Currency Converter API

This application was built for educational purposes and is not intended for production use.

Overview

This is a subscription based currency converter API.

Motives

The main reason for creating this application was to learn new technologies and build a real-world application from scratch.

Main features:

• FastAPI framework
• async HTTP requests using httpx library
• caching with async Redis using aioredis library
• database operations using async Mongo DB with motor
• authentication via request headers
• use of pydantic for data models and validation
• custom error handling
• API call credit counter
• unified API call response model

Currency converter

Currency rates are provided by an external API https://www.fastforex.io/.

Supported operations are:

• Fetch all supported currencies
• Fetch a single exchange rate
• Fetch all exchange rates
• Currency conversion (including historical data)

Each currency conversion operation is charged 1 credit.

Subscriptions

The API offers several subscription plans:

Subscription plan	Credits	Concurrency
Basic	100	1
Hobby	500	3
Pro	10.000	10
Enterprise	50.000	15

Each user can subscribe to the service by providing a valid email address. After successful subscription the user receives an API key that is required to use the currency converter endpoints. API also provides several internal endpoints for subscription administration purposes.

Authentication

Only subscribed users can use the API. To authenticate incoming requests, we check the api_key header.

Get started

To run the API you will need an API key from https://www.fastforex.io/. Create the .env file (use the .env.dist for reference) and add the Fast Forex API key.

Dependencies

Dependency management is handled using requirements.txt file.

Docker setup

1. Build a docker image: docker build -t currency_converter_api .
2. Start redis server with : docker-compose up -d --build --force-recreate currency_converter_api
3. Create a running container: docker run -p 80:80 currency_converter_api

Local setup

1. Install dependencies from requirements.txt file
2. Run the app: uvicorn currency_converter_api.main:app --reload

Documentation

Once the application is up and running, you can access FastAPI automatic docs at index page /.

Currency converter endpoints

Method	Endpoint	Description
GET	/currencies	fetch a list of all supported currencies
GET	/convert	convert one currency into another currency
GET	/fetch_one	fetch a single exchange rate
GET	/fetch_all	fetch all available exchange rates
GET	/historical	get historical exchange rates

Admin endpoints

Method	Endpoint	Description
POST	/subscribe	create a new subscription
GET	/all_users	list all signed-up users

Status codes

Status code	Description
200	success
400	bad request, please check your request
401	user unauthorized, check your API key
424	external dependency failed
429	rate limit violation
500	internal server error, application failed

Examples

GET /convert?amount=1&from_curr=USD&to_curr=EUR

{
  "base": "USD",
  "amount": 1,
  "result": {
    "EUR": 0.94,
    "rate": 0.9393
  },
  "ms": 1
}

Swagger UI