In #134, @tunz discovered that Rocket does not properly prevent path traversal
or local file inclusion attacks. The issue is caused by a failure to check for
some dangerous characters after decoding. In this case, the path separator '/'
was left as-is after decoding. As such, an attacker could construct a path with
containing any number of `..%2f..` sequences to traverse the file system.
This commit resolves the issue by ensuring that the decoded segment does not
contains any `/` characters. It further hardens the `FromSegments`
implementation by checking for additional risky characters: ':', '>', '<' as the
last character, and '\' on Windows. This is in addition to the already present
checks for '.' and '*' as the first character.
The behavior for a failing check has also changed. Previously, Rocket would skip
segments that contained illegal characters. In this commit, the implementation
instead return an error.
The `Error` type of the `PathBuf::FromSegment` implementations was changed to a
new `SegmentError` type that indicates the condition that failed.
Closes#134.
Sergio Benitez