docs/dev-config-schema.html

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   7     <meta name="description" content="Describes config schema framework in HTML Purifier." />
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   9     <title>Config Schema - HTML Purifier</title>
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  12
  13     <h1>Config Schema</h1>
  14
  15     <div id="filing">Filed under Development</div>
  16     <div id="index">Return to the <a href="index.html">index</a>.</div>
  17     <div id="home"><a href="http://htmlpurifier.org/">HTML Purifier</a> End-User Documentation</div>
  18
  19     <p>
  20       HTML Purifier has a fairly complex system for configuration. Users
  21       interact with a <code>HTMLPurifier_Config</code> object to
  22       set configuration directives. The values they set are validated according
  23       to a configuration schema, <code>HTMLPurifier_ConfigSchema</code>.
  24     </p>
  25
  26     <p>
  27       The schema is mostly transparent to end-users, but if you're doing development
  28       work for HTML Purifier and need to define a new configuration directive,
  29       you'll need to interact with it. We'll also talk about how to define
  30       userspace configuration directives at the very end.
  31     </p>
  32
  33     <h2>Write a directive file</h2>
  34
  35     <p>
  36       Directive files define configuration directives to be used by
  37       HTML Purifier. They are placed in <code>library/HTMLPurifier/ConfigSchema/schema/</code>
  38       in the form <code><em>Namespace</em>.<em>Directive</em>.txt</code> (I
  39       couldn't think of a more descriptive file extension.)
  40       Directive files are actually what we call <code>StringHash</code>es,
  41       i.e. associative arrays represented in a string form reminiscent of
  42       <a href="http://qa.php.net/write-test.php">PHPT</a> tests. Here's a
  43       sample directive file, <code>Test.Sample.txt</code>:
  44     </p>
  45
  46     <pre>Test.Sample
  47 TYPE: string/null
  48 DEFAULT: NULL
  49 ALLOWED: 'foo', 'bar'
  50 VALUE-ALIASES: 'baz' => 'bar'
  51 VERSION: 3.1.0
  52 --DESCRIPTION--
  53 This is a sample configuration directive for the purposes of the
  54 &lt;code&gt;dev-config-schema.html&lt;code&gt; documentation.
  55 --ALIASES--
  56 Test.Example</pre>
  57
  58     <p>
  59       Each of these segments has a specific meaning:
  60     </p>
  61
  62     <table class="table">
  63       <thead>
  64         <tr>
  65           <th>Key</th>
  66           <th>Example</th>
  67           <th>Description</th>
  68         </tr>
  69       </thead>
  70       <tbody>
  71         <tr>
  72           <td>ID</td>
  73           <td>Test.Sample</td>
  74           <td>The name of the directive, in the form Namespace.Directive
  75           (implicitly the first line)</td>
  76         </tr>
  77         <tr>
  78           <td>TYPE</td>
  79           <td>string/null</td>
  80           <td>The type of variable this directive accepts. See below for
  81           details. You can also add <code>/null</code> to the end of
  82           any basic type to allow null values too.</td>
  83         </tr>
  84         <tr>
  85           <td>DEFAULT</td>
  86           <td>NULL</td>
  87           <td>A parseable PHP expression of the default value.</td>
  88         </tr>
  89         <tr>
  90           <td>DESCRIPTION</td>
  91           <td>This is a...</td>
  92           <td>An HTML description of what this directive does.</td>
  93         </tr>
  94         <tr>
  95           <td>VERSION</td>
  96           <td>3.1.0</td>
  97           <td><em>Recommended</em>. The version of HTML Purifier this directive was added.
  98           Directives that have been around since 1.0.0 don't have this,
  99           but any new ones should.</td>
 100         </tr>
 101         <tr>
 102           <td>ALIASES</td>
 103           <td>Test.Example</td>
 104           <td><em>Optional</em>. A comma separated list of aliases for this directive.
 105           This is most useful for backwards compatibility and should
 106           not be used otherwise.</td>
 107         </tr>
 108         <tr>
 109           <td>ALLOWED</td>
 110           <td>'foo', 'bar'</td>
 111           <td><em>Optional</em>. Set of allowed value for a directive,
 112           a comma separated list of parseable PHP expressions. This
 113           is only allowed string, istring, text and itext TYPEs.</td>
 114         </tr>
 115         <tr>
 116           <td>VALUE-ALIASES</td>
 117           <td>'baz' => 'bar'</td>
 118           <td><em>Optional</em>. Mapping of one value to another, and
 119           should be a comma separated list of keypair duples. This
 120           is only allowed string, istring, text and itext TYPEs.</td>
 121         </tr>
 122         <tr>
 123           <td>DEPRECATED-VERSION</td>
 124           <td>3.1.0</td>
 125           <td><em>Not shown</em>. Indicates that the directive was
 126           deprecated this version.</td>
 127         </tr>
 128         <tr>
 129           <td>DEPRECATED-USE</td>
 130           <td>Test.NewDirective</td>
 131           <td><em>Not shown</em>. Indicates what new directive should be
 132           used instead. Note that the directives will functionally be
 133           different, although they should offer the same functionality.
