Error APDUs report that a confirmed service request could not be completed.

APDU Description (ASHRAE 135)

The BACnet-Error-PDU is used to convey the information contained in a service response primitive that indicates the reason why a previous confirmed service request failed, either in its entirety or only partially. (Clause 21)

They are the normal way a server signals a semantic failure (as opposed to a protocol problem, which would use Reject or Abort).

The class / code pair gives a standardized reason (see BACnet.Protocol.Constants.error_class/0 and BACnet.Protocol.Constants.error_code/0, and Clause 18). Many services also return additional error information in the payload field.

This module implements the BACnet.Stack.EncoderProtocol.

Decoding is performed by BACnet.Protocol.APDU.decode/1 (and BACnet.Protocol.APDU.decode_error/1).

Examples

iex> err = %Error{
...>   invoke_id: 5,
...>   service: :write_property,
...>   class: :property,
...>   code: :write_access_denied,
...>   payload: []
...> }
iex> Error.encode(err)
{:ok, <<80, 5, 15, 145, 2, 145, 40>>}

Decoding an Error APDU:

iex> raw = <<0x50, 0x05, 0x0F, 0x91, 0x02, 0x91, 0x28>>
iex> BACnet.Protocol.APDU.decode(raw)
{:ok, %Error{invoke_id: 5, service: :write_property, class: :property, code: :write_access_denied, payload: []}}