Struct ModbusMessage 

pub struct ModbusMessage {
    pub additional_address: AdditionalAddress,
    pub pdu: Pdu,
}

Represents a complete Modbus message, including the additional address, PDU and Error check.

Fields

additional_address: AdditionalAddress

The MBAP header for Modbus TCP messages.

pdu: Pdu

The Protocol Data Unit (PDU) containing the function code and data.

Implementations

impl ModbusMessage

pub fn new(additional_address: AdditionalAddress, pdu: Pdu) -> Self

Creates a new ModbusMessage instance.

Arguments

• additional_address - The additional address information (MBAP header or slave address).
• pdu - The Protocol Data Unit containing the function code and data.

Returns

A new ModbusMessage instance.

pub fn additional_address(&self) -> &AdditionalAddress

Accessor for the additional address.

pub fn pdu(&self) -> &Pdu

Accessor for the Protocol Data Unit (PDU).

The PDU contains the function code and the data payload, which are independent of the underlying transport layer (TCP, RTU, or ASCII).

pub fn unit_id_or_slave_addr(&self) -> UnitIdOrSlaveAddr

Extracts the target device identifier from the message.

This method abstracts the difference between TCP (Unit ID) and Serial (Slave Address) addressing, returning a unified UnitIdOrSlaveAddr type.

Returns

A UnitIdOrSlaveAddr representing the destination or source device.

pub fn transaction_id(&self) -> u16

Retrieves the transaction identifier for the message.

For TCP messages, this returns the ID from the MBAP header. For Serial (RTU/ASCII) messages, this returns 0 as they are inherently synchronous.

pub fn function_code(&self) -> FunctionCode

Accessor for the function code from the PDU.

pub fn data(&self) -> &Vec<u8, MAX_PDU_DATA_LEN>

Accessor for the data payload from the PDU.

pub fn data_len(&self) -> u8

Accessor for the actual length of the data payload.

pub fn to_bytes(&self) -> Result<Vec<u8, MAX_ADU_FRAME_LEN>, MbusError>

Converts the ModbusMessage into its byte representation.

This method serializes the additional address (MBAP header or slave address) followed by the PDU.

Returns

Ok(Vec<u8, MAX_ADU_LEN>) containing the ADU bytes, or an MbusError if the message cannot be serialized.

pub fn from_bytes(bytes: &[u8]) -> Result<Self, MbusError>

Creates a ModbusMessage from its byte representation (ADU).

This method parses the MBAP header and the PDU from the given byte slice.

Arguments

• bytes - A byte slice containing the complete Modbus TCP ADU.

Returns

Ok((ModbusMessage, usize)) containing the parsed message and the number of consumed bytes.

pub fn to_ascii_bytes(&self) -> Result<Vec<u8, MAX_ADU_FRAME_LEN>, MbusError>

Converts the ModbusMessage into its ASCII ADU byte representation.

This method serializes the message to binary, calculates the LRC, and then encodes the result into Modbus ASCII format (Start ‘:’, Hex, End CR LF).

Returns

Ok(Vec<u8, MAX_ADU_FRAME_LEN>) containing the ASCII ADU bytes.

Errors

Returns MbusError::BufferTooSmall if the resulting ASCII frame exceeds MAX_ADU_FRAME_LEN.

pub fn from_rtu_bytes(frame: &[u8]) -> Result<Self, MbusError>

Creates a ModbusMessage from a raw Modbus RTU byte slice.

This method validates the RTU frame by checking the minimum length and verifying the 16-bit CRC (Cyclic Redundancy Check).

Arguments

• frame - A byte slice containing the complete Modbus RTU ADU.

Returns

• Ok(ModbusMessage) if the CRC is valid and the PDU is correctly parsed.
• Err(MbusError) if the frame is too short, the checksum fails, or the PDU is invalid.

pub fn from_ascii_bytes(frame: &[u8]) -> Result<Self, MbusError>

Creates a ModbusMessage from a raw Modbus ASCII byte slice.

This method performs the following validation and transformation steps:

1. Validates the frame structure (starts with ‘:’, ends with “\r\n”).
2. Decodes the hexadecimal ASCII representation into binary data.
3. Verifies the Longitudinal Redundancy Check (LRC) checksum.
4. Parses the resulting binary into a SlaveAddress and Pdu.

Arguments

• frame - A byte slice containing the complete Modbus ASCII ADU.

Returns

• Ok(ModbusMessage) if the frame is valid and checksum matches.
• Err(MbusError) for invalid length, malformed hex, or checksum failure.

Trait Implementations

impl Clone for ModbusMessage

fn clone(&self) -> ModbusMessage

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ModbusMessage

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.