SMS Gateway

A simple SMS gateway service written in Go.

Features

• Users can top up a balance and send SMS.
• Messages are enqueued and processed by worker processes.
• Fair scheduling with least-recently-served (LRS) ordering prevents whales from starving smaller users.
• REST API for user and message operations.
• Background workers claim and deliver messages.
• Prometheus metrics and health endpoints.

Requirements

• Go 1.22+
• PostgreSQL 16+

Setup

1. Run migrations:

   make migrate

2. Start the API server:

   go run ./cmd/api

   It will listen on :8080.

3. Start the worker:

   go run ./cmd/worker

   It will process queued messages.

API

• POST /users — create user
• POST /users/{id}/topup — add balance
• GET /users/{id}/balance — get balance
• POST /messages — enqueue SMS (requires X-User-ID header)
• GET /messages — list messages
• GET /messages/{id} — get message

Health & Metrics

• API: /healthz and /metrics on port 8080.
• Worker: /healthz and /metrics on port 9090.