[PATCH 0/5] iconv: module for MODIFIED-UTF-7

[Max Gautier]

These patches implement a conversion module for "modified UTF-7"
described by RFC 3501 as part of the IMAP4rev1 specification (in section
5.1.3[1]).
This is the encoding used by convention by IMAP server to describe
internationalized mailbox names.

I'm trying to make isync[2] (an IMAP synchronizer) support that
encoding ; implementing it in glibc (vs making a custom gconv-module)
seems (to me) a sensible move, since this will allow other IMAP clients
to reuse that work. Also, it's easier to reuse the boilerplate than to
remake my own.

The conversion is based on the existing UTF-7 module ; I have merely copied
it, then changed the necessary parts to make UTF-7 into MODIFIED-UTF-7.

I am unaware of an official name for the encoding, so I used
"MODIFIED-UTF-7". There might be better choices, if someone has insights
on that.

I added test files (last patch) but I'm not sure `make check` actually
tests the stateful character sets (I'm not very familiar with iconv or
the glibc build system).

I would appreciate feedback, even if it is only to say you think that
module does not belongs in glibc.

Thank you,

Max Gautier

[1]: https://tools.ietf.org/html/rfc3501#section-5.1.3
[2]: https://isync.sourceforge.io/