fix(fastapi): Stop eagerly consuming request bodies for streamed spans

[alexander-alderman-webb]

Note: Depends on #6287

Description

Only attach cached request bodies to streamed spans to avoid relying on an eagerly consumed request body. Use the _json and _form attributes instead of json() and form() accessors to ensure that the request body is not consumed by the SDK.

Note: by using _json and _form directly we can no longer distinguish between raw data payloads and payloads that were not cached on the Request object. The attribute is therefore omitted if the request body is not cached, since the endpoint may not have accessed it.

The integration can still cause application hangs if middleware or handlers deprive the receive() callable instead of using Starlette accessors. Reliance on the overly ambitious request body access is only eliminated for streamed spans (and only persists for errors with the change).

• Remove test_request_body_data_does_not_scrub_pii_span_streaming() since test_formdata_request_body() already asserts that fields in the request body are not scrubbed.
• Remove test_request_body_data_annotated_value_top_level_span_streaming() because the attribute is no longer set if the request body is not JSON or FormData.

Issues

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[github-actions]

Codecov Results 📊

✅ 282 passed | Total: 282 | Pass Rate: 100% | Execution Time: 44.14s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

❌ Patch coverage is 6.06%. Project has 14801 uncovered lines.
✅ Project coverage is 33.6%. Comparing base (base) to head (head).

Files with missing lines (2)

File	Patch %	Lines
starlette.py	5.56%	⚠️ 391 Missing
fastapi.py	15.84%	⚠️ 85 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    33.53%    33.60%    +0.07%
==========================================
  Files          190       190         —
  Lines        22342     22290       -52
  Branches      7576      7540       -36
==========================================
+ Hits          7492      7489        -3
- Misses       14850     14801       -49
- Partials       749       747        -2

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