Sloww - Simple Slow TCP Proxy

A lightweight TCP proxy that adds configurable delays and bandwidth limits. Perfect for testing application behavior under poor network conditions.

Why Sloww?

• Simple: Single Python file, no complex configuration
• Lightweight: Uses asyncio, handles many connections efficiently
• Cross-platform: Works on Linux, macOS, Windows
• No root required: Runs in userspace
• Docker-ready: Easy containerization for development environments

Installation

pip install sloww

Usage

# Basic usage
sloww LISTEN_PORT DESTINATION:PORT [OPTIONS]

# Slow down PostgreSQL
sloww localhost:5432 -l :5433 -s 100kb -d 50ms

# Simulate 3G connection
sloww api.example.com:80 -l :8080 --preset 3g

# Listen on all interfaces
sloww db.internal:3306 -l 0.0.0.0:3307 -s 1mb

Options

• -l, --listen: Listen address (default: 127.0.0.1:RANDOM_PORT)
• -s, --speed: Speed limit (e.g., 100kb, 1mb) (default: unlimited)
• -d, --delay: Delay per packet (e.g., 50ms, 0.5s) (default: none)
• -b, --buffer-size: Buffer size in bytes (default: 8192)
• --preset: Network preset (3g, slow-3g, dialup, terrible) (default: none)
• --stats-interval: Print stats every N minute
• --connect-timeout: Timeout for establishing a connection to the origin

Network Presets

Docker

Quick Start

docker build -t sloww .

# Proxy PostgreSQL with 3G speeds
docker run -p 5433:5432 sloww your-db:5432 -l :5432 --preset 3g

Docker Compose Example

services:
  postgres:
    image: postgres:15
    environment:
      POSTGRES_PASSWORD: postgres

  postgres-slow:
    image: ghcr.io/ericgazoni/sloww:latest
    command: ["postgres:5432", "-l", "0.0.0.0:5432", "--preset", "3g"]
    ports:
      - "5433:5432"  # Access slow PG on localhost:5433

Testing Different Network Conditions

services:
  # Your API
  api:
    image: your-api:latest

  # Near region (low latency)
  api-near:
    image: ghcr.io/ericgazoni/sloww:latest
    command: ["api:8080", "-l", "0.0.0.0:8081", "-d", "20ms"]
    ports:
      - "8081:8080"

  # Remote region (medium latency)
  api-remote:
    image: ghcr.io/ericgazoni/sloww:latest
    command: ["api:8080", "-l", "0.0.0.0:8082", "-d", "100ms"]
    ports:
      - "8082:8080"

  # Far region (high latency)
  api-far:
    image: ghcr.io/ericgazoni/sloww:latest
    command: ["api:8080", "-l", "0.0.0.0:8083", "-d", "200ms"]
    ports:
      - "8083:8080"

  # Mobile 3G
  api-mobile:
    image: ghcr.io/ericgazoni/sloww:latest
    command: ["api:8080", "-l", "0.0.0.0:8084", "--preset", "3g"]
    ports:
      - "8084:8080"

Use Cases

Development & Testing

• Test timeout handling
• Verify loading states and spinners
• Test progressive data loading
• Validate error recovery
• Check connection pooling behavior

Database Testing

# Test your app with slow database
sloww production.db:5432 -l :5433 -s 50kb -d 100ms
psql postgresql://localhost:5433/myapp

# See how your ORM handles connection delays
sloww mysql.prod:3306 -l :3307 --preset slow-3g

API Testing

# Test mobile app with realistic 3G
sloww api.example.com:443 -l :8080 --preset 3g

# Simulate cross-region latency
sloww api.example.com:443 -l :8080 -d 200ms

Contributing

This is a simple tool that does one thing well. PRs welcome for:

• Additional network presets
• IPV6 Support
• Better statistics/monitoring
• Connection persistence options
• HTTP/WebSocket protocol awareness
• TLS/SSL support
• Jitter/loss

License

MIT License

Credits

Inspired by Sloxy C implementation by Jakob Egger.