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MIME::Tools::tips (3)

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NAME

MIME::Tools::tips - words of wisdom for users of MIME-tools

SYNOPSIS

This is part of the MIME-tools documentation. See MIME::Tools for the full table of contents.

DESCRIPTION

Here is all the good advice I have to give, conveniently collected into one easy-to-ignore place. :-)

Take a look at the examples

The MIME-Tools distribution comes with an ``examples'' directory. The scripts in there are basically just tossed-together, but they'll give you some ideas of how to use the parser.

Run with warnings enabled

Always run your Perl script with "-w". If you see a warning about a deprecated method, change your code ASAP. This will ease upgrades tremendously.

Avoid non-standard encodings

Don't try to MIME-encode using the non-standard MIME encodings. It's just not a good practice if you want people to be able to read your messages.

Plan for thrown exceptions

For example, if your mail-handling code absolutely must not die, then perform mail parsing like this:

    $entity = eval { $parser->parse(\*INPUT) };

Parsing is a complex process, and some components may throw exceptions if seriously-bad things happen. Since ``seriously-bad'' is in the eye of the beholder, you're better off catching possible exceptions instead of asking me to propagate "undef" up the stack. Use of exceptions in reusable modules is one of those religious issues we're never all going to agree upon; thankfully, that's what "eval{}" is good for.

Check the parser results for warnings/errors

As of 5.3xx, the parser tries extremely hard to give you a MIME::Entity. If there were any problems, it logs warnings/errors to the underlying ``results'' object (see MIME::Parser::Results). Look at that object after each parse. Print out the warnings and errors, especially if messages don't parse the way you thought they would.

Don't plan on printing exactly what you parsed!

Parsing is a (slightly) lossy operation. Because of things like ambiguities in base64-encoding, the following is not going to spit out its input unchanged in all cases:

    $entity = $parser->parse(\*STDIN);
    $entity->print(\*STDOUT);

If you're using MIME::Tools to process email, remember to save the data you parse if you want to send it on unchanged. This is vital for things like PGP-signed email.

(Sing it with me, kids: you can't / always print / what you paaaarsed...)

Understand how international characters are represented

The MIME standard allows for text strings in headers to contain characters from any character set, by using special sequences which look like this:

    =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?=

To be consistent with the existing Mail::Field classes, MIME::Tools does not automatically unencode these strings, since doing so would lose the character-set information and interfere with the parsing of fields (see ``decode_headers'' in MIME::Parser for a full explanation). That means you should be prepared to deal with these encoded strings.

The most common question then is, how do I decode these encoded strings? The answer depends on what you want to decode them to: ASCII, Latin1, UTF-8, etc. Be aware that your ``target'' representation may not support all possible character sets you might encounter; for example, Latin1 (ISO-8859-1) has no way of representing Big5 (Chinese) characters. A common practice is to represent ``untranslateable'' characters as ``?''s, or to ignore them completely.

To unencode the strings into some of the more-popular Western byte representations (e.g., Latin1, Latin2, etc.), you can use the decoders in MIME::WordDecoder (see MIME::WordDecoder). The simplest way is by using "unmime()", a function wrapped around your ``default'' decoder, as follows:

    use MIME::WordDecoder;
    ...
    $subject = unmime $entity->head->get('subject');

One place this is done automatically is in extracting the recommended filename for a part while parsing. That's why you should start by setting up the best ``default'' decoder if the default target of Latin1 isn't to your liking.