sloww 0.1.0

A lightweight TCP proxy that adds configurable delays and bandwidth limits

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

Preset	Speed	Delay	Use Case
fast-4g	9mb	60ms	Mobile 4G connection
4g	1.6mb	150ms	Regular mobile 4G connection
3g	500kb	400ms	Poor mobile 3G connection
dialup	56kb	100ms	56k modem (nostalgia!)
terrible	10kb	500ms	Worst case scenario testing

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.