Hi Ferenc, I’m not overly familiar with MiNiFi C++ but this is how it works in traditional NiFi as well. This is intended. While Processors are generally free to treat relationships as they wish, the convention is always to route the original incoming FlowFile to ‘failure’, never a modified version of it. At least with respect to content. Some attributes might be added, for example to explain why there was a failure, but the content should not be changed.
In the Python API we’ve generally moved toward being more prescriptive about some of these things. So while it’s possible to do so in Java, it should not be done. In Python, we don’t even allow it. Thanks -Mark > On Jul 31, 2024, at 10:46 AM, Ferenc Gerlits <fgerl...@apache.org> wrote: > > Hello NiFi community, > > We have implemented NiFi's FlowFileTransform API for Python processors > in MiNiFi C++, and we have written a few processors using it. We have > noticed that the "failure" relationship works like this: if the > transform() method returns > FlowFileTransformResult(relationship="failure", > contents=some_contents, attributes=some_attributes), then > - some_contents are discarded, > - some_attributes are merged with the attributes of the original flow file, > - and then the original flow file with the merged attributes is > routed to the failure relationship. [1] > > The fact that the contents are discarded was unexpected to me, and it > is not documented in the developer guide [2]. We could add this to the > developer guide, but I think it would make more sense if the failure > result worked in the same way as the success result: if contents is > None, then we use the original contents, but if contents is not None, > then it becomes the new contents of the flow file which is routed to > the failure relationship. > > What do you think? > Ferenc > > [1] > https://github.com/apache/nifi/blob/main/nifi-extension-bundles/nifi-py4j-bundle/nifi-py4j-bridge/src/main/java/org/apache/nifi/python/processor/FlowFileTransformProxy.java > [2] > https://github.com/apache/nifi/blob/main/nifi-docs/src/main/asciidoc/python-developer-guide.adoc
