Drop use of Qt Web Channel

One less possible cause of lifetime related crashes/leaks.  Plus my
custom solution has a nicer interface. It's slower but since
communication between python and js is not a bottleneck...

src/calibre/gui2/tweak_book/preview.py

@@ -14,10 +14,9 @@ from functools import partial
 from threading import Thread
 
 from PyQt5.Qt import (
-    QApplication, QBuffer, QByteArray, QFile, QIcon, QMenu, QObject, QSize, QTimer,
-    QToolBar, QUrl, QVBoxLayout, QWidget, pyqtSignal, pyqtSlot
+    QApplication, QBuffer, QByteArray, QIcon, QMenu, QSize, QTimer,
+    QToolBar, QUrl, QVBoxLayout, QWidget, pyqtSignal
 )
-from PyQt5.QtWebChannel import QWebChannel
 from PyQt5.QtWebEngineCore import QWebEngineUrlSchemeHandler
 from PyQt5.QtWebEngineWidgets import (
     QWebEnginePage, QWebEngineProfile, QWebEngineScript, QWebEngineView
@@ -31,7 +30,7 @@ from calibre.ebooks.oeb.base import OEB_DOCS, XHTML_MIME, serialize
 from calibre.ebooks.oeb.polish.parsing import parse
 from calibre.gui2 import NO_URL_FORMATTING, error_dialog, open_url
 from calibre.gui2.tweak_book import TOP, actions, current_container, editors, tprefs
-from calibre.gui2.webengine import create_script, insert_scripts, secure_webengine
+from calibre.gui2.webengine import create_script, insert_scripts, secure_webengine, Bridge, from_js, to_js
 from calibre.gui2.widgets2 import HistoryLineEdit2
 from calibre.utils.ipc.simple_worker import offload_worker
 from polyglot.builtins import unicode_type
@@ -259,15 +258,8 @@ def create_profile():
             compile_editor()
         js = P('editor.js', data=True, allow_user_override=False)
         cparser = P('csscolorparser.js', data=True, allow_user_override=False)
-        qwebchannel_js = QFile(':/qtwebchannel/qwebchannel.js')
-        if not qwebchannel_js.open(QBuffer.ReadOnly):
-            raise RuntimeError(
-                    'Failed to load qwebchannel.js with error: %s' % qwebchannel_js.errorString())
-        qwebchannel_js = bytes(qwebchannel_js.readAll()).decode('utf-8')
-        qwebchannel_js += 'window.QWebChannel = QWebChannel;'
 
         insert_scripts(ans,
-            create_script('qwebchannel.js', qwebchannel_js),
             create_script('csscolorparser.js', cparser),
             create_script('editor.js', js),
         )
@@ -281,33 +273,17 @@ def create_profile():
     return ans
 
 
-class Bridge(QObject):
+class PreviewBridge(Bridge):
 
-    sync_requested = pyqtSignal(object, object, object)
-    split_requested = pyqtSignal(object, object)
-    go_to_sourceline_address = pyqtSignal(int, 'QStringList')
-    go_to_anchor = pyqtSignal('QString')
-    set_split_mode = pyqtSignal(int)
+    request_sync = from_js(object, object, object)
+    request_split = from_js(object, object)
+
+    go_to_sourceline_address = to_js()
+    go_to_anchor = to_js()
+    set_split_mode = to_js()
 
     def __init__(self, parent=None):
-        QObject.__init__(self, parent)
-
-    @pyqtSlot('QString', 'QString', 'QJsonArray')
-    def request_sync(self, tag_name, href, sourceline_address):
-        address = [sourceline_address[0].toInt(), [x.toString() for x in sourceline_address[1].toArray()]]
-        try:
-            self.sync_requested.emit(tag_name, href, address)
-        except (TypeError, ValueError, OverflowError, AttributeError):
-            pass
-
-    @pyqtSlot('QJsonArray', 'QJsonArray')
-    def request_split(self, loc, totals):
-        actions['split-in-preview'].setChecked(False)
-        loc, totals = [x.toInt() for x in loc], [x.toInt() for x in totals]
-        if not loc or not totals:
-            return error_dialog(self.view(), _('Invalid location'),
-                                _('Cannot split on the body tag'), show=True)
-        self.split_requested.emit(loc, totals)
+        Bridge.__init__(self, parent)
 
