From 7e51af5407593a952c11c4af73ff9748317a607e Mon Sep 17 00:00:00 2001
From: Tomasz Jakut <vepomoc@gmail.com>
Date: Wed, 18 Aug 2021 16:26:49 +0200
Subject: [PATCH 01/16] Add manual test.

---
 tests/core/ckeditor/manual/geturl.html | 13 +++++++++++++
 tests/core/ckeditor/manual/geturl.md   | 10 ++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 tests/core/ckeditor/manual/geturl.html
 create mode 100644 tests/core/ckeditor/manual/geturl.md

diff --git a/tests/core/ckeditor/manual/geturl.html b/tests/core/ckeditor/manual/geturl.html
new file mode 100644
index 00000000000..444a2399e73
--- /dev/null
+++ b/tests/core/ckeditor/manual/geturl.html
@@ -0,0 +1,13 @@
+<div id="editor">
+	<p>Lorem ipsum dolor sit amet</p>
+</div>
+
+<script>
+	( function() {
+		if ( !CKEDITOR.timestamp ) {
+			return bender.ignore();
+		}
+
+		CKEDITOR.replace( 'editor' );
+	} )();
+</script>
diff --git a/tests/core/ckeditor/manual/geturl.md b/tests/core/ckeditor/manual/geturl.md
new file mode 100644
index 00000000000..012c9036175
--- /dev/null
+++ b/tests/core/ckeditor/manual/geturl.md
@@ -0,0 +1,10 @@
+@bender-tags: bug, 4.17.0, 4761
+@bender-ui: collapsed
+@bender-ckeditor-plugins: wysiwygarea, toolbar, undo, emoji, copyformatting, easyimage, tableselection
+
+**Note**: This test requires CKEDITOR with set `CKEDITOR.timestamp` (e.g. built one).
+
+1. Open developer tools and switch to "Network" tab.
+2. Refresh the page.
+
+	**Expected** CKEditor 4's resources are loaded with the cache key (`?t=<some alphanum characters>` at the end of URL).

From f48c3350cdaa564424d1d52f18ae05b231c207fc Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Tue, 21 Dec 2021 12:44:56 +0100
Subject: [PATCH 02/16] Renamed manual test=

---
 tests/core/ckeditor/manual/{geturl.html => assetscachekey.html} | 0
 tests/core/ckeditor/manual/{geturl.md => assetscachekey.md}     | 2 +-
 2 files changed, 1 insertion(+), 1 deletion(-)
 rename tests/core/ckeditor/manual/{geturl.html => assetscachekey.html} (100%)
 rename tests/core/ckeditor/manual/{geturl.md => assetscachekey.md} (92%)

diff --git a/tests/core/ckeditor/manual/geturl.html b/tests/core/ckeditor/manual/assetscachekey.html
similarity index 100%
rename from tests/core/ckeditor/manual/geturl.html
rename to tests/core/ckeditor/manual/assetscachekey.html
diff --git a/tests/core/ckeditor/manual/geturl.md b/tests/core/ckeditor/manual/assetscachekey.md
similarity index 92%
rename from tests/core/ckeditor/manual/geturl.md
rename to tests/core/ckeditor/manual/assetscachekey.md
index 012c9036175..e201fe90e18 100644
--- a/tests/core/ckeditor/manual/geturl.md
+++ b/tests/core/ckeditor/manual/assetscachekey.md
@@ -1,4 +1,4 @@
-@bender-tags: bug, 4.17.0, 4761
+@bender-tags: bug, 4.17.2, 4761
 @bender-ui: collapsed
 @bender-ckeditor-plugins: wysiwygarea, toolbar, undo, emoji, copyformatting, easyimage, tableselection
 

From e149a13fcb67fb93ed451787a88c189cce554b60 Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Tue, 21 Dec 2021 12:47:13 +0100
Subject: [PATCH 03/16] Add mobile to ignore env

---
 tests/core/ckeditor/manual/assetscachekey.html | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/core/ckeditor/manual/assetscachekey.html b/tests/core/ckeditor/manual/assetscachekey.html
index 444a2399e73..9f5e949023f 100644
--- a/tests/core/ckeditor/manual/assetscachekey.html
+++ b/tests/core/ckeditor/manual/assetscachekey.html
@@ -4,7 +4,7 @@
 
 <script>
 	( function() {
-		if ( !CKEDITOR.timestamp ) {
+		if ( bender.tools.env.mobile || !CKEDITOR.timestamp ) {
 			return bender.ignore();
 		}
 

From f3f6d2edb0c854e2aebd37e8e54c50c4118f2b08 Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 09:28:02 +0100
Subject: [PATCH 04/16] Add tests for current state of

