Allow %URI.DefaultScheme to be null.

Fixes #103.

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

NEWS

@@ -9,6 +9,10 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
     . Internal change
 ==========================
 
+4.9.0, unknown release date
+! %URI.DefaultScheme can now be set to null, in which case
+  all relative paths are removed.
+
 4.8.0, released 2016-07-16
 # By default, when a link has a target attribute associated
   with it, we now also add rel="noreferrer" in order to

configdoc/usage.xml

@@ -423,13 +423,13 @@
  </directive>
  <directive id="Cache.SerializerPath">
   <file name="HTMLPurifier/DefinitionCache/Serializer.php">
-   <line>183</line>
+   <line>185</line>
   </file>
  </directive>
  <directive id="Cache.SerializerPermissions">
   <file name="HTMLPurifier/DefinitionCache/Serializer.php">
-   <line>200</line>
-   <line>216</line>
+   <line>202</line>
+   <line>218</line>
   </file>
  </directive>
  <directive id="Filter.ExtractStyleBlocks.TidyImpl">

library/HTMLPurifier/ConfigSchema/schema/URI.DefaultScheme.txt

@@ -1,5 +1,5 @@
 URI.DefaultScheme
-TYPE: string
+TYPE: string/null
 DEFAULT: 'http'
 --DESCRIPTION--
 
@@ -7,4 +7,9 @@ DEFAULT: 'http'
     Defines through what scheme the output will be served, in order to
     select the proper object validator when no scheme information is present.
 </p>
+
+<p>
+    Starting with HTML Purifier 4.9.0, the default scheme can be null, in
+    which case we reject all URIs which do not have explicit schemes.
+</p>
 --# vim: et sw=4 sts=4

library/HTMLPurifier/URI.php

@@ -85,11 +85,13 @@ class HTMLPurifier_URI
             $def = $config->getDefinition('URI');
             $scheme_obj = $def->getDefaultScheme($config, $context);
             if (!$scheme_obj) {
-                // something funky happened to the default scheme object
-                trigger_error(
-                    'Default scheme object "' . $def->defaultScheme . '" was not readable',
-                    E_USER_WARNING
-                );
+                if ($def->defaultScheme !== null) {
+                    // something funky happened to the default scheme object
+                    trigger_error(
+                        'Default scheme object "' . $def->defaultScheme . '" was not readable',
+                        E_USER_WARNING
+                    );
+                } // suppress error if it's null
                 return false;
             }
         }

tests/HTMLPurifier/AttrDef/URITest.php

@@ -81,6 +81,12 @@ class HTMLPurifier_AttrDef_URITest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('http://example.com/foo/bar');
     }
 
+    public function testDefaultSchemeNull()
+    {
+        $this->config->set('URI.DefaultScheme', null);
+        $this->assertDef('foo', false);
+    }
+
     public function testAltSchemeNotRemoved()
     {
         $this->assertDef('mailto:this-looks-like-a-path@example.com');