Forward port fix for LP #239636 from 2.9 branch.

doc/CHANGES.txt

@@ -8,6 +8,9 @@ Zope Changes
 
     Bugs fixed
 
+      - Launchpad #239636:  Ensure that HEAD requests lock an empty body
+        for NotFound errors.
+
       - Launchpad #229549:  Don't ignore 'debug' flag when rendering
         page templates (thanks to Eric Steele for the patch).
 

lib/python/webdav/NullResource.py

@@ -71,6 +71,7 @@ class NullResource(Persistent, Acquisition.Implicit, Resource):
     def HEAD(self, REQUEST, RESPONSE):
         """Retrieve resource information without a response message body."""
         self.dav__init(REQUEST, RESPONSE)
+        RESPONSE.setBody('', lock=True)
         raise NotFound, 'The requested resource does not exist.'
 
     # Most methods return 404 (Not Found) for null resources.

lib/python/webdav/tests/testNullResource.py

@@ -20,20 +20,46 @@ class TestLockNullResource(unittest.TestCase):
 
 class TestNullResource(unittest.TestCase):
 
+    def _getTargetClass(self):
+        from webdav.NullResource import NullResource
+        return NullResource
+
+    def _makeOne(self, parent=None, name='nonesuch', **kw):
+        return self._getTargetClass()(parent, name, **kw)
+
     def test_z2interfaces(self):
         from Interface.Verify import verifyClass
-        from webdav.NullResource import NullResource
         from webdav.WriteLockInterface import WriteLockInterface
 
-        verifyClass(WriteLockInterface, NullResource)
+        verifyClass(WriteLockInterface, self._getTargetClass())
 
     def test_z3interfaces(self):
         from webdav.interfaces import IWriteLock
-        from webdav.NullResource import NullResource
         from zope.interface.verify import verifyClass
 
-        verifyClass(IWriteLock, NullResource)
+        verifyClass(IWriteLock, self._getTargetClass())
+
+    def test_HEAD_locks_empty_body_before_raising_NotFound(self):
+        from zExceptions import NotFound
+        # See https://bugs.launchpad.net/bugs/239636
+        class DummyResponse:
+            _server_version = 'Dummy' # emulate ZServer response
+            locked = False
+            body = None
+            def setHeader(self, *args):
+                pass
+            def setBody(self, body, lock=False):
+                self.body = body
+                self.locked = bool(lock)
+
+        nonesuch = self._makeOne()
+        request = {}
+        response = DummyResponse()
+
+        self.assertRaises(NotFound, nonesuch.HEAD, request, response)
 
+        self.assertEqual(response.body, '')
+        self.failUnless(response.locked)
 
 def test_suite():
     return unittest.TestSuite((