Get response body in Middleware

How do I get the response body from the StreamingResponse object in middleware?

Simple example:

class AccessMiddleware(base.BaseHTTPMiddleware):

    async def dispatch(
        self,
        request: Request,
        handler: base.RequestResponseEndpoint,
    ) -> Response:
        response: StreamingResponse = await handler(request)

        binary = b''
        async for data in response.body_iterator:
            binary += data
        body = binary.decode()
        
        print(body)

        return response  # Here body is empty

Is it possible to copy the response.body_iterator generator?
What is the best way to solve the problem of extracting final data (response body) and further post-processing?

Thanks.

[BC30138]

Just because such solution not stated yet, but it’s worked for me:

from typing import Callable, Awaitable

from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request
from starlette.responses import StreamingResponse
from starlette.concurrency import iterate_in_threadpool

class LogStatsMiddleware(BaseHTTPMiddleware):
    async def dispatch(  # type: ignore
        self, request: Request, call_next: Callable[[Request], Awaitable[StreamingResponse]],
    ) -> Response:
        response = await call_next(request)
        response_body = [section async for section in response.body_iterator]
        response.body_iterator = iterate_in_threadpool(iter(response_body))
        logging.info(f"response_body={response_body[0].decode()}")
        return response

def init_app(app):
    app.add_middleware(LogStatsMiddleware)

iterate_in_threadpool actually making from iterator object async Iterator

If you look on implementation of starlette.responses.StreamingResponse you’ll see, that this function used exactly for this

[AmmarAhmadKhan]

Just because such solution not stated yet, but it’s worked for me:

from typing import Callable, Awaitable

from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request
from starlette.responses import StreamingResponse
from starlette.concurrency import iterate_in_threadpool

class LogStatsMiddleware(BaseHTTPMiddleware):
    async def dispatch(  # type: ignore
        self, request: Request, call_next: Callable[[Request], Awaitable[StreamingResponse]],
    ) -> Response:
        response = await call_next(request)
        response_body = [section async for section in response.body_iterator]
        response.body_iterator = iterate_in_threadpool(iter(response_body))
        logging.info(f"response_body={response_body[0].decode()}")
        return response

def init_app(app):
    app.add_middleware(LogStatsMiddleware)

iterate_in_threadpool actually making from iterator object async Iterator

If you look on implementation of starlette.responses.StreamingResponse you’ll see, that this function used exactly for this

response_body[0].decode() Gives error if we return some fields with value of true or false and says “name true is not defined”. How to get rid of this issue ?