From d722bc51f4091463f46ebf115d8256516ba6115d Mon Sep 17 00:00:00 2001
From: Marko Obrovac <mobrovac@wikimedia.org>
Date: Thu, 2 Jun 2016 16:30:48 +0200
Subject: [PATCH] Send a no-cache content request on mathpurge=true

When the user specifies the mathpurge=true query parameter, the Math
extension needs to prompt RESTBase to regenerate the renders for all
formulae on the page and consequently issue Varnish purge requests. This
behaviour is achieved by including the `Cache-Control: no-cache` header
when requesting a render. Since RESTBase regenerates all of the renders
when it receives the header, send it only for the first content request;
if subsequent content requests are made, RESTBase will already have the
new renders.

Bug: T136205
Change-Id: I44482ccc1d8afdf6d40dcf8965d8debe83ef7e17
---
 MathMathML.php            |  7 ++++---
 MathRenderer.php          |  1 +
 MathRestbaseInterface.php | 20 ++++++++++++++++++++
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/MathMathML.php b/MathMathML.php
index 26ee1b3a9..722dfc994 100644
--- a/MathMathML.php
+++ b/MathMathML.php
@@ -81,12 +81,16 @@ class MathMathML extends MathRenderer {
 	public function render( $forceReRendering = false ) {
 		global $wgMathFullRestbaseURL;
 		try {
+			if ( $forceReRendering ) {
+				$this->setPurge( true );
+			}
 			if ( in_array( $this->inputType, $this->restbaseInputTypes ) &&
 				$this->mode == 'mathml'
 			) {
 				if ( !$this->rbi ) {
 					$this->rbi =
 						new MathRestbaseInterface( $this->getTex(), $this->getInputType() );
+					$this->rbi->setPurge( $this->isPurge() );
 				}
 				$rbi = $this->rbi;
 				if ( $rbi->getSuccess() ) {
@@ -99,9 +103,6 @@ class MathMathML extends MathRenderer {
 				$this->changed = false;
 				return $rbi->getSuccess();
 			}
-			if ( $forceReRendering ) {
-				$this->setPurge( true );
-			}
 			if ( $this->renderingRequired() ) {
 				return $this->doRender();
 			}
diff --git a/MathRenderer.php b/MathRenderer.php
index e5ed80444..87c427a48 100644
--- a/MathRenderer.php
+++ b/MathRenderer.php
@@ -385,6 +385,7 @@ abstract class MathRenderer {
 	 */
 	public function setRestbaseInterface( $param ) {
 		$this->rbi = $param;
+		$this->rbi->setPurge( $this->isPurge() );
 	}
 
 	/**
diff --git a/MathRestbaseInterface.php b/MathRestbaseInterface.php
index 3f4283289..bf2e59053 100644
--- a/MathRestbaseInterface.php
+++ b/MathRestbaseInterface.php
@@ -18,6 +18,8 @@ class MathRestbaseInterface {
 	private $error;
 	private $mathoidStyle;
 	private $mml;
+	/** @var boolean is there a request to purge the existing mathematical content */
+	private $purge = false;
 
 	/**
 	 * MathRestbaseInterface constructor.
@@ -66,6 +68,18 @@ class MathRestbaseInterface {
 		}
 	}
 
+	/**
+	 * Lets this instance know if this is a purge request. When set to true,
+	 * it will cause the object to issue the first content request with a
+	 * 'Cache-Control: no-cache' header to prompt the regeneration of the
+	 * renders.
+	 *
+	 * @param bool $purge whether this is a purge request
+	 */
+	public function setPurge( $purge = true ) {
+		$this->purge = $purge;
+	}
+
 	/**
 	 * @return string MathML code
 	 * @throws MWException
@@ -383,6 +397,12 @@ class MathRestbaseInterface {
 			'method' => 'GET',
 			'url' => $this->getUrl( "media/math/render/$type/{$this->hash}" )
 		];
+		if ( $this->purge ) {
+			$request['headers'] = [
+				'Cache-Control' => 'no-cache'
+			];
+			$this->purge = false;
+		}
 		return $request;
 	}