💾 CLI Downloader (C++)

A custom-built command-line downloader written in C++ with support for multithreaded downloads using HTTP Range requests.

About

This project is a custom CLI downloader designed to explore how file transfers work under the hood.

The goal was not to compete with tools like aria2, but to deeply understand:

• how HTTP transfers work under the hood
• how data is streamed and written to disk
• how to design a modular system in C++
• how to build a clean, extensible architecture

⚙️ Features (v0.2)

• Download files over HTTP/HTTPS
• Streaming download (no full file buffering in memory)
• Binary-safe file writing
• Header parsing (Content-Length)
• Multithreaded downloads (HTTP Range-based)
• Chunk-based downloading with concurrent workers
• Automatic fallback to single-thread when range is unsupported
• Preallocated file writing (safe concurrent writes)
• CLI interface

📐 Architecture

CLI (main.cpp)
↓
Downloader
↓
Worker (multi-thread)
↓
HttpClient (libcurl)
↓
FileWriter

Each module has a single responsibility

• HttpClient → handles HTTP communication
• FileWriter → writes binary data to disk
• Worker → downloads a specific byte range (chunk)
• Downloader → orchestrates the process
• CLI (main) → UI

Usage

Build

make

Run

./build/downloader <URL> <output_file> <threads_num>

Example

./build/downloader "http://speedtest.tele2.net/100MB.zip" test.zip 10

🧪 Tested on

• Large files (100MB+)
• Chrome installer (Google CDN)
• Wikimedia dumps (~300MB)
• Servers with and without HTTP Range support

⚠️ Limitations

• Multithreaded mode requires server support for HTTP Range (206)
• No retry mechanism yet (planned)
• No resume support yet (planned)

🛠 Tech Stack

• C++17
• libcurl
• Makefile

📈 Future Plans

• Retry mechanism
• Resume support
• Progress bar (CLI UI)
• Batch downloads
• Scheduler