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Handlers: document NULL-browser guards and log instead of silent return
Add why-comments and Debug() logging to the CefFrame::GetBrowser()==NULL guards across the V8 context, load, lifespan and cookie-access handlers so these skipped callbacks are diagnosable rather than silently dropped. - v8context: explain the async-IPC frame-detach case; document why bindings are re-sent on each new V8 context. - cookie filter: drop the incorrect issue cztomczak#676 attribution (that was the callbacks-not-called bug, fixed separately); document in RequestHandler.md that requests without a browser/frame cannot be filtered. - load handler: comment + log OnLoadStart/OnLoadEnd/OnLoadError. - lifespan: fix the OnBeforePopup comment (return false ALLOWS the popup, it does not cancel) and defer to CEF's default, matching the other guards. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Lines changed: 66 additions & 15 deletions

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‎api/RequestHandler.md‎

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@@ -46,6 +46,11 @@ Table of contents:
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Called on the IO thread before a cookie is sent with a network request.
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Return `True` to allow the cookie or `False` to block it.
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Limitation: requests with no associated browser/frame (e.g. service workers,
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`CefURLRequest`, and some cross-origin subresource requests on the IO thread)
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cannot be filtered. The callback is not called for them and the cookie is
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allowed by default, matching CEF's own default.
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### CanSaveCookie
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@@ -61,6 +66,11 @@ Return `True` to allow the cookie or `False` to block it.
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Called on the IO thread before a cookie received from a network response is
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saved. Return `True` to allow the cookie or `False` to block it.
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Limitation: requests with no associated browser/frame (e.g. service workers,
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`CefURLRequest`, and some cross-origin subresource requests on the IO thread)
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cannot be filtered. The callback is not called for them and the cookie is
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allowed by default, matching CEF's own default.
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### GetAuthCredentials
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‎src/handlers/cookie_access_filter.pyx‎

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@@ -25,13 +25,15 @@ cdef public cpp_bool CookieAccessFilter_CanSendCookie(
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# browser was closed.
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if IsBrowserClosed(cef_browser):
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return False
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# Issue #676: This callback runs on the IO thread, where
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# CefFrame::GetBrowser() may return NULL (observed for cross-origin
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# subresource requests). CEF also documents browser/frame as optional
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# ("may be NULL for requests originating from service workers or
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# CefURLRequest", cef_resource_request_handler.h > CefCookieAccessFilter).
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# Without a resolvable browser we cannot build a PyFrame to dispatch on,
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# so log and allow the cookie by default (CEF's own default is true).
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# This callback runs on the IO thread, where CefFrame::GetBrowser()
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# may return NULL (observed for cross-origin subresource requests). CEF
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# also documents browser/frame as optional ("may be NULL for requests
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# originating from service workers or CefURLRequest",
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# cef_resource_request_handler.h > CefCookieAccessFilter). Without a
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# resolvable browser we cannot build a PyFrame to dispatch on, so log
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# and allow the cookie by default (CEF's own default is true). The app
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# therefore cannot filter these cookies - documented as a limitation in
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# api/RequestHandler.md.
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if not cef_frame.get() or not cef_frame.get().GetBrowser().get():
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Debug("CanSendCookie: no resolvable browser for the request"
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" (IO-thread / service-worker request); allowing by default")
@@ -75,10 +77,11 @@ cdef public cpp_bool CookieAccessFilter_CanSaveCookie(
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# browser was closed.
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if IsBrowserClosed(cef_browser):
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return False
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# Issue #676: see CanSendCookie above. On the IO thread
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# CefFrame::GetBrowser() may be NULL (and CEF documents browser/frame
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# as optional). Without a resolvable browser we cannot build a PyFrame,
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# so log and allow the cookie by default.
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# See CanSendCookie above. On the IO thread CefFrame::GetBrowser() may
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# be NULL (and CEF documents browser/frame as optional). Without a
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# resolvable browser we cannot build a PyFrame, so log and allow the
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# cookie by default; the app cannot filter these cookies (see
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# api/RequestHandler.md).
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if not cef_frame.get() or not cef_frame.get().GetBrowser().get():
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Debug("CanSaveCookie: no resolvable browser for the request"
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" (IO-thread / service-worker request); allowing by default")

