text: module.exports = parseUdpRequest
  
  const ipLib = require('ip')
  const common = require('../common')
  
  function parseUdpRequest (msg, rinfo) {
    if (msg.length < 16) throw new Error('received packet is too short')
  
    const params = {
      connectionId: msg.slice(0, 8), // 64-bit
      action: msg.readUInt32BE(8),
      transactionId: msg.readUInt32BE(12),
      type: 'udp'
    }
  
    if (!common.CONNECTION_ID.equals(params.connectionId)) {
      throw new Error('received packet with invalid connection id')
    }
  
    if (params.action === common.ACTIONS.CONNECT) {
      // No further params
    } else if (params.action === common.ACTIONS.ANNOUNCE) {
      params.info_hash = msg.slice(16, 36).toString('hex') // 20 bytes
      params.peer_id = msg.slice(36, 56).toString('hex') // 20 bytes
      params.downloaded = fromUInt64(msg.slice(56, 64)) // TODO: track this?
      params.left = fromUInt64(msg.slice(64, 72))
      params.uploaded = fromUInt64(msg.slice(72, 80)) // TODO: track this?
  
      params.event = common.EVENT_IDS[msg.readUInt32BE(80)]
      if (!params.event) throw new Error('invalid event') // early return
  
      const ip = msg.readUInt32BE(84) // optional
      params.ip = ip
        ? ipLib.toString(ip)
        : rinfo.address
  
      params.key = msg.readUInt32BE(88) // Optional: unique random key from client
  
      // never send more than MAX_ANNOUNCE_PEERS or else the UDP packet will get bigger than
      // 512 bytes which is not safe
      params.numwant = Math.min(
        msg.readUInt32BE(92) || common.DEFAULT_ANNOUNCE_PEERS, // optional
        common.MAX_ANNOUNCE_PEERS
      )
  
      params.port = msg.readUInt16BE(96) || rinfo.port // optional
      params.addr = `${params.ip}:${params.port}` // TODO: ipv6 brackets
      params.compact = 1 // udp is always compact
    } else if (params.action === common.ACTIONS.SCRAPE) { // scrape message
      if ((msg.length - 16) % 20 !== 0) throw new Error('invalid scrape message')
      params.info_hash = []
      for (let i = 0, len = (msg.length - 16) / 20; i < len; i += 1) {
        const infoHash = msg.slice(16 + (i * 20), 36 + (i * 20)).toString('hex') // 20 bytes
        params.info_hash.push(infoHash)
      }
    } else {
      throw new Error(`Invalid action in UDP packet: ${params.action}`)
    }
  
    return params
  }
  
  const TWO_PWR_32 = (1 << 16) * 2
  
  /**
   * Return the closest floating-point representation to the buffer value. Precision will be
   * lost for big numbers.
   */
  function fromUInt64 (buf) {
    const high = buf.readUInt32BE(0) | 0 // force
    const low = buf.readUInt32BE(4) | 0
    const lowUnsigned = (low >= 0) ? low : TWO_PWR_32 + low
  
    return (high * TWO_PWR_32) + lowUnsigned
  }
  