Change approach to fallback PNG in the header to fix blank data URI from triggering CSP error

CHANGELOG.md

@@ -5,6 +5,8 @@
 ### Fixes
 
 - [#2228: Fix display of checkboxes in Internet Explorer 8](https://github.com/alphagov/govuk-frontend/pull/2228)
+- [#2229: Change approach to fallback PNG in the header to fix blank data URI from triggering Content Security Policy errors](https://github.com/alphagov/govuk-frontend/pull/2229)
+- [#2229: Fix alignment of fallback PNG in the header](https://github.com/alphagov/govuk-frontend/pull/2229)
 
 ## 3.12.0 (Feature release)
 

src/govuk/components/header/_index.scss

@@ -62,7 +62,7 @@
     width: 36px;
     height: 32px;
     border: 0;
-    vertical-align: middle;
+    vertical-align: bottom;
   }
 
   .govuk-header__product-name {

src/govuk/components/header/template.njk

@@ -4,6 +4,7 @@
     <div class="govuk-header__logo">
       <a href="{{ params.homepageUrl | default('/') }}" class="govuk-header__link govuk-header__link--homepage">
         <span class="govuk-header__logotype">
+          <!--[if gt IE 8]><!-->
           {#- We use an inline SVG for the crown so that we can cascade the
           currentColor into the crown whilst continuing to support older browsers
           which do not support external SVGs without a Javascript polyfill. This
@@ -29,18 +30,11 @@
               fill="currentColor" fill-rule="evenodd"
               d="M25 30.2c3.5 1.5 7.7-.2 9.1-3.7 1.5-3.6-.2-7.8-3.9-9.2-3.6-1.4-7.6.3-9.1 3.9-1.4 3.5.3 7.5 3.9 9zM9 39.5c3.6 1.5 7.8-.2 9.2-3.7 1.5-3.6-.2-7.8-3.9-9.1-3.6-1.5-7.6.2-9.1 3.8-1.4 3.5.3 7.5 3.8 9zM4.4 57.2c3.5 1.5 7.7-.2 9.1-3.8 1.5-3.6-.2-7.7-3.9-9.1-3.5-1.5-7.6.3-9.1 3.8-1.4 3.5.3 7.6 3.9 9.1zm38.3-21.4c3.5 1.5 7.7-.2 9.1-3.8 1.5-3.6-.2-7.7-3.9-9.1-3.6-1.5-7.6.3-9.1 3.8-1.3 3.6.4 7.7 3.9 9.1zm64.4-5.6c-3.6 1.5-7.8-.2-9.1-3.7-1.5-3.6.2-7.8 3.8-9.2 3.6-1.4 7.7.3 9.2 3.9 1.3 3.5-.4 7.5-3.9 9zm15.9 9.3c-3.6 1.5-7.7-.2-9.1-3.7-1.5-3.6.2-7.8 3.7-9.1 3.6-1.5 7.7.2 9.2 3.8 1.5 3.5-.3 7.5-3.8 9zm4.7 17.7c-3.6 1.5-7.8-.2-9.2-3.8-1.5-3.6.2-7.7 3.9-9.1 3.6-1.5 7.7.3 9.2 3.8 1.3 3.5-.4 7.6-3.9 9.1zM89.3 35.8c-3.6 1.5-7.8-.2-9.2-3.8-1.4-3.6.2-7.7 3.9-9.1 3.6-1.5 7.7.3 9.2 3.8 1.4 3.6-.3 7.7-3.9 9.1zM69.7 17.7l8.9 4.7V9.3l-8.9 2.8c-.2-.3-.5-.6-.9-.9L72.4 0H59.6l3.5 11.2c-.3.3-.6.5-.9.9l-8.8-2.8v13.1l8.8-4.7c.3.3.6.7.9.9l-5 15.4v.1c-.2.8-.4 1.6-.4 2.4 0 4.1 3.1 7.5 7 8.1h.2c.3 0 .7.1 1 .1.4 0 .7 0 1-.1h.2c4-.6 7.1-4.1 7.1-8.1 0-.8-.1-1.7-.4-2.4V34l-5.1-15.4c.4-.2.7-.6 1-.9zM66 92.8c16.9 0 32.8 1.1 47.1 3.2 4-16.9 8.9-26.7 14-33.5l-9.6-3.4c1 4.9 1.1 7.2 0 10.2-1.5-1.4-3-4.3-4.2-8.7L108.6 76c2.8-2 5-3.2 7.5-3.3-4.4 9.4-10 11.9-13.6 11.2-4.3-.8-6.3-4.6-5.6-7.9 1-4.7 5.7-5.9 8-.5 4.3-8.7-3-11.4-7.6-8.8 7.1-7.2 7.9-13.5 2.1-21.1-8 6.1-8.1 12.3-4.5 