[Libguestfs] [nbdkit PATCH] python: Make sure callbacks are actually callable

[Richard W.M. Jones]

On Thu, Apr 05, 2018 at 05:25:55PM -0500, Eric Blake wrote:
> Rather than catching a Python error at runtime when trying to
> call an object that wasn't callable, just ignore that object
> up front when loading the plugin.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
> 
> Various examples on calling Python functions from C recommend
> doing this filtering check.
> 
>  plugins/python/python.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/plugins/python/python.c b/plugins/python/python.c
> index 0206b80..35e8df2 100644
> --- a/plugins/python/python.c
> +++ b/plugins/python/python.c
> @@ -94,6 +94,11 @@ callback_defined (const char *name, PyObject **obj_rtn)
>    obj = PyObject_GetAttrString (module, name);
>    if (!obj)
>      return 0;
> +  if (!PyCallable_Check (obj)) {
> +    nbdkit_debug ("object %s isn't callable", name);
> +    Py_DECREF (obj);
> +    return 0;
> +  }
> 
>    if (obj_rtn != NULL)
>      *obj_rtn = obj;

ACK.

Rich.

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