fix(fastapi): do not consume request body

[alexander-alderman-webb]

You can mount any ASGI app to a FastAPI or Starlette route. You can also parse the request body manually using the receive callable on FastAPI's and Starlette's Request objects.

In either case, reading json(), form() or body() in the patched route handler consumes the request body stream, leaving no stream for the application to read. If the user relies on these high-level Starlette methods then there is no issue because Starlette caches the result. Combining our FastAPI or Starlette integrations with low-level ASGI request body parsing is problematic.

Approach in this PR:

• Attach the request body in the event processor, not in the route handler itself.
• If the user calls json(), form() or body(), cache the result on the ASGI scope and attach the result to events as before.
• Cache the raw request body on the ASGI scope. If none of the above methods are called try to parse the request body and attach the result to events. An exception could be raised before any of the above methods are invoked.

Closes #4764

[codecov]

❌ 11 Tests Failed:

Tests completed	Failed	Passed	Skipped
22013	11	22002	2108

View the top 3 failed test(s) by shortest run time

::tests.integrations.ariadne.test_ariadne

Stack Traces | 0s run time

.../integrations/ariadne/test_ariadne.py:8: in <module>
    from sentry_sdk.integrations.fastapi import FastApiIntegration
sentry_sdk/integrations/fastapi.py:18: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:654: in <module>
    class MultipartPart:
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

::tests.integrations.ariadne.test_ariadne

Stack Traces | 0s run time

.../integrations/ariadne/test_ariadne.py:8: in <module>
    from sentry_sdk.integrations.fastapi import FastApiIntegration
sentry_sdk/integrations/fastapi.py:18: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:654: in <module>
    class MultipartPart:
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

::tests.integrations.graphene.test_graphene

Stack Traces | 0s run time

.../integrations/graphene/test_graphene.py:7: in <module>
    from sentry_sdk.integrations.fastapi import FastApiIntegration
sentry_sdk/integrations/fastapi.py:18: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:653: in <module>
    @dataclass
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

::tests.integrations.starlette.test_starlette

Stack Traces | 0s run time

.../integrations/starlette/test_starlette.py:16: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:654: in <module>
    class MultipartPart:
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

::tests.integrations.starlette.test_starlette

Stack Traces | 0s run time

.../integrations/starlette/test_starlette.py:16: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:654: in <module>
    class MultipartPart:
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

::tests.integrations.starlette.test_starlette

Stack Traces | 0s run time

.../integrations/starlette/test_starlette.py:16: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:653: in <module>
    @dataclass
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

::tests.integrations.starlette.test_starlette

Stack Traces | 0s run time

.../integrations/starlette/test_starlette.py:16: in <module>
    from sentry_sdk.integrations.starlette import (
sentry_sdk/integrations/starlette.py:653: in <module>
    @dataclass
sentry_sdk/integrations/starlette.py:655: in MultipartPart
    content_disposition: bytes | None = None
E   TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

tests.integrations.starlette.test_starlette::test_starletterequestextractor_form_bytes

Stack Traces | 0.065s run time

.../integrations/starlette/test_starlette.py:465: in test_starletterequestextractor_form_bytes
    form_data = request_info["data"]
E   TypeError: 'NoneType' object is not subscriptable

tests.integrations.starlette.test_starlette::test_starletterequestextractor_form_bytes

Stack Traces | 0.067s run time

.../integrations/starlette/test_starlette.py:465: in test_starletterequestextractor_form_bytes
    form_data = request_info["data"]
                ^^^^^^^^^^^^^^^^^^^^
E   TypeError: 'NoneType' object is not subscriptable

tests.integrations.starlette.test_starlette::test_starletterequestextractor_form_bytes

Stack Traces | 0.077s run time

.../integrations/starlette/test_starlette.py:465: in test_starletterequestextractor_form_bytes
    form_data = request_info["data"]
                ^^^^^^^^^^^^^^^^^^^^
E   TypeError: 'NoneType' object is not subscriptable

tests.integrations.starlette.test_starlette::test_starletterequestextractor_form_bytes

Stack Traces | 0.082s run time

.../integrations/starlette/test_starlette.py:465: in test_starletterequestextractor_form_bytes
    form_data = request_info["data"]
                ^^^^^^^^^^^^^^^^^^^^
E   TypeError: 'NoneType' object is not subscriptable

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[alexander-alderman-webb]

Closing for the reasons in #4764 (comment)