@biancoroyal/bacstack/lib/bvlc.js

A BACnet protocol stack written in pure JavaScript.

'use strict';

const baEnum      = require('./enum');

const DefaultBACnetPort = 47808;

module.exports.encode = (buffer, func, msgLength, originatingIP) => {
  buffer[0] = baEnum.BVLL_TYPE_BACNET_IP;
  buffer[1] = func;
  buffer[2] = (msgLength & 0xFF00) >> 8;
  buffer[3] = (msgLength & 0x00FF) >> 0;
  if (originatingIP) {
    // This is always a FORWARDED_NPDU regardless of the 'func' parameter.
    if (func !== baEnum.BvlcResultPurpose.FORWARDED_NPDU) {
      throw new Error('Cannot specify originatingIP unless '
        + 'BvlcResultPurpose.FORWARDED_NPDU is used.');
    }
    // Encode the IP address and optional port into bytes.
    const [ipstr, portstr] = originatingIP.split(':');
    const port = parseInt(portstr) || DefaultBACnetPort;
    const ip = ipstr.split('.');
    buffer[4] = parseInt(ip[0]);
    buffer[5] = parseInt(ip[1]);
    buffer[6] = parseInt(ip[2]);
    buffer[7] = parseInt(ip[3]);
    buffer[8] = (port & 0xFF00) >> 8;
    buffer[9] = (port & 0x00FF) >> 0;
    return 6 + baEnum.BVLC_HEADER_LENGTH;
  } else {
    if (func === baEnum.BvlcResultPurpose.FORWARDED_NPDU) {
      throw new Error('Must specify originatingIP if '
        + 'BvlcResultPurpose.FORWARDED_NPDU is used.');
    }
  }
  return baEnum.BVLC_HEADER_LENGTH;
};

module.exports.decode = (buffer, offset) => {
  let len;
  const func = buffer[1];
  const msgLength = (buffer[2] << 8) | (buffer[3] << 0);
  if (buffer[0] !== baEnum.BVLL_TYPE_BACNET_IP || buffer.length !== msgLength) return;
  let originatingIP = null;
  switch (func) {
    case baEnum.BvlcResultPurpose.BVLC_RESULT:
    case baEnum.BvlcResultPurpose.ORIGINAL_UNICAST_NPDU:
    case baEnum.BvlcResultPurpose.ORIGINAL_BROADCAST_NPDU:
    case baEnum.BvlcResultPurpose.DISTRIBUTE_BROADCAST_TO_NETWORK:
    case baEnum.BvlcResultPurpose.REGISTER_FOREIGN_DEVICE:
    case baEnum.BvlcResultPurpose.READ_FOREIGN_DEVICE_TABLE:
    case baEnum.BvlcResultPurpose.DELETE_FOREIGN_DEVICE_TABLE_ENTRY:
    case baEnum.BvlcResultPurpose.READ_BROADCAST_DISTRIBUTION_TABLE:
    case baEnum.BvlcResultPurpose.WRITE_BROADCAST_DISTRIBUTION_TABLE:
    case baEnum.BvlcResultPurpose.READ_BROADCAST_DISTRIBUTION_TABLE_ACK:
    case baEnum.BvlcResultPurpose.READ_FOREIGN_DEVICE_TABLE_ACK:
      len = 4;
      break;
    case baEnum.BvlcResultPurpose.FORWARDED_NPDU:
      // Work out where the packet originally came from before the BBMD
      // forwarded it to us, so we can tell the BBMD where to send any reply to.
      const port = (buffer[8] << 8) | buffer[9];
      originatingIP = buffer.slice(4, 8).join('.');

      // Only add the port if it's not the usual one.
      if (port !== DefaultBACnetPort) {
        originatingIP += ':' + port;
      }

      len = 10;
      break;
    case baEnum.BvlcResultPurpose.SECURE_BVLL:
      // unimplemented
      return;
    default:
      return;
  }
  return {
    len: len,
    func: func,
    msgLength: msgLength,
    // Originating IP is set to the IP address of the node that originally
    // sent the packet, when it has been forwarded to us by a BBMD (since the
    // BBMD's IP address will be in the sender field.
    originatingIP: originatingIP,
  };
};