Struct Header 

pub struct Header {
    pub transaction_id: u16,
    pub protocol_id: u16,
    pub length: u16,
    pub unit_id: UnitId,
}

Modbus Application Protocol (Data Unit) header aka «MBAP header».

Fields

transaction_id: u16

Transaction ID used to match responses with requests.

protocol_id: u16

Protocol ID. Always 0 for Modbus.

length: u16

Number of following codec, including the Unit Identifier and data fields.

unit_id: UnitId

Unit identifier aka «slave ID».

Identification of a remote slave connected on a serial line or on other buses.

Implementations

impl Header

pub const N_BYTES: usize = 7

pub const fn payload_length(&self) -> u16

Expected PDU length.

TCP transport implementation should read exactly this number of codec and parse as crate::protocol::Response.

impl Header

pub const PROTOCOL_ID: u16 = 0

Trait Implementations

impl Clone for Header

fn clone(&self) -> Header

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Decode for Header

fn decode(from: &mut impl Buf) -> Result<Self, Error>

Decode a header.

Example

use fennec_modbus::{
    protocol::codec::Decode,
    tcp::{Header, UnitId},
};

let mut bytes: &[u8] = &[
    0x15, 0x01, // transaction ID: high, low
    0x00, 0x00, // protocol ID
    0x00, 0x06, // length
    0xFF, // unit ID
];
let header = Header::decode(&mut bytes).unwrap();

assert_eq!(header.transaction_id, 0x1501);
assert_eq!(header.protocol_id, 0);
assert_eq!(header.unit_id, UnitId::NonSignificant);

impl Encode for Header

fn encode(&self, buf: &mut impl BufMut)

Encode the header.

Example

use fennec_modbus::{
    protocol::codec::Encode,
    tcp::{Header, UnitId, header},
};

const EXPECTED: &[u8] = &[
    0x15, 0x01, // transaction ID: high, low
    0x00, 0x00, // protocol ID
    0x00, 0x06, // length
    0xFF, // unit ID
];

let header = Header {
    unit_id: UnitId::NonSignificant,
    transaction_id: 0x1501,
    length: 6,
    protocol_id: 0,
};
let mut bytes = Vec::new();
header.encode(&mut bytes);
assert_eq!(bytes, EXPECTED);

fn to_bytes(&self) -> Vec<u8>