added URL validation to webpage part

app.rb

@@ -34,6 +34,20 @@ class App < Roda
         flash['message'] = "Please enter a valid URL";
         r.redirect '/'
       end
+
+      begin
+        OpenURI.open_uri(url)
+      rescue URI::BadURIError
+        flash['message'] = "Invalid URL"
+        r.redirect '/'
+      rescue OpenURI::HTTPError
+        flash['message'] = "URL not found"
+        r.redirect '/'
+      rescue SocketError => e
+        flash['message'] = "URL does not resolve"
+        r.redirect '/'
+      end
+
       if links.filter(:url => url).first.nil?
         code = SecureRandom.urlsafe_base64 4
         links.insert(url: url, code: code)