How to get metadata from VertexAI of GCP?

[JANGSOONMYUN]

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Example Code

import os

from langchain_google_vertexai import VertexAI
from langchain_google_vertexai import HarmBlockThreshold, HarmCategory
from langchain.output_parsers import StructuredOutputParser, ResponseSchema
from langchain.prompts import ChatPromptTemplate, HumanMessagePromptTemplate, SystemMessagePromptTemplate
from langchain_core.messages import HumanMessage, SystemMessage

class MyLLMInterface:
    def __init__(self, model, config):
        self.config = config
        self.llm = VertexAI(
            project=PROJECT_ID,
            location=REGION,
            model=model,
            temperature=self.config.temperature,
            max_output_tokens=self.config.max_tokens_output,
            safety_settings={
                HarmCategory.HARM_CATEGORY_DANGEROUS_CONTENT: HarmBlockThreshold.BLOCK_NONE,
                HarmCategory.HARM_CATEGORY_HARASSMENT: HarmBlockThreshold.BLOCK_NONE,
                HarmCategory.HARM_CATEGORY_HATE_SPEECH: HarmBlockThreshold.BLOCK_NONE,
                HarmCategory.HARM_CATEGORY_SEXUALLY_EXPLICIT: HarmBlockThreshold.BLOCK_ONLY_HIGH
            },
        )

    def set_json_output(self, output_dict):
        response_schemas = []
        for k, v in output_dict.items():
            response_schemas.append(ResponseSchema(name=k, description=v))
        output_parser = StructuredOutputParser.from_response_schemas(response_schemas)
        return output_parser

    def generate_response(self, output_parser, instructions, prompts):
        sys_msg = SystemMessage(instructions)
        hum_msg =  HumanMessagePromptTemplate.from_template(
            prompts + \
            "\n{format_instructions}"
        )
        # 메시지와 입력 변수를 정의
        messages = [
                        sys_msg,
                        hum_msg
                    ]
        input_dict = {"prompt": 'say anything'}
        
        # ChatPromptTemplate을 사용하여 프롬프트를 정의
        prompt_template = ChatPromptTemplate(
            messages=messages,
            input_variables=list(input_dict.keys()),
            partial_variables={"format_instructions": output_parser.get_format_instructions()}
        )
        
        # RunnableSequence를 사용하여 prompt_template와 llm을 연결
        sequence = (prompt_template | self.llm)
        
        # invoke 메서드를 사용하여 응답 생성
        response = sequence.invoke(input_dict)
        
        # 디버깅을 위해 text_to_parse 출력
        print(type(response))
        print("text_to_parse:", response)
        
        # JSON 응답이 올바른지 확인
        try:
            parsed_response = output_parser.parse(response)
            print("Parsed JSON:", parsed_response)
        except Exception as e:
            print("JSON parsing error:", e)
        
        return response


class Config:
    temperature = 0.0
    max_tokens_output = 512


model = "gemini-1.5-flash"
config = Config()
llm_interface = MyLLMInterface(model, config)

output_dict = {
    "tool_name": "Tool name",
    "tool_description": "Tool description",
}
output_parser = llm_interface.set_json_output(output_dict)

instructions = "Generate a tool name and description."
prompts = "Generate a tool name and description."

response = llm_interface.generate_response(output_parser, instructions, prompts)

print(response)

Description

I'm trying to use VertexAI from Google but it seems different to the GoogleGenAI

If I use ChatGoogleGenerativeAI with langchain, it returns <class 'langchain_core.messages.ai.AIMessage'> data type and includes content, response_metadata and usage_metadata
But in VertexAI with langchain, it returns only <class 'str'> type data.

I would like to get all metadata from VertexAI.

System Info

langchain 0.3.4
langchain-community 0.3.3
langchain-core 0.3.12
langchain-google-genai 2.0.1
langchain-google-vertexai 2.0.5
langchain-openai 0.2.3
langchain-text-splitters 0.3.0

[JANGSOONMYUN]

Use ChatVertexAI, not VertexAI