Encode::MIME::Header(3pm) Perl Programmers Reference Guide
NAME
Encode::MIME::Header -- MIME encoding for an unstructured email header
SYNOPSIS
use Encode qw(encode decode);
my $mime_str = encode("MIME-Header", "Sample:Text \N{U+263A}");
# $mime_str is "=?UTF-8?B?U2FtcGxlOlRleHQg4pi6?="
my $mime_q_str = encode("MIME-Q", "Sample:Text \N{U+263A}");
# $mime_q_str is "=?UTF-8?Q?Sample=3AText_=E2=98=BA?="
my $str = decode("MIME-Header",
"=?ISO-8859-1?B?SWYgeW91IGNhbiByZWFkIHRoaXMgeW8=?=\r\n " .
"=?ISO-8859-2?B?dSB1bmRlcnN0YW5kIHRoZSBleGFtcGxlLg==?="
);
# $str is "If you can read this you understand the example."
use Encode qw(decode :fallbacks);
use Encode::MIME::Header;
local $Encode::MIME::Header::STRICT_DECODE = 1;
my $strict_string = decode("MIME-Header", $mime_string, FB_CROAK);
# use strict decoding and croak on errors
ABSTRACT
This module implements RFC 2047 <https://tools.ietf.org/html/rfc2047>
MIME encoding for an unstructured field body of the email header. It
can also be used for RFC 822 <https://tools.ietf.org/html/rfc822>
'text' token. However, it cannot be used directly for the whole header
with the field name or for the structured header fields like From, To,
Cc, Message-Id, etc... There are 3 encoding names supported by this
module: "MIME-Header", "MIME-B" and "MIME-Q".
DESCRIPTION
Decode method takes an unstructured field body of the email header (or
RFC 822 <https://tools.ietf.org/html/rfc822> 'text' token) as its input
and decodes each MIME encoded-word from input string to a sequence of
bytes according to RFC 2047 <https://tools.ietf.org/html/rfc2047> and
RFC 2231 <https://tools.ietf.org/html/rfc2231>. Subsequently, each
sequence of bytes with the corresponding MIME charset is decoded with
the Encode module and finally, one output string is returned. Text
parts of the input string which do not contain MIME encoded-word stay
unmodified in the output string. Folded newlines between two
consecutive MIME encoded-words are discarded, others are preserved in
the output string. "MIME-B" can decode Base64 variant, "MIME-Q" can
decode Quoted-Printable variant and "MIME-Header" can decode both of
them. If Encode module does not support particular MIME charset or
chosen variant then an action based on CHECK flags is performed (by
default, the MIME encoded-word is not decoded).
Encode method takes a scalar string as its input and uses strict UTF-8
encoder for encoding it to UTF-8 bytes. Then a sequence of UTF-8 bytes
is encoded into MIME encoded-words ("MIME-Header" and "MIME-B" use a
Base64 variant while "MIME-Q" uses a Quoted-Printable variant) where
each MIME encoded-word is limited to 75 characters. MIME encoded-words
are separated by "CRLF SPACE" and joined to one output string. Output
string is suitable for unstructured field body of the email header.
Both encode and decode methods propagate CHECK flags when encoding and
decoding the MIME charset.
BUGS
Versions prior to 2.22 (part of Encode 2.83) have a malfunctioning
decoder and encoder. The MIME encoder infamously inserted additional
spaces or discarded white spaces between consecutive MIME encoded-
words, which led to invalid MIME headers produced by this module. The
MIME decoder had a tendency to discard white spaces, incorrectly
interpret data or attempt to decode Base64 MIME encoded-words as
Quoted-Printable. These problems were fixed in version 2.22. It is
highly recommended not to use any version prior 2.22!
Versions prior to 2.24 (part of Encode 2.87) ignored CHECK flags. The
MIME encoder used not strict utf8 encoder for input Unicode strings
which could lead to invalid UTF-8 sequences. MIME decoder used also
not strict utf8 decoder and additionally called the decode method with
a "Encode::FB_PERLQQ" flag (thus user-specified CHECK flags were
ignored). Moreover, it automatically croaked when a MIME encoded-word
contained unknown encoding. Since version 2.24, this module uses
strict UTF-8 encoder and decoder. And CHECK flags are correctly
propagated.
Since version 2.22 (part of Encode 2.83), the MIME encoder should be
fully compliant to RFC 2047 <https://tools.ietf.org/html/rfc2047> and
RFC 2231 <https://tools.ietf.org/html/rfc2231>. Due to the
aforementioned bugs in previous versions of the MIME encoder, there is
a less strict compatible mode for the MIME decoder which is used by
default. It should be able to decode MIME encoded-words encoded by pre
2.22 versions of this module. However, note that this is not correct
according to RFC 2047 <https://tools.ietf.org/html/rfc2047>.
In default not strict mode the MIME decoder attempts to decode every
substring which looks like a MIME encoded-word. Therefore, the MIME
encoded-words do not need to be separated by white space. To enforce a
correct strict mode, set variable $Encode::MIME::Header::STRICT_DECODE
to 1 e.g. by localizing:
use Encode::MIME::Header;
local $Encode::MIME::Header::STRICT_DECODE = 1;
AUTHORS
Pali <pali@cpan.org>
SEE ALSO
Encode(3), RFC 822 <https://tools.ietf.org/html/rfc822>, RFC 2047
<https://tools.ietf.org/html/rfc2047>, RFC 2231
<https://tools.ietf.org/html/rfc2231>
perl v5.38.2 2023-11-28 Encode::MIME::Header(3pm)
perl 5.38.2 - Generated Thu Dec 5 10:33:44 CST 2024