Take the reply command. The first thing it needs to do is read the
original email data to generate the draft template for editing. The
initial read operation is filtered thru the Encoder first. The result
is passed into the nmh engine to parse header fields and other jazz to
create the draft message (all of this is done in the UTF8 world). When
writing the draft, the data is piped thru the encoder then written to
disk before launching the editor (hopefully it is a no-op, but if in a
non-UTF8 locale...).
So I was about to say that we don't know what to do in that case, but
I took a look at RFC 6587. It turns out that it spells out exactly
how to 'downgrade' a message to only ASCII. This requires encoding
domains in Punycode, using RFC 2047 and RFC 2231 where appropriate, and
use RFC 2047 for addr-spec if the mailbox name contains UTF-8.
This does not strike me as terrible, and the code is mostly written
(well not to convert U-labels to A-labels, but pretty much every Unicode
string library we've looked at has a Punycode encoder-decoder).
So that suggests to me:
- Handle everything internally as UTF-8.
- For _display_, try to convert all of the characters to the native
character set (yes, using the locale, dammit!).
- For things like _replies_, if we are not in an UTF-8 locale then downgrade
things like the addresses using RFC 6587 rules (well, the subject as well ...
I think the way it would work is the format engine would do the encoding
for you behind the scenes for all components).
- Reconvert such messages to 'canonical' standard while sending. Well, I
think just for addresses; leaving everything else as an encoded word might
not be harmful. But I'd have to think about it.
- But this also makes it clear that the thoughts of having an 'external'
decoder stage will simply not work; you need to know too much about each
header, because they're all handled differently.
Thoughts?
--Ken
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