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<title>MHonArc Resources: TEXTENCODE</title>
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<h1>TEXTENCODE</h1>
<!--X-TOC-Start-->
<ul>
<li><a href="#syntax">Syntax</a>
<li><a href="#description">Description</a>
<ul>
<li><small><a href="#vscharsetconverters">TEXTENCODE vs CHARSETCONVERTERS</a></small>
<li><small><a href="#writeencoder">Writing Encoders</a></small>
</ul>
<li><a href="#encoders">Available Encoders</a>
<ul>
<li><small><a href="#MHonArc::UTF8::to_utf8"><tt>MHonArc::UTF8::to_utf8</tt></a></small>
<li><small><a href="#MHonArc::Encode::from_to"><tt>MHonArc::Encode::from_to</tt></a></small>
</ul>
<li><a href="#default">Default Setting</a>
<li><a href="#rcvars">Resource Variables</a>
<li><a href="#examples">Examples</a>
<li><a href="#version">Version</a>
<li><a href="#seealso">See Also</a>
</ul>
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<hr>
<h2><a name="syntax">Syntax</a></h2>
<dl>
<dt><strong>Envariable</strong></dt>
<dd><p>N/A
</p>
</dd>
<dt><strong>Element</strong></dt>
<dd><p>
<code><TEXTENCODE></code><br>
<var>charset</var>; <var>perl_function</var>; <var>source_file</var><br>
<code></TEXTENCODE></code><br>
</p>
</dd>
<dt><strong>Command-line Option</strong></dt>
<dd><p>N/A
</p>
</dd>
</dl>
<!-- *************************************************************** -->
<hr>
<h2><a name="description">Description</a></h2>
<p>TEXTENCODE allows you to specify a destination character encoding
for all message text data. For each message read, textual data,
-- including message header fields and text body parts --
is translated from the charset(s) used in the message
to the charset specified by the TEXTENCODE resource.
</p>
<p>For example, the following resource setting,
</p>
<pre class="code">
<b><TextEncode></b>
utf-8; MHonArc::UTF8::to_utf8; MHonArc/UTF8.pm
<b></TextEncode></b>
</pre>
<p>converts message text to UTF-8 (Unicode) by using the
<a href="#MHonArc::UTF8::to_utf8"><tt>MHonArc::UTF8::to_utf8</tt></a>
function. List of available encoding functions is provided
<a href="#encoders">below</a>.
</p>
<table class="note" width="100%">
<tr valign="baseline">
<td><strong>NOTE:</strong></td>
<td width="100%"><p>The terms <em>character set (charset)</em> and
<em>character encoding</em> are used interchangeably within MHonArc
documentation. The reasoning is <em>charset</em> is used within
the MIME RFCs, but it blurs the concepts of <em>character encoding</em>
and <em>coded characer set</em> and probably a few other things.
For the purposes of this document, such details are not really
necessary, but if you want to learn more, see
<a href="http://www.unicode.org/unicode/reports/tr17/"
><cite>Unicode Technical Report #17: Character Encoding Model</cite></a>
and
<a href="http://www.w3.org/MarkUp/html-spec/charset-harmful.html"
><cite>Character Set Considered Harmful</cite></a>.
</p>
</td>
</tr>
</table>
<p>The syntax of the TEXTENCODE resource is as follows:
</p>
<P><var>charset</var><CODE>;</CODE><var>routine-name</var><CODE>;</CODE><var>file-of-routine</var> </P>
<P>The definition of each semi-colon-separated value is as follows:
</P>
<DL>
<DT><var>charset</var>
<DD><P>Character set name. See the
<a href="charsetconverters.html">CHARSETCONVERTERS</a> and
<a href="charsetaliases.html">CHARSETALIASES</a> for character sets
MHonArc is aware of. The official list of registered character
sets for use on the Internet is available from
<a href="http://www.iana.org/assignments/character-sets">IANA</a>.
