Add qt.workarounds.remove_service_workers setting

See #5656, #5634

doc/changelog.asciidoc

@@ -94,6 +94,10 @@ Added
 - New `:bookmark-list` command which lists all bookmarks/quickmarks. The
   corresponding `qute://bookmarks` URL already existed since v0.8.0, but it was
   never exposed as a command.
+- New `qt.workarounds.remove_service_workers` setting which can be used to
+  remove the "Service Workers" directory on every start. Usage of this option is
+  generally discouraged, except in situations where the underlying QtWebEngine bug
+  is a known cause for crashes.
 - New userscripts:
   * `kodi` to play videos in Kodi
   * `qr` to generate a QR code of the current URL

doc/help/settings.asciidoc

@@ -282,6 +282,7 @@
 |<<qt.highdpi,qt.highdpi>>|Turn on Qt HighDPI scaling.
 |<<qt.low_end_device_mode,qt.low_end_device_mode>>|When to use Chromium's low-end device mode.
 |<<qt.process_model,qt.process_model>>|Which Chromium process model to use.
+|<<qt.workarounds.remove_service_workers,qt.workarounds.remove_service_workers>>|Delete the QtWebEngine Service Worker directory on every start.
 |<<scrolling.bar,scrolling.bar>>|When/how to show the scrollbar.
 |<<scrolling.smooth,scrolling.smooth>>|Enable smooth scrolling for web pages.
 |<<search.ignore_case,search.ignore_case>>|When to find text on a page case-insensitively.
@@ -3638,6 +3639,16 @@ Default: +pass:[process-per-site-instance]+
 
 This setting is only available with the QtWebEngine backend.
 
+[[qt.workarounds.remove_service_workers]]
+=== qt.workarounds.remove_service_workers
+Delete the QtWebEngine Service Worker directory on every start.
+This workaround can help with certain crashes caused by an unknown QtWebEngine bug related to Service Workers. Those crashes happen seemingly immediately on Windows; after one hour of operation on other systems.
+Note however that enabling this option *can lead to data loss* on some pages (as Service Worker data isn't persisted) and will negatively impact start-up time.
+
+Type: <<types,Bool>>
+
+Default: +pass:[false]+
+
 [[scrolling.bar]]
 === scrolling.bar
 When/how to show the scrollbar.

qutebrowser/config/configdata.yml

@@ -286,6 +286,19 @@ qt.highdpi:
     As an alternative to this, it's possible to set font sizes and the
     `zoom.default` setting.
 
+qt.workarounds.remove_service_workers:
+  type: Bool
+  default: false
+  desc: >-
+    Delete the QtWebEngine Service Worker directory on every start.
+
+    This workaround can help with certain crashes caused by an unknown QtWebEngine bug
+    related to Service Workers. Those crashes happen seemingly immediately on Windows;
+    after one hour of operation on other systems.
+
+    Note however that enabling this option *can lead to data loss* on some pages (as
+    Service Worker data isn't persisted) and will negatively impact start-up time.
+
 ## auto_save
 
 auto_save.interval:

qutebrowser/misc/backendproblem.py

@@ -403,21 +403,22 @@ class _BackendProblemChecker:
             # Nuke the service worker directory once for every install with Qt
             # 5.14, given that it seems to cause a variety of segfaults.
             configfiles.state['general']['serviceworker_workaround'] = '514'
-            affected = True
+            reason = 'Qt 5.14'
+        elif configfiles.state.qt_version_changed:
+            reason = 'Qt version changed'
+        elif config.val.qt.workarounds.remove_service_workers:
+            reason = 'Explicitly enabled'
         else:
-            # Otherwise, just nuke it when the Qt version changed.
-            affected = configfiles.state.qt_version_changed
-
-        if not affected:
             return
 
-        service_worker_dir = os.path.join(standarddir.data(), 'webengine',
-                                          'Service Worker')
+        service_worker_dir = os.path.join(
+            standarddir.data(), 'webengine', 'Service Worker')
         bak_dir = service_worker_dir + '-bak'
         if not os.path.exists(service_worker_dir):
             return
 
-        log.init.info("Qt version changed, removing service workers")
+        log.init.info(
+            f"Removing service workers at {service_worker_dir} (reason: {reason})")
 
         # Keep one backup around - we're not 100% sure what persistent data
         # could be in there, but this folder can grow to ~300 MB.

tests/end2end/data/service-worker/data.json

@@ -0,0 +1 @@
+{"foo": "bar"}

tests/end2end/data/service-worker/index.html

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <meta charset="utf-8">
+        <title>Service worker test</title>
+        <script>navigator.serviceWorker.register('worker.js')</script>
+    </head>
+    <body>
+        This page will register a service worker when loaded.
+    </body>
+</html>

tests/end2end/data/service-worker/worker.js

@@ -0,0 +1,8 @@
+self.addEventListener('install', event => {
+    console.log("Installing service worker");
+    event.waitUntil(
+      caches.open('example-cache')
+        .then(cache => cache.add('data.json'))
+        .then(self.skipWaiting())
+    );
+});

tests/end2end/test_invocations.py

@@ -19,6 +19,7 @@
 
 """Test starting qutebrowser with special arguments/environments."""
 
+import configparser
 import subprocess
 import sys
 import logging
@@ -435,3 +436,57 @@ def test_preferred_colorscheme(request, quteproc_new):
 
     quteproc_new.send_cmd(':jseval matchMedia("(prefers-color-scheme: dark)").matches')
     quteproc_new.wait_for(message='True')
+
+
+@pytest.mark.qtwebkit_skip
+@pytest.mark.parametrize('reason', [
+    'Explicitly enabled',
+    pytest.param('Qt 5.14', marks=utils.qt514),
+    'Qt version changed',
+    None,
+])
+def test_service_worker_workaround(
+        request, server, quteproc_new, short_tmpdir, reason):
+    """Make sure we remove the QtWebEngine Service Worker directory if configured."""
+    args = _base_args(request.config) + ['--basedir', str(short_tmpdir)]
+    if reason == 'Explicitly enabled':
+        settings_args = ['-s', 'qt.workarounds.remove_service_workers', 'true']
+    else:
+        settings_args = []
+
+    service_worker_dir = short_tmpdir / 'data' / 'webengine' / 'Service Worker'
+
+    # First invocation: Create directory
+    quteproc_new.start(args)
+    quteproc_new.open_path('data/service-worker/index.html')
+    server.wait_for(verb='GET', path='/data/service-worker/data.json')
+    quteproc_new.send_cmd(':quit')
+    quteproc_new.wait_for_quit()
+    assert service_worker_dir.exists()
+
+    # Edit state file if needed
+    state_file = short_tmpdir / 'data' / 'state'
+    if reason == 'Qt 5.14':
+        state_file.remove()
+    elif reason == 'Qt version changed':
+        parser = configparser.ConfigParser()
+        parser.read(state_file)
+        del parser['general']['qt_version']
+        with state_file.open('w', encoding='utf-8') as f:
+            parser.write(f)
+
+    # Second invocation: Directory gets removed (if workaround enabled)
+    quteproc_new.start(args + settings_args)
+    if reason is not None:
+        quteproc_new.wait_for(
+            message=(f'Removing service workers at {service_worker_dir} '
+                     f'(reason: {reason})'))
+
+    quteproc_new.send_cmd(':quit')
+    quteproc_new.wait_for_quit()
+
+    if reason is None:
+        assert service_worker_dir.exists()
+        quteproc_new.ensure_not_logged(message='Removing service workers at *')
+    else:
+        assert not service_worker_dir.exists()