automatically dump dictionary to json in encode_response while Streaming

[aniketmaurya]

For a typical Streaming example, if the LitAPI.encode_response yields a dictionary or any non primitive dtype then server might run into error since FastAPI StreamingResponse doesn't accept dictionary.

Proposal: LitServe automatically detects and dumps a dictionary or Pydantic object into a JSON string value of the same so that FastAPI doesn't run into the following error.

During handling of the above exception, another exception occurred:

  + Exception Group Traceback (most recent call last):
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/uvicorn/protocols/http/h11_impl.py", line 407, in run_asgi
  |     result = await app(  # type: ignore[func-returns-value]
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/uvicorn/middleware/proxy_headers.py", line 69, in __call__
  |     return await self.app(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/fastapi/applications.py", line 1054, in __call__
  |     await super().__call__(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/applications.py", line 123, in __call__
  |     await self.middleware_stack(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/middleware/errors.py", line 186, in __call__
  |     raise exc
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/middleware/errors.py", line 164, in __call__
  |     await self.app(scope, receive, _send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 65, in __call__
  |     await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/_exception_handler.py", line 64, in wrapped_app
  |     raise exc
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  |     await app(scope, receive, sender)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/routing.py", line 756, in __call__
  |     await self.middleware_stack(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/routing.py", line 776, in app
  |     await route.handle(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/routing.py", line 297, in handle
  |     await self.app(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/routing.py", line 77, in app
  |     await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/_exception_handler.py", line 64, in wrapped_app
  |     raise exc
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  |     await app(scope, receive, sender)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/routing.py", line 75, in app
  |     await response(scope, receive, send)
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/responses.py", line 258, in __call__
  |     async with anyio.create_task_group() as task_group:
  |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 678, in __aexit__
  |     raise BaseExceptionGroup(
  | exceptiongroup.ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/responses.py", line 261, in wrap
    |     await func()
    |   File "/home/zeus/miniconda3/envs/cloudspace/lib/python3.10/site-packages/starlette/responses.py", line 252, in stream_response
    |     chunk = chunk.encode(self.charset)
    | AttributeError: 'dict' object has no attribute 'encode'

cc: @lantiga