blocking_client.py

import socket
import select
from pymodbus.client.sync import ModbusTcpClient, _logger
from pymodbus.constants import Defaults
from pymodbus.exceptions import ConnectionException


class ModbusTcpClientBlocking(ModbusTcpClient):

    def connect(self):
        """
        Connect to the modbus tcp server

        :returns: True if connection succeeded, False otherwise
        """
        if self.socket:
            return True
        try:
            self.socket = socket.create_connection((self.host, self.port), Defaults.Timeout)

        except socket.error, msg:
            _logger.error('Connection to (%s, %s) failed: %s' % (self.host, self.port, msg))
            self.close()
        return self.socket is not None

    def _recv(self, size):
        """
        Reads data from the underlying descriptor

        :param size: The number of bytes to read
        :return: The bytes read
        """

        _logger.info('Receiving data with length: %s' % size)

        if not self.socket:
            raise ConnectionException(self.__str__())

        data = ''
        while len(data) < size:
            try:
                chunk = self.socket.recv(size-len(data))
                _logger.info('Received chunk: 0x%s with length: %s' % (chunk.encode('hex'), len(chunk)))

            except socket.timeout:
                _logger.error('Giving up, timeout ...')
                break

            if chunk == '':
                _logger.error('Socket connection broken')
                return False

            data = data + chunk

        if len(data) > 0:
            _logger.info('Complete data: 0x%s with length: %s' % (data.encode('hex'), len(data)))

        return data