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'
  $doc->loadHTML(mb_convert_encoding($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
    CSS vs. JS Animation: Which is Faster?

    How is it possible that JavaScript-based animation has secretly always been as fast — or faster — than CSS transitions? And, how is it possible that Adobe and Google consistently release media-rich mobile sites that rival the performance of native apps? This article serves as a point-by-point...

  • By
    Designing for Simplicity

    Before we get started, it's worth me spending a brief moment introducing myself to you. My name is Mark (or @integralist if Twitter happens to be your communication tool of choice) and I currently work for BBC News in London England as a principal engineer/tech...

Incredible Demos

  • By
    Making the Firefox Logo from HTML

    When each new t-shirt means staving off laundry for yet another day, swag quickly becomes the most coveted perk at any tech company. Mozilla WebDev had pretty much everything going for it: brilliant people, interesting problems, awesome office. Everything except a t-shirt. That had to change. The basic...

  • By
    Select Dropdowns, MooTools, and CSS Print

    I know I've harped on this over and over again but it's important to enhance pages for print. You can do some things using simple CSS but today's post features MooTools and jQuery. We'll be taking the options of a SELECT element and generating...

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!