fastapi_app.py

from fastapi import FastAPI, HTTPException
from fastapi.responses import JSONResponse
from fastapi.testclient import TestClient

GENERIC_ERROR_CODE = "generic_error"

class CustomHTTPException(HTTPException):
    error_code: str | None = None

    def __init__(self, detail: str, error_code: str = None):
        self.error_code = error_code
        super().__init__(status_code=400, detail=detail)

def http_exception_handler(request, exc):
    # Check if the exception has an error_code attribute
    error_code = exc.error_code if hasattr(exc, "error_code") else GENERIC_ERROR_CODE

    return JSONResponse(
        status_code=exc.status_code,
        content={"code": error_code, "message": exc.detail},
    )

# FastAPI application
fastapi_app = FastAPI()

# Register exception handler for FastAPI
fastapi_app.add_exception_handler(HTTPException, http_exception_handler)

@fastapi_app.get("/foo")
def fastapi_endpoint():
    raise CustomHTTPException("FastAPI error occurred", error_code="fast_api_error")

client = TestClient(fastapi_app)
res = client.get("/foo")
print(res.json())