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<title>Speeding up HTML Purifier - HTML Purifier</title>

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<h1 class="subtitled">Speeding up HTML Purifier</h1>
<div class="subtitle">...also known as the HELP ME LIBRARY IS TOO SLOW MY PAGE TAKE TOO LONG page</div>

<div id="filing">Filed under End-User</div>
<div id="index">Return to the <a href="index.html">index</a>.</div>
<div id="home"><a href="http://htmlpurifier.org/">HTML Purifier</a> End-User Documentation</div>

<p>HTML Purifier is a very powerful library. But with power comes great 
responsibility, in the form of longer execution times.  Remember, this 
library isn't lightly grazing over submitted HTML: it's deconstructing 
the whole thing, rigorously checking the parts, and then putting it back 
together. </p>

<p>So, if it so turns out that HTML Purifier is kinda too slow for outbound 
filtering, you've got a few options: </p>

<h2>Inbound filtering</h2>

<p>Perform filtering of HTML when it's submitted by the user. Since the 
user is already submitting something, an extra half a second tacked on 
to the load time probably isn't going to be that huge of a problem.  
Then, displaying the content is a simple a manner of outputting it 
directly from your database/filesystem. The trouble with this method is 
that your user loses the original text, and when doing edits, will be 
handling the filtered text.  While this may be a good thing, especially 
if you're using a WYSIWYG editor, it can also result in data-loss if a 
user makes a typo. </p>

<p>Example (non-functional):</p>

<pre>&lt;?php
    /**
     * FORM SUBMISSION PAGE
     * display_error($message) : displays nice error page with message
     * display_success() : displays a nice success page
     * display_form() : displays the HTML submission form
     * database_insert($html) : inserts data into database as new row
     */
    if (!empty($_POST)) {
        require_once '/path/to/library/HTMLPurifier.auto.php';
        require_once 'HTMLPurifier.func.php';
        $dirty_html = isset($_POST['html']) ? $_POST['html'] : false;
        if (!$dirty_html) {
            display_error('You must write some HTML!');
        }
        $html = HTMLPurifier($dirty_html);
        database_insert($html);
        display_success();
        // notice that $dirty_html is *not* saved
    } else {
        display_form();
    }
?&gt;</pre>

<h2>Caching the filtered output</h2>

<p>Accept the submitted text and put it unaltered into the database, but 
then also generate a filtered version and stash that in the database.  
Serve the filtered version to readers, and the unaltered version to 
editors.  If need be, you can invalidate the cache and have the cached 
filtered version be regenerated on the first page view.  Pros? Full data 
retention. Cons? It's more complicated, and opens other editors up to 
XSS if they are using a WYSIWYG editor (to fix that, they'd have to be 
able to get their hands on the *really* original text served in 
plaintext mode). </p>

<p>Example (non-functional):</p>

<pre>&lt;?php
    /**
     * VIEW PAGE
     * display_error($message) : displays nice error page with message
     * cache_get($id) : retrieves HTML from fast cache (db or file)
     * cache_insert($id, $html) : inserts good HTML into cache system
     * database_get($id) : retrieves raw HTML from database
     */
    $id = isset($_GET['id']) ? (int) $_GET['id'] : false;
    if (!$id) {
        display_error('Must specify ID.');
        exit;
    }
    $html = cache_get($id); // filesystem or database
    if ($html === false) {
        // cache didn't have the HTML, generate it
        $raw_html = database_get($id);
        require_once '/path/to/library/HTMLPurifier.auto.php';
        require_once 'HTMLPurifier.func.php';
        $html = HTMLPurifier($raw_html);
        cache_insert($id, $html);
    }
    echo $html;
?&gt;</pre>

<h2>Summary</h2>

<p>In short, inbound filtering is the simple option and caching is the
robust option (albeit with bigger storage requirements). </p>

<p>There is a third option, independent of the two we've discussed: profile 
and optimize HTMLPurifier yourself. Be sure to report back your results 
if you decide to do that! Especially if you port HTML Purifier to C++. 
<tt>;-)</tt></p>

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