---
 tests/core/tools.js | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tests/core/tools.js b/tests/core/tools.js
index 0aa0a86c302..eb9cbbe60de 100644
--- a/tests/core/tools.js
+++ b/tests/core/tools.js
@@ -1177,6 +1177,47 @@
 			assert.areSame( 2, testSpy.callCount );
 			assert.areSame( testObj, testSpy.getCall( 0 ).thisValue );
 			assert.isTrue( testSpy.calledWithExactly( 'baz', 100, 'bar' ) );
+		},
+
+		// (#4761)
+		'test buidStyleHtml returns relative URL for passed relative URL string': function() {
+			var relativeUrl = '/file.css',
+				styledStringElem = CKEDITOR.tools.buildStyleHtml( relativeUrl );
+
+			assert.areSame( -1, styledStringElem.indexOf( 'http' ), 'http should not be present in relative URL' );
+		},
+
+		// (#4761)
+		'test buidStyleHtml returns absolute URL for passed absolute URL string': function() {
+			var relatedUrl = 'http://example.com/file.css',
+				styledStringElem = CKEDITOR.tools.buildStyleHtml( relatedUrl ),
+				httpPosition = styledStringElem.indexOf( 'http' );
+
+			assert.isTrue( httpPosition > -1 , 'Absolute URL missed http protocol' );
+		},
+
+		// (#4761)
+		'test buidStyleHtml returns passed style text embeded in style element': function() {
+			var styleText = '*{color:red}',
+				expected = '<style>' + styleText + '</style>',
+				styledStringElem = CKEDITOR.tools.buildStyleHtml( styleText );
+
+			assert.areSame( expected, styledStringElem, 'Styled text wasnt exact same wrapped in style elem' );
+		},
+
+		// (#4761)
+		'test buildStyleHtml with no timestamp returns stylesheet URL without cache key for passed string': function() {
+			var originalTimestamp = CKEDITOR.timestamp,
+				relativeUrl = '/file.css',
+				expectedHref = 'href="' + relativeUrl + '"',
+				html;
+
+			CKEDITOR.timestamp = '';
+			html = CKEDITOR.tools.buildStyleHtml( relativeUrl );
+			var expectedPosition = html.indexOf( expectedHref );
+
+			CKEDITOR.timestamp = originalTimestamp;
+			assert.isTrue( expectedPosition > -1, 'Built HTML includes correct stylesheet link' );
 		}
 	} );
 } )();

From ad23aace703b267f04d086994fb33e9744dbf04a Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 09:32:13 +0100
Subject: [PATCH 05/16] Modernize test for  & no timestamp

---
 tests/core/dom/document.js | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/tests/core/dom/document.js b/tests/core/dom/document.js
index 7a164ba7ea9..5637766e7d7 100644
--- a/tests/core/dom/document.js
+++ b/tests/core/dom/document.js
@@ -15,21 +15,21 @@ bender.test( appendDomObjectTests(
 			assert.areSame( document, doc.$ );
 		},
 
-		test_appendStyleSheet: function() {
-			var cssUrl = CKEDITOR.basePath + 'tests/_assets/sample.css';
+		// (#4761)
+		'test appendStyleSheet without timestamp': function() {
+			var originalTimestamp = CKEDITOR.timestamp,
+				cssUrl = CKEDITOR.basePath + 'tests/_assets/sample.css';
 
+			CKEDITOR.timestamp = '';
 			var doc = new CKEDITOR.dom.document( document );
-			doc.appendStyleSheet( cssUrl );
+			doc.appendStyleSheet( cssUrl );// this makes absolute URL no matter what is passed
 
 			var links = document.getElementsByTagName( 'link' );
-			var succeed = false;
-			for ( var i = 0 ; i < links.length ; i++ ) {
-				if ( links[ i ].href == cssUrl ) {
-					succeed = true;
-					break;
-				}
-			}
+			var succeed = CKEDITOR.tools.array.some( links, function( link ) {
+				return link.href === cssUrl;
+			} );
 
+			CKEDITOR.timestamp = originalTimestamp;
 			assert.isTrue( succeed, 'The link element was not found' );
 		},
 

From 10beb40af13f021cb987a7cb6bbc88faff81a5ec Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 10:06:01 +0100
Subject: [PATCH 06/16] Add test & apply cache key to styleHtml element'

---
 core/tools.js       |  7 +++++--
 tests/core/tools.js | 22 +++++++++++++++++++---
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/core/tools.js b/core/tools.js
index 4083a319f70..831a005321c 100644
--- a/core/tools.js
+++ b/core/tools.js
@@ -420,14 +420,17 @@
 		buildStyleHtml: function( css ) {
 			css = [].concat( css );
 			var item,
+				cacheKey = CKEDITOR.timestamp ? '?t=' + CKEDITOR.timestamp : '',
 				retval = [];
 			for ( var i = 0; i < css.length; i++ ) {
 				if ( ( item = css[ i ] ) ) {
 					// Is CSS style text ?
-					if ( /@import|[{}]/.test( item ) )
+					if ( /@import|[{}]/.test( item ) ) {
 						retval.push( '<style>' + item + '</style>' );
-					else
+					} else {
+						item = item + cacheKey;
 						retval.push( '<link type="text/css" rel=stylesheet href="' + item + '">' );
+					}
 				}
 			}
 			return retval.join( '' );
diff --git a/tests/core/tools.js b/tests/core/tools.js
index eb9cbbe60de..0af8cea97ba 100644
--- a/tests/core/tools.js
+++ b/tests/core/tools.js
@@ -1197,12 +1197,12 @@
 		},
 
 		// (#4761)
-		'test buidStyleHtml returns passed style text embeded in style element': function() {
+		'test buidStyleHtml returns passed style text embedded in style element': function() {
 			var styleText = '*{color:red}',
 				expected = '<style>' + styleText + '</style>',
 				styledStringElem = CKEDITOR.tools.buildStyleHtml( styleText );
 
-			assert.areSame( expected, styledStringElem, 'Styled text wasnt exact same wrapped in style elem' );
+			assert.areSame( expected, styledStringElem, 'Styled text was not exact same wrapped in style elem' );
 		},
 
 		// (#4761)
@@ -1217,7 +1217,23 @@
 			var expectedPosition = html.indexOf( expectedHref );
 
 			CKEDITOR.timestamp = originalTimestamp;
-			assert.isTrue( expectedPosition > -1, 'Built HTML includes correct stylesheet link' );
+			assert.isTrue( expectedPosition > -1, 'Built HTML does not contains expected href attribute' );
+		},
+
+		// (#4761)
+		'test buildStyleHtml adds timestamp as cache key to provided URL': function() {
+			var originalTimestamp = CKEDITOR.timestamp,
+				relativeUrl = '/file.css',
+				fakeTimestamp = 'cke4',
+				expectedHref = 'href="' + relativeUrl + '?t=' + fakeTimestamp + '"',
+				html;
+
+			CKEDITOR.timestamp = fakeTimestamp;
+			html = CKEDITOR.tools.buildStyleHtml( relativeUrl );
+			var expectedPosition = html.indexOf( expectedHref );
+
+			CKEDITOR.timestamp = originalTimestamp;
+			assert.isTrue( expectedPosition > -1, 'Built HTML does not contains expected href with timestamp' );
 		}
 	} );
 } )();

