Implemented zconn_at for zodb4 and zodb3

lib/zodb.py

@@ -27,6 +27,8 @@ from ZODB.utils import p64, u64
 from persistent import Persistent
 from weakref import WeakSet
 import gc
+from persistent.TimeStamp import TimeStamp
+import time
 
 import pkg_resources
 
@@ -177,25 +179,41 @@ def zconn_at(zconn): # -> tid
 
         raise AssertionError("zconn_at: TODO: add support for zstor %r" % zstor)
 
-    # ZODB4
+    # ZODB3, ZODB4
     #   
-    # Connection:
-    #     .before     !None for historic connections
-    #
-    #     ._txn_time  - if !None - set to tid of _next_ transaction
-    #                   XXX set to None initially - what to do?
-    #
-    #     # XXX do something like that ZODB5 is doing:
-    #     zconn._start = zconn._storage.lastTransaction() + 1
-    #     # XXX _and_ check out queued invalidations
-    elif zmajor == 4:
-        raise AssertionError("zconn_at: TODO: add support for ZODB4")
-
-
-    # ZODB3
+    # If historic connection, convert and return zconn.before. Otherwise
+    # returns tid of last transaction, if viewing latest db state, or if  
+    # later db state exists, returns tid of db state previous to later
+    # state   
     else:
-        raise AssertionError("zconn_at: TODO: add support for ZODB3")
-
+        if __isHistoricConnection(zconn):
+            return before2at(zconn.before)
+        else:
+            last_transaction = zconn.db().lastTransaction()
+            if __viewingLatestState(zconn):
+                return last_transaction
+            else:
+                return __tidOfDbStateBefore(zconn._storage, before2at(zconn._txn_time)) 
+
+# looks through OOBTree storing all tids of storage to find the tid previous
+# to before
+def __tidOfDbStateBefore(storage, before):
+    # lookup should be O(log n) but unsure of the overhead space 
+    # implication of this operation, perhaps there is a less
+    # expensive way of getting this value
+    return storage._transactions.maxKey(before)
+
+# returns true/false if zconn is viewing latest db state at time of 
+# function call
+def __viewingLatestState(zconn):
+    return True if zconn._txn_time is None else False        
+
+# returns true/false if zconn is a historical connection 
+def __isHistoricConnection(zconn):
+    if zmajor >= 5:
+        return isinstance(zconn._storage, ZODB.mvccadapter.HistoricalStorageAdapter)
+    else:
+        return True if not(zconn.before is None) else False
 
 # before2at converts tid that specifies database state as "before" into tid that
 # specifies database state as "at".
@@ -264,6 +282,8 @@ ZODB.Connection.Connection.open = Connection_open
 # patch for ZODB.Connection to support callback on after database view is changed
 ZODB.Connection.Connection._onResyncCallbacks = None
 def Connection_onResyncCallback(self, f):
+    if zmajor <= 4:
+        raise AssertionError("onResyncCallback: TODO: add support for ZODB34")
     if self._onResyncCallbacks is None:
         # NOTE WeakSet does not work for bound methods - they are always created
         # anew for each obj.method access, and thus will go away almost immediately
@@ -273,14 +293,10 @@ def Connection_onResyncCallback(self, f):
 assert not hasattr(ZODB.Connection.Connection, 'onResyncCallback')
 ZODB.Connection.Connection.onResyncCallback = Connection_onResyncCallback
 
-# ZODB5: hook into Connection.newTransaction        XXX .newTransaction .afterCompletion ?
-# ZODB4: hook into Connection._storage_sync         XXX .newTransaction .afterCompletion ?
-# ZODB3: TODO
-# XXX ZODB5 only for now
-# XXX ERP5Type/patches/ZODBConnection.py overrides newTransaction without calling orig_newTransaction
-#     -> fix it there.
-_orig_Connection_newTransaction = ZODB.Connection.Connection.newTransaction
-def _ZConnection_newTransaction(self, transaction, sync=True):
+# ZODB5: hook into Connection.newTransaction
+if zmajor >= 5:
+    _orig_Connection_newTransaction = ZODB.Connection.Connection.newTransaction
+    def _ZConnection_newTransaction(self, transaction, sync=True):
         _orig_Connection_newTransaction(self, transaction, sync)
 
         # FIXME method name hardcoded. Better not do it and allow f to be general
@@ -290,4 +306,31 @@ def _ZConnection_newTransaction(self, transaction, sync=True):
             for f in self._onResyncCallbacks:
                 f.on_connection_resync()
 
-ZODB.Connection.Connection.newTransaction = _ZConnection_newTransaction
+    ZODB.Connection.Connection.newTransaction = _ZConnection_newTransaction
+
+
+# ZODB4: hook into Connection._storage_sync
+elif zmajor == 4:
+    pass    # raises in onResyncCallback
+
+
+# ZODB3: TODO
+else:
+    pass    # raises in onResyncCallback
+
+
+
+# zstor_2zurl converts a ZODB storage to URL to access it.
+def zstor_2zurl(zstor):
+    # There is, sadly, no unified way to do it, as even if storages are created via
+    # zodburi, after creation its uri is lost. And storages could be created not
+    # only through URI but e.g. via ZConfig and manually. We want to support all
+    # those cases...
+    #
+    # For this reason extract URL with important for wcfs use-case parameters in
+    # ad-hoc way.
+    if isinstance(zstor, FileStorage):
+        return "file://%s" % (zstor._file_name,)
+
+    # TODO ZEO + NEO support
+    raise NotImplementedError("don't know how to extract zurl from %r" % zstor)