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What is a Seed Node?

A seed node is a peer that has the complete file and shares it with other peers in the network. When you start a seed node, it:
  • Opens a TCP server on the specified port to accept incoming connections
  • Calculates the SHA-1 hash of the file for verification
  • Divides the file into pieces (64 KiB by default)
  • Waits for leechers to connect and request pieces
The seed node automatically calculates and verifies the file hash during startup. For files smaller than 64 KiB, the piece size is automatically adjusted to match the file size.

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Starting a Seed Node

1

Prepare the file

Ensure the file you want to share exists on your system. The seed node requires read access to this file.
2

Start the seed using npm script

Use the seed npm script to start sharing a file:
npm run seed -- --port 6881 --file ./path/to/file.ext
Or use the start script directly:
npm start -- --port 6881 --file "/ruta/al/archivo.ext"
3

Verify the seed is running

You should see output similar to:
Nodo P2P iniciado. ID: ab12cd34ef56, escuchando en puerto 6881.
Archivo disponible para compartir: "video.mkv" (150000000 bytes). Esperando conexiones de pares...
4

Monitor peer connections

As leechers connect and download pieces, you’ll see messages like:
Peer 3a1f88b5e2d4 ha obtenido la pieza 0.

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Command-Line Usage

The basic syntax for starting a seed node is: 
node src/peer.js --port <puerto> --file <rutaArchivo>

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Example: Sharing a video file

node src/peer.js --port 6881 --file "video.mkv"

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Example: Using absolute paths

node src/peer.js --port 6881 --file "/home/user/files/document.pdf"

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Console Output

When running as a seed, you’ll see the following output: Initial startup: 
Nodo P2P iniciado. ID: ab12cd34ef56 escuchar en puerto 6881.
Archivo disponible: "video.mkv" (150 MB). Esperando conexiones...
When peers connect and download: 
Peer 3a1f88b5e2d4 obtuvo la pieza 0.
Recibido mapa de piezas de peer 3a1f88b5e2d4: 0 piezas disponibles.

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File Verification and Hash Calculation

The seed node automatically calculates the SHA-1 hash of the complete file during initialization. This hash is shared with leechers during the handshake to ensure file integrity.
The hash calculation happens in src/node.js:56-60: 
try {
    this.fileHash = await this.fileManager.computeHash();
} catch (err) {
    console.error('Error calculando hash del archivo:', err);
    process.exit(1);
}
This ensures that:
  • All peers are sharing the same file
  • Leechers can verify the downloaded file integrity
  • The network rejects peers trying to share different files

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Technical Details

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Piece Size

By default, files are divided into 64 KiB (65,536 bytes) pieces. This is defined in src/node.js:13: 
this.pieceSize = 65536; // Tamaño de cada pieza en bytes (64 KiB por defecto)

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Number of Pieces

The total number of pieces is calculated as: 
this.numPieces = Math.ceil(this.fileSize / this.pieceSize);
For a 150 MB file:
  • File size: 157,286,400 bytes
  • Piece size: 65,536 bytes
  • Number of pieces: 2,400 pieces
Make sure the port you specify is not blocked by your firewall and is available for incoming connections. The seed node must accept TCP connections from leechers.

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