[PyQt] Object lifetime issues with QWebEngineUrlSchemeHandler and QBuffer

[Florian Bruhin]

Hey,

I tried implementing a custom QWebEngineUrlSchemeHandler yesterday,
and ran into some weird object lifetime issues I can't quite explain.

The attached request1.py is the one which works fine, and displays
"Hello World" with a custom test:foo URL.


In request2.py, I removed a global reference to SchemeHandler, so
"handler" is local in install_scheme_handler().

Now, despite setting the parent of SchemeHandler to the QApplication
instance, it seems to go away somehow and I get an
"ERR_UNKNOWN_URL_SCHEME" error page.

Why?


In request3.py, the global reference is back, but I use a QBuffer to
which I pass a byte string instead of writing to it in requestStarted.
Here, I get a segfault:

    #0  QBuffer::readData (this=0xe06740, data=0x7fffd4013000 "", len=32768) at io/qbuffer.cpp:412
    #1  0x00007fffecd579ae in ?? () from /usr/lib/python3.5/site-packages/PyQt5/QtCore.so
    #2  0x00007ffff4ae3e0a in QIODevice::read (this=0xe06740, data=0x7fffd4013000 "", maxSize=32768) at io/qiodevice.cpp:1047
    #3  0x00007fffe734232a in QtWebEngineCore::URLRequestCustomJob::ReadRawData (this=<optimized out>, buf=0x7fff9c1692c0, bufSize=32768)
    [...]

I explicitly keep a reference to both the QBuffer and to the
underlying byte string, to make sure they never get collected, so why
is this happening?


Also, with request1.py, I never delete the QBuffer - when can I do so?
Should I do job.destroyed.connect(buf.deleteLater)?


Thanks,

Florian

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