Error Validation¶

Validate API error responses using Pydantic models.

Using responses Parameter¶

The responses parameter allows defining Pydantic models for different HTTP status codes.

Basic Example¶

from fasthttp import FastHTTP
from fasthttp.response import Response
from pydantic import BaseModel

app = FastHTTP(debug=True, security=False)


class Error404(BaseModel):
    message: str
    documentation_url: str
    status: str


@app.get(
    url="https://api.github.com/gist",
    responses={404: {"model": Error404}}
)
async def handle_404(resp: Response) -> dict:
    return resp.json()


app.run()

When server returns an error: 1. FastHTTP looks for model for this status 2. If found, validates JSON response 3. Validated data available via resp.json()

Multiple Status Codes¶

class Error404(BaseModel):
    message: str


class Error500(BaseModel):
    error: str
    details: str


@app.get(
    url="https://api.example.com/data",
    responses={
        404: {"model": Error404},
        500: {"model": Error500}
    }
)
async def handle_errors(resp: Response) -> dict:
    return resp.json()

Success and Error Responses¶

class SuccessResponse(BaseModel):
    id: int
    name: str


class Error404(BaseModel):
    message: str


@app.get(
    url="https://api.example.com/users/1",
    response_model=SuccessResponse,
    responses={404: {"model": Error404}}
)
async def get_user(resp: Response) -> dict:
    return resp.json()

Different HTTP Methods¶

class Error403(BaseModel):
    message: str


# POST with error handling
@app.post(
    url="https://api.example.com/users",
    json={"name": "John"},
    responses={403: {"model": Error403}}
)
async def create_user(resp: Response) -> dict:
    return resp.json()


# DELETE with error handling
@app.delete(
    url="https://api.example.com/users/1",
    responses={
        403: {"model": Error403},
        404: {"model": Error403}
    }
)
async def delete_user(resp: Response) -> dict:
    return resp.json()

Important Notes¶

responses works only for APIs returning JSON with errors
If API returns error without JSON, standard error handling triggers
Model must match API response structure
Dictionary key is always integer (HTTP status code)