</P>
<DT><var>routine-name</var>
<DD><P>The actual routine name of the encoder. The name
should be fully qualified by the package it is defined in
(e.g. "<tt class="icode">mypackage::filter</tt>"). </P>
<DT><var>file-of-routine</var>
<DD><P>The name of the file that defines
<var>routine-name</var>. If the file is not a full
pathname, MHonArc finds the file by looking in the
standard include paths of Perl, and the paths specified by the
<A HREF="perlinc.html">PERLINC</A>
resource.
</P>
</DL>
<H3><a name="vscharsetconverters">TEXTENCODE vs CHARSETCONVERTERS</a></H3>
<p>It is important to clarify the differences between
TEXTENCODE and <a href="charsetconverters.html">CHARSETCONVERTERS</a>
since reading about both resources may generate confusion.
</p>
<p>The main difference between TEXTENCODE and CHARSETCONVERTERS is that
TEXTENCODE is applied as the message is read, before the message
is converted to HTML. TEXTENCODE's primary role is converting
characters from one charset to another charset.
CHARSETCONVERTERS' role is to convert characters into HTML.
</p>
<p>The following crude text diagram shows the path message text
data takes when converted to HTML:
</p>
<pre>
message-text --> TEXTENCODE --> CHARSETCONVERTERS --> HTML
</pre>
<p>
<p>In addition, TEXTENCODE is applied only once to message text data.
Since MHonArc stores some message header information in the
<a href="dbfile.html">archive database</a>,
the message header text is stored in "raw" form,
which can include non-ASCII MIME encoded data like
the following:
</p>
<pre class="code">
From: =?US-ASCII?Q?Earl_Hood?= <earl<!--
-->@<!--
-->earlhood.com>
Subject: =?ISO-8859-1?B?SWYgeW91IGNhbiByZWFkIHRoaXMgeW8=?=
=?ISO-8859-2?B?dSB1bmRlcnN0YW5kIHRoZSBleGFtcGxlLg==?=
</pre>
<p>Therefore, when a resource variable like <tt>$SUBJECT$</tt> is
used, the <tt class="icode">=?ISO-8859-1?B?SWYgeW9...</tt> data
must be parsed and converted every time.
</p>
<p>If TEXTENCODE is active, the message subject
<tt class="icode">=?ISO-8859-1?B?SWYgeW9...</tt> is parsed and translated
to the destination encoding when the message is first parsed,
with the final result stored in the
archive database. The non-ASCII MIME encoding is removed, and it no
longer has to be parsed each time <tt>$SUBJECT$</tt> is used.
</p>
<p>In either case, CHARSETCONVERTERS is still invoked, but in
the former <tt class="icode">=?ISO-8859-1?B?SWYgeW9...</tt> case,
CHARSETCONVERTERS must handle the various character sets specified.
In the TEXTENCODE case, CHARSETCONVERTERS only has to deal with the
<var>charset</var> specified in the TEXTENCODE resource. Therefore,
using TEXTENCODE vastly simplifies the CHARSETCONVERTERS resource
value, where only the <tt>default</tt> converter needs to be
defined. This is highlighted in the Usage sections for the
<a href="#encoders"><cite>Available Encoders</cite></a> listed
below.
</p>
<H3><a name="writeencoder">Writing Encoders</a></H3>
<table class="note" width="100%">
<tr valign="baseline">
<td><strong>NOTE:</strong></td>
<td width="100%"><p>Before writing your own, first check out the
<a href="#encoders">list of available encoders</a> to see
if one already exists that satisfies your needs.
</p>
</td>
</tr>
</table>
<p>If you want to write your own text encode for use in MHonArc,
you need to know the Perl programming language. The following
information assumes you know Perl.
