fix: guard against NULL CefBrowser during rapid frame lifecycle transitions

CefFrame::GetBrowser() can return a null CefRefPtr while a frame is being
created or destroyed during rapid navigation (e.g. heavy pages with many
iframes).  The naked .get().GetIdentifier() chain in GetPyFrame() was a
latent SIGSEGV; all handler entry points that call GetPyFrame() or dereference
the frame's browser pointer now return their safe defaults when the browser
pointer is NULL.

Affected files:
- src/frame.pyx: store GetBrowser() result, check .get() before chaining
- src/handlers/load_handler.pyx: OnLoadStart / OnLoadEnd / OnLoadError
- src/handlers/display_handler.pyx: OnAddressChange
- src/handlers/v8context_handler.pyx: OnContextCreated
- src/handlers/request_handler.pyx: OnBeforeBrowse, OnBeforeResourceLoad,
  GetResourceHandler, OnResourceRedirect, GetAuthCredentials
- src/handlers/cookie_access_filter.pyx: CanSendCookie, CanSaveCookie
- src/handlers/lifespan_handler.pyx: OnBeforePopup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: linesight

src/frame.pyx

@@ -28,7 +28,15 @@ cdef PyFrame GetPyFrame(CefRefPtr[CefFrame] cefFrame):
 
     cdef PyFrame pyFrame
     cdef CefString frameId = cefFrame.get().GetIdentifier()
-    cdef int browserId = cefFrame.get().GetBrowser().get().GetIdentifier()
+    cdef CefRefPtr[CefBrowser] cefBrowser = cefFrame.get().GetBrowser()
+    if not cefBrowser.get():
+        # GetBrowser() can return NULL when a frame is being created or
+        # destroyed during rapid navigation (e.g. iframes on heavy pages).
+        # Raising here prevents a SIGSEGV from the naked .get().GetIdentifier()
+        # chain that was here before this check.
+        raise Exception("GetPyFrame(): CefBrowser is NULL"
+                        " (frame lifecycle transition during navigation?)")
+    cdef int browserId = cefBrowser.get().GetIdentifier()
     if not browserId:
         raise Exception("GetPyFrame(): browserId is 0 (browser not yet initialised)")
     # frameId may be empty for internal frames that CEF creates before the

src/handlers/cookie_access_filter.pyx

@@ -25,6 +25,8 @@ cdef public cpp_bool CookieAccessFilter_CanSendCookie(
         # browser was closed.
         if IsBrowserClosed(cef_browser):
             return False
+        if not cef_frame.get().GetBrowser().get():
+            return True  # default: allow cookie
 
         browser = GetPyBrowser(cef_browser, "CanSendCookie")
         frame = GetPyFrame(cef_frame)
@@ -64,6 +66,8 @@ cdef public cpp_bool CookieAccessFilter_CanSaveCookie(
         # browser was closed.
         if IsBrowserClosed(cef_browser):
             return False
+        if not cef_frame.get().GetBrowser().get():
+            return True  # default: allow cookie
 
         browser = GetPyBrowser(cef_browser, "CanSaveCookie")
         frame = GetPyFrame(cef_frame)

src/handlers/display_handler.pyx

@@ -15,6 +15,8 @@ cdef public void DisplayHandler_OnAddressChange(
     cdef object pyUrl
     cdef object callback
     try:
+        if not cefFrame.get().GetBrowser().get():
+            return
         pyBrowser = GetPyBrowser(cefBrowser, "OnAddressChange")
         pyFrame = GetPyFrame(cefFrame)
         pyUrl = CefToPyString(cefUrl)

src/handlers/lifespan_handler.pyx

@@ -48,6 +48,8 @@ cdef public cpp_bool LifespanHandler_OnBeforePopup(
     cdef object callback
     cdef py_bool returnValue
     try:
+        if not cefFrame.get().GetBrowser().get():
+            return False  # frame is being destroyed; cancel popup
         pyBrowser = GetPyBrowser(cefBrowser, "OnBeforePopup")
         pyFrame = GetPyFrame(cefFrame)
         pyTargetUrl = CefToPyString(targetUrl)