From 03ab4c4e726ce261db7aaedd5f858d96d61e8f22 Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 10:40:22 +0100
Subject: [PATCH 07/16] Add test case for timestamp with array of urls

---
 tests/core/tools.js | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tests/core/tools.js b/tests/core/tools.js
index 0af8cea97ba..13e6d5a2ab2 100644
--- a/tests/core/tools.js
+++ b/tests/core/tools.js
@@ -1234,6 +1234,28 @@
 
 			CKEDITOR.timestamp = originalTimestamp;
 			assert.isTrue( expectedPosition > -1, 'Built HTML does not contains expected href with timestamp' );
+		},
+
+		// (#4761)
+		'test buildStyleHtml adds timestamp as cache key to provided URLs': function() {
+			var originalTimestamp = CKEDITOR.timestamp,
+				relativeUrls = [ '/file.css', '../file2.css' ],
+				fakeTimestamp = 'cke4',
+				expectedHrefs = [
+					'href="' + relativeUrls[ 0 ] + '?t=' + fakeTimestamp + '"',
+					'href="' + relativeUrls[ 1 ] + '?t=' + fakeTimestamp + '"'
+				],
+				html;
+
+			CKEDITOR.timestamp = fakeTimestamp;
+			html = CKEDITOR.tools.buildStyleHtml( relativeUrls );
+
+			CKEDITOR.timestamp = originalTimestamp;
+
+			CKEDITOR.tools.array.forEach( expectedHrefs, function( expectedHref ) {
+				var expectedPosition = html.indexOf( expectedHref );
+				assert.isTrue( expectedPosition > -1, 'Built HTML does not contains expected hrefs with timestamp' );
+			} );
 		}
 	} );
 } )();

From cc875e0455af2122ea8809eacea58efaf347c80e Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 11:00:23 +0100
Subject: [PATCH 08/16] Add cache key to css Url via

---
 core/dom/document.js       |  3 +++
 tests/core/dom/document.js | 28 ++++++++++++++++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/core/dom/document.js b/core/dom/document.js
index 438b1fc8738..a4cf5fb04e4 100644
--- a/core/dom/document.js
+++ b/core/dom/document.js
@@ -43,6 +43,9 @@ CKEDITOR.tools.extend( CKEDITOR.dom.document.prototype, {
 	 * @param {String} cssFileUrl The CSS file URL.
 	 */
 	appendStyleSheet: function( cssFileUrl ) {
+		var cacheKey = CKEDITOR.timestamp ? '?t=' + CKEDITOR.timestamp : '';
+		cssFileUrl += cacheKey;
+
 		if ( this.$.createStyleSheet )
 			this.$.createStyleSheet( cssFileUrl );
 		else {
diff --git a/tests/core/dom/document.js b/tests/core/dom/document.js
index 5637766e7d7..bfac3ef6239 100644
--- a/tests/core/dom/document.js
+++ b/tests/core/dom/document.js
@@ -24,10 +24,30 @@ bender.test( appendDomObjectTests(
 			var doc = new CKEDITOR.dom.document( document );
 			doc.appendStyleSheet( cssUrl );// this makes absolute URL no matter what is passed
 
-			var links = document.getElementsByTagName( 'link' );
-			var succeed = CKEDITOR.tools.array.some( links, function( link ) {
-				return link.href === cssUrl;
-			} );
+			var links = document.getElementsByTagName( 'link' ),
+				succeed = CKEDITOR.tools.array.some( links, function( link ) {
+					return link.href === cssUrl;
+				} );
+
+			CKEDITOR.timestamp = originalTimestamp;
+			assert.isTrue( succeed, 'The link element was not found' );
+		},
+
+		// (#4761)
+		'test appendStyleSheet with timestamp': function() {
+			var originalTimestamp = CKEDITOR.timestamp,
+				fakeTimestamp = 'cke4',
+				cssUrl = CKEDITOR.basePath + 'tests/_assets/sample.css',
+				expectedCssUrl = cssUrl + '?t=' + fakeTimestamp;
+
+			CKEDITOR.timestamp = fakeTimestamp;
+			var doc = new CKEDITOR.dom.document( document );
+			doc.appendStyleSheet( cssUrl );// this makes absolute URL no matter what is passed
+
+			var links = document.getElementsByTagName( 'link' ),
+				succeed = CKEDITOR.tools.array.some( links, function( link ) {
+					return link.href === expectedCssUrl;
+				} );
 
 			CKEDITOR.timestamp = originalTimestamp;
 			assert.isTrue( succeed, 'The link element was not found' );

From d452039e1f453b2dfe8b9798c7dc1ab9b9bc166f Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 12:32:32 +0100
Subject: [PATCH 09/16] Extract key cache appending logic to separate method

