Adapt to python3 shelve.open behavior changes

When running tests between python2 and python3, shelve.open's behavior
has changed. These changes make it so that a previous run of one python
version of tests will not interfere with the current run. There are
still some issues with the database filename which may need to be
addressed.

Author: SpamapS

src/saml2/cache.py

@@ -23,7 +23,7 @@ class CacheError(SAMLError):
 class Cache(object):
     def __init__(self, filename=None):
         if filename:
-            self._db = shelve.open(filename, writeback=True)
+            self._db = shelve.open(filename, writeback=True, protocol=2)
             self._sync = True
         else:
             self._db = {}

src/saml2/ident.py

@@ -78,7 +78,7 @@ class IdentDB(object):
     """
     def __init__(self, db, domain="", name_qualifier=""):
         if isinstance(db, six.string_types):
-            self.db = shelve.open(db)
+            self.db = shelve.open(db, protocol=2)
         else:
             self.db = db
         self.domain = domain

src/saml2/s2repoze/plugins/sp.py

@@ -100,11 +100,13 @@ def __init__(self, rememberer_name, config, saml_client, wayf, cache,
         except KeyError:
             self.metadata = None
         if sid_store:
-            self.outstanding_queries = shelve.open(sid_store, writeback=True)
+            self.outstanding_queries = shelve.open(sid_store, writeback=True,
+                                                   protocol=2)
         else:
             self.outstanding_queries = {}
         if sid_store_cert:
-            self.outstanding_certs = shelve.open(sid_store_cert, writeback=True)
+            self.outstanding_certs = shelve.open(sid_store_cert, writeback=True,
+                                                 protocol=2)
         else:
             self.outstanding_certs = {}
 

src/saml2/server.py

@@ -9,6 +9,7 @@
 import os
 
 import importlib
+import dbm
 import shelve
 import six
 import threading
@@ -56,6 +57,17 @@
     "subject_locality": "subject_locality"
 }
 
+def _shelve_compat(name, *args, **kwargs):
+    try:
+        return shelve.open(name, *args, **kwargs)
+    except dbm.error[0]:
+        # Python 3 whichdb needs to try .db to determine type
+        if name.endswith('.db'):
+            name = name.rsplit('.db', 1)[0]
+            return shelve.open(name, *args, **kwargs)
+        else:
+            raise
+
 
 class Server(Entity):
     """ A class that does things that IdPs or AAs do """
@@ -118,12 +130,12 @@ def init_config(self, stype="idp"):
         if not dbspec:
             idb = {}
         elif isinstance(dbspec, six.string_types):
-            idb = shelve.open(dbspec, writeback=True)
+            idb = _shelve_compat(dbspec, writeback=True, protocol=2)
         else:  # database spec is a a 2-tuple (type, address)
             #print(>> sys.stderr, "DBSPEC: %s" % (dbspec,))
             (typ, addr) = dbspec
             if typ == "shelve":
-                idb = shelve.open(addr, writeback=True)
+                idb = _shelve_compat(addr, writeback=True, protocol=2)
             elif typ == "memcached":
                 import memcache