Mock Data Middleware

Overview

The Mock Data Middleware allows you to easily configure and manage mock responses for your FastAPI application. This document provides a comprehensive guide on how to use decorators to specify mocking behavior for your APIs.

Decorator Usage

You can use the decorator to describe the mocking behavior for specific APIs. The default parameters will be derived from the FastMockDecorator declaration using @mock or @mock(). However, you can also specify parameter values for each API individually.

To utilize the decorator, initialize it and apply it to your API endpoint as shown in the following example:

from fastapi import FastAPI, status
from pydantic import BaseModel

from fastmock.decorator import FastMockDecorator
from fastmock.middleware import FastMockMiddleware

app = FastAPI()
app.add_middleware(FastMockMiddleware)

mock = FastMockDecorator()

class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None

@mock(element_size=3)
@app.get("/items",
         status_code=status.HTTP_200_OK,
         responses={
             status.HTTP_200_OK: {"model": list[Item]}
         })
def read_items():
    return []

In the code above, the decorator @mock(element_size=3) overrides the default middleware parameters, setting the element size of the API output to 3.

Request Header

You can override the default middleware parameters using request headers. Each parameter can be overridden by using the X-FASTMOCK-<PARAMETER> format. For example, to set the element size of the API output to 3, you can send the header X-FASTMOCK-ELEMENT-SIZE: 3 as shown below:

curl -H "X-FASTMOCK-ELEMENT-SIZE: 3" http://127.0.0.1:8000/items

Data Retrieval Order

During middleware initialization, you can provide custom functions to override the default data retrieval functions or their order with the attribute retrieve_data_function_list. The default order of operations is as follows, with each step potentially overriding the data from the previous step if parameters are defined:

1. Middleware initialization
2. Decorator initialization
3. API Decorator
4. Header request

This structure ensures that headers can dynamically adjust the behavior of the middleware on a per-request basis.