20.8-4.7-5.4-12.1-2.5-9.5 6.2 3.4-5.2 7.9-2 7.2 3.1-.6 4.3-6.4 7.8-13.5 7.2-10.3-.9-10.9-8-11.2-13.8 2.5-.5 7.1 1.8 11 7.3L80.2 60c-4.1 4.4-8 5.3-12.3 5.4 1.4-4.4 8-11.6 8-11.6H55.5s6.4 7.2 7.9 11.6c-4.2-.1-8-1-12.3-5.4l1.4 16.4c3.9-5.5 8.5-7.7 10.9-7.3-.3 5.8-.9 12.8-11.1 13.8-7.2.6-12.9-2.9-13.5-7.2-.7-5 3.8-8.3 7.1-3.1 2.7-8.7-4.6-11.6-9.4-6.2 3.7-8.5 3.6-14.7-4.6-20.8-5.8 7.6-5 13.9 2.2 21.1-4.7-2.6-11.9.1-7.7 8.8 2.3-5.5 7.1-4.2 8.1.5.7 3.3-1.3 7.1-5.7 7.9-3.5.7-9-1.8-13.5-11.2 2.5.1 4.7 1.3 7.5 3.3l-4.7-15.4c-1.2 4.4-2.7 7.2-4.3 8.7-1.1-3-.9-5.3 0-10.2l-9.5 3.4c5 6.9 9.9 16.7 14 33.5 14.8-2.1 30.8-3.2 47.7-3.2z"
             ></path>
-            {#- Fallback PNG image for older browsers.
-
-            The <image> element is a valid SVG element. In SVG, you would specify
-            the URL of the image file with the xlink:href – as we don't reference an
-            image it has no effect. It's important to include an empty data URI
-            as the xlink:href attribute as this prevents versions of IE which
-            support SVG from downloading the fallback image when they don't need to.
-
-            In other browsers <image> is synonymous for the <img> tag and will be
-            interpreted as such, displaying the fallback image. #}
-            <image src="{{ params.assetsPath | default('/assets/images') }}/govuk-logotype-crown.png" xlink:href="data:," display="none" class="govuk-header__logotype-crown-fallback-image" width="36" height="32"></image>
           </svg>
+          <!--<![endif]-->
+          <!--[if IE 8]>
+          <img src="{{ params.assetsPath | default('/assets/images') }}/govuk-logotype-crown.png" class="govuk-header__logotype-crown-fallback-image" width="36" height="32">
+          <![endif]-->
           <span class="govuk-header__logotype-text">
             GOV.UK
           </span>

src/govuk/components/header/template.test.js

@@ -218,17 +218,8 @@ describe('header', () => {
     describe('fallback PNG', () => {
       const $fallbackImage = $('.govuk-header__logotype-crown-fallback-image')
 
-      it('uses the <image> tag which is a valid SVG element', () => {
-        expect($fallbackImage[0].tagName).toEqual('image')
-      })
-
-      it('sets an empty data URI xlink:href to prevent IE from downloading both the SVG and the PNG', () => {
-        // Cheerio converts xhref to href - https://github.com/cheeriojs/cheerio/issues/1101
-        expect($fallbackImage.attr('href')).toEqual('data:,')
-      })
-
-      it('hides the image when SVG is supported by using the SVG display attribute', () => {
-        expect($fallbackImage.attr('display')).toEqual('none')
+      it('is invisible to modern browsers', () => {
+        expect($fallbackImage.length).toEqual(0)
       })
     })
   })