[kmail2] [Bug 448112] New: Parsing broken subjects and other possibly UTF-8-encoded headers

[ratijas]

https://bugs.kde.org/show_bug.cgi?id=448112

            Bug ID: 448112
           Summary: Parsing broken subjects and other possibly
                    UTF-8-encoded headers
           Product: kmail2
           Version: unspecified
          Platform: Other
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: kdepim-bugs at kde.org
          Reporter: me at ratijas.tk
  Target Milestone: ---

SUMMARY

Sometimes I'm getting automated emails from systems that could not properly
encode multi-line UTF-8 subjects.
For example:

> Кассовый чек 500 ₽ от «ПАО "ТАТ��ЕЛЕКОМ"»

In the source view of that email it was represented in one line as this:

> From: "OFD.RU" <noreply at ofd.ru>
> Subject: =?UTF-8?B?0JrQsNGB0YHQvtCy0YvQuSDRh9C10LogNTAw?==?UTF-8?B?IOKCvSDQvtGCIMKr0J/QkNCeICLQotCQ0KLQ?==?UTF-8?B?otCV0JvQldCa0J7QnCLCuw==?=

The are two problems, as far as I can tell:

1. It was supposed to be split in multiple lines, after each closing ?=
sequence
2. Unicode code-points should not be split across multiple =?UTF-8?B?...?=
chunks.

But maybe we could make our lives easier by trying to recover broken subjects?

At least, we are already doing a good job of recovering from unspecified
encoding, such as in this follow-up email I got from my internet provider:

> From: <pay at ais.tattelecom.ru>
> Subject: ÐвиÑанÑÐ¸Ñ Ð¿Ð¾ оплаÑе ÑÑлÑг ÑвÑзи ÐÐР«ТаÑÑелеком»

…which KMail tried hard to «correctly» recover as

> Квитанция по оплате услуг связи ПАО «Таттелеком»

STEPS TO REPRODUCE
1. Get an email from OFD.RU

OBSERVED RESULT

Unicode symbols shred into pieces, as in

> "ТАТ��ЕЛЕКОМ"

EXPECTED RESULT

> "ТАТТЕЛЕКОМ"

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.23.80
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2
Kernel Version: 5.15.12-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-6700HQ CPU @ 2.60GHz
Memory: 15.6 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 970M/PCIe/SSE2

ADDITIONAL INFORMATION

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