Cloud Function Java Background Function Support

[wko27]

We are using the relatively recent Java 11 Cloud Functions and following the quickstart tutorials.

Having used this PubSub library previously, I assumed that the following two libraries played well with each other:

<dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>google-cloud-pubsub</artifactId>
      <version>1.108.1</version>
    </dependency>

<dependency>
      <groupId>com.google.cloud.functions</groupId>
      <artifactId>functions-framework-api</artifactId>
      <version>1.0.1</version>
      <scope>provided</scope>
    </dependency>

This does NOT seem to be the case, i.e. the BackgroundFunction type parameter PubSubMessage MUST be a simple POJO and can not be the com.google.pubsub.v1.PubsubMessage class.

We were able to successfully deploy cloud functions with the type signature BackgroundFunction but found runtime failures where the PubsubMessage's field variables were not populated.

This is both a documentation request to clarify that this library should NOT be used with the new Java Cloud functions library, and/or a feature request to add support so that the two libraries are indeed compatible.

[anguillanneuf]

👋 @wko27 Thank you for trying out the blogpost and tutorial!

Unfortunately the two libraries don't play well together currently, and we've also seen similar issues with functions-framework-nodejs:
GoogleCloudPlatform/functions-framework-nodejs#41
GoogleCloudPlatform/functions-framework-nodejs#96

@grant @ace-n I think a note on functions-framework-java on is probably more appropriate than putting it in this repo. Wdyt?

Cc: @glaforge

[glaforge]

Cc @eamonnmcmanus as well

[meredithslota]

Based on @anguillanneuf's comment, I'm going to transfer this to the functions-framework-java repo. Please let me know if this is incorrect.

[meredithslota]

Hilariously, I cannot (don't have right permissions). @eamonnmcmanus can you?

[eamonnmcmanus]

I don't have write permission to this repo (googleapis/java-pubsub) so I can't transfer the issue. @meredithslota I've sent you an invite with write access to functions-framework-java which will probably allow you to do the transfer.

[anguillanneuf]

@wko27 @eamonnmcmanus @meredithslota With GoogleCloudPlatform/functions-framework-java#98, Functions Framework works with Pub/Sub emulator in Java now. I have tested this myself and published the steps that have worked for me in my personal repo if you'd like to reference: https://github.com/anguillanneuf/PubSubEmulatorExamples#java