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diff --git a/www/wiki/includes/Storage/RevisionSlots.php b/www/wiki/includes/Storage/RevisionSlots.php
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+++ b/www/wiki/includes/Storage/RevisionSlots.php
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+<?php
+/**
+ * Value object representing the set of slots belonging to a revision.
+ *
+ * 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
+ */
+
+namespace MediaWiki\Storage;
+
+use Content;
+use LogicException;
+use Wikimedia\Assert\Assert;
+
+/**
+ * Value object representing the set of slots belonging to a revision.
+ *
+ * @since 1.31
+ */
+class RevisionSlots {
+
+	/** @var SlotRecord[]|callable */
+	protected $slots;
+
+	/**
+	 * @param SlotRecord[]|callable $slots SlotRecords,
+	 *        or a callback that returns such a structure.
+	 */
+	public function __construct( $slots ) {
+		Assert::parameterType( 'array|callable', $slots, '$slots' );
+
+		if ( is_callable( $slots ) ) {
+			$this->slots = $slots;
+		} else {
+			$this->setSlotsInternal( $slots );
+		}
+	}
+
+	/**
+	 * @param SlotRecord[] $slots
+	 */
+	private function setSlotsInternal( array $slots ) {
+		$this->slots = [];
+
+		// re-key the slot array
+		foreach ( $slots as $slot ) {
+			$role = $slot->getRole();
+			$this->slots[$role] = $slot;
+		}
+	}
+
+	/**
+	 * Implemented to defy serialization.
+	 *
+	 * @throws LogicException always
+	 */
+	public function __sleep() {
+		throw new LogicException( __CLASS__ . ' is not serializable.' );
+	}
+
+	/**
+	 * Returns the Content of the given slot.
+	 * Call getSlotNames() to get a list of available slots.
+	 *
+	 * Note that for mutable Content objects, each call to this method will return a
+	 * fresh clone.
+	 *
+	 * @param string $role The role name of the desired slot
+	 *
+	 * @throws RevisionAccessException if the slot does not exist or slot data
+	 *        could not be lazy-loaded.
+	 * @return Content
+	 */
+	public function getContent( $role ) {
+		// Return a copy to be safe. Immutable content objects return $this from copy().
+		return $this->getSlot( $role )->getContent()->copy();
+	}
+
+	/**
+	 * Returns the SlotRecord of the given slot.
+	 * Call getSlotNames() to get a list of available slots.
+	 *
+	 * @param string $role The role name of the desired slot
+	 *
+	 * @throws RevisionAccessException if the slot does not exist or slot data
+	 *        could not be lazy-loaded.
+	 * @return SlotRecord
+	 */
+	public function getSlot( $role ) {
+		$slots = $this->getSlots();
+
+		if ( isset( $slots[$role] ) ) {
+			return $slots[$role];
+		} else {
+			throw new RevisionAccessException( 'No such slot: ' . $role );
+		}
+	}
+
+	/**
+	 * Returns whether the given slot is set.
+	 *
+	 * @param string $role The role name of the desired slot
+	 *
+	 * @return bool
+	 */
+	public function hasSlot( $role ) {
+		$slots = $this->getSlots();
+
+		return isset( $slots[$role] );
+	}
+
+	/**
+	 * Returns the slot names (roles) of all slots present in this revision.
+	 * getContent() will succeed only for the names returned by this method.
+	 *
+	 * @return string[]
+	 */
+	public function getSlotRoles() {
+		$slots = $this->getSlots();
+		return array_keys( $slots );
+	}
+
+	/**
+	 * Computes the total nominal size of the revision's slots, in bogo-bytes.
+	 *
+	 * @warn This is potentially expensive! It may cause all slot's content to be loaded
+	 * and deserialized.
+	 *
+	 * @return int
+	 */
+	public function computeSize() {
+		return array_reduce( $this->getSlots(), function ( $accu, SlotRecord $slot ) {
+			return $accu + $slot->getSize();
+		}, 0 );
+	}
+
+	/**
+	 * Returns an associative array that maps role names to SlotRecords. Each SlotRecord
+	 * represents the content meta-data of a slot, together they define the content of
+	 * a revision.
+	 *
+	 * @note This may cause the content meta-data for the revision to be lazy-loaded.
+	 *
+	 * @return SlotRecord[] revision slot/content rows, keyed by slot role name.
+	 */
+	public function getSlots() {
+		if ( is_callable( $this->slots ) ) {
+			$slots = call_user_func( $this->slots );
+
+			Assert::postcondition(
+				is_array( $slots ),
+				'Slots info callback should return an array of objects'
+			);
+
+			$this->setSlotsInternal( $slots );
+		}
+
+		return $this->slots;
+	}
+
+	/**
+	 * Computes the combined hash of the revisions's slots.
+	 *
+	 * @note For backwards compatibility, the combined hash of a single slot
+	 * is that slot's hash. For consistency, the combined hash of an empty set of slots
+	 * is the hash of the empty string.
+	 *
+	 * @warn This is potentially expensive! It may cause all slot's content to be loaded
+	 * and deserialized, then re-serialized and hashed.
+	 *
+	 * @return string
+	 */
+	public function computeSha1() {
+		$slots = $this->getSlots();
+		ksort( $slots );
+
+		if ( empty( $slots ) ) {
+			return SlotRecord::base36Sha1( '' );
+		}
+
+		return array_reduce( $slots, function ( $accu, SlotRecord $slot ) {
+			return $accu === null
+				? $slot->getSha1()
+				: SlotRecord::base36Sha1( $accu . $slot->getSha1() );
+		}, null );
+	}
+
+}