cleanup: Filter invalid file names for inbound file transfers

[JFreegman]

Addressing #111

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This change is 

[zoff99]

Reviewed 1 of 1 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained

[zoff99]

maybe use a whilelist of characters instead of a blacklist.
because not sure which OS has what special bad chars.

maybe '<' '>' '|' and whatnot ...

also windos filename can not contain certain chars anyway.

[JFreegman]

maybe use a whilelist of characters instead of a blacklist.
because not sure which OS has what special bad chars.

maybe '<' '>' '|' and whatnot ...

also windos filename can not contain certain chars anyway.

Toxic is only concerned with Posix compatibility. As far as Posix/unix-like goes, only the - character at the start of a file name and the '/' character and are disallowed. Fully portable Posix only supports ASCII alphanumeric characters and -_., but we still want to allow unicode for other languages, and there are way too many unicode characters for a whitelist. There's also probably nothing wrong with allowing punctuation. I think the focus should be on preventing malicious behaviour.