Only call body_data if we have a data handler #4

Only call `$c->req->body_data` if the request content type is one
there's a data handler for - otherwise we'll cause an exception e.g.:

```
  [error] Caught exception in engine "multipart/form-data does not have
    an available data handler. Valid data_handlers are application/json,
    application/x-www-form-urlencoded." <at /usr/local/lib/perl5/Catalyst.pm line 2420>
```

Also, add tests for multi-part file uploads, to ensure that the content
of uploaded files is left alone, but any other normal POST parameters
are still scrubbed.

lib/Catalyst/Plugin/HTML/Scrubber.pm

@@ -48,9 +48,13 @@ sub html_scrub {
     my ($c, $conf) = @_;
 
     # If there's body_data - for e.g. a POSTed JSON body that was decoded -
-    # then we need to walk through it, scrubbing as appropriate
-    if (my $body_data = $c->request->body_data) {
-	$c->_scrub_recurse($conf, $c->request->body_data);
+    # then we need to walk through it, scrubbing as appropriate; don't call
+    # body_data unless the content type is one there's a data handler for
+    # though, otherwise we'll trigger an exception (see GH#4)
+    if (exists $c->req->data_handlers->{ $c->req->content_type }) {
+        if (my $body_data = $c->request->body_data) {
+            $c->_scrub_recurse($conf, $c->request->body_data);
+        }
     }
 
     # And if Catalyst::Controller::REST is in use so we have $req->data,

t/03_params.t

@@ -101,5 +101,34 @@ JSON
     );
 }
 
+# multi-part file upload testing - ensure that an uploaded file's contents are
+# not fiddled with, and that we don't explode trying to process it 
+# (e.g. by calling $c->req->body_data causing an exception because there's
+# no data handler for this content type)
+{
+    my $content = "<p>File content, <b>with HTML</b> in it.</p>";
+    diag "Uploaded file left alone, but other form fields still scrubbed";
+    my $req = POST '/upload',
+     Content_Type => 'form-data',
+     Content      => [
+         foo  => 'Form field <script>window.alert("with XSS!");</script>',
+         myfile => [ 
+             undef, "fake.file", 'Content-Type' => 'text/fake', Content => $content
+         ],
+    ];
+    my ($res, $c) = ctx_request($req);
+    is($res->code, RC_OK, 'response ok');
+    is(
+        $c->req->param('foo'),
+        'Form field ',
+        'XSS still stripped from normal POST body param in multi-part upload',
+    );
+    is(
+        $c->req->upload('myfile')->slurp,
+        "<p>File content, <b>with HTML</b> in it.</p>",,
+        "File content left alone",
+    );
+
+}
 done_testing();
 

t/lib/MyApp03/Controller/Root.pm

@@ -13,5 +13,10 @@ sub index : Path : Args(0) {
     $c->res->body('index');
 }
 
+sub upload : Local : Args(0) {
+    my ($self, $c) = @_;
+    $c->res->body("Uploaded file content: " . $c->req->upload('myfile')->slurp);
+}
+
 1;