[jira] [Resolved] (KAFKA-7055) Kafka Streams Processor API allows you to add sinks and processors without parent

["Matthias J. Sax (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-7055?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax resolved KAFKA-7055.
------------------------------------
       Resolution: Fixed
    Fix Version/s: 2.0.0

> Kafka Streams Processor API allows you to add sinks and processors without parent
> ---------------------------------------------------------------------------------
>
>                 Key: KAFKA-7055
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7055
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 1.0.0
>            Reporter: Nikki Thean
>            Assignee: Nikki Thean
>            Priority: Minor
>              Labels: easyfix
>             Fix For: 2.0.0
>
>
> The Kafka Streams Processor API allows you to define a Topology and connect sources, processors, and sinks. From reading through the code, it seems that you cannot forward a message to a downstream node unless it is explicitly connected to the upstream node (from which you are forwarding the message) as a child. Here is an example where you forward using name of downstream node rather than child index ([https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L117]).
> However, I've been able to connect processors and sinks to the topology without including parent names, i.e with empty vararg, using this method: [https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/Topology.java#L423].
> As any attempt to forward a message to those nodes will throw a StreamsException, I suggest throwing an exception if a processor or sink is added without at least one upstream node. There is a method in `InternalTopologyBuilder` that allows you to connect processors by name after you add them to the topology, but it is not part of the external Processor API.
> In addition (or alternatively), I suggest making [the error message for when users try to forward messages to a node that is not connected|https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L119] more descriptive, like this one for when a user attempts to access a state store that is not connected to the processor: [https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L75-L81]



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