Using DOMDocument to Modify HTML with PHP

By  on  
One of the first things you learn when wanting to implement a service worker on a website is that the site requires SSL (an https address).  Ever since I saw the blinding speed service workers can provide a website, I've been obsessed with readying my site for SSL.  Enforcing SSL with .htaccess was easy -- the hard part is updating asset links in blog content.  You start out by feeling as though regular expressions will be the quick cure but anyone that has experience with regular expression knows that working with URLs is a nightmare and regex is probably the wrong decision. The right decision is DOMDocument, a native PHP object which allows you to work with HTML in a logical, pleasant fashion.  You start by loading the HTML into a DOMDocument instance and then using its predictable functions to make things happen.
// Formats post content for SSL
function format_post_content($content = '') {
  $document = new DOMDocument();
  // Ensure UTF-8 is respected by using 'mb_convert_encoding'
  $document->loadHTML(mb_convert_encoding($content, 'HTML-ENTITIES', 'UTF-8'));
  
  $tags = $document->getElementsByTagName('img');
  foreach ($tags as $tag) {
    $tag->setAttribute('src', 
      str_replace('http://davidwalsh.name', 
                  'https://davidwalsh.name', 
                  $tag->getAttribute('src')
      )
    );
  }
  return $document->saveHTML();
}
In my example above, I find all img elements and replace their protocol with https://.  I will end up doing the same with iframe src, a href, and a few other rarely used tags.  When my modifications are done, I call saveHTML to get the new string. Don't fall into the trap of trying to use regular expressions with HTML -- you're in for a future of failure.  DOMDocument is lightweight and will make your code infinitely more maintainable.

Recent Features

  • By
    How to Create a Twitter Card

    One of my favorite social APIs was the Open Graph API adopted by Facebook.  Adding just a few META tags to each page allowed links to my article to be styled and presented the way I wanted them to, giving me a bit of control...

  • By
    9 Mind-Blowing Canvas Demos

    The <canvas> element has been a revelation for the visual experts among our ranks.  Canvas provides the means for incredible and efficient animations with the added bonus of no Flash; these developers can flash their awesome JavaScript skills instead.  Here are nine unbelievable canvas demos that...

Incredible Demos

  • By
    Background Animations Using MooTools

    One of the sweet effects made easy by JavaScript frameworks like MooTools and jQuery is animation. I ran across this great jQuery tutorial that walks you through animating a background image of a page. Here's a quick MooTools code snippet that...

  • By
    Xbox Live Gamer API

    My sharpshooter status aside, I've always been surprised upset that Microsoft has never provided an API for the vast amount of information about users, the games they play, and statistics within the games. Namely, I'd like to publicly shame every n00b I've baptized with my...

Discussion

  1. Manny Fleurmond

    So do you know if there is a performance hit with creating an element using this vs creating a string of html?

  2. zakius

    The right decision is skipping domain entirely if it isn’t hosted on some subdomain (/path/to/asset), and skipping protocol if it is ((//example.com/path/to/asset)

  3. David, rather than str_replace all your (internal) http:// strings with https:// you should replace them with // – that way your links become protocol-agnostic — a more future-proof solution.

  4. Why don’t you use the search-replace function in WP-CLI?

  5. Silvestre

    Why not remove the protocol completely?

    //davidwalsh.name/ would default to whatever protocol is used in the address bar.

  6. I agree that // would be better but some RSS feed readers use http, others https. I’m asserting complete control.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!