---
 ckeditor.js           |  2 +-
 core/ckeditor_base.js | 21 +++++++++++++++++++--
 core/dom/document.js  |  3 +--
 core/tools.js         |  3 +--
 4 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/ckeditor.js b/ckeditor.js
index 203ce84ed46..9d9d5fbd079 100644
--- a/ckeditor.js
+++ b/ckeditor.js
@@ -7,7 +7,7 @@
 /* jshint ignore:start */
 /* jscs:disable */
 // replace_start
-window.CKEDITOR||(window.CKEDITOR=function(){var o,d=/(^|.*[\\\/])ckeditor\.js(?:\?.*|;.*)?$/i,e={timestamp:"",version:"%VERSION%",revision:"%REV%",rnd:Math.floor(900*Math.random())+100,_:{pending:[],basePathSrcPattern:d},status:"unloaded",basePath:function(){var t=window.CKEDITOR_BASEPATH||"";if(!t)for(var e=document.getElementsByTagName("script"),n=0;n<e.length;n++){var a=e[n].src.match(d);if(a){t=a[1];break}}if(-1==t.indexOf(":/")&&"//"!=t.slice(0,2)&&(t=0===t.indexOf("/")?location.href.match(/^.*?:\/\/[^\/]*/)[0]+t:location.href.match(/^[^\?]*\/(?:)/)[0]+t),!t)throw'The CKEditor installation path could not be automatically detected. Please set the global variable "CKEDITOR_BASEPATH" before creating editor instances.';return t}(),getUrl:function(t){return-1==t.indexOf(":/")&&0!==t.indexOf("/")&&(t=this.basePath+t),this.timestamp&&"/"!=t.charAt(t.length-1)&&!/[&?]t=/.test(t)&&(t+=(0<=t.indexOf("?")?"&":"?")+"t="+this.timestamp),t},domReady:(o=[],function(t){if(o.push(t),"complete"===document.readyState&&setTimeout(i,1),1==o.length)if(document.addEventListener)document.addEventListener("DOMContentLoaded",i,!1),window.addEventListener("load",i,!1);else if(document.attachEvent){document.attachEvent("onreadystatechange",i),window.attachEvent("onload",i);var e=!1;try{e=!window.frameElement}catch(n){}document.documentElement.doScroll&&e&&!function a(){try{document.documentElement.doScroll("left")}catch(n){return void setTimeout(a,1)}i()}()}})};function i(){try{document.addEventListener?(document.removeEventListener("DOMContentLoaded",i,!1),window.removeEventListener("load",i,!1),n()):document.attachEvent&&"complete"===document.readyState&&(document.detachEvent("onreadystatechange",i),window.detachEvent("onload",i),n())}catch(t){}}function n(){for(var t;t=o.shift();)t()}var a,r=window.CKEDITOR_GETURL;return r&&(a=e.getUrl,e.getUrl=function(t){return r.call(e,t)||a.call(e,t)}),e}());
+window.CKEDITOR||(window.CKEDITOR=function(){var o,d=/(^|.*[\\\/])ckeditor\.js(?:\?.*|;.*)?$/i,e={timestamp:"",version:"%VERSION%",revision:"%REV%",rnd:Math.floor(900*Math.random())+100,_:{pending:[],basePathSrcPattern:d},status:"unloaded",basePath:function(){var t=window.CKEDITOR_BASEPATH||"";if(!t)for(var e=document.getElementsByTagName("script"),n=0;n<e.length;n++){var a=e[n].src.match(d);if(a){t=a[1];break}}if(-1==t.indexOf(":/")&&"//"!=t.slice(0,2)&&(t=0===t.indexOf("/")?location.href.match(/^.*?:\/\/[^\/]*/)[0]+t:location.href.match(/^[^\?]*\/(?:)/)[0]+t),!t)throw'The CKEditor installation path could not be automatically detected. Please set the global variable "CKEDITOR_BASEPATH" before creating editor instances.';return t}(),getUrl:function(t){return-1==t.indexOf(":/")&&0!==t.indexOf("/")&&(t=this.basePath+t),t=this.appendTimestamp(t)},appendTimestamp:function(t){return this.timestamp&&"/"!=t.charAt(t.length-1)&&!/[&?]t=/.test(t)&&(t+=(0<=t.indexOf("?")?"&":"?")+"t="+this.timestamp),t},domReady:(o=[],function(t){if(o.push(t),"complete"===document.readyState&&setTimeout(i,1),1==o.length)if(document.addEventListener)document.addEventListener("DOMContentLoaded",i,!1),window.addEventListener("load",i,!1);else if(document.attachEvent){document.attachEvent("onreadystatechange",i),window.attachEvent("onload",i);var e=!1;try{e=!window.frameElement}catch(n){}document.documentElement.doScroll&&e&&!function a(){try{document.documentElement.doScroll("left")}catch(n){return void setTimeout(a,1)}i()}()}})};function i(){try{document.addEventListener?(document.removeEventListener("DOMContentLoaded",i,!1),window.removeEventListener("load",i,!1),n()):document.attachEvent&&"complete"===document.readyState&&(document.detachEvent("onreadystatechange",i),window.detachEvent("onload",i),n())}catch(t){}}function n(){for(var t;t=o.shift();)t()}var a,r=window.CKEDITOR_GETURL;return r&&(a=e.getUrl,e.getUrl=function(t){return r.call(e,t)||a.call(e,t)}),e}());
 // replace_end
 /* jscs:enable */
 /* jshint ignore:end */
diff --git a/core/ckeditor_base.js b/core/ckeditor_base.js
index dcd1b6bfa30..9b036dddda2 100644
--- a/core/ckeditor_base.js
+++ b/core/ckeditor_base.js
@@ -174,9 +174,26 @@ if ( !window.CKEDITOR ) {
 				if ( resource.indexOf( ':/' ) == -1 && resource.indexOf( '/' ) !== 0 )
 					resource = this.basePath + resource;
 
