45 lines
1.4 KiB
Python
45 lines
1.4 KiB
Python
"""Modbus Socket frame implementation."""
|
|
from __future__ import annotations
|
|
|
|
from pymodbus.framer.base import FramerBase
|
|
from pymodbus.logging import Log
|
|
|
|
|
|
class FramerSocket(FramerBase):
|
|
"""Modbus Socket frame type.
|
|
|
|
[ MBAP Header ] [ Function Code] [ Data ]
|
|
[ tid ][ pid ][ length ][ uid ]
|
|
2b 2b 2b 1b 1b Nb
|
|
|
|
* length = uid + function code + data
|
|
"""
|
|
|
|
MIN_SIZE = 8
|
|
|
|
def decode(self, data: bytes) -> tuple[int, int, int, bytes]:
|
|
"""Decode ADU."""
|
|
if (used_len := len(data)) < self.MIN_SIZE:
|
|
Log.debug("Very short frame (NO MBAP): {} wait for more data", data, ":hex")
|
|
return 0, 0, 0, self.EMPTY
|
|
msg_tid = int.from_bytes(data[0:2], 'big')
|
|
msg_len = int.from_bytes(data[4:6], 'big') + 6
|
|
msg_dev = int(data[6])
|
|
if used_len < msg_len:
|
|
Log.debug("Short frame: {} wait for more data", data, ":hex")
|
|
return 0, 0, 0, self.EMPTY
|
|
if msg_len == 8 and used_len == 9:
|
|
msg_len = 9
|
|
return msg_len, msg_tid, msg_dev, data[7:msg_len]
|
|
|
|
def encode(self, pdu: bytes, device_id: int, tid: int) -> bytes:
|
|
"""Encode ADU."""
|
|
packet = (
|
|
tid.to_bytes(2, 'big') +
|
|
b'\x00\x00' +
|
|
(len(pdu) + 1).to_bytes(2, 'big') +
|
|
device_id.to_bytes(1, 'big') +
|
|
pdu
|
|
)
|
|
return packet
|