Ruby regexp does not catch targeted expression

Question

I am using a validation to reject any string containing  or  (equivalent in html characters of the p html tag).

I tried with a string that did contain it and strings with  tag are rejected but not those with 

validates_format_of :message_content,
                      :with => /\A((?!<p>).)*\z/i,
                      :message => "pb1"             


validates_format_of :message_content,
                      :with => /\A((?!&lt;p&gt;).)*\z/i,
                      :message => "pb2"

Should I escape some of the special characters of ! ,which could create issues for the regexp ? How ?

how about using a custom validator and gsubbing the escaped html entities before performing the regex? — max pleaner
– max pleaner, Commented Dec 12, 2017 at 16:29
I see no need for escaping characters. Doesn't r = Regexp.new("|") #=> /|/ work (i.e., str !~ r)? — Cary Swoveland
– Cary Swoveland, Commented Dec 12, 2017 at 16:55
I think you should take a different approach using the sanitize helper. Insert something like before_validation :sanitize_content, :on => :create and then in your sanitize_content method use ActionController::Base.helpers.sanitize(field, tags) configured appropriately. Your meager attempt at preventing p tags is easily fooled (e.g. by whitespace ) — Mark Thomas
– Mark Thomas, Commented Dec 12, 2017 at 17:50
^^ This. I'm 95% sure you're asking the wrong question here. Trying to block HTML input via a regex validation screams of bad design; there's almost certainly a better solution to your problem. — Tom Lord
– Tom Lord, Commented Dec 12, 2017 at 17:52

Thomas · Accepted Answer · 2017-12-12 17:42:54Z

2

You can try to validate that a regexp is not match. You will have simplier regexp that are easier to implement :

validates :message_content, format: { without: /<p>/i, message: 'pb1' }
validates :message_content, format: { without: /&lt;p&gt;/i, message: 'pb2' }

answered Dec 12, 2017 at 17:42

Thomas

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