[jira] [Commented] (BEAM-5967) ProtoCoder doesn't support DynamicMessage

["Alex Van Boxel (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-5967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16827886#comment-16827886 ] 

Alex Van Boxel commented on BEAM-5967:
--------------------------------------

Design decision: Although DynamicMessage could in theory have a different schema per message in a single stream this doesn't make sense. The common use-case for using DynamicMessages is when the schema is *not known at compile type*, build is *known at pipeline build time* (example, like pulled from a schema registry).

With this restriction we only need to store the schema (or descriptor) once when the pipeline is serialized and send to the workers. 

> ProtoCoder doesn't support DynamicMessage
> -----------------------------------------
>
>                 Key: BEAM-5967
>                 URL: https://issues.apache.org/jira/browse/BEAM-5967
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-java-core
>    Affects Versions: 2.8.0
>            Reporter: Alex Van Boxel
>            Assignee: Alex Van Boxel
>            Priority: Major
>              Labels: triaged
>
> The ProtoCoder does make some assumptions about static messages being available. The DynamicMessage doesn't have some of them, mainly because the proto schema is defined at runtime and not at compile time.
> Does it make sense to make a special coder for DynamicMessage or build it into the normal ProtoCoder.
> Here is an example of the assumtion being made in the current Codec:
> {code:java}
> try {
>   @SuppressWarnings("unchecked")
>   T protoMessageInstance = (T) protoMessageClass.getMethod("getDefaultInstance").invoke(null);
>   @SuppressWarnings("unchecked")
>   Parser<T> tParser = (Parser<T>) protoMessageInstance.getParserForType();
>   memoizedParser = tParser;
> } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
>   throw new IllegalArgumentException(e);
> }
> {code}



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