 134           If they are identical, use an alias instead.</td>
 135         </tr>
 136         <tr>
 137           <td>EXTERNAL</td>
 138           <td>CSSTidy</td>
 139           <td><em>Not shown</em>. Indicates if there is an external library
 140           the user will need to download and install to use this configuration
 141           directive. As of right now, this is merely a Google-able name; future
 142           versions may also provide links and instructions.</td>
 143         </tr>
 144       </tbody>
 145     </table>
 146
 147     <p>
 148       Some notes on format and style:
 149     </p>
 150
 151     <ul>
 152       <li>
 153         Each of these keys can be expressed in the short format
 154         (<code>KEY: Value</code>) or the long format
 155         (<code>--KEY--</code> with value beneath). You must use the
 156         long format if multiple lines are needed, or if a long format
 157         has been used already (that's why <code>ALIASES</code> in our
 158         example is in the long format); otherwise, it's user preference.
 159       </li>
 160       <li>
 161         The HTML descriptions should be wrapped at about 80 columns; do
 162         not rely on editor word-wrapping.
 163       </li>
 164     </ul>
 165
 166     <p>
 167       Also, as promised, here is the set of possible types:
 168     </p>
 169
 170     <table class="table">
 171       <thead>
 172         <tr>
 173           <th>Type</th>
 174           <th>Example</th>
 175           <th>Description</th>
 176         </tr>
 177       </thead>
 178       <tbody>
 179         <tr>
 180           <td>string</td>
 181           <td>'Foo'</td>
 182           <td><a href="http://docs.php.net/manual/en/language.types.string.php">String</a> without newlines</td>
 183         </tr>
 184         <tr>
 185           <td>istring</td>
 186           <td>'foo'</td>
 187           <td>Case insensitive ASCII string without newlines</td>
 188         </tr>
 189         <tr>
 190           <td>text</td>
 191           <td>"A<em>\n</em>b"</td>
 192           <td>String with newlines</td>
 193         </tr>
 194         <tr>
 195           <td>itext</td>
 196           <td>"a<em>\n</em>b"</td>
 197           <td>Case insensitive ASCII string without newlines</td>
 198         </tr>
 199         <tr>
 200           <td>int</td>
 201           <td>23</td>
 202           <td>Integer</td>
 203         </tr>
 204         <tr>
 205           <td>float</td>
 206           <td>3.0</td>
 207           <td>Floating point number</td>
 208         </tr>
 209         <tr>
 210           <td>bool</td>
 211           <td>true</td>
 212           <td>Boolean</td>
 213         </tr>
 214         <tr>
 215           <td>lookup</td>
 216           <td>array('key' => true)</td>
 217           <td>Lookup array, used with <code>isset($var[$key])</code></td>
 218         </tr>
 219         <tr>
 220           <td>list</td>
 221           <td>array('f', 'b')</td>
 222           <td>List array, with ordered numerical indexes</td>
 223         </tr>
 224         <tr>
 225           <td>hash</td>
 226           <td>array('key' => 'val')</td>
 227           <td>Associative array of keys to values</td>
 228         </tr>
 229         <tr>
 230           <td>mixed</td>
 231           <td>new stdclass</td>
 232           <td>Any PHP variable is fine</td>
 233         </tr>
 234       </tbody>
 235     </table>
 236
 237     <p>
 238       The examples represent what will be returned out of the configuration
 239       object; users have a little bit of leeway when setting configuration
 240       values (for example, a lookup value can be specified as a list;
 241       HTML Purifier will flip it as necessary.) These types are defined
 242       in <a href="http://repo.or.cz/w/htmlpurifier.git?a=blob;hb=HEAD;f=library/HTMLPurifier/VarParser.php">
 243       library/HTMLPurifier/VarParser.php</a>.
 244     </p>
 245
 246     <p>
 247       For more information on what values are allowed, and how they are parsed,
 248       consult <a href="http://repo.or.cz/w/htmlpurifier.git?a=blob;hb=HEAD;f=library/HTMLPurifier/ConfigSchema/InterchangeBuilder.php">
 249       library/HTMLPurifier/ConfigSchema/InterchangeBuilder.php</a>, as well
 250       as <a href="http://repo.or.cz/w/htmlpurifier.git?a=blob;hb=HEAD;f=library/HTMLPurifier/ConfigSchema/Interchange/Directive.php">
 251       library/HTMLPurifier/ConfigSchema/Interchange/Directive.php</a> for
 252       the semantics of the parsed values.