</P>
<H4>Function Interface of Encoder</H4>
<P>MHonArc interfaces with encoder by calling a routine
with a specific set of arguments. The prototype of the interface
routine is as follows: </P>
<PRE class="code">
sub <var>text_encoder</var> {
my(<b>$text_ref</b>, <b>$from_charset</b>, <b>$to_charset</b>) = <!--
-->@<!--
-->_;
<var># code here
# The last statement should be the return value, unless an
# explicit return is done. See the following for the format of the
# return value.</var>
}
</PRE>
<H5>Parameter Descriptions</H5>
<table cellspacing=1 border=0 cellpadding=4>
<tr valign=top>
<td><strong><code>$text_ref</code></strong></td>
<td><p>A reference to the string to encode. The routine should
do the text encoding in-place.
</p>
</tr>
<tr valign=top>
<td><strong><code>$from_charset</code></strong></td>
<td><p>Name of the source character encoding of <tt>$$text_ref</tt>.
</p>
</td>
</tr>
<tr valign=top>
<td><strong><code>$to_charset</code></strong></td>
<td><p>The destination encoding for <tt>$$text_ref</tt>.
<tt>$to_charset</tt> is be set to the <var>charset</var>
component of the TEXTENCODE resource value.
</p>
</td>
</tr>
</table>
<H5>Return Value</H5>
<p>On error, the routine should return <tt>undef</tt>. Otherwise,
it should return any true value.
</p>
<table class="caution" width="100%">
<tr valign="baseline">
<td><strong style="color: red;">CAUTION:</strong></td>
<td width="100%"><p>If your routine encounters an error, try to
preserve the original value of <tt>$$text_ref</tt> or data may
be lost in archive output.
</p>
</td>
</tr>
</table>
<!-- *************************************************************** -->
<hr>
<h2><a name="encoders">Available Encoders</a></h2>
<p>The standard MHonArc distribution provides the following character
encoding routines:
</p>
<h3><a name="MHonArc::UTF8::to_utf8"><tt>MHonArc::UTF8::to_utf8</tt></a></h3>
<dl>
<dt><strong>Usage</strong></dt>
<dd><pre class="code">
<b><TextEncode></b>
utf-8; MHonArc::UTF8::to_utf8; MHonArc/UTF8.pm
<b></TextEncode></b>
<-- With data translated to UTF-8, it simplifies CHARSETCONVERTERS -->
<<a href="charsetconverters.html">CharsetConverters</a> override>
default; <a href="charsetconverters.html#mhonarc::htmlize">mhonarc::htmlize</a>
</CharsetConverters>
<-- Need to also register UTF-8-aware text clipping function -->
<<a href="textclipfunc.html">TextClipFunc</a>>
MHonArc::UTF8::clip; MHonArc/UTF8.pm
</TextClipFunc>
</pre>
</dd>
<dt><strong>Description</strong></dt>
<dd><p><tt>MHonArc::UTF8::to_utf8</tt> converts text to
UTF-8 (Unicode). Unicode is designed to represents all characters
of all languages. UTF-8 is an encoding of Unicode that is 8-bit clean
and immune to byte ordering of computer systems. Most modern
browsers support UTF-8 and UTF-8 is a good choice if dealing with
multi-lingual archives.
</p>
<p><tt>MHonArc::UTF8::to_utf8</tt> is designed to work with
older versions of Perl that do not support UTF-8, but also
utilizing UTF-8 aware modules in later versions of Perl.
<tt>MHonArc::UTF8</tt> checks for the following, in order of
preference, when loaded:
</p>
<ol>
<li><p><b><tt>Encode</tt></b>: <tt>Encode</tt> comes standard
with Perl v5.8 and provides conversion capbilities between
various character encodings.
</p>
<li><p><b><tt>Unicode::MapUTF8</tt></b>: <tt>Unicode::MapUTF8</tt>
is available via <a href="http://www.cpan.org/">CPAN</a>,
and provides conversion capabilities between various
character encodings to, and from, UTF-8. <tt>Unicode::MapUTF8</tt>
depends on other modules, see <tt>Unicode::MapUTF8</tt>
module documentation for details.
