Download function gives a error (Invalid Block Size)

[iambeluchi]

Hello Team,

I am here again... lol

I am trying to download an OB content to the PLC, and I keep getting an invalid block size error.

Please see my code below:

      import snap7
      import scapy
      from scapy.all import *
      from scapy.all import wrpcap
      import re
      import binascii

      plc = snap7.client.Client()
      plc.connect('192.168.0.1', 0, 2)
      db_number = 100
      start_add = 1
      packets = rdpcap(r"s7comm_downloading_block_db1.pcap")
      a = len(packets)

      for i in range(1, a):
       if (len(packets[i]) > 200):
       for pkt in packets[i]:
        ab = pkt[Raw]
        #print (ab)
        type(ab)
        pkt = binascii.hexlify(bytes(ab))
        sea_byte = pkt.find(b'32')
        data_protocol = pkt [sea_byte:sea_byte+2]
        response_msg = pkt.find (b'fb')

        data_funct_codes = """{
                                "00":"Cpu_services",
                                "f0":"Setup_communication",
                                "04":"Read_Variable",
                                "05":"Write_Variable",
                                "1a":"Request_download",
                                "1b":"Download_block",
                                "1c":"Download_ended",
                                "1d":"Start_upload",
                                "1e":"U_Upload",
                                "1f":"End_upload",
                                "28":"Plc_Control",
                                "29":"Plc_Stop"
                                }"""

            search_download_block = pkt.find(b'1b')
           search_upload_block = pkt.find(b'1e')
           search_data_block = pkt.find(b'7070')

        if (search_download_block > 0):
            print('this is a download code')
            print("The response to this request is:")
            download_res = (pkt[response_msg + 2:])
            b = download_res
            g = bytearray(b)
            print(g)

            plc.ab_write(0, g)
            plc.download(g, 1)


         plc.plc_stop()
         plc.plc_hot_start()

         print("Close communication PLC")

         plc.disconnect()

The plc.ab_write part works. But the plc.download keeps giving error. The code is to download the data part of a pcap file to the PLC.

Please I need help... I saw a related article but cant seem to make sense of it.