Unexpected behavior in KIO::MimeTypeFinderJob

[David Faure]

On mercredi 7 août 2024 11:54:20 heure d’été d’Europe centrale David Faure 
wrote:
> On mercredi 7 août 2024 08:30:43 heure d’été d’Europe centrale Stefano
> Crocco
> wrote:
> > Hello to everyone,
> > while investigating a bug in Konqueror, I just found what in my opinion is
> > an unexpected behavior of KIO::MimeTypeFinderJob. If I'm reading the code
> > correctly, when it uses KIO::get() to determine the mimetype [1], it lets
> > the TransferJob go on even after it detected the mimetype.
> > 
> > The documentation for KIO::get() states:
> > "Special case: if you want to determine the MIME type of the file first,
> > and then read it with the appropriate component, you can still use a
> > KIO::get() directly. When that job emits the mimeType signal, (which is
> > guaranteed to happen before it emits any data), put the job on hold". 
> > Since the task of MimeTypeFinderJob is finding the mimetype of the URL, I
> > expected it would put the job on hold as soon as it has determined the
> > mimetype, coherently with the KIO::get() documentation.
> 
> Right, that's what KRun::foundMimeType was doing, and I did that in
> MimeTypeFinderJob initially.
> 
> But see commit 621585f0e818cd9f75cdd3bcc8665da7ac708283
> and bug 452729. Seems weird. Talk to Harald ;)

Of course in KF5 it was a bit different because another process could resume 
the slave on hold, made available by klauncher. AFAIK nowadays that's gone so 
resuming the slave on hold only works if the *same* process is going to fetch 
that URL. I guess that's the issue. If another process gets started instead 
(to open that URL in e.g. an image viewer), that slave on hold stays there 
forever. We need a way to discard it then, somehow.

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
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