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https://issues.apache.org/jira/browse/ZOOKEEPER-1906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13956308#comment-13956308
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Nikita Vetoshkin commented on ZOOKEEPER-1906:
---------------------------------------------
I don't think it's possible to create an empty node (i.e. buff = null, size =
-1) from python, we only can create node with empty string as valud (i.e. buff
= '', size = 0).
> 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
> Affects Versions: 3.4.6, 3.5.0
> Environment: FreeBSD
> Reporter: Nikita Vetoshkin
> Fix For: 3.4.7, 3.5.0
>
>
> 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 write 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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