Allow connection.notices and notifies to be replaced.

Close #326

NEWS

@@ -10,6 +10,9 @@ New features:
   `~psycopg2.extensions.libpq_version()` to inspect the version of the
   ``libpq`` library the module was compiled/loaded with
   (:tickets:`#35, #323`).
+- The attributes `~connection.notices` and `~connection.notifies` can be
+  customized replacing them with any object exposing an `!append()` method
+  (:ticket:`#326`).
 
 
 What's new in psycopg 2.6.1

doc/src/advanced.rst

@@ -312,6 +312,10 @@ received from a previous version server will have the
     Added `~psycopg2.extensions.Notify` object and handling notification
     payload.
 
+.. versionchanged:: 2.7
+    The `~connection.notifies` attribute is writable: it is possible to
+    replace it with any object exposing an `!append()` method. An useful
+    example would be to use a `~collections.deque` object.
 
 
 .. index::

doc/src/connection.rst

@@ -483,8 +483,16 @@ The ``connection`` class
             ['NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "foo_pkey" for table "foo"\n',
              'NOTICE:  CREATE TABLE will create implicit sequence "foo_id_seq" for serial column "foo.id"\n']
 
+        .. versionchanged:: 2.7
+            The `!notices` attribute is writable: the user may replace it
+            with any Python object exposing an `!append()` method. If
+            appending raises an exception the notice is silently
+            dropped.
+
         To avoid a leak in case excessive notices are generated, only the last
-        50 messages are kept.
+        50 messages are kept. This check is only in place if the `!notices`
+        attribute is a list: if any other object is used it will be up to the
+        user to guard from leakage.
 
         You can configure what messages to receive using `PostgreSQL logging
         configuration parameters`__ such as ``log_statement``,
@@ -506,6 +514,12 @@ The ``connection`` class
             the payload was not accessible. To keep backward compatibility,
             `!Notify` objects can still be accessed as 2 items tuples.
 
+        .. versionchanged:: 2.7
+            The `!notifies` attribute is writable: the user may replace it
+            with any Python object exposing an `!append()` method. If
+            appending raises an exception the notification is silently
+            dropped.
+
 
     .. attribute:: cursor_factory
 

psycopg/connection_int.c

@@ -111,41 +111,60 @@ void
 conn_notice_process(connectionObject *self)
 {
     struct connectionObject_notice *notice;
-    Py_ssize_t nnotices;
+    PyObject *msg = NULL;
+    PyObject *tmp = NULL;
+    static PyObject *append;
 
     if (NULL == self->notice_pending) {
         return;
     }
 
-    notice =  self->notice_pending;
+    if (!append) {
+        if (!(append = Text_FromUTF8("append"))) {
+            goto error;
+        }
+    }
 
+    notice = self->notice_pending;
     while (notice != NULL) {
-        PyObject *msg;
-        msg = conn_text_from_chars(self, notice->message);
         Dprintf("conn_notice_process: %s", notice->message);
 
-        if (msg) {
-            PyList_Append(self->notice_list, msg);
-            Py_DECREF(msg);
-        }
-        else {
-            /* We don't really have a way to report errors, so gulp it.
-             * The function should only fail for out of memory, so we are
-             * likely going to die anyway. */
-            PyErr_Clear();
+        if (!(msg = conn_text_from_chars(self, notice->message))) { goto error; }
+
+        if (!(tmp = PyObject_CallMethodObjArgs(
+                self->notice_list, append, msg, NULL))) {
+
+            goto error;
         }
 
+        Py_DECREF(tmp); tmp = NULL;
+        Py_DECREF(msg); msg = NULL;
+
         notice = notice->next;
     }
 
     /* Remove the oldest item if the queue is getting too long. */
+    if (PyList_Check(self->notice_list)) {
+        Py_ssize_t nnotices;
         nnotices = PyList_GET_SIZE(self->notice_list);
         if (nnotices > CONN_NOTICES_LIMIT) {
-        PySequence_DelSlice(self->notice_list,
-            0, nnotices - CONN_NOTICES_LIMIT);
+            if (-1 == PySequence_DelSlice(self->notice_list,
+                    0, nnotices - CONN_NOTICES_LIMIT)) {
+                PyErr_Clear();
+            }
+        }
     }
 
     conn_notice_clean(self);
+    return;
+
+error:
+    Py_XDECREF(tmp);
+    Py_XDECREF(msg);
+    conn_notice_clean(self);
+
+    /* TODO: the caller doesn't expects errors from us */
+    PyErr_Clear();
 }
 
 void
@@ -177,6 +196,15 @@ conn_notifies_process(connectionObject *self)
     PGnotify *pgn = NULL;
     PyObject *notify = NULL;
     PyObject *pid = NULL, *channel = NULL, *payload = NULL;
+    PyObject *tmp = NULL;
+
+    static PyObject *append;
+
+    if (!append) {
+        if (!(append = Text_FromUTF8("append"))) {
+            goto error;
+        }
+    }
 
     while ((pgn = PQnotifies(self->pgconn)) != NULL) {
 
@@ -196,7 +224,11 @@ conn_notifies_process(connectionObject *self)
         Py_DECREF(channel); channel = NULL;
         Py_DECREF(payload); payload = NULL;
 
