From 46df493ac069b48dff7673d9b2cf24aae891a0fc Mon Sep 17 00:00:00 2001
From: Timo Tijhof <krinklemail@gmail.com>
Date: Mon, 27 Jun 2016 13:21:14 +0200
Subject: [PATCH] Remove incomplete and dated 'wgUseETag' experiment

Follows-up:
* 8ff36ebd (r9793) Set ETag header on article views.
* 8167b89e (r16205) Add $wgUseETag, false by default (broke Squid; T9098).

ETag is a useful alternative for If-Modified-Since (see T33639, T49529 about
use cases and bugs it may fix). However the current incomplete implementation
isn't useful.

It's a feature flag that has been disabled since 2006. Enabling it stores
ParserCache::getETag in OutputPage and sends it out as a response header.
It's ignored on incoming requests. We don't check If-None-Match for
'304 Not Modified' anywhere.

ResourceLoader has a working implementation that could be leveraged.

To be re-evaluated in the future. ParserCache::getETag() could use
improvement as well.

Change-Id: I37fd9d0ce1ce9bffb79243c6ae340403fdfd769f
---
 includes/DefaultSettings.php |  6 ------
 includes/OutputPage.php      | 24 ++++--------------------
 includes/page/Article.php    |  6 +-----
 3 files changed, 5 insertions(+), 31 deletions(-)

diff --git a/includes/DefaultSettings.php b/includes/DefaultSettings.php
index 39e22a0277..b8e1486376 100644
--- a/includes/DefaultSettings.php
+++ b/includes/DefaultSettings.php
@@ -2551,12 +2551,6 @@ $wgSidebarCacheExpiry = 86400;
  */
 $wgUseGzip = false;
 
-/**
- * Whether MediaWiki should send an ETag header. Seems to cause
- * broken behavior with Squid 2.6, see bug 7098.
- */
-$wgUseETag = false;
-
 /**
  * Clock skew or the one-second resolution of time() can occasionally cause cache
  * problems when the user requests two pages within a short period of time. This
diff --git a/includes/OutputPage.php b/includes/OutputPage.php
index 5c7203d907..15b70c8324 100644
--- a/includes/OutputPage.php
+++ b/includes/OutputPage.php
@@ -104,22 +104,11 @@ class OutputPage extends ContextSource {
 	protected $mStatusCode;
 
 	/**
-	 * @var string Variable mLastModified and mEtag are used for sending cache control.
+	 * @var string Used for sending cache control.
 	 *   The whole caching system should probably be moved into its own class.
 	 */
 	protected $mLastModified = '';
 
-	/**
-	 * Contains an HTTP Entity Tags (see RFC 2616 section 3.13) which is used
-	 * as a unique identifier for the content. It is later used by the client
-	 * to compare its cached version with the server version. Client sends
-	 * headers If-Match and If-None-Match containing its locally cached ETAG value.
-	 *
-	 * To get more information, you will have to look at HTTP/1.1 protocol which
-	 * is properly described in RFC 2616 : http://tools.ietf.org/html/rfc2616
-	 */
-	private $mETag = false;
-
 	/** @var array */
 	protected $mCategoryLinks = [];
 
@@ -694,12 +683,10 @@ class OutputPage extends ContextSource {
 	}
 
 	/**
-	 * Set the value of the ETag HTTP header, only used if $wgUseETag is true
-	 *
-	 * @param string $tag Value of "ETag" header
+	 * @deprecated since 1.28 Obsolete - wgUseETag experiment was removed.
+	 * @param string $tag
 	 */
-	function setETag( $tag ) {
-		$this->mETag = $tag;
+	public function setETag( $tag ) {
 	}
 
 	/**
@@ -2156,9 +2143,6 @@ class OutputPage extends ContextSource {
 	public function sendCacheControl() {
 		$response = $this->getRequest()->response();
 		$config = $this->getConfig();
-		if ( $config->get( 'UseETag' ) && $this->mETag ) {
-			$response->header( "ETag: $this->mETag" );
-		}
 
 		$this->addVaryHeader( 'Cookie' );
 		$this->addAcceptLanguage();
diff --git a/includes/page/Article.php b/includes/page/Article.php
index 1f1e8d6f55..2a6f88c577 100644
--- a/includes/page/Article.php
+++ b/includes/page/Article.php
@@ -467,7 +467,7 @@ class Article implements Page {
 	 * page of the given title.
 	 */
 	public function view() {
-		global $wgUseFileCache, $wgUseETag, $wgDebugToolbar, $wgMaxRedirects;
+		global $wgUseFileCache, $wgDebugToolbar, $wgMaxRedirects;
 
 		# Get variables from query string
 		# As side effect this will load the revision and update the title
@@ -520,10 +520,6 @@ class Article implements Page {
 
 		# Try client and file cache
 		if ( !$wgDebugToolbar && $oldid === 0 && $this->mPage->checkTouched() ) {
-			if ( $wgUseETag ) {
-				$outputPage->setETag( $parserCache->getETag( $this->mPage, $parserOptions ) );
-			}
-
 			# Use the greatest of the page's timestamp or the timestamp of any
 			# redirect in the chain (bug 67849)
 			$timestamp = $this->mPage->getTouched();
-- 
2.20.1