Kludge JSON/multi-format support back in.

I need to fix these docstrings but this is the right idea at
least. Maybe MultiFormatResource could use a name less easily confused
with its predecessor MultiFormatPage.

src/allmydata/web/common.py

@@ -461,6 +461,63 @@ class MultiFormatPage(Page):
 
 
 
+class MultiFormatResource(resource.Resource, object):
+    """
+    ```MultiFormatPage`` is a ``rend.Page`` that can be rendered in a number
+    of different formats.
+
+    Rendered format is controlled by a query argument (given by
+    ``self.formatArgument``).  Different resources may support different
+    formats but ``json`` is a pretty common one.
+    """
+    formatArgument = "t"
+    formatDefault = None
+
+    def render(self, req):
+        """
+        Dispatch to a renderer for a particular format, as selected by a query
+        argument.
+
+        A renderer for the format given by the query argument matching
+        ``formatArgument`` will be selected and invoked.  The default ``Page``
+        rendering behavior will be used if no format is selected (either by
+        query arguments or by ``formatDefault``).
+
+        :return: The result of the selected renderer.
+        """
+        t = get_arg(req, self.formatArgument, self.formatDefault)
+        renderer = self._get_renderer(t)
+        return renderer(req)
+
+
+    def _get_renderer(self, fmt):
+        """
+        Get the renderer for the indicated format.
+
+        :param bytes fmt: The format.  If a method with a prefix of
+            ``render_`` and a suffix of this format (upper-cased) is found, it
+            will be used.
+
+        :return: A callable which takes a Nevow context and renders a
+            response.
+        """
+        renderer = None
+
+        if fmt is not None:
+            try:
+                renderer = getattr(self, "render_{}".format(fmt.upper()))
+            except AttributeError:
+                raise WebError(
+                    "Unknown {} value: {!r}".format(self.formatArgument, fmt),
+                )
+
+        if renderer is None:
+            renderer = self.render_HTML
+
+        return renderer
+
+
+
 class SlotsSequenceElement(template.Element):
     def __init__(self, tag, seq):
         self.loader = template.TagLoader(tag)

src/allmydata/web/introweb.py

@@ -13,16 +13,14 @@ from allmydata.util import idlib
 from allmydata.web.common import (
     getxmlfile,
     render_time,
-    MultiFormatPage,
+    MultiFormatResource,
     SlotsSequenceElement,
 )
 
 
-class IntroducerRoot(resource.Resource):
+class IntroducerRoot(MultiFormatResource):
     def __init__(self, introducer_node):
-        resource.Resource.__init__(self)
-        # probably should fix this.. Resource isn't new-style in py2
-        #super(IntroducerRoot, self).__init__()
+        super(IntroducerRoot, self).__init__()
         self.introducer_node = introducer_node
         self.introducer_service = introducer_node.getServiceNamed("introducer")
         # necessary as a root Resource
@@ -31,8 +29,8 @@ class IntroducerRoot(resource.Resource):
         for filen in os.listdir(static_dir):
             self.putChild(filen, nevow_File(os.path.join(static_dir, filen)))
 
-    def render(self, request):
-        return renderElement(request, IntroducerRootElement(
+    def render_HTML(self, req):
+        return renderElement(req, IntroducerRootElement(
             self.introducer_node, self.introducer_service))
 
     def render_JSON(self, req):