Try to always set the default webengine profile's cache path to the calibre cache directory

src/calibre/constants.py

@@ -39,6 +39,7 @@ isworker = hasenv('CALIBRE_WORKER') or hasenv('CALIBRE_SIMPLE_WORKER')
 if isworker:
     os.environ.pop(environ_item('CALIBRE_FORCE_ANSI'), None)
 FAKE_PROTOCOL, FAKE_HOST = 'clbr', 'internal.invalid'
+SPECIAL_TITLE_FOR_WEBENGINE_COMMS = '__webengine_messages_pending__'
 VIEWER_APP_UID = 'com.calibre-ebook.viewer'
 EDITOR_APP_UID = 'com.calibre-ebook.edit-book'
 MAIN_APP_UID = 'com.calibre-ebook.main-gui'

src/calibre/ebooks/conversion/plugins/pdf_output.py

@@ -155,6 +155,8 @@ class PDFOutput(OutputFormatPlugin):
         scheme.setFlags(QWebEngineUrlScheme.Flag.SecureScheme)
         QWebEngineUrlScheme.registerScheme(scheme)
         must_use_qt()
+        from calibre.utils.webengine import setup_default_profile
+        setup_default_profile()
         self.input_fmt = input_fmt
 
         if opts.pdf_use_document_margins:

src/calibre/ebooks/render_html.py

@@ -99,6 +99,8 @@ def main(path_to_html, tdir, image_format='jpeg'):
     if image_format not in ('jpeg', 'png'):
         raise ValueError('Image format must be either jpeg or png')
     must_use_qt()
+    from calibre.utils.webengine import setup_default_profile
+    setup_default_profile()
     path_to_html = os.path.abspath(path_to_html)
     os.chdir(tdir)
     renderer = Render()

src/calibre/gui2/toc/main.py

@@ -1188,6 +1188,8 @@ def main(shm_name=None):
 
         override = 'calibre-gui' if islinux else None
         app = Application([], override_program_name=override)
+        from calibre.utils.webengine import setup_default_profile
+        setup_default_profile()
         d = TOCEditor(path, title=title, write_result_to=path + '.result')
         d.start()
         ok = 0

src/calibre/gui2/tweak_book/main.py

@@ -71,6 +71,8 @@ def _run(args, notify=None):
     decouple('edit-book-'), set_gui_prefs(tprefs)
     override = 'calibre-ebook-edit' if islinux else None
     app = Application(args, override_program_name=override, color_prefs=tprefs, windows_app_uid=EDITOR_APP_UID)
+    from calibre.utils.webengine import setup_default_profile
+    setup_default_profile()
     app.file_event_hook = EventAccumulator()
     app.load_builtin_fonts()
     app.setWindowIcon(QIcon.ic('tweak.png'))

src/calibre/gui2/viewer/main.py

@@ -5,15 +5,15 @@
 import json
 import os
 import sys
+from contextlib import closing
 from qt.core import QIcon, QObject, Qt, QTimer, pyqtSignal
 from qt.webengine import QWebEngineUrlScheme
-from contextlib import closing
 
 from calibre.constants import FAKE_PROTOCOL, VIEWER_APP_UID, islinux
 from calibre.gui2 import Application, error_dialog, setup_gui_option_parser
+from calibre.gui2.listener import send_message_in_process
 from calibre.gui2.viewer.config import get_session_pref, vprefs
 from calibre.gui2.viewer.ui import EbookViewer, is_float
-from calibre.gui2.listener import send_message_in_process
 from calibre.ptempfile import reset_base_dir
 from calibre.utils.config import JSONConfig
 from calibre.utils.ipc import viewer_socket_address
@@ -194,6 +194,8 @@ def main(args=sys.argv):
                 pass
     args = processed_args
     app = Application(args, override_program_name=override, windows_app_uid=VIEWER_APP_UID)
+    from calibre.utils.webengine import setup_default_profile
+    setup_default_profile()
 
     parser = option_parser()
     opts, args = parser.parse_args(args)
@@ -204,8 +206,8 @@ def main(args=sys.argv):
         raise SystemExit(f'Not a valid --open-at value: {opts.open_at}')
 
     if get_session_pref('singleinstance', False):
-        from calibre.utils.lock import SingleInstance
         from calibre.gui2.listener import Listener
+        from calibre.utils.lock import SingleInstance
         with SingleInstance(singleinstance_name) as si:
             if si:
                 try:

