How to validate text isn't blank in Rails

if I do

  validates :body, :presence => true, :length => {:maximum => 30000, :message => ' is a bit long...'}
  validates :body, :length => {:minimum => 10, :message => ' is a bit short...'}

I still have a possibility of having a text which includes only spaces and /r or /n - non visible chars, which while the text isn't blank by definition, it is blank by looking at it

How can I validate that the text had a min and max length listed above and is also visible (not 10 spaces)

Rails adds the handy method blank? which checks for false, nil and empty strings as described here.
Rails also adds the handy validator allow_blank: false.

So in your case it should be:

validates :body, presence: true, allow_blank: false

Edit (original answer above):

As stated in the answer below, allow_blank: false is not needed as that's the default behaviour of presence: true.