Use pkg_resources to determine if ZServer/webdav is available.

There are so many import dependencies between OFS and webdav, it's
otherwise too easy to accidentally cause a cycle and silently break
one module.

src/OFS/Application.py

@@ -27,6 +27,7 @@ from App.ApplicationManager import ApplicationManager
 from App import FactoryDispatcher
 from App.ProductContext import ProductContext
 from DateTime import DateTime
+from OFS import bbb
 from OFS.metaconfigure import get_packages_to_initialize
 from OFS.metaconfigure import package_initialized
 from OFS.userfolder import UserFolder
@@ -40,10 +41,10 @@ from FindSupport import FindSupport
 from interfaces import IApplication
 from misc_ import Misc_
 
-try:
+if bbb.HAS_ZSERVER:
     from webdav.NullResource import NullResource
-except ImportError:
-    NullResource = None
+else:
+    NullResource = bbb.NullResource
 
 LOG = getLogger('Application')
 

src/OFS/Folder.py

@@ -19,6 +19,7 @@ from AccessControl.class_init import InitializeClass
 from App.special_dtml import DTMLFile
 from zope.interface import implements
 
+from OFS import bbb
 from OFS.FindSupport import FindSupport
 from OFS.interfaces import IFolder
 from OFS.Lockable import LockableItem
@@ -27,19 +28,10 @@ from OFS.PropertyManager import PropertyManager
 from OFS.role import RoleManager
 from OFS.SimpleItem import Item
 
-try:
+if bbb.HAS_ZSERVER:
     from webdav.Collection import Collection
-except ImportError:
-    class Collection(object):
-        def dav__init(self, request, response):
-            pass
-
-        def dav__validate(self, object, methodname, REQUEST):
-            pass
-
-        def dav__simpleifhandler(self, request, response, method='PUT',
-                                 col=0, url=None, refresh=0):
-            pass
+else:
+    Collection = bbb.Collection
 
 
 manage_addFolderForm = DTMLFile('dtml/folderAdd', globals())

src/OFS/ObjectManager.py

@@ -54,6 +54,7 @@ from zope.interface.interfaces import ComponentLookupError
 from zope.lifecycleevent import ObjectAddedEvent
 from zope.lifecycleevent import ObjectRemovedEvent
 
+from OFS import bbb
 from OFS.CopySupport import CopyContainer
 from OFS.interfaces import IObjectManager
 from OFS.Traversable import Traversable
@@ -65,19 +66,10 @@ from OFS.XMLExportImport import importXML
 from OFS.XMLExportImport import exportXML
 from OFS.XMLExportImport import magic
 
-try:
+if bbb.HAS_ZSERVER:
     from webdav.Collection import Collection
-except ImportError:
-    class Collection(object):
-        def dav__init(self, request, response):
-            pass
-
-        def dav__validate(self, object, methodname, REQUEST):
-            pass
-
-        def dav__simpleifhandler(self, request, response, method='PUT',
-                                 col=0, url=None, refresh=0):
-            pass
+else:
+    Collection = bbb.Collection
 
 # Constants: __replaceable__ flags:
 NOT_REPLACEABLE = 0

src/OFS/PropertySheets.py

@@ -28,17 +28,17 @@ from App.Dialogs import MessageDialog
 from App.Management import Tabs
 from App.special_dtml import DTMLFile
 from ExtensionClass import Base
+from OFS import bbb
 from Persistence import Persistent
 from Traversable import Traversable
 from zExceptions import BadRequest
 from zExceptions import Redirect
 from ZPublisher.Converters import type_converters
 
-try:
+if bbb.HAS_ZSERVER:
     from webdav.PropertySheet import DAVPropertySheetMixin
-except ImportError:
-    class DAVPropertySheetMixin(object):
-        pass
+else:
+    DAVPropertySheetMixin = bbb.DAVPropertySheetMixin
 
 
 class Virtual:
@@ -408,11 +408,10 @@ InitializeClass(DefaultProperties)
 