-				// Add the timestamp, except for directories.
-				if ( this.timestamp && resource.charAt( resource.length - 1 ) != '/' && !( /[&?]t=/ ).test( resource ) )
+				resource = this.appendTimestamp( resource );
+
+				return resource;
+			},
+
+			/**
+			 * Appends {@link CKEDITOR#timestamp} to the provided URL as querystring parameter ("t").
+			 *
+			 * Leaves the URL unchanged if it is a directory URL or it already contains querystring parameter.
+			 *
+			 * @param {String} resource The resource whose URL we want to affect with the timestamp.
+			 * @returns The resource URL with cache key appended whenever possible.
+			 */
+			appendTimestamp: function( resource ) {
+				if ( this.timestamp &&
+					resource.charAt( resource.length - 1 ) != '/' &&
+					!( /[&?]t=/ ).test( resource )
+				) {
 					resource += ( resource.indexOf( '?' ) >= 0 ? '&' : '?' ) + 't=' + this.timestamp;
+				}
 
 				return resource;
 			},
diff --git a/core/dom/document.js b/core/dom/document.js
index a4cf5fb04e4..2ada517a963 100644
--- a/core/dom/document.js
+++ b/core/dom/document.js
@@ -43,8 +43,7 @@ CKEDITOR.tools.extend( CKEDITOR.dom.document.prototype, {
 	 * @param {String} cssFileUrl The CSS file URL.
 	 */
 	appendStyleSheet: function( cssFileUrl ) {
-		var cacheKey = CKEDITOR.timestamp ? '?t=' + CKEDITOR.timestamp : '';
-		cssFileUrl += cacheKey;
+		cssFileUrl = CKEDITOR.appendTimestamp( cssFileUrl );
 
 		if ( this.$.createStyleSheet )
 			this.$.createStyleSheet( cssFileUrl );
diff --git a/core/tools.js b/core/tools.js
index 831a005321c..201cdb11f2a 100644
--- a/core/tools.js
+++ b/core/tools.js
@@ -420,7 +420,6 @@
 		buildStyleHtml: function( css ) {
 			css = [].concat( css );
 			var item,
-				cacheKey = CKEDITOR.timestamp ? '?t=' + CKEDITOR.timestamp : '',
 				retval = [];
 			for ( var i = 0; i < css.length; i++ ) {
 				if ( ( item = css[ i ] ) ) {
@@ -428,7 +427,7 @@
 					if ( /@import|[{}]/.test( item ) ) {
 						retval.push( '<style>' + item + '</style>' );
 					} else {
-						item = item + cacheKey;
+						item = CKEDITOR.appendTimestamp( item );
 						retval.push( '<link type="text/css" rel=stylesheet href="' + item + '">' );
 					}
 				}

From 9917c7fa27eb723bcc410574f2f1ca2c338dbf6d Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 12:51:58 +0100
Subject: [PATCH 10/16] Refactor cache key appending funtion to be easier
 readable

---
 ckeditor.js           |  2 +-
 core/ckeditor_base.js | 11 ++++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/ckeditor.js b/ckeditor.js
index 9d9d5fbd079..a6129132c03 100644
--- a/ckeditor.js
+++ b/ckeditor.js
@@ -7,7 +7,7 @@
 /* jshint ignore:start */
 /* jscs:disable */
 // replace_start
-window.CKEDITOR||(window.CKEDITOR=function(){var o,d=/(^|.*[\\\/])ckeditor\.js(?:\?.*|;.*)?$/i,e={timestamp:"",version:"%VERSION%",revision:"%REV%",rnd:Math.floor(900*Math.random())+100,_:{pending:[],basePathSrcPattern:d},status:"unloaded",basePath:function(){var t=window.CKEDITOR_BASEPATH||"";if(!t)for(var e=document.getElementsByTagName("script"),n=0;n<e.length;n++){var a=e[n].src.match(d);if(a){t=a[1];break}}if(-1==t.indexOf(":/")&&"//"!=t.slice(0,2)&&(t=0===t.indexOf("/")?location.href.match(/^.*?:\/\/[^\/]*/)[0]+t:location.href.match(/^[^\?]*\/(?:)/)[0]+t),!t)throw'The CKEditor installation path could not be automatically detected. Please set the global variable "CKEDITOR_BASEPATH" before creating editor instances.';return t}(),getUrl:function(t){return-1==t.indexOf(":/")&&0!==t.indexOf("/")&&(t=this.basePath+t),t=this.appendTimestamp(t)},appendTimestamp:function(t){return this.timestamp&&"/"!=t.charAt(t.length-1)&&!/[&?]t=/.test(t)&&(t+=(0<=t.indexOf("?")?"&":"?")+"t="+this.timestamp),t},domReady:(o=[],function(t){if(o.push(t),"complete"===document.readyState&&setTimeout(i,1),1==o.length)if(document.addEventListener)document.addEventListener("DOMContentLoaded",i,!1),window.addEventListener("load",i,!1);else if(document.attachEvent){document.attachEvent("onreadystatechange",i),window.attachEvent("onload",i);var e=!1;try{e=!window.frameElement}catch(n){}document.documentElement.doScroll&&e&&!function a(){try{document.documentElement.doScroll("left")}catch(n){return void setTimeout(a,1)}i()}()}})};function i(){try{document.addEventListener?(document.removeEventListener("DOMContentLoaded",i,!1),window.removeEventListener("load",i,!1),n()):document.attachEvent&&"complete"===document.readyState&&(document.detachEvent("onreadystatechange",i),window.detachEvent("onload",i),n())}catch(t){}}function n(){for(var t;t=o.shift();)t()}var a,r=window.CKEDITOR_GETURL;return r&&(a=e.getUrl,e.getUrl=function(t){return r.call(e,t)||a.call(e,t)}),e}());
+window.CKEDITOR||(window.CKEDITOR=function(){var o,d=/(^|.*[\\\/])ckeditor\.js(?:\?.*|;.*)?$/i,e={timestamp:"",version:"%VERSION%",revision:"%REV%",rnd:Math.floor(900*Math.random())+100,_:{pending:[],basePathSrcPattern:d},status:"unloaded",basePath:function(){var t=window.CKEDITOR_BASEPATH||"";if(!t)for(var e=document.getElementsByTagName("script"),n=0;n<e.length;n++){var a=e[n].src.match(d);if(a){t=a[1];break}}if(-1==t.indexOf(":/")&&"//"!=t.slice(0,2)&&(t=0===t.indexOf("/")?location.href.match(/^.*?:\/\/[^\/]*/)[0]+t:location.href.match(/^[^\?]*\/(?:)/)[0]+t),!t)throw'The CKEditor installation path could not be automatically detected. Please set the global variable "CKEDITOR_BASEPATH" before creating editor instances.';return t}(),getUrl:function(t){return-1==t.indexOf(":/")&&0!==t.indexOf("/")&&(t=this.basePath+t),t=this.appendTimestamp(t)},appendTimestamp:function(t){if(!this.timestamp||"/"===t.charAt(t.length-1)||/[&?]t=/.test(t))return t;var e=0<=t.indexOf("?")?"&":"?";return t+e+"t="+this.timestamp},domReady:(o=[],function(t){if(o.push(t),"complete"===document.readyState&&setTimeout(i,1),1==o.length)if(document.addEventListener)document.addEventListener("DOMContentLoaded",i,!1),window.addEventListener("load",i,!1);else if(document.attachEvent){document.attachEvent("onreadystatechange",i),window.attachEvent("onload",i);var e=!1;try{e=!window.frameElement}catch(n){}document.documentElement.doScroll&&e&&!function a(){try{document.documentElement.doScroll("left")}catch(n){return void setTimeout(a,1)}i()}()}})};function i(){try{document.addEventListener?(document.removeEventListener("DOMContentLoaded",i,!1),window.removeEventListener("load",i,!1),n()):document.attachEvent&&"complete"===document.readyState&&(document.detachEvent("onreadystatechange",i),window.detachEvent("onload",i),n())}catch(t){}}function n(){for(var t;t=o.shift();)t()}var a,r=window.CKEDITOR_GETURL;return r&&(a=e.getUrl,e.getUrl=function(t){return r.call(e,t)||a.call(e,t)}),e}());
 // replace_end
 /* jscs:enable */
 /* jshint ignore:end */
diff --git a/core/ckeditor_base.js b/core/ckeditor_base.js
index 9b036dddda2..ac1e1939e8f 100644
--- a/core/ckeditor_base.js
+++ b/core/ckeditor_base.js
@@ -188,14 +188,15 @@ if ( !window.CKEDITOR ) {
 			 * @returns The resource URL with cache key appended whenever possible.
 			 */
 			appendTimestamp: function( resource ) {
-				if ( this.timestamp &&
-					resource.charAt( resource.length - 1 ) != '/' &&
-					!( /[&?]t=/ ).test( resource )
+				if ( !this.timestamp ||
+					resource.charAt( resource.length - 1 ) === '/' ||
+					( /[&?]t=/ ).test( resource )
 				) {
-					resource += ( resource.indexOf( '?' ) >= 0 ? '&' : '?' ) + 't=' + this.timestamp;
+					return resource;
 				}
 