 
 class WebPage(QWebEnginePage):
@@ -315,10 +291,7 @@ class WebPage(QWebEnginePage):
     def __init__(self, parent):
         QWebEnginePage.__init__(self, create_profile(), parent)
         secure_webengine(self, for_viewer=True)
-        self.channel = c = QWebChannel(self)
-        self.bridge = Bridge(self)
-        self.setWebChannel(c, QWebEngineScript.ApplicationWorld)
-        c.registerObject('bridge', self.bridge)
+        self.bridge = PreviewBridge(self)
 
     def javaScriptConsoleMessage(self, level, msg, linenumber, source_id):
         prints('%s:%s: %s' % (source_id, linenumber, msg))
@@ -348,7 +321,8 @@ class WebPage(QWebEnginePage):
         self.bridge.go_to_sourceline_address.emit(lnum, tags)
 
     def split_mode(self, enabled):
-        self.bridge.set_split_mode.emit(1 if enabled else 0)
+        if self.bridge.ready:
+            self.bridge.set_split_mode.emit(1 if enabled else 0)
 
 
 class WebView(QWebEngineView):
@@ -426,8 +400,8 @@ class Preview(QWidget):
         self.setLayout(l)
         l.setContentsMargins(0, 0, 0, 0)
         self.view = WebView(self)
-        self.view._page.bridge.sync_requested.connect(self.request_sync)
-        self.view._page.bridge.split_requested.connect(self.request_split)
+        self.view._page.bridge.request_sync.connect(self.request_sync)
+        self.view._page.bridge.request_split.connect(self.request_split)
         self.view._page.loadFinished.connect(self.load_finished)
         self.inspector = self.view.inspector
         l.addWidget(self.view)
@@ -510,6 +484,10 @@ class Preview(QWidget):
             self.sync_requested.emit(self.current_name, lnum)
 
     def request_split(self, loc, totals):
+        actions['split-in-preview'].setChecked(False)
+        if not loc or not totals:
+            return error_dialog(self, _('Invalid location'),
+                                _('Cannot split on the body tag'), show=True)
         if self.current_name:
             self.split_requested.emit(self.current_name, loc, totals)
 

src/calibre/gui2/webengine.py

@@ -4,7 +4,13 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-from PyQt5.QtWebEngineWidgets import QWebEngineScript
+import json
+
+from PyQt5.Qt import QObject, pyqtSignal
+from PyQt5.QtWebEngineWidgets import QWebEngineScript, QWebEngineView
+
+from calibre import prints
+from calibre.utils.rapydscript import special_title
 
 
 def secure_webengine(view_or_page_or_settings, for_viewer=False):
@@ -40,3 +46,106 @@ def create_script(name, src, world=QWebEngineScript.ApplicationWorld, injection_
     script.setInjectionPoint(injection_point)
     script.setRunsOnSubFrames(on_subframes)
     return script
+
+
+from_js = pyqtSignal
+
+
+class to_js(type('')):
+
+    def __call__(self, *a):
+        prints('WARNING: Calling {}() before the javascript bridge is ready'.format(self.name))
+    emit = __call__
+
+
+class to_js_bound(QObject):
+
+    def __init__(self, bridge, name):
+        QObject.__init__(self, bridge)
+        self.name = name
+
+    def __call__(self, *args):
+        self.parent().page.runJavaScript('if (window.python_comm) python_comm._from_python({}, {})'.format(
+            json.dumps(self.name), json.dumps(args)), QWebEngineScript.ApplicationWorld)
+    emit = __call__
+
+
+class Bridge(QObject):
+
+    def __init__(self, page):
+        QObject.__init__(self, page)
+        self._signals = json.dumps(tuple({k for k, v in self.__class__.__dict__.iteritems() if isinstance(v, pyqtSignal)}))
+        self._signals_registered = False
+        page.titleChanged.connect(self._title_changed)
+        for k, v in self.__class__.__dict__.iteritems():
+            if isinstance(v, to_js):
+                v.name = k
+
+    @property
+    def page(self):
+        return self.parent()
+
+    @property
+    def ready(self):
+        return self._signals_registered
+
+    def _title_changed(self, title):
+        if title.startswith(special_title):
+            self._poll_for_messages()
+
+    def _register_signals(self):
+        self._signals_registered = True
+        for k, v in self.__class__.__dict__.iteritems():
+            if isinstance(v, to_js):
+                setattr(self, k, to_js_bound(self, k))
+        self.page.runJavaScript('python_comm._register_signals(' + self._signals + ')', QWebEngineScript.ApplicationWorld)
+
+    def _poll_for_messages(self):
+        self.page.runJavaScript('python_comm._poll()', QWebEngineScript.ApplicationWorld, self._dispatch_messages)
+
+    def _dispatch_messages(self, messages):
+        try:
+            for msg in messages:
+                if isinstance(msg, dict):
+                    mt = msg.get('type')
+                    if mt == 'signal':
+                        signal = getattr(self, msg['name'], None)
+                        if signal is None:
+                            prints('WARNING: No js-to-python signal named: ' + msg['name'])
+                        else:
+                            args = msg['args']
+                            if args:
+                                signal.emit(*args)
+                            else:
+                                signal.emit()
+                    elif mt == 'qt-ready':
+                        self._register_signals()
+        except Exception:
+            import traceback
+            traceback.print_exc()
+
+
+if __name__ == '__main__':
+    from calibre.gui2 import Application
+    from calibre.gui2.tweak_book.preview import WebPage
+    from PyQt5.Qt import QMainWindow
+    app = Application([])
+    view = QWebEngineView()
+    page = WebPage(view)
+    view.setPage(page)
+    w = QMainWindow()
+    w.setCentralWidget(view)
+
+    class Test(Bridge):
+        s1 = from_js(object)
+        j1 = to_js()
+    t = Test(view.page())
+    t.s1.connect(print)
+    w.show()
+    view.setHtml('''
+<p>hello</p>
+    ''')
+    app.exec_()
+    del t
+    del page
+    del app

