Add HTMLPurifier to extlib

HTMLPurifier defangs arbitrary submitted HTML. We're using it in the
OStatus plugin, but it may be valuable for other parts of the codebase
(I think OEmbed might benefit, for example).

extlib/HTMLPurifier/HTMLPurifier/VarParser/Flexible.php

@@ -0,0 +1,96 @@
+<?php
+
+/**
+ * Performs safe variable parsing based on types which can be used by
+ * users. This may not be able to represent all possible data inputs,
+ * however.
+ */
+class HTMLPurifier_VarParser_Flexible extends HTMLPurifier_VarParser
+{
+
+    protected function parseImplementation($var, $type, $allow_null) {
+        if ($allow_null && $var === null) return null;
+        switch ($type) {
+            // Note: if code "breaks" from the switch, it triggers a generic
+            // exception to be thrown. Specific errors can be specifically
+            // done here.
+            case self::MIXED :
+            case self::ISTRING :
+            case self::STRING :
+            case self::TEXT :
+            case self::ITEXT :
+                return $var;
+            case self::INT :
+                if (is_string($var) && ctype_digit($var)) $var = (int) $var;
+                return $var;
+            case self::FLOAT :
+                if ((is_string($var) && is_numeric($var)) || is_int($var)) $var = (float) $var;
+                return $var;
+            case self::BOOL :
+                if (is_int($var) && ($var === 0 || $var === 1)) {
+                    $var = (bool) $var;
+                } elseif (is_string($var)) {
+                    if ($var == 'on' || $var == 'true' || $var == '1') {
+                        $var = true;
+                    } elseif ($var == 'off' || $var == 'false' || $var == '0') {
+                        $var = false;
+                    } else {
+                        throw new HTMLPurifier_VarParserException("Unrecognized value '$var' for $type");
+                    }
+                }
+                return $var;
+            case self::ALIST :
+            case self::HASH :
+            case self::LOOKUP :
+                if (is_string($var)) {
+                    // special case: technically, this is an array with
+                    // a single empty string item, but having an empty
+                    // array is more intuitive
+                    if ($var == '') return array();
+                    if (strpos($var, "\n") === false && strpos($var, "\r") === false) {
+                        // simplistic string to array method that only works
+                        // for simple lists of tag names or alphanumeric characters
+                        $var = explode(',',$var);
+                    } else {
+                        $var = preg_split('/(,|[\n\r]+)/', $var);
+                    }
+                    // remove spaces
+                    foreach ($var as $i => $j) $var[$i] = trim($j);
+                    if ($type === self::HASH) {
+                        // key:value,key2:value2
+                        $nvar = array();
+                        foreach ($var as $keypair) {
+                            $c = explode(':', $keypair, 2);
+                            if (!isset($c[1])) continue;
+                            $nvar[$c[0]] = $c[1];
+                        }
+                        $var = $nvar;
+                    }
+                }
+                if (!is_array($var)) break;
+                $keys = array_keys($var);
+                if ($keys === array_keys($keys)) {
+                    if ($type == self::ALIST) return $var;
+                    elseif ($type == self::LOOKUP) {
+                        $new = array();
+                        foreach ($var as $key) {
+                            $new[$key] = true;
+                        }
+                        return $new;
+                    } else break;
+                }
+                if ($type === self::LOOKUP) {
+                    foreach ($var as $key => $value) {
+                        $var[$key] = true;
+                    }
+                }
+                return $var;
+            default:
+                $this->errorInconsistent(__CLASS__, $type);
+        }
+        $this->errorGeneric($var, $type);
+    }
+
+}
+
+// vim: et sw=4 sts=4

extlib/HTMLPurifier/HTMLPurifier/VarParser/Native.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * This variable parser uses PHP's internal code engine. Because it does
+ * this, it can represent all inputs; however, it is dangerous and cannot
+ * be used by users.
+ */
+class HTMLPurifier_VarParser_Native extends HTMLPurifier_VarParser
+{
+
+    protected function parseImplementation($var, $type, $allow_null) {
+        return $this->evalExpression($var);
+    }
+
+    protected function evalExpression($expr) {
+        $var = null;
+        $result = eval("\$var = $expr;");
+        if ($result === false) {
+            throw new HTMLPurifier_VarParserException("Fatal error in evaluated code");
+        }
+        return $var;
+    }
+
+}
+
+// vim: et sw=4 sts=4