python-rados: implement new aio_stat.

This change adds python API for the following C methods:
* rados_aio_stat

Signed-off-by: Iain Buclaw <iain.buclaw@sociomantic.com>

src/pybind/rados/rados.pyx

@@ -221,6 +221,7 @@ cdef extern from "rados/librados.h" nogil:
 
     int rados_aio_create_completion(void * cb_arg, rados_callback_t cb_complete, rados_callback_t cb_safe, rados_completion_t * pc)
     void rados_aio_release(rados_completion_t c)
+    int rados_aio_stat(rados_ioctx_t io, const char *oid, rados_completion_t completion, uint64_t *psize, time_t *pmtime)
     int rados_aio_write(rados_ioctx_t io, const char * oid, rados_completion_t completion, const char * buf, size_t len, uint64_t off)
     int rados_aio_append(rados_ioctx_t io, const char * oid, rados_completion_t completion, const char * buf, size_t len)
     int rados_aio_write_full(rados_ioctx_t io, const char * oid, rados_completion_t completion, const char * buf, size_t len)
@@ -1944,6 +1945,51 @@ cdef class Ioctx(object):
         completion_obj.rados_comp = completion
         return completion_obj
 
+    def aio_stat(self, object_name, oncomplete):
+        """
+        Asynchronously get object stats (size/mtime)
+
+        oncomplete will be called with the returned size and mtime
+        as well as the completion:
+
+        oncomplete(completion, size, mtime)
+
+        :param object_name: the name of the object to get stats from
+        :type object_name: str
+        :param oncomplete: what to do when the stat is complete
+        :type oncomplete: completion
+
+        :raises: :class:`Error`
+        :returns: completion object
+        """
+
+        object_name = cstr(object_name, 'object_name')
+
+        cdef:
+            Completion completion
+            char *_object_name = object_name
+            uint64_t psize
+            time_t pmtime
+
+        def oncomplete_(completion_v):
+            cdef Completion _completion_v = completion_v
+            return_value = _completion_v.get_return_value()
+            if return_value >= 0:
+                return oncomplete(_completion_v, psize, time.localtime(pmtime))
+            else:
+                return oncomplete(_completion_v, None, None)
+
+        completion = self.__get_completion(oncomplete_, None)
+        self.__track_completion(completion)
+        with nogil:
+            ret = rados_aio_stat(self.io, _object_name, completion.rados_comp,
+                                 &psize, &pmtime)
+
+        if ret < 0:
+            completion._cleanup()
+            raise make_ex(ret, "error stating %s" % object_name)
+        return completion
+
     def aio_write(self, object_name, to_write, offset=0,
                   oncomplete=None, onsafe=None):
         """