[Kde-pim] KMail's quoting of text in replies and format=flowed

[Jan Kundrát]

Hi,
TL;DR: I've noticed that Laurent's and Christian's recent messages to this 
list are apparently created by prepending the original lines with "> ". 
This conflicts with RFC 3676, and results in Trojita treating the "> > 
something" as a block of text "> something" which is within a one-level 
deep quote. Such mails should be only quoted by a sindle ">".

The longer version -- there's been no standard for how a quoted mail looks 
like prior to RFC 2646 (nowadays RFC 3676). While ">" is a pretty standard 
thing, some people use "|", maybe because it looks better on their ASCII 
terminals. This lack of standardization results in all sorts of funny 
artifacts, such as sometimes treating the actual greater-than sign as a 
quote indicator when it happens to end up at the first character of a line, 
etc. KMail attempts to deal with this through its X-KMail-QuotePrefix, but 
nobody else recognize this non-standard header.

Back in 1999, an RFC defining how a MIME type "text/plain; format=flowed" 
looks like, and the only allowed quote character is ">". There's an example 
[1] which clearly says that no spaces are allowed within the quote marks. 
Nothing is wrong with quoting "a text" as "> a text", but quoting "> a 
text" *must* be done as ">> a text" and *not* as "> > a text". The 
underlying mechanism is called "space stuffing".

I would like to propose removing support for specifying the quote character 
in KMail's configuration templates. The goal is to increase 
interoperability by making sure it produces e-mails that conform to the 
oficially blessed counting style.

A correct change would be rather complex; one should track whether each 
line is quoted or not when processing them, and not rely on the leading ">" 
of the actual line content. The algorithm which we use in Trojita is 
available in UiUtils::plaintextToHtml at [2]. Trojita's composer is still a 
bit broken, it won't space-stuff lines which happen to start with a ">" 
correctly, so they end up as quoterd. In order to change this, each 
paragraph in the composer will have to maintain its quote level 
out-of-band, and that is something which still remains to be done for 
Trojita.

A little easier (and also dirtier) fix for KMail would be to check whether 
each line starts with a ">" already, and only quote these with another ">". 
Every other line should still be quoted by a "> ". This algorithm is prone 
to false quoting, but it's an improvement on what KMail does today.

I wonder what's your opinion on this one. I could help with some patches 
for the quick&dirty approach if you like the direction. I guess that 
removing the GUI and functionality but leaving the accessors (if any) etc 
in place is the way to go?

With kind regards,
Jan

[1] http://tools.ietf.org/html/rfc2646#section-4.5
[2] 
http://quickgit.kde.org/?p=trojita.git&a=blob&h=c1fefa0a13969d8461ebc6ee7c5be2a891ce97f2&hb=7ded880c12dac7dfc1f97a1c7f4e4de09a80d917&f=src%2FUiUtils%2FPlainTextFormatter.cpp 
, line 209

-- 
Trojitá, a fast Qt IMAP e-mail client -- http://trojita.flaska.net/
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