Fix sticky bag problem

[zouyujiang]

I'm glad your project helped me. During the project, I found the following problems:

The receiving function in the project has a sticky package problem (In the type3e.py line 149):
origin code:

def _recv(self):
        """recieve mc protocol data

        Returns:
            recv_data
        """
        recv_data = self._sock.recv(self._SOCKBUFSIZE)
        return recv_data

fix code:

def _recv(self):
        """recieve mc protocol data with proper TCP fragmentation handling

        Reads the response frame in two stages to avoid sticky packet issues:
        1. Read the header to determine the total frame length from the Data Length field
        2. Read remaining data in a loop until the complete frame is received

        Returns:
            recv_data (bytes): complete mc protocol response data
        """
        # Stage 1: Read header (up to Status field, which includes Data Length)
        header_size = self._get_answerstatus_index()
        data = b''

        while len(data) < header_size:
            chunk = self._sock.recv(header_size - len(data))
            if not chunk:
                raise ConnectionError("Connection closed by PLC")
            data += chunk

        # Parse Data Length from header
        dl_start = header_size - self._wordsize
        if self.commtype == const.COMMTYPE_BINARY:
            data_length = int.from_bytes(data[dl_start:header_size], "little")
        else:
            data_length = int(data[dl_start:header_size].decode(), 16)

        total_len = header_size + data_length

        # Stage 2: Read remaining data until complete frame
        while len(data) < total_len:
            chunk = self._sock.recv(total_len - len(data))
            if not chunk:
                raise ConnectionError("Connection closed by PLC")
            data += chunk

        return data

This is the revised type3e.py attachment: type3e.py