Better documentation for UploadedFile

[fabpot]

People have a hard time with the way we manage uploaded file extension and mime type. And also the difference between what the client send and what we guess. I've just sent a PR on symfony/symfony to clarify the PHPdoc, but I think we need some documentation here about this topic.

see symfony/symfony#7809 (this PR also references interesting tickets that might help writing the doc).

[wouterj]

This information should be added to /cookbook/doctrine/file_uploads and /reference/forms/types/file.

[wouterj]

I disagree with my previous comment now.

We should instead add a new section to http://symfony.com/doc/current/components/http_foundation/introduction.html, talking about files. It should then explain how the mime type guessing works.

[valioDOTch]

+1

[HeahDude]

Some references from #7953, that should be clarified too:

• How this MIME type detection works: how does Symfony selects the guesser (file extension based, binary file detection, etc.), how to configure/change that behavior.
• What can I do when the guess has issues; for example for Microsoft Office file types: MS Office upload and mime type detection issues symfony#22702
• How can I define my own MIME types; to avoid issues when FileinfoMimeTypeGuesser fails: FileinfoMimeTypeGuesser fails for max files symfony#22888

[javiereguiluz]

Closing this in favor of the file uploading meta-issue: #8255.