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As a point of reference: in Python, the citation metadata is kept at the level of the equivalent LlmResponse object.
https://github.com/google/adk-python/blob/bbad9ec64ce1617bc45148de97e6246752845b98/src/google/adk/models/llm_response.py#L132

Wouldn't that be a better place for holding the citation metadata information?
Wouldn't that suit your need to have access to this metadata?

@glaforge
That is correct. First of all, I have added the citationMetadata property to the LlmResponse class.

Regarding your question, I believe you were asking about adding the property to the Event class. Since the Event class already contains groundingMetadata, I thought citationMetadata belonged at the same level of information and added it there as well:

Do you think it should only be added to LlmResponse? If so, I will remove it from the Event class. Please let me know your thoughts.

@flex-myeonghyeon Hmmm... That's interesting...
I was pointing at Python to see what they had done there, but their event derives from llm response which has that citation metadata. But in Java, our Event class doesn't extend LlmResponse at all.
And indeed, I also noticed that GroundingMetadata was on Event, so CitationMetadata could very well have its place there.

I'm also curious: what lead you to this pull request? When/how did you need the citation metadata? What was the use case?

@glaforge
I am currently using the GoogleSearchAgentTool.

When the GoogleSearchAgentTool is used in an ADK response, I wanted to be able to verify the search information that was referenced. My primary goal is to validate the basis of the response, but I also intend to pass this as citation information to the client if needed.

While I noticed that the Event class already provides groundingMetadata, I realized that it was missing citationMetadata. That is why I decided to add it.