downpour

A brutally fast, highly concurrent, multi-worker file downloader built in Go

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Build & Run

Prerequisites: Go 1.26.1, Make

Clone the repo:

git clone "https://github.com/notblankz/downpour.git"
cd downpour/

Build for your platform:

Linux / macOS

make linux-amd64    # Linux x86_64
make linux-arm64    # Linux ARM64
make darwin-amd64   # macOS Intel
make darwin-arm64   # macOS Apple Silicon

Windows (via WSL or Git Bash)

make windows-amd64  # Windows x86_64
make windows-arm64  # Windows ARM64

Or build all platforms at once:

make all

Binaries are output to the builds/ directory.

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Usage:

# Normal Download
./builds/downpour-linux-amd64 "https://ash-speed.hetzner.com/1GB.bin"

# Enable Telemetry
./builds/downpour-linux-amd64 -tel "https://sin-speed.hetzner.com/1GB.bin"

# Generate HTTP Trace Logs
./builds/downpour-linux-amd64 -hl "https://example.com/file.zip"

# Show Help
./builds/downpour-linux-amd64 -h

On Windows use .\builds\downpour-windows-amd64.exe instead.

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Current Status

• Status: Implemented a Health Monitor go routine that restarts slow workers
  • Monitor smoothened worker speeds per worker for stable restart decisions
  • Calculates the trimmed mean speed across all the workers (15% trim each side) to exclude outliers
  • Restart workers slower than 0.3x trimmed mean speed in hopes of it being routed better and can perform better
  • Skip restarts in final 2% of download to avoid TCP slow-start at tail
  • 5s grace period per worker to allow TCP slow-start ramp up of the worker before evaluating it's speed
  • Non-blocking restart signal via buffered chan struct{} size 1 - this is to prevent health monitor blocking on a busy worker
• Current Throughput: 10GB sustained download at 22.86 MB/s average
• Test Environment:
  • Tested on local machine (AMD Ryzen 7 250 + 16GB RAM + RTX 5060 Laptop GPU)
  • Test download: "https://sin-speed.hetzner.com/10GB.bin"
• Time Taken: 448.55s (12.8s faster than before)

Below is the raw Global telemetry visualization from the 10GB stress test

Below is the telemetry for download speeds of each worker