Link Layer#

icspacket.proto.dnp3.link.LPDU_HEADER_MIN_LENGTH = 5#: Minimum number of bytes required to represent an LPDU header.

icspacket.proto.dnp3.link.LPDU_HEADER_MAX_LENGTH = 255#: Maximum possible size of an LPDU header in bytes.

icspacket.proto.dnp3.link.LPDU_USER_DATA_MAX_LENGTH = 250#: Maximum user data size (250 bytes) that a single LPDU can contain.

class icspacket.proto.dnp3.link.LinkDirection(*values)[source]#

Values for the DNP3 link layer’s direction bit (DIR field), used by this library to tag which kind of station produced a frame.

(See DNP3 Specification, Section 9.2.4.1.3.1)

MASTER = 1#: Marks a frame as originating from a Master device.

OUTSTATION = 0#: Marks a frame as originating from an Outstation device.

class icspacket.proto.dnp3.link.LinkPrimaryFunctionCode(*values)[source]#

Function codes this library uses for frames traveling from a primary station to a secondary station.

These codes are valid when the PRM bit is set (PRM = 1). (See DNP3 Specification, Table 9-1)

RESET_LINK_STATES = 0#: Resets the secondary station’s link-layer state.

TEST_LINK_STATES = 2#: Tests whether the secondary station’s link layer is still responsive.

CONFIRMED_USER_DATA = 3#: Carries user data that the secondary station must acknowledge.

UNCONFIRMED_USER_DATA = 4#: Carries user data that does not require an acknowledgement.

REQUEST_LINK_STATUS = 9#: Asks the secondary station to report its current link status.

class icspacket.proto.dnp3.link.LinkSecondaryFunctionCode(*values)[source]#

Function codes this library uses for frames traveling from a secondary station back to a primary station.

These codes are valid when the PRM bit is clear (PRM = 0). (See DNP3 Specification, Table 9-2)

ACK = 0#: Confirms that the previous frame from the primary station was accepted.

NACK = 1#: Reports that the previous frame from the primary station was rejected.

LINK_STATUS = 11#: Carries the secondary station’s answer to a REQUEST_LINK_STATUS query.

NOT_SUPPORTED = 15#: Tells the primary station that the requested link function code is not implemented.

class icspacket.proto.dnp3.link.LinkControl(direction: LinkDirection = LinkDirection.MASTER, primary_message: bool = False, frame_count_bit: bool = False, frame_count_valid: bool = False, function_code: int = 0)[source]#

This bitfield models the LPDU’s control octet, exposing a frame’s direction, transaction role, retry-detection flags, and function code as individual attributes instead of raw bits. (See DNP3 Specification, Section 9.2.4.1.3)

direction: LinkDirection = 1#: DIR bit. Records which kind of station - Master or Outstation - originated the frame.

primary_message: bool = False#

PRM bit.

True This frame opens a new transaction.
False This frame completes an existing transaction.

frame_count_bit: bool = False#: FCB bit. Toggled on primary-to-secondary frames so the secondary station can detect lost or duplicated frames.

frame_count_valid: bool = False#: FCV bit. Tells the secondary station whether it should pay attention to the FCB carried in this frame.

function_code: int = 0#: Raw 4-bit function code; decode it with pri2sec_code or sec2pri_code depending on whether this is a primary or secondary frame.

property data_flow_control: bool#

Expose the DFC bit as a boolean.

A True value signals that the sending station’s Data Link Layer receive buffer has too little free space to accept more data.

Returns:: True if buffer space is insufficient, False otherwise.
Return type:: bool

property pri2sec_code: LinkPrimaryFunctionCode#

Interpret the function code for Primary-to-Secondary frames.

Returns:: Link layer function code for PRM = 1.
Return type:: LinkPrimaryFunctionCode

property sec2pri_code: LinkSecondaryFunctionCode#

Interpret the function code for Secondary-to-Primary frames.

Returns:: Link layer function code for PRM = 0.
Return type:: LinkSecondaryFunctionCode

class icspacket.proto.dnp3.link.LPDU(*, start: bytes = b'\x05d', length: int = 0, control: LinkControl = None, destination: int = 0, source: int = 0, crc16: int = 0, user_data: TPDU | None = None)[source]#

Link-layer Protocol Data Unit (LPDU).

This struct models a complete LPDU as a fixed-size header followed by zero or more variable-length data blocks, each one closed off with its own 16-bit CRC. (See DNP3 Specification, Section 9.2.4)

start: bytes = b'\x05d'#: Fixed two-byte sync sequence (0x05, 0x64) at the start of every LPDU.

length: int = 0#: Length field: count of the non-CRC bytes that follow it, spanning the CONTROL, DESTINATION, SOURCE, and USER DATA fields.

control: LinkControl = None#: Control octet for the frame, modeled by LinkControl, holding the direction, function code, and status flags.

destination: int = 0#: Address of the data-link frame’s destination station.

source: int = 0#: Address of the data-link frame’s source station.

crc16: int = 0#: Checksum protecting the LPDU header block.

user_data: TPDU | None = None#: The frame’s payload, held as one or more user-data chunks via LinkUserData.

build() → bytes[source]#

Construct a serialized LPDU with correct length.

Returns:: Encoded LPDU bytes.
Return type:: bytes

static from_octets(data: bytes) → LPDU[source]#

Parse an LPDU from a raw byte sequence.

Changed in version 0.2.0: Renamed from from_bytes to from_octets

Parameters:: data (bytes) – Encoded LPDU bytes.
Returns:: Decoded LPDU instance.
Return type:: LPDU

property apdu: APDU#: Parse the APDU contained in the TPDU.

property tpdu: TPDU#: The TPDU contained in the LPDU.