Bug#907891: perl: MIME-Q (RFC2047 eMail header) encoding broken since post-stretch

[Russ Allbery]

Thorsten Glaser <tg at mirbsd.de> writes:

> (sid)$ printf '%s' 'Subject: UNNAMED PROJECT branch bnewplus updated. f9dfb215c29bc17b5ca12c0e8bb509aa4949787e' | perl -C7 -0777 -Mutf8 -MEncode -e "print encode('MIME-Q', <>);"; echo
> =?UTF-8?Q?Subject=3A_UNNAMED_PROJECT_branch_bnewplus_updated=2E_f9dfb215c?=
>  =?UTF-8?Q?29bc17b5ca12c0e8bb509aa4949787e?=

This doesn't directly address the rest of your bug report, but I'm fairly
sure that including the email header in the text you're encoding is a bug
in your code.  RFC 2047 encoding is defined on a string, and the encoder
has no way of knowing that the initial "Subject: " is magical and should
be treated not as part of the string.  It could well be part of the
content of the header field.

Regardless of the rest of the issues here with excessive encoding, your
code should be encoding the contents of the field and then separately
adding the header field name.  This happens to accidentally work if the
encoding reproduces pure ASCII words in the output text without encoding
them, but it's technically incorrect because it's not valid in the email
format to encode the header field name using RFC 2047 encoding.

-- 
Russ Allbery (rra at debian.org)               <http://www.eyrie.org/~eagle/>