Rewrite user stylesheet injection for WebEngine

This now works correctly in XML documents. The stylesheet is applied at
document creation to reduce flickering, and is updated if the
user_stylesheets setting is changed after page load.

qutebrowser/browser/webengine/webenginesettings.py

@@ -37,7 +37,7 @@ from qutebrowser.browser import shared
 from qutebrowser.browser.webengine import spell
 from qutebrowser.config import config, websettings
 from qutebrowser.utils import (utils, standarddir, javascript, qtutils,
-                               message, log)
+                               message, log, objreg)
 
 # The default QWebEngineProfile
 default_profile = None
@@ -153,33 +153,41 @@ class DictionaryLanguageSetter(DefaultProfileSetter):
 def _init_stylesheet(profile):
     """Initialize custom stylesheets.
 
-    Mostly inspired by QupZilla:
+    Partially inspired by QupZilla:
     https://github.com/QupZilla/qupzilla/blob/v2.0/src/lib/app/mainapplication.cpp#L1063-L1101
-    https://github.com/QupZilla/qupzilla/blob/v2.0/src/lib/tools/scripts.cpp#L119-L132
     """
     old_script = profile.scripts().findScript('_qute_stylesheet')
     if not old_script.isNull():
         profile.scripts().remove(old_script)
 
     css = shared.get_user_stylesheet()
-    source = """
+    source = '\n'.join([
-        (function() {{
+        '"use strict";',
-            var css = document.createElement('style');
+        'window._qutebrowser = window._qutebrowser || {};',
-            css.setAttribute('type', 'text/css');
+        utils.read_file('javascript/stylesheet.js'),
-            css.appendChild(document.createTextNode('{}'));
+        javascript.assemble('stylesheet', 'set_css', css),
-            document.getElementsByTagName('head')[0].appendChild(css);
+    ])
-        }})()
-    """.format(javascript.string_escape(css))
 
     script = QWebEngineScript()
     script.setName('_qute_stylesheet')
-    script.setInjectionPoint(QWebEngineScript.DocumentReady)
+    script.setInjectionPoint(QWebEngineScript.DocumentCreation)
     script.setWorldId(QWebEngineScript.ApplicationWorld)
     script.setRunsOnSubFrames(True)
     script.setSourceCode(source)
     profile.scripts().insert(script)
 
 
+def _update_stylesheet():
+    """Update the custom stylesheet in existing tabs."""
+    css = shared.get_user_stylesheet()
+    code = javascript.assemble('stylesheet', 'set_css', css)
+    for win_id in objreg.window_registry:
+        tab_registry = objreg.get('tab-registry', scope='window',
+                                  window=win_id)
+        for tab in tab_registry.values():
+            tab.run_js_async(code)
+
+
 def _set_http_headers(profile):
     """Set the user agent and accept-language for the given profile.
 
@@ -199,6 +207,7 @@ def _update_settings(option):
     if option in ['scrolling.bar', 'content.user_stylesheets']:
         _init_stylesheet(default_profile)
         _init_stylesheet(private_profile)
+        _update_stylesheet()
     elif option in ['content.headers.user_agent',
                     'content.headers.accept_language']:
         _set_http_headers(default_profile)

qutebrowser/browser/webengine/webenginetab.py

@@ -533,7 +533,7 @@ class WebEngineTab(browsertab.AbstractTab):
     def _init_js(self):
         js_code = '\n'.join([
             '"use strict";',
-            'window._qutebrowser = {};',
+            'window._qutebrowser = window._qutebrowser || {};',
             utils.read_file('javascript/scroll.js'),
             utils.read_file('javascript/webelem.js'),
         ])

