From 8f8b0de93282ba4124da3b577ed5f96d8210ad18 Mon Sep 17 00:00:00 2001
From: Timo Tijhof <krinklemail@gmail.com>
Date: Fri, 20 Apr 2018 16:00:32 +0100
Subject: [PATCH] OutputPage: Factor out CdnCacheEpoch logic and cover with
 tests

Bug: T178629
Change-Id: Ife7dd79677c2b5353317e06ac7ed521edd6193cc
---
 includes/OutputPage.php                   | 19 +++++++++--
 tests/phpunit/includes/OutputPageTest.php | 41 +++++++++++++++++++++++
 2 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/includes/OutputPage.php b/includes/OutputPage.php
index dd64413fd4..37527cf100 100644
--- a/includes/OutputPage.php
+++ b/includes/OutputPage.php
@@ -752,8 +752,10 @@ class OutputPage extends ContextSource {
 			'epoch' => $config->get( 'CacheEpoch' )
 		];
 		if ( $config->get( 'UseSquid' ) ) {
-			// T46570: the core page itself may not change, but resources might
-			$modifiedTimes['sepoch'] = wfTimestamp( TS_MW, time() - $config->get( 'SquidMaxage' ) );
+			$modifiedTimes['sepoch'] = wfTimestamp( TS_MW, $this->getCdnCacheEpoch(
+				time(),
+				$config->get( 'SquidMaxage' )
+			) );
 		}
 		Hooks::run( 'OutputPageCheckLastModified', [ &$modifiedTimes, $this ] );
 
@@ -815,6 +817,19 @@ class OutputPage extends ContextSource {
 		return true;
 	}
 
+	/**
+	 * @param int $reqTime Time of request (eg. now)
+	 * @param int $maxAge Cache TTL in seconds
+	 * @return int Timestamp
+	 */
+	private function getCdnCacheEpoch( $reqTime, $maxAge ) {
+		// Ensure Last-Modified is never more than (wgSquidMaxage) in the past,
+		// because even if the wiki page content hasn't changed since, static
+		// resources may have changed (skin HTML, interface messages, urls, etc.)
+		// and must roll-over in a timely manner (T46570)
+		return $reqTime - $maxAge;
+	}
+
 	/**
 	 * Override the last modified timestamp
 	 *
diff --git a/tests/phpunit/includes/OutputPageTest.php b/tests/phpunit/includes/OutputPageTest.php
index 81bbcd7ea4..0a657d886f 100644
--- a/tests/phpunit/includes/OutputPageTest.php
+++ b/tests/phpunit/includes/OutputPageTest.php
@@ -124,6 +124,47 @@ class OutputPageTest extends MediaWikiTestCase {
 		] );
 	}
 
+	public static function provideCdnCacheEpoch() {
+		$base = [
+			'pageTime' => '2011-04-01T12:00:00+00:00',
+			'maxAge' => 24 * 3600,
+		];
+		return [
+			'after 1s' => [ $base + [
+				'reqTime' => '2011-04-01T12:00:01+00:00',
+				'expect' => '2011-04-01T12:00:00+00:00',
+			] ],
+			'after 23h' => [ $base + [
+				'reqTime' => '2011-04-02T11:00:00+00:00',
+				'expect' => '2011-04-01T12:00:00+00:00',
+			] ],
+			'after 24h and a bit' => [ $base + [
+				'reqTime' => '2011-04-02T12:34:56+00:00',
+				'expect' => '2011-04-01T12:34:56+00:00',
+			] ],
+			'after a year' => [ $base + [
+				'reqTime' => '2012-05-06T00:12:07+00:00',
+				'expect' => '2012-05-05T00:12:07+00:00',
+			] ],
+		];
+	}
+
+	/**
+	 * @dataProvider provideCdnCacheEpoch
+	 */
+	public function testCdnCacheEpoch( $params ) {
+		$out = TestingAccessWrapper::newFromObject( $this->newInstance() );
+		$reqTime = strtotime( $params['reqTime'] );
+		$pageTime = strtotime( $params['pageTime'] );
+		$actual = max( $pageTime, $out->getCdnCacheEpoch( $reqTime, $params['maxAge'] ) );
+
+		$this->assertEquals(
+			$params['expect'],
+			gmdate( DateTime::ATOM, $actual ),
+			'cdn epoch'
+		);
+	}
+
 	/**
 	 * Tests screen requests, without either query parameter set
 	 * @covers OutputPage::transformCssMedia
-- 
2.20.1