title: Given a webpage url, how can I fetch it's content data to generate link preview like in Facebook and Slack?
body: <p>For example, in Slack, when I paste the following url 
  <a href="http://time.com/4023256/hillary-clinton-donald-trump-unfortunate-development/?xid=homepage" rel="nofollow noreferrer">http://time.com/4023256/hillary-clinton-donald-trump-unfortunate-development/?xid=homepage</a></p>
  
  <p>slack's shows a preview of it's content
  <a href="https://i.stack.imgur.com/8R84o.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8R84o.png" alt="enter image description here"></a></p>
  
  <p>How can I implement such function in my iOS app? </p>