-				return resource;
+				var concatenateSign = resource.indexOf( '?' ) >= 0 ? '&' : '?';
+				return resource + concatenateSign + 't=' + this.timestamp;
 			},
 
 			/**

From efadb3fd153d97b1fc449f21a70c3caa1162f4c3 Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 22 Dec 2021 12:58:25 +0100
Subject: [PATCH 11/16] Add tests for CKEDITOR.getUrl()

---
 tests/core/ckeditor/geturl.js | 157 ++++++++++++++++++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 tests/core/ckeditor/geturl.js

diff --git a/tests/core/ckeditor/geturl.js b/tests/core/ckeditor/geturl.js
new file mode 100644
index 00000000000..e1c3cc0bb46
--- /dev/null
+++ b/tests/core/ckeditor/geturl.js
@@ -0,0 +1,157 @@
+/* bender-tags: editor */
+
+( function() {
+	'use strict';
+
+	var FAKE_BASE_PATH = 'http://some.example:1030/subdir/ckeditor/',
+		testCases = [
+			{
+				url: 'just.js',
+				expected: FAKE_BASE_PATH + 'just.js',
+				timestamp: ''
+			},
+
+			{
+				url: 'just.js',
+				expected: FAKE_BASE_PATH + 'just.js?t=347',
+				timestamp: '347'
+			},
+
+			{
+				url: './test.css',
+				expected: FAKE_BASE_PATH + './test.css',
+				timestamp: ''
+			},
+
+			{
+				url: './test.css',
+				expected: FAKE_BASE_PATH + './test.css?t=tr4',
+				timestamp: 'tr4'
+			},
+
+			{
+				url: '../whatever.js',
+				expected: FAKE_BASE_PATH + '../whatever.js',
+				timestamp: ''
+			},
+
+			{
+				url: '../whatever.js',
+				expected: FAKE_BASE_PATH + '../whatever.js?t=qwerty',
+				timestamp: 'qwerty'
+			},
+
+			{
+				url: '/file',
+				expected: '/file',
+				timestamp: ''
+			},
+
+			{
+				url: '/file',
+				expected: '/file?t=cke4',
+				timestamp: 'cke4'
+			},
+
+			{
+				url: 'http://some.site:47/file.js',
+				expected: 'http://some.site:47/file.js',
+				timestamp: ''
+			},
+
+			{
+				url: 'http://some.site:47/file.js',
+				expected: 'http://some.site:47/file.js?t=cv3',
+				timestamp: 'cv3'
+			},
+
+			{
+				url: 'https://whatever/file',
+				expected: 'https://whatever/file',
+				timestamp: ''
+			},
+
+			{
+				url: 'https://whatever/file',
+				expected: 'https://whatever/file?t=1er',
+				timestamp: '1er'
+			},
+
+			{
+				url: '//cksource.com/file.css',
+				expected: '//cksource.com/file.css',
+				timestamp: ''
+			},
+
+			{
+				url: '//cksource.com/file.css',
+				expected: '//cksource.com/file.css?t=try6',
+				timestamp: 'try6'
+			},
+
+			{
+				url: 'file.t?something=here',
+				expected: FAKE_BASE_PATH + 'file.t?something=here&t=wer',
+				timestamp: 'wer'
+			},
+
+			{
+				url: '/file.t?something=here',
+				expected: '/file.t?something=here&t=wer',
+				timestamp: 'wer'
+			},
+
+			{
+				url: 'http://dot.example/file.t?something=here',
+				expected: 'http://dot.example/file.t?something=here&t=wer',
+				timestamp: 'wer'
+			},
+
+			{
+				url: 'https://dot.example/file.t?something=here',
+				expected: 'https://dot.example/file.t?something=here&t=wer',
+				timestamp: 'wer'
+			},
+
+			{
+				url: '//dot.example/file.t?something=here',
+				expected: '//dot.example/file.t?something=here&t=wer',
+				timestamp: 'wer'
+			}
+		],
+		tests = createGetUrlTests( testCases );
+
+	bender.test( tests );
+
+	function createGetUrlTests( testCases ) {
+		return CKEDITOR.tools.array.reduce( testCases, function( tests, testCase ) {
+			var test = {},
+				testName = 'test CKEDITOR.getUrl( \'' + testCase.url + '\' ) with timestamp \'' +
+					testCase.timestamp + '\'';
+
+			test[ testName ] = createTest( testCase );
+
+			return CKEDITOR.tools.object.merge( tests, test );
+		}, {} );
+
+		function createTest( options ) {
+			var url = options.url,
+				expected = options.expected,
+				timestamp = options.timestamp;
+
+			return function() {
+				var originalBasePath = CKEDITOR.basePath,
+					originalTimestamp = CKEDITOR.timestamp,
+					actualResult;
+
+				CKEDITOR.basePath = FAKE_BASE_PATH;
+				CKEDITOR.timestamp = timestamp;
+				actualResult = CKEDITOR.getUrl( url );
+				CKEDITOR.basePath = originalBasePath;
+				CKEDITOR.timestamp = originalTimestamp;
+
+				assert.areSame( expected, actualResult, 'Invalid URL generated from the ' + url );
+			};
+		}
+	}
+} )();