</p>
<li><p><em>fallback</em>: If none of the above are present, then
the fallback implementation is used. Fallback code is written in
pure Perl, so it may not be as efficient as the modules
listed above. However, many popular character encodings are
supported.
</p>
<table class="note" width="100%">
<tr valign="baseline">
<td><strong>NOTE:</strong></td>
<td width="100%"><p>Fallback code is automatically
invoked for character encodings not recognized by the
above listed modules.
</p>
</td>
</tr>
</table>
</ol>
</dd>
</dl>
<h3><a name="MHonArc::Encode::from_to"><tt>MHonArc::Encode::from_to</tt></a></h3>
<dl>
<dt><strong>Usage</strong></dt>
<dd><pre class="code">
<b><TextEncode></b>
<var>charset</var>; MHonArc::Encode::from_to; MHonArc/Encode.pm
<b></TextEncode></b>
</pre>
</dd>
<dt><strong>Description</strong></dt>
<dd><p><tt>MHonArc::Encode::from_to</tt> converts texts to
the specified <var>charset</var> encoding. This routine is
useful for locales that prefer to have all archive data translated
to the locale-prefered character set.
</p>
<table class="note" width="100%">
<tr valign="baseline">
<td><strong>NOTE:</strong></td>
<td width="100%"><p>Since most locale-specific character sets are
not universal sets (like Unicode), characters may be lost during
translation.
</p>
</td>
</tr>
</table>
<p> </p>
<table class="note" width="100%">
<tr valign="baseline">
<td><strong>NOTE:</strong></td>
<td width="100%"><p>For UTF-8 encoding,
use <a href=#MHonArc::UTF8::to_utf8"><tt>MHonArc::UTF8::to_utf8</tt></a>
instead since it provides more robust fallback capabilities and
works under non-UTF-8-aware versions of Perl.
</p>
</td>
</tr>
</table>
<p><tt>MHonArc::Encode:from_to</tt> works only if one of the
following modules are available, in order of preference, when
<tt>MHonArc::Encode</tt> is located:
</p>
<ol>
<li><p><b><tt>Encode</tt></b>: <tt>Encode</tt> comes standard
with Perl v5.8 and provides conversion capbilities between
various character encodings.
</p>
<li><p><b><tt>Unicode::MapUTF8</tt></b>: <tt>Unicode::MapUTF8</tt>
is available via <a href="http://www.cpan.org/">CPAN</a>,
and provides conversion capabilities between various
character encodings to, and from, UTF-8. <tt>Unicode::MapUTF8</tt>
depends on other modules, see <tt>Unicode::MapUTF8</tt>
module documentation for details.
</p>
</ol>
<p><b>No</b> fallback implentations are available.
</p>
<p>If converting to a multi-byte encoding, the default
<a href="textclipfunc.html">TEXTCLIPFUNC</a> may not be adequate.
Therefore, you may have to avoid using resource variables with
maximum length specifiers.
</p>
<table class="note" width="100%">
<tr valign="baseline">
<td><strong>NOTE:</strong></td>
<td width="100%"><p>There is support for <tt>ISO-2022-JP</tt>
(Japanese). The following resource settings should serve
as a basis when encoding to <tt>iso-2022-jp</tt>:
</p>
<pre class="code">
<b><TextEncode></b>
iso-2022-jp; MHonArc::Encode::from_to; MHonArc/Encode.pm
<b></TextEncode></b>
<-- Make sure to use iso-2022-jp aware charset converter -->
<<a href="charsetconverters.html">CharsetConverters</a> override>
default; <a href="charsetconverters.html#iso2022jp">iso_2022_jp::str2html</a>; iso2022jp.pl
</CharsetConverters>
<-- Need to also register iso-2022-jp-aware text clipping function -->
<<a href="textclipfunc.html">TextClipFunc</a>>
iso_2022_jp::clip; iso2022jp.pl
</TextClipFunc>
</pre>
<p>For more information about using MHonArc in a Japanese locale,
see (documents in Japanese):
<a href="http://www.mhonarc.jp/"><http://www.mhonarc.jp/></a>.
