@pr4j3sh/bitter/src/message.js

bittorrent client

const { Buffer } = require("node:buffer");
const parser = require("./parser");
const utils = require("./utils");

module.exports.buildHandshake = (torrent) => {
  const buf = Buffer.alloc(68);
  buf.writeUInt8(19, 0);
  buf.write("BitTorrent protocol", 1);
  buf.writeUInt32BE(0, 20);
  buf.writeUInt32BE(0, 24);
  parser.infoHash(torrent).copy(buf, 28);
  utils.genId().copy(buf, 48);
  return buf;
};

module.exports.buildKeepAlive = () => Buffer.alloc(4);

module.exports.buildChoke = () => {
  const buf = Buffer.alloc(5);
  buf.writeUInt32BE(1, 0);
  buf.writeUInt8(0, 4);
  return buf;
};

module.exports.buildUnchoke = () => {
  const buf = Buffer.alloc(5);
  buf.writeUInt32BE(1, 0);
  buf.writeUInt8(1, 4);
  return buf;
};

module.exports.buildInterested = () => {
  const buf = Buffer.alloc(5);
  buf.writeUInt32BE(1, 0);
  buf.writeUInt8(2, 4);
  return buf;
};

module.exports.buildUninterested = () => {
  const buf = Buffer.alloc(5);
  buf.writeUInt32BE(1, 0);
  buf.writeUInt8(3, 4);
  return buf;
};

module.exports.buildHave = (payload) => {
  const buf = Buffer.alloc(9);
  buf.writeUInt32BE(5, 0);
  buf.writeUInt8(4, 4);
  buf.writeUInt32BE(payload, 5);
  return buf;
};

module.exports.buildBitfield = (bitfield) => {
  const buf = Buffer.alloc(bitfield.length + 1 + 4);
  buf.writeUInt32BE(payload.length + 1, 0);
  buf.writeUInt8(5, 4);
  bitfield.copy(buf, 5);
  return buf;
};

module.exports.buildRequest = (payload) => {
  const buf = Buffer.alloc(17);
  buf.writeUInt32BE(13, 0);
  buf.writeUInt8(6, 4);
  buf.writeUInt32BE(payload.index, 5);
  buf.writeUInt32BE(payload.begin, 9);
  buf.writeUInt32BE(payload.length, 13);
  return buf;
};

module.exports.buildPiece = (payload) => {
  const buf = Buffer.alloc(payload.block.length + 13);
  buf.writeUInt32BE(payload.block.length + 9, 0);
  buf.writeUInt8(7, 4);
  buf.writeUInt32BE(payload.index, 5);
  buf.writeUInt32BE(payload.begin, 9);
  payload.block.copy(buf, 13);
  return buf;
};

module.exports.buildCancel = (payload) => {
  const buf = Buffer.alloc(17);
  buf.writeUInt32BE(13, 0);
  buf.writeUInt8(8, 4);
  buf.writeUInt32BE(payload.index, 5);
  buf.writeUInt32BE(payload.begin, 9);
  buf.writeUInt32BE(payload.length, 13);
  return buf;
};

module.exports.buildPort = (payload) => {
  const buf = Buffer.alloc(7);
  buf.writeUInt32BE(3, 0);
  buf.writeUInt8(9, 4);
  buf.writeUInt16BE(payload, 5);
  return buf;
};

module.exports.parse = (msg) => {
  const id = msg.length > 4 ? msg.readInt8(4) : null;
  let payload = msg.length > 5 ? msg.slice(5) : null;

  if (id === 6 || id === 7 || id === 8) {
    const rest = payload.slice(8);
    payload = {
      index: payload.readInt32BE(0),
      begin: payload.readInt32BE(4),
    };
    payload[id === 7 ? "block" : "length"] = rest;
  }

  return {
    size: msg.readInt32BE(0),
    id,
    payload,
  };
};