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Date: Fri, 23 Apr 2021 15:48:30 +0200
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Subject: Case folding with following whitespace in MIME headers
From: cmbecker69@gmx.de ("Christoph M. Becker")

Hi all,

while working on a fix[1] for bug #80259[2], I noticed that
iconv_mime_decode() and mb_decode_mimeheader() collapse all whitespace
after a case folding marker (CRLF) to a single space[3].  This appears
to be in violation of RFC 5322, section 2.2.3:

| Unfolding is accomplished by simply removing any CRLF
| that is immediately followed by WSP.

imap_utf8() properly keeps the whitespace.  (ext/imap is not available
on 3v4l.org)

I wonder whether it's worth to fix it, due to the obvious BC break, or
whether we want to treat that as a documentation issue.  If we're going
for a fix (what I would suggest), which version should that target?

[1] <https://github.com/php/php-src/pull/6865>
[2] <https://bugs.php.net/80259>
[3] <https://3v4l.org/E92VT>

=2D-
Christoph M. Becker