File: utf7.el.html

UTF-7 - A Mail-Safe Transformation Format of Unicode - RFC 2152 This is a transformation format of Unicode that contains only 7-bit ASCII octets and is intended to be readable by humans in the limiting case that the document consists of characters from the US-ASCII repertoire. In short, runs of characters outside US-ASCII are encoded as base64 inside delimiters. A variation of UTF-7 is specified in IMAP 4rev1 (RFC 2060) as the way to represent characters outside US-ASCII in mailbox names in IMAP. This library supports both variants, but the IMAP variation was the reason I wrote it. The routines convert UTF-7 -> UTF-16 (16 bit encoding of Unicode)
-> current character set, and vice versa.
However, until Emacs supports Unicode, the only Emacs character set supported here is ISO-8859.1, which can trivially be converted to/from Unicode. When decoding results in a character outside the Emacs character set, an error is thrown. It is up to the application to recover.

UTF-7 should be done by providing a coding system. Mule-UCS does already, but I don't know if it does the IMAP version and it's not clear whether that should really be a coding system. The UTF-16 part of the conversion can be done with coding systems available with Mule-UCS or some versions of Emacs. Unfortunately these were done wrongly (regarding handling of byte-order marks and how the variants were named), so we don't have a consistent name for the necessary coding system. The code below doesn't seem to DTRT generally. E.g.:

(utf7-encode "a+£")
  => "a+ACsAow-"

$ echo "a+£"|iconv -f utf-8 -t utf-7
a+-+AKM

 -- fx

Defined variables (3)

Defined functions (10)

Defined faces (0)