src/calibre/utils/rapydscript.py

@@ -26,6 +26,7 @@ from polyglot.builtins import itervalues, range, exec_path, raw_input, error_mes
 from polyglot.queue import Empty, Queue
 
 COMPILER_PATH = 'rapydscript/compiler.js.xz'
+special_title = '__webengine_messages_pending__'
 
 
 def abspath(x):
@@ -215,7 +216,7 @@ def compile_editor():
     rapydscript_dir = os.path.join(base, 'src', 'pyj')
     fname = os.path.join(rapydscript_dir, 'editor.pyj')
     with lopen(fname, 'rb') as f:
-        js = compile_fast(f.read(), fname, js_version=6)
+        js = compile_fast(f.read(), fname, js_version=6).replace('__SPECIAL_TITLE__', special_title, 1)
     base = os.path.join(base, 'resources')
     atomic_write(base, 'editor.js', js)
 

src/pyj/editor.pyj

@@ -5,6 +5,9 @@ from __python__ import bound_methods, hash_literals
 
 from elementmaker import E
 
+from qt import to_python, from_python
+
+
 def is_hidden(elem):
     while elem:
         if (elem.style and (elem.style.visibility is 'hidden' or elem.style.display is 'none')):
@@ -243,142 +246,126 @@ def scroll_to_node(node):
         node.scrollIntoView()
 
 
-class PreviewIntegration:
+state = {'blocks_found': False, 'in_split_mode': False}
 
-    ###
-    # Namespace to expose all the functions used for integration with the Tweak
-    # Book Preview Panel.
-    ###
 
-    def __init__(self):
-        self.blocks_found = False
-        self.in_split_mode = False
-        if window is window.top:
-            setTimeout(self.connect_channel, 10)
-        document.body.addEventListener('click', self.onclick, True)
-        document.documentElement.appendChild(E.style(
-            type='text/css',
-            '[data-in-split-mode="1"] [data-is-block="1"]:hover { cursor: pointer !important; border-top: solid 5px green !important }'
-        ))
 
-    def go_to_line(self, lnum):
-        for node in document.querySelectorAll(f'[data-lnum="{lnum}"]'):
-            if is_hidden(node):
-                continue
-            scroll_to_node(node)
+def go_to_line(lnum):
+    for node in document.querySelectorAll(f'[data-lnum="{lnum}"]'):
+        if is_hidden(node):
+            continue
+        scroll_to_node(node)
+        break
+
+@from_python
+def go_to_sourceline_address(sourceline, tags):
+    nodes = document.querySelectorAll(f'[data-lnum="{sourceline}"]')
+    for index in range(nodes.length):
+        node = nodes[index]
+        if index >= tags.length or node.tagName.toLowerCase() is not tags[index]:
             break
+        if index == tags.length - 1 and not is_hidden(node):
+            return scroll_to_node(node)
+    go_to_line(sourceline)
 