From b5d6eb769bfa5cdc1a3213c7ab6e517410bc7ed0 Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Wed, 5 Jan 2022 13:24:00 +0100
Subject: [PATCH 12/16] Correct typos

---
 tests/core/tools.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/core/tools.js b/tests/core/tools.js
index 13e6d5a2ab2..8d3d508260e 100644
--- a/tests/core/tools.js
+++ b/tests/core/tools.js
@@ -1180,7 +1180,7 @@
 		},
 
 		// (#4761)
-		'test buidStyleHtml returns relative URL for passed relative URL string': function() {
+		'test buildStyleHtml returns relative URL for passed relative URL string': function() {
 			var relativeUrl = '/file.css',
 				styledStringElem = CKEDITOR.tools.buildStyleHtml( relativeUrl );
 
@@ -1188,7 +1188,7 @@
 		},
 
 		// (#4761)
-		'test buidStyleHtml returns absolute URL for passed absolute URL string': function() {
+		'test buildStyleHtml returns absolute URL for passed absolute URL string': function() {
 			var relatedUrl = 'http://example.com/file.css',
 				styledStringElem = CKEDITOR.tools.buildStyleHtml( relatedUrl ),
 				httpPosition = styledStringElem.indexOf( 'http' );
@@ -1197,12 +1197,12 @@
 		},
 
 		// (#4761)
-		'test buidStyleHtml returns passed style text embedded in style element': function() {
+		'test buildStyleHtml returns passed style text embedded in style element': function() {
 			var styleText = '*{color:red}',
 				expected = '<style>' + styleText + '</style>',
 				styledStringElem = CKEDITOR.tools.buildStyleHtml( styleText );
 
-			assert.areSame( expected, styledStringElem, 'Styled text was not exact same wrapped in style elem' );
+			assert.areSame( expected, styledStringElem, 'Styled text was not exact same wrapped in style element' );
 		},
 
 		// (#4761)

From d17ee14c46fad6d20315ca312f2cd0046923d01d Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Fri, 7 Jan 2022 18:16:35 +0100
Subject: [PATCH 13/16] Add timestamp tests

---
 tests/core/ckeditor/appendtimestamp.js | 54 ++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 tests/core/ckeditor/appendtimestamp.js

diff --git a/tests/core/ckeditor/appendtimestamp.js b/tests/core/ckeditor/appendtimestamp.js
new file mode 100644
index 00000000000..ab2173de80c
--- /dev/null
+++ b/tests/core/ckeditor/appendtimestamp.js
@@ -0,0 +1,54 @@
+/* bender-tags: editor */
+
+( function() {
+	'use strict';
+
+	bender.test( {
+		'test append timestamp returns the same resource path if there is no timestamp': performTimestampTest(
+				'',
+				'style.css',
+				'style.css',
+				'Resource path was modified without timestamp in CKEDITOR'
+		),
+
+		'test append timestamp returns resource path with timestamp': performTimestampTest(
+			'cke4',
+			'style.css',
+			'style.css?t=cke4',
+			'Resource path was modified without timestamp in CKEDITOR'
+		),
+
+		'test append timestamp returns the same resource path if it is a directory path': performTimestampTest(
+			'cke4',
+			'style/',
+			'style/',
+			'Resource path to directory should not be changed'
+		),
+
+		'test append timestamp to resource path with only timestamp does not change it': performTimestampTest(
+			'cke4',
+			'style.css?t=qaz1',
+			'style.css?t=qaz1',
+			'Resource path with timestamp was affected with new timestamp'
+		),
+
+		'test append timestamp to resource path with chained timestamp does not change it': performTimestampTest(
+			'cke4',
+			'style.css?q=abc&t=qaz1',
+			'style.css?q=abc&t=qaz1',
+			'Resource path with chained timestamp was affected with new timestamp'
+		)
+	} );
+
+	function performTimestampTest( timestamp, resourcePath, expected, message ) {
+		return function() {
+			var originalTimestamp = CKEDITOR.timestamp;
+			CKEDITOR.timestamp = timestamp;
+
+			var result = CKEDITOR.appendTimestamp( resourcePath );
+
+			CKEDITOR.timestamp = originalTimestamp;
+			assert.areSame( expected, result, message );
+		};
+	}
+} )();

