Class: Dap::Filter::FilterDecodeBacnetRPMReply

Inherits:

Object

• Object
• Dap::Filter::FilterDecodeBacnetRPMReply

Includes:

BaseDecoder

Defined in:

lib/dap/filter/udp.rb

Overview

Decode a BACnet Read Property Multiple reply

Constant Summary

TAG_TYPE_LENGTHS =

{
  2 => 2,
  10 => 4,
  11 => 4,
}

Instance Attribute Summary

Attributes included from Base

#name, #opts

Instance Method Summary

• #decode(sdata) ⇒ Object

Methods included from BaseDecoder

#process

Methods included from Base

#initialize, #process

Instance Method Details

#decode(sdata) ⇒ Object

# File 'lib/dap/filter/udp.rb', line 379

def decode(sdata)
  info = {}
  return if sdata.length < 9

  data = sdata.dup

  bacnet_vlc_type, bacnet_vlc_function, bacnet_vlc_length = data.slice!(0,4).unpack("CCn")
  # if this isn't a BACnet/IP (0x81) original unicast NPDU (0x0a), abort
  if bacnet_vlc_type != 0x81 || bacnet_vlc_function != 0x0a
    return info
  else
    info['bacnet_vlc_type'] = bacnet_vlc_type
    info['bacnet_vlc_function'] = bacnet_vlc_function
    info['bacnet_vlc_length'] = bacnet_vlc_length
  end

  # we only know how to decode version 1, so abort if it is anything else
  # but store the version in the event that we want to parse these later
  bacnet_npdu_version, bacnet_npdu_control = data.slice!(0,2).unpack("CC")
  info['bacnet_npdu_version'] = bacnet_npdu_version
  info['bacnet_npdu_control'] = bacnet_npdu_control
  return info if bacnet_npdu_version != 1

  bacnet_apdu_type_flags, bacnet_apdu_invoke_id, bacnet_apdu_service_choice = data.slice!(0,3).unpack("CCC")
  bacnet_apdu_type = bacnet_apdu_type_flags >> 4
  bacnet_apdu_flags = bacnet_apdu_type_flags & 0b00001111
  info['bacnet_apdu_type'] = bacnet_apdu_type
  info['bacnet_apdu_flags'] = bacnet_apdu_flags
  info['bacnet_apdu_invoke_id'] = bacnet_apdu_invoke_id
  info['bacnet_apdu_service_choice'] = bacnet_apdu_service_choice
  return info unless (bacnet_apdu_type == 3 && bacnet_apdu_service_choice == 14)

  return info unless data.size > 5
  # XXX: don't know what to do with this right now
  bacnet_object_id = data.slice!(0,5)
  return info unless data.slice!(0,1).unpack('C').first == 0x1e
  props = {}
  # XXX: I think this is ASN.1, but still need to confirm
  while (true) do
    #puts "size is #{data.size}, data is #{data.each_byte.map { |b| b.to_s(16) }.join(' ')}"
    break if data.size < 4
    property_tag, property_id = data.slice!(0,2).unpack('CC')
    props[property_id] = true
    # slice off the opening tag
    otag = data.slice!(0,1).unpack('C').first
    if otag == 0x5e
      data.slice!(0,5)
      #puts "Property #{property_id} unknown"
      props[property_id] = nil
    else
      # it isn't clear if the length is one byte wide followed by one byte of
      # 0x00 for spacing or if it is two bytes little endian.  Looks like the later.
      # XXX?
      tag_flags = data.slice!(0,1).unpack('C').first
      tag_type = tag_flags >> 4
      if TAG_TYPE_LENGTHS.key?(tag_type)
        #puts "Know how to handle property #{property_id}'s tag type #{tag_type}"
        props[property_id] = data.slice!(0, TAG_TYPE_LENGTHS[tag_type])
      else
        if tag_type == 7
          property_length = data.slice!(0,2).unpack('v').first
          #puts "Handled property #{property_id}'s #{property_length}-byte tag type #{tag_type}"
            property_length -= 1
            # handle String
            props[property_id] = data.slice!(0, property_length)
        else
          #puts "Don't know how to handle property #{property_id}'s tag type #{tag_type}"
        end
      end

      ctag = data.slice!(0,1).unpack('C')
    end
    if data.size == 0
      #puts "done"
      break
    else
      #puts "going"
    end
  end

  props.each do |k,v|
    info[k] = v
  end


  info
end