-    def go_to_sourceline_address(self, sourceline, tags):
-        nodes = document.querySelectorAll(f'[data-lnum="{sourceline}"]')
-        for index in range(nodes.length):
-            node = nodes[index]
-            if index >= tags.length or node.tagName.toLowerCase() is not tags[index]:
-                break
-            if index == tags.length - 1 and not is_hidden(node):
-                return scroll_to_node(node)
-        self.go_to_line(sourceline)
+def line_numbers():
+    found_body = False
+    ans = v'[]'
+    for node in document.getElementsByTagName('*'):
+        if not found_body and node.tagName.toLowerCase() is "body":
+            found_body = True
+        if found_body:
+            ans.push(node.dataset.lnum)
+    return ans
 
-    def line_numbers(self):
-        found_body = False
-        ans = v'[]'
-        for node in document.getElementsByTagName('*'):
-            if not found_body and node.tagName.toLowerCase() is "body":
-                found_body = True
-            if found_body:
-                ans.push(node.dataset.lnum)
-        return ans
+def find_blocks():
+    if state.blocks_found:
+        return
+    for elem in document.body.getElementsByTagName('*'):
+        if is_block(elem) and not in_table(elem):
+            elem.setAttribute('data-is-block', '1')
+    state.blocks_found = True
 
-    def find_blocks(self):
-        if self.blocks_found:
-            return
-        for elem in document.body.getElementsByTagName('*'):
-            if is_block(elem) and not in_table(elem):
-                elem.setAttribute('data-is-block', '1')
-        self.blocks_found = True
+@from_python
+def set_split_mode(enabled):
+    state.in_split_mode = enabled
+    document.body.dataset.inSplitMode = '1' if enabled else '0'
+    if enabled:
+        find_blocks()
 
-    def set_split_mode(self, enabled):
-        self.in_split_mode = enabled
-        document.body.dataset.inSplitMode = '1' if enabled else '0'
-        if enabled:
-            self.find_blocks()
+def report_split(node):
+    loc = v'[]'
+    totals = v'[]'
+    parent = find_containing_block(node)
+    while parent and parent.tagName.toLowerCase() is not 'body':
+        totals.push(parent.parentNode.children.length)
+        num = 0
+        sibling = parent.previousElementSibling
+        while sibling:
+            num += 1
+            sibling = sibling.previousElementSibling
+        loc.push(num)
+        parent = parent.parentNode
+    loc.reverse()
+    totals.reverse()
+    to_python.request_split(loc, totals)
 
-    def report_split(self, node):
-        loc = v'[]'
-        totals = v'[]'
-        parent = find_containing_block(node)
-        while parent and parent.tagName.toLowerCase() is not 'body':
-            totals.push(parent.parentNode.children.length)
-            num = 0
-            sibling = parent.previousElementSibling
-            while sibling:
-                num += 1
-                sibling = sibling.previousElementSibling
-            loc.push(num)
-            parent = parent.parentNode
-        loc.reverse()
-        totals.reverse()
-        self.bridge.request_split(loc, totals)
+def onclick(event):
+    event.preventDefault()
+    if state.in_split_mode:
+        report_split(event.target)
+    else:
+        e = event.target
+        address = get_sourceline_address(e)
+        # Find the closest containing link, if any
+        href = tn = ''
+        while e and e is not document.body and e is not document and e is not document.documentElement and (tn is not 'a' or not href):
+            tn = e.tagName.toLowerCase() if e.tagName else ''
+            href = e.getAttribute('href')
+            e = e.parentNode
+        to_python.request_sync(tn, href, address)
+    return False
 
-    def connect_channel(self):
-        self.qwebchannel = new window.QWebChannel(window.qt.webChannelTransport, def(channel):
-            self.bridge = channel.objects.bridge
-            self.bridge.go_to_sourceline_address.connect(self.go_to_sourceline_address)
-            self.bridge.go_to_anchor.connect(self.go_to_anchor)
-            self.bridge.set_split_mode.connect(self.set_split_mode)
-        )
+@from_python
+def go_to_anchor(anchor):
+    elem = document.getElementById(anchor)
+    if not elem:
+        elem = document.querySelector(f'[name="{anchor}"]')
+    if elem:
+        elem.scrollIntoView()
+        address = get_sourceline_address(elem)
+        to_python.request_sync('', '', address)
 
