PubSub Example

This project is a small backend example that shows how to:

• publish messages through an API,
• process them through Redis Pub/Sub,
• store them in MongoDB,
• read them back with pagination.

It is intentionally simple and meant for learning/demo purposes.

What Happens In This Project

1. Client sends POST /publish/ with a message.
2. API publishes that message to a Redis channel.
3. Background listener receives the message from Redis.
4. Listener saves the message into MongoDB.
5. Client reads saved messages using GET /messages/.

Tech Stack

• FastAPI: HTTP API
• Redis: Pub/Sub transport
• MongoDB (Motor): message storage

API Endpoints

• POST /publish/
  • Body: {"message":"hello world"}
  • Result: publishes a message to Redis
• GET /messages/?limit=10&cursor=<cursor>
  • Result: returns saved messages and next_cursor
• GET /health/
  • Result: basic Redis and Mongo connectivity check

Quick Start

1. Create env file:

cp .env.dist .env

2. Install dependencies:

pip install -r requirements.txt

3. Run API server:

uvicorn main:app --reload

Example Requests

Publish:

curl -X POST http://127.0.0.1:8000/publish/ \
  -H "Content-Type: application/json" \
  -d '{"message":"hello world"}'

Read messages:

curl "http://127.0.0.1:8000/messages/?limit=10"

Health:

curl http://127.0.0.1:8000/health/

Environment Variables

Defined in .env.dist:

• MONGODB_URI
• REDIS_HOST
• REDIS_PORT
• REDIS_DB
• REDIS_CHANNEL
• DEFAULT_MESSAGES_LIMIT
• MAX_MESSAGES_LIMIT

Tests

pip install -r requirements-dev.txt
pytest -q