src/calibre/utils/rapydscript.py

@@ -11,15 +11,15 @@ import sys
 
 from calibre import force_unicode
 from calibre.constants import (
-    FAKE_HOST, FAKE_PROTOCOL, __appname__, __version__, builtin_colors_dark,
-    builtin_colors_light, builtin_decorations, dark_link_color
+    FAKE_HOST, FAKE_PROTOCOL, SPECIAL_TITLE_FOR_WEBENGINE_COMMS, __appname__,
+    __version__, builtin_colors_dark, builtin_colors_light, builtin_decorations,
+    dark_link_color
 )
 from calibre.ptempfile import TemporaryDirectory
 from calibre.utils.filenames import atomic_rename
 from polyglot.builtins import as_bytes, as_unicode, exec_path
 
 COMPILER_PATH = 'rapydscript/compiler.js.xz'
-special_title = '__webengine_messages_pending__'
 
 
 def abspath(x):
@@ -59,8 +59,9 @@ def compiler():
 
     from calibre import walk
     from calibre.gui2 import must_use_qt
-    from calibre.utils.webengine import secure_webengine
+    from calibre.utils.webengine import secure_webengine, setup_default_profile
     must_use_qt()
+    setup_default_profile()
 
     with lzma.open(P(COMPILER_PATH, allow_user_override=False)) as lzf:
         compiler_script = lzf.read().decode('utf-8')
@@ -124,7 +125,7 @@ document.title = 'compiler initialized';
     class Compiler(QWebEnginePage):
 
         def __init__(self):
-            QWebEnginePage.__init__(self)
+            super().__init__()
             self.errors = []
             secure_webengine(self)
             script = compiler_script
@@ -330,17 +331,19 @@ def atomic_write(base, name, content):
 
 
 def run_rapydscript_tests():
-    from urllib.parse import parse_qs
     from qt.core import QApplication, QByteArray, QEventLoop, QUrl
     from qt.webengine import (
         QWebEnginePage, QWebEngineProfile, QWebEngineScript, QWebEngineUrlRequestJob,
         QWebEngineUrlScheme, QWebEngineUrlSchemeHandler
     )
+    from urllib.parse import parse_qs
 
     from calibre.constants import FAKE_HOST, FAKE_PROTOCOL
     from calibre.gui2 import must_use_qt
     from calibre.gui2.viewer.web_view import send_reply
-    from calibre.utils.webengine import secure_webengine, insert_scripts, create_script
+    from calibre.utils.webengine import (
+        create_script, insert_scripts, secure_webengine
+    )
     must_use_qt()
     scheme = QWebEngineUrlScheme(FAKE_PROTOCOL.encode('ascii'))
     scheme.setSyntax(QWebEngineUrlScheme.Syntax.Host)
@@ -418,7 +421,7 @@ def run_rapydscript_tests():
 
 def set_data(src, **kw):
     for k, v in {
-        '__SPECIAL_TITLE__': special_title,
+        '__SPECIAL_TITLE__': SPECIAL_TITLE_FOR_WEBENGINE_COMMS,
         '__FAKE_PROTOCOL__': FAKE_PROTOCOL,
         '__FAKE_HOST__': FAKE_HOST,
         '__CALIBRE_VERSION__': __version__,

src/calibre/utils/webengine.py

@@ -3,11 +3,18 @@
 # License: GPL v3 Copyright: 2021, Kovid Goyal <kovid at kovidgoyal.net>
 
 
-import json
+import json, os
 from qt.core import QBuffer, QIODevice, QObject, pyqtSignal, sip
-from qt.webengine import QWebEngineScript, QWebEngineSettings
+from qt.webengine import QWebEngineScript, QWebEngineSettings, QWebEngineProfile
 
-from calibre.utils.rapydscript import special_title
+from calibre.constants import cache_dir, SPECIAL_TITLE_FOR_WEBENGINE_COMMS
+
+
+def setup_default_profile():
+    p = QWebEngineProfile.defaultProfile()
+    q = os.path.join(cache_dir(), 'qt-webeng')
+    if p.cachePath() != q:
+        p.setCachePath(q)
 
 
 def send_reply(rq, mime_type, data):
@@ -112,7 +119,7 @@ class Bridge(QObject):
         return self._signals_registered
 
     def _title_changed(self, title):
-        if title.startswith(special_title):
+        if title.startswith(SPECIAL_TITLE_FOR_WEBENGINE_COMMS):
             self._poll_for_messages()
 
     def _register_signals(self):