 
 # import cycles
-try:
+if bbb.HAS_ZSERVER:
     from webdav.PropertySheets import DAVProperties
-except ImportError:
-    class DAVProperties(object):
-        pass
+else:
+    DAVProperties = bbb.DAVProperties
 
 
 class PropertySheets(Traversable, Implicit, Tabs):

src/OFS/SimpleItem.py

@@ -51,6 +51,7 @@ from zExceptions import Redirect
 from zExceptions.ExceptionFormatter import format_exception
 from zope.interface import implements
 
+from OFS import bbb
 from OFS.interfaces import IItem
 from OFS.interfaces import IItemWithName
 from OFS.interfaces import ISimpleItem
@@ -60,19 +61,10 @@ from OFS.Lockable import LockableItem
 from OFS.role import RoleManager
 from OFS.Traversable import Traversable
 
-try:
+if bbb.HAS_ZSERVER:
     from webdav.Resource import Resource
-except ImportError:
-    class Resource(object):
-        def dav__init(self, request, response):
-            pass
-
-        def dav__validate(self, object, methodname, REQUEST):
-            pass
-
-        def dav__simpleifhandler(self, request, response, method='PUT',
-                                 col=0, url=None, refresh=0):
-            pass
+else:
+    Resource = bbb.Resource
 
 logger = logging.getLogger()
 
@@ -276,7 +268,7 @@ class Item(Base,
     def manage(self, URL1):
         """
         """
-        raise Redirect, "%s/manage_main" % URL1
+        raise Redirect("%s/manage_main" % URL1)
 
     # This keeps simple items from acquiring their parents
     # objectValues, etc., when used in simple tree tags.

src/OFS/Traversable.py

@@ -26,6 +26,7 @@ from Acquisition import aq_base
 from Acquisition import aq_inner
 from Acquisition import aq_parent
 from Acquisition.interfaces import IAcquirer
+from OFS import bbb
 from OFS.interfaces import ITraversable, IApplication
 from zExceptions import NotFound
 from ZPublisher.interfaces import UseTraversalDefault
@@ -195,10 +196,10 @@ class Traversable:
             obj = self
 
         # import time ordering problem
-        try:
+        if bbb.HAS_ZSERVER:
             from webdav.NullResource import NullResource
-        except ImportError:
-            NullResource = None
+        else:
+            NullResource = bbb.NullResource
 
         resource = _marker
         try:

src/OFS/bbb.py

+##############################################################################
+#
+# Copyright (c) 2002 Zope Foundation and Contributors.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE
+#
+##############################################################################
+
+import pkg_resources
+
+HAS_ZSERVER = True
+try:
+    dist = pkg_resources.get_distribution('ZServer')
+except pkg_resources.DistributionNotFound:
+    HAS_ZSERVER = False
+
+NullResource = None
+
+
+class Resource(object):
+    def dav__init(self, request, response):
+        pass
+
+    def dav__validate(self, object, methodname, REQUEST):
+        pass
+
+    def dav__simpleifhandler(self, request, response, method='PUT',
+                             col=0, url=None, refresh=0):
+        pass
+
+
+class Collection(Resource):
+    pass
+
+
+class DAVPropertySheetMixin(object):
+    pass
+
+
+class DAVProperties(object):
+    pass

src/OFS/tests/testApplication.py

@@ -91,10 +91,11 @@ class ApplicationTests(unittest.TestCase):
         self.assertRaises(KeyError, app.__bobo_traverse__, request, 'NONESUCH')
 
     def test___bobo_traverse__attribute_key_miss_R_M_not_GET_POST(self):
-        try:
+        from OFS import bbb
+        if bbb.HAS_ZSERVER:
             from webdav.NullResource import NullResource
-        except ImportError:
-            NullResource = None
+        else:
+            NullResource = bbb.NullResource
 
         if NullResource is None:
             return