If PDF viewer is not enabled, PDFs are downloaded

Chrome on Android doesn't support displaying PDF documents inline so an
attempt to load a PDF into the Kiwix viewer iframe fails in a way that
may be confusing to the users. In such situations it is better to offer
to the users to download the PDF file so that they can view it with a
dedicated application. Making the clicked PDF link to open in a new
tab/window achieves exactly that effect.

static/skin/viewer.js

@@ -352,14 +352,19 @@ function linkShouldBeOpenedInANewWindow(linkElement, mouseEvent) {
       || mouseEvent.metaKey /* on Macs */;
 }
 
+function goingToOpenALinkToAnUndisplayableResource(url) {
+  return !navigator.pdfViewerEnabled && url.pathname.endsWith('.pdf');
+}
+
 function onClickEvent(e) {
   const iframeDocument = contentIframe.contentDocument;
   const target = matchingAncestorElement(e.target, iframeDocument, "a");
   if (target !== null && "href" in target) {
     const target_href = getRealHref(target);
     const target_url = new URL(target_href, iframeDocument.location);
     const isExternalAppUrl = urlMustBeHandledByAnExternalApp(target_url);
-    if ( isExternalAppUrl && !viewerSettings.linkBlockingEnabled ) {
+    if ( (isExternalAppUrl && !viewerSettings.linkBlockingEnabled)
+         || goingToOpenALinkToAnUndisplayableResource(target_url) ) {
         target.setAttribute("target", "_blank");
     }
 

test/server.cpp

@@ -75,7 +75,7 @@ const ResourceCollection resources200Compressible{
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/taskbar.css" },
   { STATIC_CONTENT,  "/ROOT%23%3F/skin/taskbar.css?cacheid=80d56607" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/viewer.js" },
-  { STATIC_CONTENT,  "/ROOT%23%3F/skin/viewer.js?cacheid=fdec37a7" },
+  { STATIC_CONTENT,  "/ROOT%23%3F/skin/viewer.js?cacheid=787e61d4" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/fonts/Poppins.ttf" },
   { STATIC_CONTENT,  "/ROOT%23%3F/skin/fonts/Poppins.ttf?cacheid=af705837" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/fonts/Roboto.ttf" },
@@ -327,7 +327,7 @@ R"EXPECTEDRESULT(    <link type="text/css" href="./skin/kiwix.css?cacheid=2158fa
     <script type="text/javascript" src="./skin/polyfills.js?cacheid=a0e0343d"></script>
     <script type="module" src="./skin/i18n.js?cacheid=071abc9a" defer></script>
     <script type="text/javascript" src="./skin/languages.js?cacheid=ee7d95b5" defer></script>
-    <script type="text/javascript" src="./skin/viewer.js?cacheid=fdec37a7" defer></script>
+    <script type="text/javascript" src="./skin/viewer.js?cacheid=787e61d4" defer></script>
     <script type="text/javascript" src="./skin/autoComplete/autoComplete.min.js?cacheid=1191aaaf"></script>
       const blankPageUrl = root + "/skin/blank.html?cacheid=6b1fa032";
           <label for="kiwix_button_show_toggle"><img src="./skin/caret.png?cacheid=22b942b4" alt=""></label>