 253     </p>
 254
 255     <h2>Refreshing the cache</h2>
 256
 257     <p>
 258       You may have noticed that your directive file isn't doing anything
 259       yet. That's because it hasn't been added to the runtime
 260       <code>HTMLPurifier_ConfigSchema</code> instance. Run
 261       <code>maintenance/generate-schema-cache.php</code> to fix this.
 262       If there were no errors, you're good to go! Don't forget to add
 263       some unit tests for your functionality!
 264     </p>
 265
 266     <p>
 267       If you ever make changes to your configuration directives, you
 268       will need to run this script again.
 269     </p>
 270
 271     <h2>Errors</h2>
 272
 273     <p>
 274       All directive files go through a rigorous validation process
 275       through <a href="http://repo.or.cz/w/htmlpurifier.git?a=blob;hb=HEAD;f=library/HTMLPurifier/ConfigSchema/Validator.php">
 276       library/HTMLPurifier/ConfigSchema/Validator.php</a>, as well
 277       as some basic checks during building. While
 278       listing every error out here is out-of-scope for this document, we
 279       can give some general tips for interpreting error messages.
 280       There are two types of errors: builder errors and validation errors.
 281     </p>
 282
 283     <h3>Builder errors</h3>
 284
 285     <blockquote>
 286       <p>
 287         <strong>Exception:</strong> Expected type string, got
 288         integer in DEFAULT in directive hash 'Ns.Dir'
 289       </p>
 290     </blockquote>
 291
 292     <p>
 293       You can identify a builder error by the keyword "directive hash."
 294       These are the easiest to deal with, because they directly correspond
 295       with your directive file. Find the offending directive file (which
 296       is the directive hash plus the .txt extension), find the
 297       offending index ("in DEFAULT" means the DEFAULT key) and fix the error.
 298       This particular error would occur if your default value is not the same
 299       type as TYPE.
 300     </p>
 301
 302     <h3>Validation errors</h3>
 303
 304     <blockquote>
 305       <p>
 306         <strong>Exception:</strong> Alias 3 in valueAliases in directive
 307         'Ns.Dir' must be a string
 308       </p>
 309     </blockquote>
 310
 311     <p>
 312       These are a little trickier, because we're not actually validating
 313       your directive file, or even the direct string hash representation.
 314       We're validating an Interchange object, and the error messages do
 315       not mention any string hash keys.
 316     </p>
 317
 318     <p>
 319       Nevertheless, it's not difficult to figure out what went wrong.
 320       Read the "context" statements in reverse:
 321     </p>
 322
 323     <dl>
 324       <dt>in directive 'Ns.Dir'</dt>
 325         <dd>This means we need to look at the directive file <code>Ns.Dir.txt</code></dd>
 326       <dt>in valueAliases</dt>
 327         <dd>There's no key actually called this, but there's one that's close:
 328           VALUE-ALIASES. Indeed, that's where to look.</dd>
 329       <dt>Alias 3</dt>
 330         <dd>The value alias that is equal to 3 is the culprit.</dd>
 331     </dl>
 332
 333     <p>
 334       In this particular case, you're not allowed to alias integers values to
 335       strings values.
 336     </p>
 337
 338     <p>
 339       The most difficult part is translating the Interchange member variable (valueAliases)
 340       into a directive file key (VALUE-ALIASES), but there's a one-to-one
 341       correspondence currently. If the two formats diverge, any discrepancies
 342       will be described in <a href="http://repo.or.cz/w/htmlpurifier.git?a=blob;hb=HEAD;f=library/HTMLPurifier/ConfigSchema/InterchangeBuilder.php">
 343       library/HTMLPurifier/ConfigSchema/InterchangeBuilder.php</a>.
 344     </p>
 345
 346     <h2>Internals</h2>
 347
 348     <p>
 349       Much of the configuration schema framework's codebase deals with
 350       shuffling data from one format to another, and doing validation on this
 351       data.
 352       The keystone of all of this is the <code>HTMLPurifier_ConfigSchema_Interchange</code>
 353       class, which represents the purest, parsed representation of the schema.
 354     </p>
 355
 356     <p>
 357       Hand-writing this data is unwieldy, however, so we write directive files.
 358       These directive files are parsed by <code>HTMLPurifier_StringHashParser</code>
 359       into <code>HTMLPurifier_StringHash</code>es, which then
 360       are run through <code>HTMLPurifier_ConfigSchema_InterchangeBuilder</code>
 361       to construct the interchange object.
 362     </p>
 363
 364     <p>
 365       From the interchange object, the data can be siphoned into other forms
 366       using <code>HTMLPurifier_ConfigSchema_Builder</code> subclasses.
 367       For example, <code>HTMLPurifier_ConfigSchema_Builder_ConfigSchema</code>
 368       generates a runtime <code>HTMLPurifier_ConfigSchema</code> object,
 369       which <code>HTMLPurifier_Config</code> uses to validate its incoming
 370       data. There is also an XML serializer, which is used to build documentation.
 371     </p>
 372
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