Eru: Multi-threaded File Downloader

Eru is a small multi-threaded file downloader written in C++. It splits the target file into chunks, fetches them in parallel over HTTP/HTTPS with libcurl, and stitches the result back together. It also downloads BitTorrent magnet links and .torrent files using aria2. I built it because I wanted IDM-like behaviour without paying for IDM or pirating it.

On Linux and macOS, libaria2 is compiled straight into the binary, so torrent support is fully self-contained. On Windows, Eru shells out to an external aria2c binary (choco install aria2).

Features

• Multi-threaded HTTP/HTTPS downloading
• BitTorrent support via magnet links and .torrent files (powered by aria2)
• Progress bar with real-time updates
• Automatic filename detection from URL
• Customizable number of download threads
• Displays download speed and estimated time remaining
• Automatic merging of downloaded chunks

Requirements

• C++17 compatible compiler
• CMake 3.16 or higher
• Nodus 0.0.1-alpha or newer
• To embed torrent support (Linux/macOS): autoconf, automake, libtool, pkg-config, gettext, plus OpenSSL and zlib headers — used to build the bundled libaria2 from source
• Windows only: aria2 installed at runtime for torrent/magnet downloads

Eru's CMake dependencies are declared in nodus.toml and locked in cmake/nodus/package-lock.cmake. Nodus uses CPM.cmake to acquire CPR, CLI11, and indicators; no manual libcurl installation is required for that path.

Building from Source

1. Clone the repository:

   git clone https://github.com/Dank-del/eru.git
   cd eru
   

2. Install the locked source dependencies:

   nodus install
   

3. Configure the project with CMake:

   cmake -S . -B build
   

4. Build the project:

   cmake --build build
   

On Linux/macOS, omit no options to build embedded aria2 support. To build only the HTTP downloader while setting up the project, use:

cmake -S . -B build -DERU_EMBED_ARIA2=OFF

Eru statically links the GNU runtime by default. If your distribution does not provide the static libstdc++ archive, configure with -DERU_STATIC_RUNTIME=OFF instead.

Usage

After building, you can run Eru using the following command:

./src/eru --url <download_url_or_magnet_or_torrent> [options]

Eru auto-detects the source type: magnet: links and paths ending in .torrent are downloaded over BitTorrent, everything else over HTTP/HTTPS.

Options

• -u, --url <url>: URL to download, a magnet: link, or a path to a .torrent file (required)
• -o, --output <path>: Output filename for HTTP downloads, or the save directory for torrents (optional)
• -t, --threads <number>: Number of download threads for HTTP (default: 4; ignored for torrents)
• -a, --about: Display information about Eru
• -h, --help: Show help message

Examples

1. Download a file using default settings:

   ./src/eru --url https://example.com/large_file.zip
   

2. Download a file with a custom output name and 8 threads:

   ./src/eru --url https://example.com/large_file.zip --output my_file.zip --threads 8
   

3. Download a magnet link into a folder:

   ./src/eru --url "magnet:?xt=urn:btih:..." --output ./downloads
   

4. Download from a local .torrent file:

   ./src/eru --url ./ubuntu.torrent --output ./downloads
   

5. Display information about Eru:

   ./src/eru --about
   

Contributing

Pull requests welcome.

License

MIT. See LICENSE.

Author

Sayan Biswas

• Email: me@sayanbiswas.in

Acknowledgments

• CPR for HTTP requests
• CLI11 for command-line parsing
• indicators for progress bars
• aria2 for BitTorrent downloads