Implement data URI scheme.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/URIScheme/data.php

@@ -0,0 +1,93 @@
+<?php
+
+/**
+ * Implements data: URI for base64 encoded images supported by GD.
+ */
+class HTMLPurifier_URIScheme_data extends HTMLPurifier_URIScheme {
+
+    public $browsable = true;
+    public $allowed_types = array(
+        // you better write validation code for other types if you
+        // decide to allow them
+        'image/jpeg' => true,
+        'image/gif' => true,
+        'image/png' => true,
+        );
+
+    public function validate(&$uri, $config, $context) {
+        $result = explode(',', $uri->path, 2);
+        $is_base64 = false;
+        $charset = null;
+        $content_type = null;
+        if (count($result) == 2) {
+            list($metadata, $data) = $result;
+            // do some legwork on the metadata
+            $metas = explode(';', $metadata);
+            while(!empty($metas)) {
+                $cur = array_shift($metas);
+                if ($cur == 'base64') {
+                    $is_base64 = true;
+                    break;
+                }
+                if (substr($cur, 0, 8) == 'charset=') {
+                    // doesn't match if there are arbitrary spaces, but
+                    // whatever dude
+                    if ($charset !== null) continue; // garbage
+                    $charset = substr($cur, 8); // not used
+                } else {
+                    if ($content_type !== null) continue; // garbage
+                    $content_type = $cur;
+                }
+            }
+        } else {
+            $data = $result[0];
+        }
+        if ($content_type !== null && empty($this->allowed_types[$content_type])) {
+            return false;
+        }
+        if ($charset !== null) {
+            // error; we don't allow plaintext stuff
+            $charset = null;
+        }
+        $data = rawurldecode($data);
+        if ($is_base64) {
+            $raw_data = base64_decode($data);
+        } else {
+            $raw_data = $data;
+        }
+        // XXX probably want to refactor this into a general mechanism
+        // for filtering arbitrary content types
+        $file = tempnam("/tmp", "");
+        file_put_contents($file, $raw_data);
+        if (function_exists('exif_imagetype')) {
+            $image_code = exif_imagetype($file);
+        } elseif (function_exists('getimagesize')) {
+            set_error_handler(array($this, 'muteErrorHandler'));
+            $info = getimagesize($file);
+            restore_error_handler();
+            if ($info == false) return false;
+            $image_code = $info[2];
+        } else {
+            trigger_error("could not find exif_imagetype or getimagesize functions", E_USER_ERROR);
+        }
+        $real_content_type = image_type_to_mime_type($image_code);
+        if ($real_content_type != $content_type) {
+            // we're nice guys; if the content type is something else we
+            // support, change it over
+            if (empty($this->allowed_types[$real_content_type])) return false;
+            $content_type = $real_content_type;
+        }
+        // ok, it's kosher, rewrite what we need
+        $uri->userinfo = null;
+        $uri->host = null;
+        $uri->port = null;
+        $uri->fragment = null;
+        $uri->query = null;
+        $uri->path = "$content_type;base64," . base64_encode($raw_data);
+        return true;
+    }
+
+    public function muteErrorHandler($errno, $errstr) {}
+
+}
+