Support Async call for RestAPITool

[sandangel]

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Describe the bug
A clear and concise description of what the bug is.
Currently RestAPITool is using requests to call API, however since this is not async, we are not able to use it in our API server to serve multiple users concurrently.

To Reproduce
Steps to reproduce the behavior:

1. Install 'adk-python'
2. Run 'adk api_server openapi_tool_agent'
3. Send concurrent API requests
4. Request is executed in sync mode.

Expected behavior
A clear and concise description of what you expected to happen.

Should use httpx or asyncio.to_thread to turn the blocking code to async

Screenshots
If applicable, add screenshots to help explain your problem.

https://github.com/google/adk-python/blob/main/src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py#L455-L503

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Python version(python -V):
• ADK version(pip show google-adk):

Additional context
Add any other context about the problem here.

[wolf-4bit]

I can work on this issue. asyncio.to_thread will cause to spin another thread to handle off the blocking operation, might not be a reliable solution to work upon. We already have httpx as sub-dependencies of some package and has native async support.

We'll have to refactor some instances of implementation of that function as well as test cases of related functions.

Could you please give green flag for the aforementioned changes?

[sandangel]

httpx is great. I would vote for that one instead of to_thread

[boyangsvl]

Hi @wolf-4bit, please feel free to work on this issue. Thanks!

[seanzhou1023]

mainly we need an async replacement of this line :
https://github.com/google/adk-python/blob/5d2a876ca8b68b038a81d0ae8d289bfdec945d41/src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py#L513C25-L513C32

[wolf-4bit]

Noted, will look into it. We have to transform other functions to async which are consuming this function.

Could you give green flag for the usage of httpx to do the task? is there any other recommendation?