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<refentry id="gmime-filters">
<refmeta>
<refentrytitle>GMime Stream Filters</refentrytitle>
<refmiscinfo>GMime Library</refmiscinfo>
</refmeta>
<refnamediv>
<refname>GMime Stream Filters</refname>
<refpurpose>How to use GMime Stream Filters</refpurpose>
</refnamediv>
<refsect1 id="filter-overview">
<title>Overview of Filters</title>
<para>Stream filters are an efficient way of converting data from
one format to another. To use a stream filter, you must first
construct a GMimeStreamFilter stream and then add the desired
filters to it.</para>
<para>GMime comes equipped with some basic filters such as
GMimeFilterBasic, GMimeFilterCharset, GMimeFilterCRLF,
GMimeFilterFrom and GMimeFilterHTML.</para>
<para>The GMimeFilterBasic filter is actually a collection of
filters for common transfer encodings used by MIME. So far, it is
able to handle encoding and decoding of base64, quoted-printable
and (x-)uuencode.</para>
<para>For internationalization support, GMime also includes a
filter for converting between any 2 charsets,
GMimeFilterCharset. With this filter, mail user agents can allow
the user to read the message content in his or her own
charset.</para>
<para>A common conversion needed for text is CRLF -> LF and LF ->
CRLF which is needed for most (all?) internet protocols. Luckily,
GMime comes equipped with a filter to handle this for you,
GMimeFilterCRLF. You'll notice that GMimeFilterCRLF can also
handle dot-escaping, which is especially useful for SMTP
(rfc821).</para>
<para>On Unix systems, mail often resides in spools in mbox
format. Mbox uses a line that starts with "From " to delimit
messages which means that message bodies are forbidden to contain
lines starting with "From ". The common way to escape these from
lines in message bodies is to prepend the line with a greater-than
character ('>') producing ">From ". You'll find GMimeFilterFrom
handy when dealing with this.</para>
<para>The GMimeFilterHTML filter converts a normal text stream
into an html stream. This is especially useful if you are using a
widget such as GtkHTML to display the contents of an email
message.</para>
</refsect1>
</refentry>
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