bug#74624: 29.4.50; Gnus cannot parse some filenames(UTF8) in an attachment

[Eli Zaretskii <eliz@gnu.org>]

> From: Konstantin <reich-cv@yandex.ru>
> Date: Sat, 30 Nov 2024 18:59:25 +0300
> 
> >From time to time i get emails with attachments from my colleges, which they send from
> "Roundcube" web-interface. 
> 
> Often, i cannot open these attachments by =RET=(gnus-article-press-button)
> or save them =o=(gnus-mime-save-part) with correct name.
> (interestingly =X-m=(gnus-summary-save-parts) works correctly)
> 
> The reason is gnus cannot parse correctly some attached filenames.
> 
> The example of such attachment (I took it from gnus-summary-show-raw-article)
> 
>  --=_d38c0abddd645077f401d42fa430d9d5
> Content-Transfer-Encoding: base64
> Content-Type: application/vnd.openxmlformats-officedocument.wordprocessingml.document;
>  name="=?UTF-8?Q?=D0=9E=D0=B1=D0=B7=D0=BE=D1=80_2024_=28=D0=BD=D0=B0_=2Ed?=
>  =?UTF-8?Q?ocx?="
> Content-Disposition: attachment;
>  filename*0*=UTF-8''%D0%9E%D0%B1%D0%B7%D0%BE%D1%80%202024%20%28%D0%BD%D0;
>  filename*1*=%B0%20.docx;
>  size=10
> 
> c2Rmc2FmYXNmCg==
> --=_d38c0abddd645077f401d42fa430d9d5--
> 
> I have tried to examine the reason. As i see it,  
> gnus-data for such attachment is formed incorrectly:
> 
> (#<buffer  *mm*-480444>
>      ("application/vnd.openxmlformats-officedocument.word..."
>      (name . "Обзор 2024 (на .docx"))
>      base64 nil
>      ("attachment" (size . "10")
>      (filename . "Обзор 2024 (н\320")) nil nil nil)
> 
> One can see that the filename is broken.
> It should be "Обзор 2024 (на .docx" just like the name.

It looks like Gnus fails to decipher the file name when it is split in
the middle of a UTF-8 sequence.

I don't know Gnus.  If you can help me by showing where the value of
'gnus-data property is calculated, I might be able to find the bug and
suggest a fix.

Thanks.