## Stream Filters Stream Filters — How to use Stream Filters |

## Overview of Filters

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.

GMime comes equipped with some basic filters such as GMimeFilterBasic, GMimeFilterCharset, GMimeFilterDos2Unix, GMimeFilterUnix2Dos, GMimeFilterFrom and GMimeFilterHTML.

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.

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.

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 set of filters to handle this for you: GMimeFilterDos2Unix and GMimeFilterUnix2Dos.

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.

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.