src/handlers/load_handler.pyx

@@ -33,6 +33,8 @@ cdef public void LoadHandler_OnLoadStart(
     cdef PyFrame pyFrame
     cdef object clientCallback
     try:
+        if not cefFrame.get().GetBrowser().get():
+            return
         pyBrowser = GetPyBrowser(cefBrowser, "OnLoadStart")
         pyFrame = GetPyFrame(cefFrame)
         clientCallback = pyBrowser.GetClientCallback("OnLoadStart")
@@ -51,6 +53,8 @@ cdef public void LoadHandler_OnLoadEnd(
     cdef PyFrame pyFrame
     cdef object clientCallback
     try:
+        if not cefFrame.get().GetBrowser().get():
+            return
         pyBrowser = GetPyBrowser(cefBrowser, "OnLoadEnd")
         pyFrame = GetPyFrame(cefFrame)
         clientCallback = pyBrowser.GetClientCallback("OnLoadEnd")
@@ -78,6 +82,8 @@ cdef public void LoadHandler_OnLoadError(
         # the error code will be ERR_ABORTED. In such cases calls
         # to OnLoadError should be ignored and not handled by user
         # scripts. The wxpython example implements such behavior.
+        if not cefFrame.get().GetBrowser().get():
+            return
         pyBrowser = GetPyBrowser(cefBrowser, "OnLoadError")
         pyFrame = GetPyFrame(cefFrame)
         errorTextOut = [CefToPyString(cefErrorText)]

src/handlers/request_handler.pyx

@@ -74,6 +74,8 @@ cdef public cpp_bool RequestHandler_OnBeforeBrowse(
         # browser was closed.
         if IsBrowserClosed(cefBrowser):
             return False
+        if not cefFrame.get().GetBrowser().get():
+            return False
 
         pyBrowser = GetPyBrowser(cefBrowser, "OnBeforeBrowse")
         pyFrame = GetPyFrame(cefFrame)
@@ -109,6 +111,8 @@ cdef public cpp_bool RequestHandler_OnBeforeResourceLoad(
         # browser was closed.
         if IsBrowserClosed(cefBrowser):
             return False
+        if not cefFrame.get().GetBrowser().get():
+            return False
 
         pyBrowser = GetPyBrowser(cefBrowser, "OnBeforeResourceLoad")
         pyFrame = GetPyFrame(cefFrame)
@@ -142,6 +146,8 @@ cdef public CefRefPtr[CefResourceHandler] RequestHandler_GetResourceHandler(
         # browser was closed.
         if IsBrowserClosed(cefBrowser):
             return <CefRefPtr[CefResourceHandler]>nullptr
+        if not cefFrame.get().GetBrowser().get():
+            return <CefRefPtr[CefResourceHandler]>nullptr
 
         pyBrowser = GetPyBrowser(cefBrowser, "GetResourceHandler")
         pyFrame = GetPyFrame(cefFrame)
@@ -183,6 +189,8 @@ cdef public void RequestHandler_OnResourceRedirect(
         # browser was closed.
         if IsBrowserClosed(cefBrowser):
             return
+        if not cefFrame.get().GetBrowser().get():
+            return
 
         pyBrowser = GetPyBrowser(cefBrowser, "OnResourceRedirect")
         pyFrame = GetPyFrame(cefFrame)
@@ -233,6 +241,8 @@ cdef public cpp_bool RequestHandler_GetAuthCredentials(
         # browser was closed.
         if IsBrowserClosed(cefBrowser):
             return False
+        if not cefFrame.get().GetBrowser().get():
+            return False
 
         pyBrowser = GetPyBrowser(cefBrowser, "GetAuthCredentials")
         pyFrame = GetPyFrame(cefFrame)

src/handlers/v8context_handler.pyx

@@ -22,6 +22,8 @@ cdef public void V8ContextHandler_OnContextCreated(
     cdef object clientCallback
     cdef JavascriptBindings jsBindings
     try:
+        if not cefFrame.get().GetBrowser().get():
+            return
         pyBrowser = GetPyBrowser(cefBrowser, "OnContextCreated")
         pyBrowser.SetUserData("__v8ContextCreated", True)
         pyFrame = GetPyFrame(cefFrame)