ApacheConEU - part 10
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In the next session Jukka introduced Tika - a toolkit for parsing content from files including a heuristics based component for guessing the file type: Based on file extension, magic and certain patterns in the file the file type can be guessed rather reliably. Some anecdotes:
- not all mime types are registered with IANA, there are of course conflicting file extensions,
- Microsoft Word not only localises their interface but also the magic in the file,
- html detection is particularly hard as there is quite some overlap with other file formats (e.g. there are such things as html mails...)
- xhtml parsing is quite reliable by using an actual xml parser for the first few bytes to identify the namespace of the document
- identifying odf documents is easy - though zipped the magic is preserved uncompressed at a pre-defined location in the file
- for ooxml the file has to be unpacked to identify it
- plain text content is hardest - there are a few heuristics based on UTF BOMs, ASCII stats, line ending stats, byte histograms, still it's not fool proof.
In addition Tika can extract metadata: For text that can be as easy as encoding, length, content type and comments. For images that is extended by image size and potentially EXIF data. For pdf data it gets even more comprehensive including information on the file creator, save date and more (same applies for MS office documents). Most document metadata is based on the doublin core standard, for images there’s EXIF and IPCT - soon there’ll also be xmb related data that can be discovered.