FastAPI CSV Upload Service Had Four Bugs Its Tests Missed

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The author found that a CSV upload endpoint returned a plain 500 error instead of the intended 413 response when a file exceeded the size limit. The root cause was a nonexistent status constant name in the Starlette version used, which raised an AttributeError that the service's error handling did not catch. The service also lacked an encoding policy, so Latin-1 files and binary files renamed as CSVs were handled without validation. A size check that ran only after the entire file was read, along with a more permissive-than-expected CORS configuration, were also identified as problems. The author fixed each issue and added targeted tests, including one that checks rejection of oversized files by temporarily lowering the limit.

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ProgrammingDEV Community ·

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