Error Responses with Problem Details (RFC 9457)

def problem(status: int, type_: str, title: str, detail: str | None = None, **ext):
    body = {"type": f"https://api.example.com/problems/{type_}", "title": title, "status": status, **ext}
    if detail:
        body["detail"] = detail
    return JSONResponse(body, status_code=status, media_type="application/problem+json")

@app.exception_handler(OutOfStock)
async def out_of_stock(request: Request, exc: OutOfStock):
    return problem(409, "out-of-stock", "Item out of stock", f"Only {exc.available} left", sku=exc.sku)

app.use((err: unknown, req: Request, res: Response, _next: NextFunction) => {
  if (err instanceof OutOfStock) {
    return res.status(409).type("application/problem+json").json({
      type: "https://api.example.com/problems/out-of-stock",
      title: "Item out of stock", status: 409,
      detail: `Only ${err.available} left`, sku: err.sku, request_id: req.id,
    });
  }
  res.status(500).type("application/problem+json").json({ title: "Internal Server Error", status: 500, request_id: req.id });
});

@ExceptionHandler(OutOfStockException.class)
ProblemDetail outOfStock(OutOfStockException ex) {
    ProblemDetail pd = ProblemDetail.forStatusAndDetail(HttpStatus.CONFLICT, "Only " + ex.available() + " left");
    pd.setType(URI.create("https://api.example.com/problems/out-of-stock"));
    pd.setTitle("Item out of stock");
    pd.setProperty("sku", ex.sku());
    return pd;
}