import uvicorn
from fastapi import FastAPI, Query, Body, Request, HTTPException, status, Path
from fastapi.responses import JSONResponse
from pydantic import BaseModel, Field
from typing import Annotated


class MyCustomException(Exception):
    def __init__(self, message="Default custom exception handler message"):
        self.message = message
        super().__init__(self.message)

    def __str__(self):
        return self.message


app = FastAPI(description="Checking my fastapi middleware")


@app.exception_handler(MyCustomException)
async def custom_exception_handler(request: Request, exc: MyCustomException):
    return JSONResponse(status_code=status.HTTP_401_UNAUTHORIZED, content={"message": str(exc)})


@app.middleware("http")
async def header_check(request: Request, call_next):
    auth_header = request.headers.get("x-Auth")
    if auth_header != "anilpatro":
        raise MyCustomException(message="Authentication failure")
    response = await call_next(request)
    response.headers["x-auth"] = "validated"
    return response


class UserBase(BaseModel):
    name: str = Field(description="User name", max_length=10)
    sur_name: str | None = Field(description="Optional surname field")
    salary: int = Field(default=100, lt=10000)


class User(UserBase):
    password: str = Field(description="User password field", max_length=10)


@app.post("/usr/{user_id}")
async def get_user(user: Annotated[User, Body()],
                   user_id: Annotated[int, Path(description="user id field", gt=0)],
                   q: Annotated[int, Query(default=1)]):
    response = {"user": user.dict(), "user_id": user_id}
    if q:
        response.update({"q": q})
    return response


if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

In the above code the proper curl – curl -X POST “http://0.0.0.0:8000/usr/1?q=5” -H “x-Auth: anilpatro” -H “Content-Type: application/json” -d ‘{“name”: “John”, “sur_name”: “Doe”, “salary”: 900, “password”: “secret”}’

is working fine, how ever for testing purpose – curl -X POST “http://0.0.0.0:8000/usr/1?q=5” -H “x-Auth: wrongheader” -H “Content-Type: application/json” -d ‘{“name”: “John”, “sur_name”: “Doe”, “salary”: 900, “password”: “secret”}’

I am expecting an unauthorised exception. Am I making any mistake while calling exception handler in middleware or fastapi does not support that ?

Appreciate the support 🙂

In the above code the proper curl – curl -X POST “http://0.0.0.0:8000/usr/1?q=5” -H “x-Auth: anilpatro” -H “Content-Type: application/json” -d ‘{“name”: “John”, “sur_name”: “Doe”, “salary”: 900, “password”: “secret”}’

is working fine, how ever for testing purpose – curl -X POST “http://0.0.0.0:8000/usr/1?q=5” -H “x-Auth: wrongheader” -H “Content-Type: application/json” -d ‘{“name”: “John”, “sur_name”: “Doe”, “salary”: 900, “password”: “secret”}’

I am expecting an unauthorised exception. Am I ma`