lib/zodb: Add patch to ZODB.Connection to support callback on connection DB view change

Wendelin.core 2 will need to hook into when client ZODB.Connection
changes its database view and readjust WCFS-level client connection
accordingly.

ZODB.Connection can change its view on either connection reopen, or even
without reopen on start of new transaction.

This patch implements ZODB.Connection.onResyncCallback for ZODB5 only.

ZODB4 and ZODB3 support is TODO.

lib/tests/test_zodb.py

@@ -306,6 +306,51 @@ def test_zconn_at():
     assert zconn_at(conn_at0) == at0
 
 
+# verify that ZODB.Connection.onResyncCallback works
+@xfail(zmajor < 5, reason="ZODB.Connection.onResyncCallback is TODO for ZODB4 and ZODB3")
+@func
+def test_zodb_onresync():
+    stor = testdb.getZODBStorage()
+    defer(stor.close)
+    db  = DB(stor)
+
+    class T:
+        def __init__(t):
+            t.nresync = 0
+        def on_connection_resync(t):
+            t.nresync += 1
+
+    t = T()
+
+    conn = db.open()
+    conn.onResyncCallback(t)
+    assert t.nresync == 0
+
+    # abort makes conn to enter new transaction
+    transaction.abort()
+    assert t.nresync == 1
+
+    # close/reopen -> new transaction
+    conn.close()
+    assert t.nresync == 1
+    conn_ = db.open()
+    assert conn_ is conn
+    assert t.nresync == 2
+
+    # commit -> new transaction
+    root = conn.root()
+    root['r'] = 1
+    assert t.nresync == 2
+    transaction.commit()
+    assert t.nresync == 3
+    transaction.commit()
+    assert t.nresync == 4
+    transaction.commit()
+    assert t.nresync == 5
+
+    conn.close()
+
+
 # ---- misc ----
 
 # zsync syncs ZODB storage.

lib/zodb.py

@@ -259,3 +259,43 @@ def Connection_open(self, transaction_manager=None, delegate=True):
             f.on_connection_open()
 
 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
+        self._onResyncCallbacks = WeakSet()
+    self._onResyncCallbacks.add(f)
+
+assert not hasattr(ZODB.Connection.Connection, 'onResyncCallback')
+ZODB.Connection.Connection.onResyncCallback = Connection_onResyncCallback
+
+# 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
+        # callable, but that does not work with bound method - see above.
+        # ( Something like WeakMethod from py3 could help )
+        if self._onResyncCallbacks:
+            for f in self._onResyncCallbacks:
+                f.on_connection_resync()
+
+    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