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.\" ========================================================================
.\"
.IX Title "Encode::MIME::Header 3"
.TH Encode::MIME::Header 3 "2021-08-09" "perl v5.16.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
Encode::MIME::Header \-\- MIME encoding for an unstructured email header
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Encode qw(encode decode);
\&
\&    my $mime_str = encode("MIME\-Header", "Sample:Text \eN{U+263A}");
\&    # $mime_str is "=?UTF\-8?B?U2FtcGxlOlRleHQg4pi6?="
\&
\&    my $mime_q_str = encode("MIME\-Q", "Sample:Text \eN{U+263A}");
\&    # $mime_q_str is "=?UTF\-8?Q?Sample=3AText_=E2=98=BA?="
\&
\&    my $str = decode("MIME\-Header",
\&        "=?ISO\-8859\-1?B?SWYgeW91IGNhbiByZWFkIHRoaXMgeW8=?=\er\en " .
\&        "=?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
.Ve
.SH "ABSTRACT"
.IX Header "ABSTRACT"
This module implements \s-1RFC 2047\s0 <https://tools.ietf.org/html/rfc2047> \s-1MIME\s0
encoding for an unstructured field body of the email header.  It can also be
used for \s-1RFC 822\s0 <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: \f(CW\*(C`MIME\-Header\*(C'\fR, \f(CW\*(C`MIME\-B\*(C'\fR and
\&\f(CW\*(C`MIME\-Q\*(C'\fR.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Decode method takes an unstructured field body of the email header (or
\&\s-1RFC 822\s0 <https://tools.ietf.org/html/rfc822> 'text' token) as its input and
decodes each \s-1MIME\s0 encoded-word from input string to a sequence of bytes
according to \s-1RFC 2047\s0 <https://tools.ietf.org/html/rfc2047> and
\&\s-1RFC 2231\s0 <https://tools.ietf.org/html/rfc2231>.  Subsequently, each sequence
of bytes with the corresponding \s-1MIME\s0 charset is decoded with
the Encode module and finally, one output string is returned.  Text
parts of the input string which do not contain \s-1MIME\s0 encoded-word stay
unmodified in the output string.  Folded newlines between two consecutive \s-1MIME\s0
encoded-words are discarded, others are preserved in the output string.
\&\f(CW\*(C`MIME\-B\*(C'\fR can decode Base64 variant, \f(CW\*(C`MIME\-Q\*(C'\fR can decode Quoted-Printable
variant and \f(CW\*(C`MIME\-Header\*(C'\fR can decode both of them.  If Encode module
does not support particular \s-1MIME\s0 charset or chosen variant then an action based
on \s-1CHECK\s0 flags is performed (by default, the
\&\s-1MIME\s0 encoded-word is not decoded).
.PP
Encode method takes a scalar string as its input and uses
strict \s-1UTF\-8\s0 encoder for encoding it to \s-1UTF\-8\s0
bytes.  Then a sequence of \s-1UTF\-8\s0 bytes is encoded into \s-1MIME\s0 encoded-words
(\f(CW\*(C`MIME\-Header\*(C'\fR and \f(CW\*(C`MIME\-B\*(C'\fR use a Base64 variant while \f(CW\*(C`MIME\-Q\*(C'\fR uses a
Quoted-Printable variant) where each \s-1MIME\s0 encoded-word is limited to 75
characters.  \s-1MIME\s0 encoded-words are separated by \f(CW\*(C`CRLF SPACE\*(C'\fR and joined to
one output string.  Output string is suitable for unstructured field body of
the email header.
.PP
Both encode and decode methods propagate
\&\s-1CHECK\s0 flags when encoding and decoding the
\&\s-1MIME\s0 charset.
.SH "BUGS"
.IX Header "BUGS"
Versions prior to 2.22 (part of Encode 2.83) have a malfunctioning decoder
and encoder.  The \s-1MIME\s0 encoder infamously inserted additional spaces or
discarded white spaces between consecutive \s-1MIME\s0 encoded-words, which led to
invalid \s-1MIME\s0 headers produced by this module.  The \s-1MIME\s0 decoder had a tendency
to discard white spaces, incorrectly interpret data or attempt to decode Base64
\&\s-1MIME\s0 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!
.PP
Versions prior to 2.24 (part of Encode 2.87) ignored
\&\s-1CHECK\s0 flags.  The \s-1MIME\s0 encoder used
not strict utf8 encoder for input Unicode
strings which could lead to invalid \s-1UTF\-8\s0 sequences.  \s-1MIME\s0 decoder used also
not strict utf8 decoder and additionally
called the decode method with a \f(CW\*(C`Encode::FB_PERLQQ\*(C'\fR flag (thus user-specified
\&\s-1CHECK\s0 flags were ignored).  Moreover, it
automatically croaked when a \s-1MIME\s0 encoded-word contained unknown encoding.
Since version 2.24, this module uses
strict \s-1UTF\-8\s0 encoder and decoder.  And
\&\s-1CHECK\s0 flags are correctly propagated.
.PP
Since version 2.22 (part of Encode 2.83), the \s-1MIME\s0 encoder should be fully
compliant to \s-1RFC 2047\s0 <https://tools.ietf.org/html/rfc2047> and
\&\s-1RFC 2231\s0 <https://tools.ietf.org/html/rfc2231>.  Due to the aforementioned
bugs in previous versions of the \s-1MIME\s0 encoder, there is a \fIless strict\fR
compatible mode for the \s-1MIME\s0 decoder which is used by default.  It should be
able to decode \s-1MIME\s0 encoded-words encoded by pre 2.22 versions of this module.
However, note that this is not correct according to
\&\s-1RFC 2047\s0 <https://tools.ietf.org/html/rfc2047>.
.PP
In default \fInot strict\fR mode the \s-1MIME\s0 decoder attempts to decode every substring
which looks like a \s-1MIME\s0 encoded-word.  Therefore, the \s-1MIME\s0 encoded-words do not
need to be separated by white space.  To enforce a correct \fIstrict\fR mode, set
variable \f(CW$Encode::MIME::Header::STRICT_DECODE\fR to 1 e.g. by localizing:
.PP
.Vb 2
\&  use Encode::MIME::Header;
\&  local $Encode::MIME::Header::STRICT_DECODE = 1;
.Ve
.SH "AUTHORS"
.IX Header "AUTHORS"
Pali <[email protected]>
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Encode,
\&\s-1RFC 822\s0 <https://tools.ietf.org/html/rfc822>,
\&\s-1RFC 2047\s0 <https://tools.ietf.org/html/rfc2047>,
\&\s-1RFC 2231\s0 <https://tools.ietf.org/html/rfc2231>