‎src/handlers/lifespan_handler.pyx‎

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Original file line numberDiff line numberDiff line change
@@ -48,8 +48,17 @@ cdef public cpp_bool LifespanHandler_OnBeforePopup(
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cdef object callback
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cdef py_bool returnValue
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try:
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# CefFrame::GetBrowser() can be NULL when the opener frame is detached
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# during a rapid lifecycle transition. Without a resolvable browser we
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# cannot build a PyFrame to pass to the user callback, so fall back to
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# CEF's default, consistent with the other NULL-browser guards. Note
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# that returning false ALLOWS the popup (CEF: return true cancels,
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# false allows - see cef_life_span_handler.h); this defers popup
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# handling to CEF rather than silently suppressing it.
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if not cefFrame.get().GetBrowser().get():
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return False # frame is being destroyed; cancel popup
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Debug("OnBeforePopup: frame has no browser (detached during"
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" lifecycle transition); deferring to CEF default")
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return False
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pyBrowser = GetPyBrowser(cefBrowser, "OnBeforePopup")
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pyFrame = GetPyFrame(cefFrame)
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pyTargetUrl = CefToPyString(targetUrl)

‎src/handlers/load_handler.pyx‎

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Original file line numberDiff line numberDiff line change
@@ -33,7 +33,14 @@ cdef public void LoadHandler_OnLoadStart(
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cdef PyFrame pyFrame
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cdef object clientCallback
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try:
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# A frame torn down mid-navigation (rapid create -> navigate -> destroy)
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# can already be detached by the time this UI-thread callback runs, in
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# which case CefFrame::GetBrowser() returns NULL. There is then no
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# browser to resolve a PyBrowser/PyFrame from and the load event refers
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# to a frame that no longer exists, so skipping is correct.
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if not cefFrame.get().GetBrowser().get():
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Debug("OnLoadStart: frame has no browser (detached during"
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" lifecycle transition), skipping")
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return
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pyBrowser = GetPyBrowser(cefBrowser, "OnLoadStart")
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pyFrame = GetPyFrame(cefFrame)
@@ -53,7 +60,11 @@ cdef public void LoadHandler_OnLoadEnd(
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cdef PyFrame pyFrame
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cdef object clientCallback
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try:
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# See OnLoadStart: a detached frame yields a NULL CefFrame::GetBrowser()
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# on the UI thread; nothing to dispatch on, so skip.
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if not cefFrame.get().GetBrowser().get():
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Debug("OnLoadEnd: frame has no browser (detached during"
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" lifecycle transition), skipping")
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return
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pyBrowser = GetPyBrowser(cefBrowser, "OnLoadEnd")
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pyFrame = GetPyFrame(cefFrame)
@@ -82,7 +93,11 @@ cdef public void LoadHandler_OnLoadError(
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# the error code will be ERR_ABORTED. In such cases calls
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# to OnLoadError should be ignored and not handled by user
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# scripts. The wxpython example implements such behavior.
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# See OnLoadStart: a detached frame yields a NULL CefFrame::GetBrowser()
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# on the UI thread; nothing to dispatch on, so skip.
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if not cefFrame.get().GetBrowser().get():
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Debug("OnLoadError: frame has no browser (detached during"
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" lifecycle transition), skipping")
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return
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pyBrowser = GetPyBrowser(cefBrowser, "OnLoadError")
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pyFrame = GetPyFrame(cefFrame)

‎src/handlers/v8context_handler.pyx‎

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Original file line numberDiff line numberDiff line change
@@ -22,14 +22,28 @@ cdef public void V8ContextHandler_OnContextCreated(
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cdef object clientCallback
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cdef JavascriptBindings jsBindings
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try:
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# These V8 events are reconstructed in the browser process from
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# asynchronous IPC messages sent by the renderer (see note at the top
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# of this file), so a frame from a rapid create -> navigate -> destroy
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# sequence can already be detached by the time we run here, in which
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# case CefFrame::GetBrowser() returns NULL. There is then no browser to
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# bind to or dispatch a callback for, so skipping is the correct thing
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# to do.
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if not cefFrame.get().GetBrowser().get():
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Debug("OnContextCreated: frame has no browser (detached during"
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" lifecycle transition), skipping")
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return
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pyBrowser = GetPyBrowser(cefBrowser, "OnContextCreated")
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pyBrowser.SetUserData("__v8ContextCreated", True)
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pyFrame = GetPyFrame(cefFrame)
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# Re-send bindings before user callback so that any ExecuteJavascript
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# the user sends from OnContextCreated has globals already registered
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# when it arrives at the renderer (both travel the same IPC channel).
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# Re-send the JS bindings to the renderer. OnContextCreated fires for
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# each new V8 context (page load, navigation, cross-origin navigation
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# under site isolation); a fresh context has none of the previously
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# injected globals, so they must be resent or bindings would be lost
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# after navigation. Do this before the user callback so that any
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# ExecuteJavascript the user issues from OnContextCreated finds its
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# globals already registered when it reaches the renderer (both travel
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# the same IPC channel).
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if pyFrame.IsMain():
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jsBindings = pyBrowser.GetJavascriptBindings()
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if jsBindings:

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