**
+	 * @param $data string
+	 * @param $wiki string
+	 * @return string|bool The URL of the stored data item, or false on error
+	 * @throws MWException
+	 */
+	public static function insertToForeignDefault( $data, $wiki ) {
+		return self::insertToDefault( $data, array( 'wiki' => $wiki ) );
+	}
+}