-        PyList_Append(self->notifies, (PyObject *)notify);
+        if (!(tmp = PyObject_CallMethodObjArgs(
+                self->notifies, append, notify, NULL))) {
+            goto error;
+        }
+        Py_DECREF(tmp); tmp = NULL;
 
         Py_DECREF(notify); notify = NULL;
         PQfreemem(pgn); pgn = NULL;
@@ -205,6 +237,7 @@ conn_notifies_process(connectionObject *self)
 
 error:
     if (pgn) { PQfreemem(pgn); }
+    Py_XDECREF(tmp);
     Py_XDECREF(notify);
     Py_XDECREF(pid);
     Py_XDECREF(channel);

psycopg/connection_type.c

@@ -1001,8 +1001,8 @@ static struct PyMemberDef connectionObject_members[] = {
         "True if the connection is closed."},
     {"encoding", T_STRING, offsetof(connectionObject, encoding), READONLY,
         "The current client encoding."},
-    {"notices", T_OBJECT, offsetof(connectionObject, notice_list), READONLY},
-    {"notifies", T_OBJECT, offsetof(connectionObject, notifies), READONLY},
+    {"notices", T_OBJECT, offsetof(connectionObject, notice_list), 0},
+    {"notifies", T_OBJECT, offsetof(connectionObject, notifies), 0},
     {"dsn", T_STRING, offsetof(connectionObject, dsn), READONLY,
         "The current connection string."},
     {"async", T_LONG, offsetof(connectionObject, async), READONLY,

tests/test_connection.py

@@ -129,6 +129,42 @@ class ConnectionTests(ConnectingTestCase):
         self.assertEqual(50, len(conn.notices))
         self.assert_('table99' in conn.notices[-1], conn.notices[-1])
 
+    def test_notices_deque(self):
+        from collections import deque
+
+        conn = self.conn
+        self.conn.notices = deque()
+        cur = conn.cursor()
+        if self.conn.server_version >= 90300:
+            cur.execute("set client_min_messages=debug1")
+
+        cur.execute("create temp table table1 (id serial); create temp table table2 (id serial);")
+        cur.execute("create temp table table3 (id serial); create temp table table4 (id serial);")
+        self.assertEqual(len(conn.notices), 4)
+        self.assert_('table1' in conn.notices.popleft())
+        self.assert_('table2' in conn.notices.popleft())
+        self.assert_('table3' in conn.notices.popleft())
+        self.assert_('table4' in conn.notices.popleft())
+        self.assertEqual(len(conn.notices), 0)
+
+        # not limited, but no error
+        for i in range(0, 100, 10):
+            sql = " ".join(["create temp table table2_%d (id serial);" % j for j in range(i, i+10)])
+            cur.execute(sql)
+
+        self.assertEqual(100, len(conn.notices))
+
+    def test_notices_noappend(self):
+        conn = self.conn
+        self.conn.notices = None    # will make an error swallowes ok
+        cur = conn.cursor()
+        if self.conn.server_version >= 90300:
+            cur.execute("set client_min_messages=debug1")
+
+        cur.execute("create temp table table1 (id serial);")
+
+        self.assertEqual(self.conn.notices, None)
+
     def test_server_version(self):
         self.assert_(self.conn.server_version)
 

tests/test_notify.py

@@ -155,6 +155,27 @@ conn.close()
         self.assertEqual('foo', notify.channel)
         self.assertEqual('Hello, world!', notify.payload)
 
+    def test_notify_deque(self):
+        from collections import deque
+        self.autocommit(self.conn)
+        self.conn.notifies = deque()
+        self.listen('foo')
+        self.notify('foo').communicate()
+        time.sleep(0.5)
+        self.conn.poll()
+        notify = self.conn.notifies.popleft()
+        self.assert_(isinstance(notify, psycopg2.extensions.Notify))
+        self.assertEqual(len(self.conn.notifies), 0)
+
+    def test_notify_noappend(self):
+        self.autocommit(self.conn)
+        self.conn.notifies = None
+        self.listen('foo')
+        self.notify('foo').communicate()
+        time.sleep(0.5)
+        self.conn.poll()
+        self.assertEqual(self.conn.notifies, None)
+
     def test_notify_init(self):
         n = psycopg2.extensions.Notify(10, 'foo')
         self.assertEqual(10, n.pid)
@@ -192,6 +213,7 @@ conn.close()
         self.assertNotEqual(hash(Notify(10, 'foo', 'bar')),
             hash(Notify(10, 'foo')))
 
+
 def test_suite():
     return unittest.TestLoader().loadTestsFromName(__name__)