From ca89dcbf357c43978904a2fdec88f82eea1c4789 Mon Sep 17 00:00:00 2001
From: sculpt0r <github@sculpt0r.net>
Date: Fri, 7 Jan 2022 18:31:39 +0100
Subject: [PATCH 14/16] Code style & new case

---
 tests/core/ckeditor/appendtimestamp.js | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/tests/core/ckeditor/appendtimestamp.js b/tests/core/ckeditor/appendtimestamp.js
index ab2173de80c..628c0f52013 100644
--- a/tests/core/ckeditor/appendtimestamp.js
+++ b/tests/core/ckeditor/appendtimestamp.js
@@ -4,14 +4,14 @@
 	'use strict';
 
 	bender.test( {
-		'test append timestamp returns the same resource path if there is no timestamp': performTimestampTest(
-				'',
-				'style.css',
-				'style.css',
-				'Resource path was modified without timestamp in CKEDITOR'
+		'test append timestamp returns the same resource path if there is no CKEDITOR.timestamp': performTimestampTest(
+			'',
+			'style.css',
+			'style.css',
+			'Resource path was modified without timestamp in CKEDITOR'
 		),
 
-		'test append timestamp returns resource path with timestamp': performTimestampTest(
+		'test append timestamp returns resource path with timestamp if there is CKEDITOR.timestamp': performTimestampTest(
 			'cke4',
 			'style.css',
 			'style.css?t=cke4',
@@ -25,7 +25,7 @@
 			'Resource path to directory should not be changed'
 		),
 
-		'test append timestamp to resource path with only timestamp does not change it': performTimestampTest(
+		'test append timestamp to resource path, with timestamp as single URL param, does not change it': performTimestampTest(
 			'cke4',
 			'style.css?t=qaz1',
 			'style.css?t=qaz1',
@@ -37,6 +37,13 @@
 			'style.css?q=abc&t=qaz1',
 			'style.css?q=abc&t=qaz1',
 			'Resource path with chained timestamp was affected with new timestamp'
+		),
+
+		'test append timestamp to resource path with URL params adds timestamp as another param': performTimestampTest(
+			'cke4',
+			'style.css?q=abc',
+			'style.css?q=abc&t=cke4',
+			'Resource path with single param has not been affected by timestamp'
 		)
 	} );
 

From 4cd90b80bd14b8e58b7b40b2b34f12e408911bfc Mon Sep 17 00:00:00 2001
From: Tomasz Jakut <vepomoc@gmail.com>
Date: Wed, 12 Jan 2022 12:00:01 +0100
Subject: [PATCH 15/16] Small improvements to API docs.

---
 core/ckeditor_base.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/core/ckeditor_base.js b/core/ckeditor_base.js
index ac1e1939e8f..cb6331ac0a6 100644
--- a/core/ckeditor_base.js
+++ b/core/ckeditor_base.js
@@ -184,8 +184,9 @@ if ( !window.CKEDITOR ) {
 			 *
 			 * Leaves the URL unchanged if it is a directory URL or it already contains querystring parameter.
 			 *
-			 * @param {String} resource The resource whose URL we want to affect with the timestamp.
-			 * @returns The resource URL with cache key appended whenever possible.
+			 * @since 4.17.2
+			 * @param {String} resource The resource URL to which the timestamp should be appended.
+			 * @returns {String} The resource URL with cache key appended whenever possible.
 			 */
 			appendTimestamp: function( resource ) {
 				if ( !this.timestamp ||

From 492b8555cbad0bc8f46ef0548a33783f555793df Mon Sep 17 00:00:00 2001
From: Tomasz Jakut <vepomoc@gmail.com>
Date: Wed, 12 Jan 2022 14:38:17 +0100
Subject: [PATCH 16/16] Add changelog entries.

---
 CHANGES.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/CHANGES.md b/CHANGES.md
index 85fb8d3ac0e..0fdcffaa6a0 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -12,10 +12,13 @@ Fixed issues:
 * [#4875](https://github.com/ckeditor/ckeditor4/issues/4875): Fixed: Not possible to delete multiple selected lists.
 * [#4873](https://github.com/ckeditor/ckeditor4/issues/4873): Fixed: Pasting content from MS Word and Outlook with horizontal lines prevents images from being uploaded.
 * [#4952](https://github.com/ckeditor/ckeditor4/issues/4952): Fixed: Dragging and dropping images within a table cells appends additional elements.
+* [#4761](https://github.com/ckeditor/ckeditor4/issues/4761): Fixed: not all resources loaded by the editor respect the cache key.
 
 API changes:
 
 * [#4918](https://github.com/ckeditor/ckeditor4/issues/4918): Explicitly set [`config.useComputedState`](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_config.html#cfg-useComputedState) default value to `true`. Thanks to [Shabab Karim](https://github.com/shabab477)!
+* [#4761](https://github.com/ckeditor/ckeditor4/issues/4761): [`CKEDITOR.appendTimestamp()`](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR.html#method-appendTimestamp) function was added.
+* [#4761](https://github.com/ckeditor/ckeditor4/issues/4761): [`CKEDITOR.dom.document#appendStyleSheet()`](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_dom_document.html#method-appendStyleSheet) and [`CKEDITOR.tools.buildStyleHtml()`](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_tools.html#method-buildStyleHtml) now use newly added [`CKEDITOR.appendTimestamp()`](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR.html#method-appendTimestamp) function to correctly handle caching of CSS files.
 
 Other changes: