[jira] [Created] (ZOOKEEPER-1906) zkpython: invalid data in GetData for empty node

["Nikita Vetoshkin (JIRA)" <ji...@apache.org>]

Nikita Vetoshkin created ZOOKEEPER-1906:
-------------------------------------------

             Summary: zkpython: invalid data in GetData for empty node
                 Key: ZOOKEEPER-1906
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1906
             Project: ZooKeeper
          Issue Type: Bug
          Components: contrib-bindings
         Environment: FreeBSD
            Reporter: Nikita Vetoshkin


In python if we ask {{zookeeper.get}} (which translates into {{pyzoo_get}}) for empty node we can get trash in result on Python level. Issue is pretty tricky. It goes like this:
  * python C extension allocates buffer with malloc (({{buffer = malloc(sizeof(char)*buffer_len);}} and calls {{zoo_wget}} providing both {{buffer}} and {{buffer_len}}.
  * deserialize_GetDataResponse deserializes empty buffer and sets {{buffer_len}} to -1 and {{zoo_wget}} returns.
  * python C extension calls {{Py_BuildValue( "(s#,N)", buffer,buffer_len ...}} with {{buffer_len}} set to -1.
  * {{Py_BuildValue}} calls {{do_mkvalue}} to build python string which falls back to {{strlen(str)}} in case string length ({{buffer_len < 0}}) - that's our case.
  * *usually* strlen returns 0, because e.g. linux uses magic zero filled page as result of mmap (which is being copied upon page fault, i.e. when you want to right to it)
  * everything works!

But on FreeBSD (not always) we can get random data in {{malloc}} result and this trash will be exposed to the user.

Not sure about the right way to fix this, but something like
{noformat}
Index: src/contrib/zkpython/src/c/zookeeper.c
===================================================================
--- src/contrib/zkpython/src/c/zookeeper.c	(revision 1583238)
+++ src/contrib/zkpython/src/c/zookeeper.c	(working copy)
@@ -1223,7 +1223,7 @@
   }
 
   PyObject *stat_dict = build_stat( &stat );
-  PyObject *ret = Py_BuildValue( "(s#,N)", buffer,buffer_len, stat_dict );
+  PyObject *ret = Py_BuildValue( "(s#,N)", buffer,buffer_len < 0 ? 0 : buffer_len, stat_dict );
   free(buffer);
 
   return ret;
{noformat}
should do the trick



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