This patch causes ZopePageTemplates to return an IStreamIterator
    when called (published), potentially allowing medusa to return the
    same response payload (via the iterator) without needing to have the
    appserver thread join it into a big string.

--- PageTemplate.py	2004-09-25 21:39:50.595938847 -0400
+++ PageTemplate.py.new	2004-09-25 21:39:31.983326567 -0400
@@ -83,7 +84,7 @@
             c['root'] = self
         return c
 
-    def pt_render(self, source=0, extra_context={}):
+    def pt_render(self, source=0, extra_context={}, iter_handler=None):
         """Render this Page Template"""
         if not self._v_cooked:
             self._cook()
@@ -100,7 +101,10 @@
                        getEngine().getContext(c),
                        output,
                        tal=not source, strictinsert=0)()
-        return output.getvalue()
+        if iter_handler is not None:
+            return iter_handler(output)
+        else:
+            return output.getvalue()
 
     def __call__(self, *args, **kwargs):
         if not kwargs.has_key('args'):
--- ZopePageTemplate.py	2004-09-25 21:37:07.956803011 -0400
+++ ZopePageTemplate.py.new	2004-09-25 21:37:23.024870003 -0400
@@ -34,6 +34,8 @@
 from OFS.Cache import Cacheable
 from OFS.Traversable import Traversable
 from OFS.PropertyManager import PropertyManager
+from ZPublisher.Iterators import IStreamIterator
+
 from PageTemplate import PageTemplate
 from Expressions import SecureModuleImporter
 from PageTemplateFile import PageTemplateFile
@@ -253,7 +255,8 @@
         # Execute the template in a new security context.
         security.addContext(self)
         try:
-            result = self.pt_render(extra_context=bound_names)
+            result = self.pt_render(extra_context=bound_names,
+                                    iter_handler=StringIOIterator)
             if keyset is not None:
                 # Store the result in the cache.
                 self.ZCacheable_set(result, keywords=keyset)
@@ -331,6 +334,26 @@
 setattr(ZopePageTemplate, 'source.xml',  ZopePageTemplate.source_dot_xml)
 setattr(ZopePageTemplate, 'source.html', ZopePageTemplate.source_dot_xml)
 
+
+class StringIOIterator:
+    """ Adapt a StringIO object to IStreamIterator.
+    """
+
+    __implements__ = (IStreamIterator,)
+
+    def __init__(self, stringio):
+        self._buflist = stringio.buflist
+        self._index = 0
+
+    def next(self):
+
+        if self._index >= len(self._buflist):
+            raise StopIteration
+
+        data, self._index = self._buflist[self._index], self._index + 1
+
+        return data
+
 # Product registration and Add support
 manage_addPageTemplateForm = PageTemplateFile(
     'www/ptAdd', globals(), __name__='manage_addPageTemplateForm')