-    def onclick(self, event):
-        event.preventDefault()
-        if self.in_split_mode:
-            self.report_split(event.target)
-        else:
-            e = event.target
-            address = get_sourceline_address(e)
-            # Find the closest containing link, if any
-            href = tn = ''
-            while e and e is not document.body and e is not document and e is not document.documentElement and (tn is not 'a' or not href):
-                tn = e.tagName.toLowerCase() if e.tagName else ''
-                href = e.getAttribute('href')
-                e = e.parentNode
-            self.bridge.request_sync(tn, href, address)
-        return False
+def live_css(sourceline, tags):
+    target = None
+    i = 0
+    for node in document.querySelectorAll(f'[data-lnum="{sourceline}"]'):
+        tn = node.tagName.toLowerCase() if node.tagName else ''
+        if tn is not tags[i]:
+            return JSON.stringify(None)
+        i += 1
+        target = node
+        if i >= tags.length:
+            break
+    all_properties = {}
+    ans = {'nodes':v'[]', 'computed_css':all_properties}
+    is_ancestor = False
+    while target and target.ownerDocument:
+        css = get_matched_css(target, is_ancestor, all_properties)
+        # We want to show the Matched CSS rules header even if no rules matched
+        if css.length > 0 or not is_ancestor:
+            tn = target.tagName.toLowerCase() if target.tagName else ''
+            ans.nodes.push({
+                'name': tn,
+                'css': css, 'is_ancestor': is_ancestor,
+                'sourceline': target.getAttribute('data-lnum')
+            })
+        target = target.parentNode
+        is_ancestor = True
+    return JSON.stringify(ans)
 
-    def go_to_anchor(self, anchor):
-        elem = document.getElementById(anchor)
-        if not elem:
-            elem = document.querySelector(f'[name="{anchor}"]')
-        if elem:
-            elem.scrollIntoView()
-            address = get_sourceline_address(elem)
-            self.bridge.request_sync('', '', address)
-
-    def live_css(self, sourceline, tags):
-        target = None
-        i = 0
-        for node in document.querySelectorAll(f'[data-lnum="{sourceline}"]'):
-            tn = node.tagName.toLowerCase() if node.tagName else ''
-            if tn is not tags[i]:
-                return JSON.stringify(None)
-            i += 1
-            target = node
-            if i >= tags.length:
-                break
-        all_properties = {}
-        ans = {'nodes':v'[]', 'computed_css':all_properties}
-        is_ancestor = False
-        while target and target.ownerDocument:
-            css = get_matched_css(target, is_ancestor, all_properties)
-            # We want to show the Matched CSS rules header even if no rules matched
-            if css.length > 0 or not is_ancestor:
-                tn = target.tagName.toLowerCase() if target.tagName else ''
-                ans.nodes.push({
-                    'name': tn,
-                    'css': css, 'is_ancestor': is_ancestor,
-                    'sourceline': target.getAttribute('data-lnum')
-                })
-            target = target.parentNode
-            is_ancestor = True
-        return JSON.stringify(ans)
-
-
-calibre_preview_integration = PreviewIntegration()
+document.body.addEventListener('click', onclick, True)
+document.documentElement.appendChild(E.style(
+    type='text/css',
+    '[data-in-split-mode="1"] [data-is-block="1"]:hover { cursor: pointer !important; border-top: solid 5px green !important }'
+))

src/pyj/qt.pyj

@@ -0,0 +1,60 @@
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+from __python__ import bound_methods, hash_literals
+
+special_title = '__SPECIAL_TITLE__'
+slots = {}
+
+def ping(suffix):
+    document.title = special_title + suffix
+
+
+def signal():
+    args = Array.from(arguments)
+    to_python._queue_message({'type': 'signal', 'name': this, 'args': args})
+
+
+class ToPython:
+
+    def __init__(self):
+        self._messages = v'[]'
+        self._last_ping_value = 0
+        self._ping_timer_id = -1
+        self._queue_message({'type': 'qt-ready'})
+
+    def _ping(self):
+        if self._ping_timer_id < 0:
+            self._last_ping_value = 0 if self._last_ping_value else 1
+            self._ping_timer_id = setTimeout(def():
+                ping(self._last_ping_value)
+                self._ping_timer_id = -1
+            , 0)
+
+    def _queue_message(self, msg):
+        self._messages.push(msg)
+        self._ping()
+
+    def _register_signals(self, signals):
+        for signal_name in signals:
+            self[signal_name] = signal.bind(signal_name)
+
+    def _poll(self):
+        ans = self._messages
+        self._messages = v'[]'
+        return ans
+
+    def _from_python(self, name, args):
+        callback = slots[name]
+        if callback:
+            callback.apply(None, args)
+        else:
+            console.warn(f'Attempt to call non-existent python-to-js slot named: {name}')
+
+
+to_python = None  # TODO: Implement this via message passing from sub-frames
+if window is window.top:
+    window.python_comm = to_python = ToPython()
+
+
+def from_python(func):
+    slots[func.name] = func