Python socketcan interface for J1939 transport protocol

Question

Using python with socketcan in the J1939 protocol, it seems that recvfrom() does not return the interface when the data is more than 8 bytes. In the J1939 protocl, when there is more than 8 data bytes, multiple CAN messages are sent since a CAN message can only hold up to 8 data bytes.

Using the program below, I see that the interface is returned for 8 data bytes, but not for 9 data bytes.

Is the issue with Python or with the kernel? How can we reach the right developer in the case this is really a bug?

Thank you.

#!/usr/bin/env python3

import socket

send_socket = socket.socket(socket.PF_CAN, socket.SOCK_DGRAM, socket.CAN_J1939) 

interface = "vcan0"

send_socket_src_name = socket.J1939_NO_NAME
send_socket_src_pgn = socket.J1939_NO_PGN 
send_socket_src_addr = 0x80
send_socket_src_sck_addr = (interface, send_socket_src_name, send_socket_src_pgn, send_socket_src_addr)
send_socket.bind(send_socket_src_sck_addr)

send_socket_dest_name = socket.J1939_NO_NAME 
send_socket_dest_pgn = 0x2300
send_socket_dest_addr = 0x81
send_socket_dest_sck_addr = (interface, send_socket_dest_name, send_socket_dest_pgn, send_socket_dest_addr)
send_socket_data_8_bytes = b'\x01\x02\x03\x04\x05\x06\x07\x08'
send_socket_data_9_bytes = b'\x01\x02\x03\x04\x05\x06\x07\x08\x09'

receive_socket = socket.socket(socket.PF_CAN, socket.SOCK_DGRAM, socket.CAN_J1939) 

receive_socket_src_name = socket.J1939_NO_NAME
receive_socket_src_pgn = socket.J1939_NO_PGN 
receive_socket_src_addr = 0x81 
receive_socket_src_sck_addr = (interface, receive_socket_src_name, receive_socket_src_pgn, receive_socket_src_addr)
receive_socket.bind(receive_socket_src_sck_addr)

send_socket.sendto(send_socket_data_8_bytes, send_socket_dest_sck_addr)
(data, sock_addr) = receive_socket.recvfrom(128)
(interface, src_name, src_pgn, src_addr) = sock_addr
print(f"interface for 8 data bytes:{interface}")

send_socket.sendto(send_socket_data_9_bytes, send_socket_dest_sck_addr)
(data, sock_addr) = receive_socket.recvfrom(128)
(interface, src_name, src_pgn, src_addr) = sock_addr
print(f"interface for 9 data bytes:{interface}")

receive_socket.close()
send_socket.close()

This is the output:

interface for 8 data bytes:vcan0
interface for 9 data bytes: