✨ Preserve json.JSONDecodeError information when handling invalid JSON in request body, to support custom exception handlers that use its information

[UKnowWhoIm]

Save JSONDecodeError to context by adding a from clause. The feature was requested because the user wants to use status code 400 for invalid response body.

Usage

from fastapi.exception_handlers import request_validation_exception_handler
from fastapi.exceptions import RequestValidationError

app = FastAPI()

@app.exception_handler(RequestValidationError)
async def handle(request: Request, exc: Exception):
    if isinstance(exc.__context__, JSONDecodeError):
        return Response(str(exc),status_code=400)
    return await request_validation_exception_handler(request, exc)

Enhancement requested #3993

[codecov]

Codecov Report

Merging #4057 (9809b51) into master (afaa039) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #4057   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          533       533           
  Lines        13755     13755           
=========================================
  Hits         13755     13755           

Impacted Files	Coverage Δ
fastapi/routing.py	100.00% <100.00%> (ø)

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[github-actions]

📝 Docs preview for commit 9809b51 at: https://630746e846ee066d37855789--fastapi.netlify.app

[tiangolo]

Awesome, thank you @UKnowWhoIm! 🙇