</p>
</td>
</tr>
</table>
</dd>
</dl>
<!-- *************************************************************** -->
<hr>
<h2><a name="default">Default Setting</a></h2>
<p>Nil.
</p>
<!-- *************************************************************** -->
<hr>
<h2><a name="rcvars">Resource Variables</a></h2>
<p>N/A
</p>
<!-- *************************************************************** -->
<hr>
<h2><a name="examples">Examples</a></h2>
<p>See the
<a href="../rcfileexs/utf-8-encode.mrc.html"><tt>utf-8-encode.mrc</tt></a>
for the basis of generating UTF-8-based archives via TEXTENCODE.
</p>
<p>If in a Japanese locale, the following generates archives in
<tt>iso-2022-jp</tt>:
</p>
<pre class="code">
<b><TextEncode></b>
iso-2022-jp; MHonArc::Encode::from_to; MHonArc/Encode.pm
<b></TextEncode></b>
<-- Make sure to use iso-2022-jp aware charset converter -->
<b><<a href="charsetconverters.html">CharsetConverters</a> override></b>
default; <a href="charsetconverters.html#iso2022jp">iso_2022_jp::str2html</a>; iso2022jp.pl
<b></CharsetConverters></b>
<-- Need to also register iso-2022-jp-aware text clipping function -->
<b><<a href="textclipfunc.html">TextClipFunc</a>></b>
iso_2022_jp::clip; iso2022jp.pl
<b></TextClipFunc></b>
<b><a href="idxpgbegin.html"><IdxPgBegin></a></b>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title><b><a href="../rcvars.html#IDXTITLE">$IDXTITLE$</a></b></title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-2022-jp">
</head>
<body>
<h1><b><a href="../rcvars.html#IDXTITLE">$IDXTITLE$</a></b></h1>
<b></IdxPgBegin></b>
<b><a href="tidxpgbegin.html"><TIdxPgBegin></a></b>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title><b><a href="../rcvars.html#TIDXTITLE">$TIDXTITLE$</a></b></title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-2022-jp">
</head>
<body>
<h1><b><a href="../rcvars.html#TIDXTITLE">$TIDXTITLE$</a></b></h1>
<b></TIdxPgBegin></b>
<b><a href="msgpgbegin.html"><MsgPgBegin></a></b>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title><b><a href="../rcvars.html#SUBJECTNA">$SUBJECTNA$</a></b></title>
<link rev="made" href="mailto:<b><a href="../rcvars.html#FROMADDR">$FROMADDR$</a></b>">
<meta http-equiv="Content-Type" content="text/html; charset=iso-2022-jp">
</head>
<body>
<b></MsgPgBegin></b>
</pre>
<!-- *************************************************************** -->
<hr>
<h2><a name="version">Version</a></h2>
<p>2.6.0
</p>
<!-- *************************************************************** -->
<hr>
<h2><a name="seealso">See Also</a></h2>
<p>
<a href="charsetconverters.html">CHARSETCONVERTERS</a>,
<a href="perlinc.html">PERLINC</a>,
<a href="textclipfunc.html">TEXTCLIPFUNC</a>
</p>
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<address>
$Date: 2005/05/13 18:50:39 $<br>
<img align="top" src="../monicon.png" alt="">
<a href="http://www.mhonarc.org/"><strong>MHonArc</strong></a><br>
Copyright © 2002, <a href="http://www.earlhood.com/"
>Earl Hood</a>, <a href="mailto:mhonarc%40mhonarc.org"
>mhonarc<!--
-->@<!--
-->mhonarc.org</a><br>
</address>
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