pub unsafe extern "C-unwind" fn SecTransformNoData() -> CFRetained<CFType>SecCustomTransform only.Expand description
Returns back A CFTypeRef from inside a processData override that says that while no data is being returned the transform is still active and awaiting data.
Returns: A ‘special’ value that allows that specifies that the transform is still active and awaiting data.
The standard behavior for the ProcessData override is that it will receive a CFDataRef and it processes that data and returns a CFDataRef that contains the processed data. When there is no more data to process the ProcessData override block is called one last time with a NULL CFDataRef. The ProcessData block should/must return the NULL CFDataRef to complete the processing. This model does not work well for some transforms. For example a digest transform needs to see ALL of the data that is being digested before it can send out the digest value.
If a ProcessData block has no data to return, it can return SecTransformNoData(), which informs the transform system that there is no data to pass on to the next transform.