Check connection type in lobject init

Fixes ticket #187.

NEWS

@@ -8,6 +8,8 @@ What's new in psycopg 2.5.2
   (:ticket:`#170`).
 - Meaningful connection errors report a meaningful message, thanks to
   Alexey Borzenkov (:ticket:`#173`).
+- Manually creating `lobject` with the wrong parameter doesn't segfault
+  (:ticket:`#187`).
 
 
 What's new in psycopg 2.5.1

psycopg/lobject_type.c

@@ -355,10 +355,12 @@ lobject_dealloc(PyObject* obj)
 {
     lobjectObject *self = (lobjectObject *)obj;
 
+    if (self->conn) {   /* if not, init failed */
         if (lobject_close(self) < 0)
             PyErr_Print();
         Py_XDECREF((PyObject*)self->conn);
         PyMem_Free(self->smode);
+    }
 
     Dprintf("lobject_dealloc: deleted lobject object at %p, refcnt = "
             FORMAT_CODE_PY_SSIZE_T, obj, Py_REFCNT(obj));
@@ -372,10 +374,11 @@ lobject_init(PyObject *obj, PyObject *args, PyObject *kwds)
     int oid = (int)InvalidOid, new_oid = (int)InvalidOid;
     const char *smode = "";
     const char *new_file = NULL;
-    PyObject *conn;
+    PyObject *conn = NULL;
 
-    if (!PyArg_ParseTuple(args, "O|iziz",
-         &conn, &oid, &smode, &new_oid, &new_file))
+    if (!PyArg_ParseTuple(args, "O!|iziz",
+         &connectionType, &conn,
+         &oid, &smode, &new_oid, &new_file))
         return -1;
 
     return lobject_setup((lobjectObject *)obj,

tests/test_lobject.py

@@ -77,6 +77,10 @@ class LargeObjectTests(LargeObjectTestCase):
         self.assertNotEqual(lo, None)
         self.assertEqual(lo.mode[0], "w")
 
+    def test_connection_needed(self):
+        self.assertRaises(TypeError,
+            psycopg2.extensions.lobject, [])
+
     def test_open_non_existent(self):
         # By creating then removing a large object, we get an Oid that
         # should be unused.