qutebrowser/javascript/stylesheet.js

@@ -0,0 +1,142 @@
+/**
+ * Copyright 2017 Ulrik de Muelenaere <ulrikdem@gmail.com>
+ *
+ * This file is part of qutebrowser.
+ *
+ * qutebrowser is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * qutebrowser is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with qutebrowser.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+"use strict";
+
+window._qutebrowser.stylesheet = (function() {
+    if (window._qutebrowser.stylesheet) {
+        return window._qutebrowser.stylesheet;
+    }
+
+    var funcs = {};
+
+    var xhtml_ns = "http://www.w3.org/1999/xhtml";
+    var svg_ns = "http://www.w3.org/2000/svg";
+
+    var root_elem;
+    var style_elem;
+    var css_content = "";
+
+    var root_observer;
+    var style_observer;
+    var initialized = false;
+
+    // Watch for rewrites of the root element and changes to its children,
+    // then move the stylesheet to the end. Partially inspired by Stylus:
+    // https://github.com/openstyles/stylus/blob/1.1.4.2/content/apply.js#L235-L355
+    function watch_root() {
+        if (root_elem !== document.documentElement) {
+            root_elem = document.documentElement;
+            root_observer.disconnect();
+            root_observer.observe(document, {"childList": true});
+            root_observer.observe(root_elem, {"childList": true});
+        }
+        if (style_elem !== root_elem.lastChild) {
+            root_elem.appendChild(style_elem);
+        }
+    }
+
+    function create_style() {
+        var ns = xhtml_ns;
+        if (document.documentElement.namespaceURI === svg_ns) {
+            ns = svg_ns;
+        }
+        style_elem = document.createElementNS(ns, "style");
+        style_elem.textContent = css_content;
+        root_observer = new MutationObserver(watch_root);
+        watch_root();
+    }
+
+    // We should only inject the stylesheet if the document already has style
+    // information associated with it. Otherwise we wait until the browser
+    // rewrites it to an XHTML document showing the document tree. As a
+    // starting point for exploring the relevant code in Chromium, see
+    // https://github.com/qt/qtwebengine-chromium/blob/cfe8c60/chromium/third_party/WebKit/Source/core/xml/parser/XMLDocumentParser.cpp#L1539-L1540
+    function check_style(node) {
+        var stylesheet = node.nodeType === Node.PROCESSING_INSTRUCTION_NODE &&
+                         node.target === "xml-stylesheet" &&
+                         node.parentNode === document;
+        var known_ns = node.nodeType === Node.ELEMENT_NODE &&
+                       (node.namespaceURI === xhtml_ns ||
+                        node.namespaceURI === svg_ns);
+        if (stylesheet || known_ns) {
+            create_style();
+            return true;
+        }
+        return false;
+    }
+
+    function check_added_style(mutations) {
+        for (var mi = 0; mi < mutations.length; ++mi) {
+            var nodes = mutations[mi].addedNodes;
+            for (var ni = 0; ni < nodes.length; ++ni) {
+                if (check_style(nodes[ni])) {
+                    style_observer.disconnect();
+                    return;
+                }
+            }
+        }
+    }
+
+    function init() {
+        initialized = true;
+        // Chromium will not rewrite a document inside a frame, so add the
+        // stylesheet even if the document is unstyled.
+        if (window !== window.top) {
+            create_style();
+            return;
+        }
+        var iter = document.createNodeIterator(document);
+        var node;
+        while ((node = iter.nextNode())) {
+            if (check_style(node)) {
+                return;
+            }
+        }
+        style_observer = new MutationObserver(check_added_style);
+        style_observer.observe(document, {"childList": true, "subtree": true});
+    }
+
+    var doc = document;
+
+    funcs.set_css = function(css) {
+        if (!initialized) {
+            init();
+        }
+        if (style_elem) {
+            style_elem.textContent = css;
+            // The browser seems to rewrite the document in same-origin frames
+            // without notifying the mutation observer. Ensure that the
+            // stylesheet is in the current document.
+            watch_root();
+        } else {
+            css_content = css;
+        }
+        // Propagate the new CSS to all child frames.
+        // FIXME:qtwebengine This does not work for cross-origin frames.
+        for (var i = 0; i < window.frames.length; ++i) {
+            var frame = window.frames[i];
+            if (frame._qutebrowser && frame._qutebrowser.stylesheet) {
+                frame._qutebrowser.stylesheet.set_css(css);
+            }
+        }
+    };
+
+    return funcs;
+})();

tests/end2end/data/downloads/mhtml/simple/simple-webengine.mht

@@ -16,11 +16,11 @@ Content-Location: http://localhost:(port)/data/downloads/mhtml/simple/simple.htm
 t/html; charset=3DUTF-8">
        =20
         <title>Simple MHTML test</title>
-    <style type=3D"text/css">
+    </head>
-html > ::-webkit-scrollbar { width: 0px; height: 0px; }</style></head>
     <body>
         <a href=3D"http://localhost:(port)/">normal link to another page</a>
    =20
 
-</body></html>
+</body><style>
+html > ::-webkit-scrollbar { width: 0px; height: 0px; }</style></html>
 -----=_qute-UUID