Sentry FastAPI middleware hangs if user middleware raises an exception

[hakanutku]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

2.38.0

Steps to Reproduce

Sentry FastAPI middleware hangs if user middleware raises an exception. If I comment out sentry_sdk.init() call, I get the correct 422 response.

fastapi==0.115.12
starlette==0.46.2

import gzip
import json
import typing
import zlib

import sentry_sdk
from fastapi import FastAPI, Request
from fastapi.testclient import TestClient
from sentry_sdk.integrations.fastapi import FastApiIntegration
from sentry_sdk.integrations.starlette import StarletteIntegration
from starlette import status
from starlette.datastructures import Headers
from starlette.exceptions import HTTPException
from starlette.types import ASGIApp, Message, Receive, Scope, Send


class GZipRequestMiddleware:
    def __init__(self, app: ASGIApp):
        self.app = app

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] == "http":
            headers = Headers(scope=scope)

            if headers.get("Content-Encoding") == "gzip":
                reader = GZipRequestReader(self.app)
                await reader(scope, receive, send)
                return

        await self.app(scope, receive, send)


class GZipRequestReader:
    def __init__(self, app: ASGIApp) -> None:
        self.app = app
        self.receive: Receive = unattached_receive
        self.scope: Scope = {}
        self.actual_body_size = 0
        self.decompressor = zlib.decompressobj(16 + zlib.MAX_WBITS)

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        self.scope = scope
        self.receive = receive
        await self.app(scope, self._receive_gzipped_request, send)

    async def _receive_gzipped_request(self) -> Message:
        message = await self.receive()
        body = message.get("body", b"")
        if body:
            try:
                message["body"] = self.decompressor.decompress(body)
            except zlib.error as e:
                raise HTTPException(
                    status.HTTP_422_UNPROCESSABLE_ENTITY, "Compressed request body is malformed!"
                ) from e
            else:
                self.actual_body_size += len(message["body"])

        if not message.get("more_body", False):
            if not self.decompressor.eof:
                raise HTTPException(
                    status.HTTP_422_UNPROCESSABLE_ENTITY, "Compressed request body is truncated or incomplete!"
                )

            headers_copy = Headers(scope=self.scope).mutablecopy()
            del headers_copy["Content-Encoding"]
            headers_copy["Content-Length"] = str(self.actual_body_size)
            self.scope["headers"] = headers_copy.raw

        return message


async def unattached_receive() -> typing.NoReturn:
    raise RuntimeError("awaitable not set")  # noqa: EM101, TRY003 # pragma: no cover


if __name__ == "__main__":
    sentry_sdk.init(
        dsn="",
        send_default_pii=True,
        traces_sample_rate=1.0,
        environment="production",
        integrations=[
            FastApiIntegration(failed_request_status_codes={*range(500, 600)}),
            StarletteIntegration(failed_request_status_codes={*range(500, 600)}),
        ],
    )
    app = FastAPI()
    app.add_middleware(GZipRequestMiddleware)

    @app.post("/test")
    async def test(request: Request):
        print(await request.body())
        return await request.body()

    test_client = TestClient(app)

    uncompressed_body = '{"test": "test"}'  # Invalid uncompressed body. Should return 422
    response = test_client.post(
        "/test", content=uncompressed_body, headers={"Content-Encoding": "gzip", "Content-Type": "application/json"}
    )

    print(response.status_code)
    print(response.text)

Expected Result

Request should not hang and return 422 with "Compressed request body is malformed!" error message.

Actual Result

Cannot get response or timeout exception. It just hangs indefinitely.

[linear]

PY-1851 Sentry FastAPI middleware hangs if user middleware raises an exception

[alexander-alderman-webb]

Thanks for the report, this is interesting.

The underlying cause may be the same as in #4764.

[alexander-alderman-webb]

Thank you for your report @hakanutku.

To keep using Sentry without your server hanging please set the option below.

sentry_sdk.init(
    ...
+   max_request_body_size="never",
)

No further changes are planned due to the constraints described in #4764 (comment).