ValueError when running CFDP receiver before sender

[bruceplai]

Run a cfdp transfer test (in either py 2.7 or py 3.7)
-In one terminal run ait_cfdp_start_receiver and leave it running
-In another terminal run ait_cfdp_start_sender.py

You will see errors like the captured sample below:

2019-11-06T09:56:13.304 | INFO | Receiver 2: Received FILE DATA PDU event
2019-11-06T09:56:13.305 | INFO | Writing file data to file /Users/blai/projects/ait-core/ait/dsn/cfdp/datasink/tempfiles/tmp_transfer_2_1 with offset 24576
2019-11-06T09:56:13.392 | WARNING | EXCEPTION: 105 is not a valid FileDirective
2019-11-06T09:56:13.393 | WARNING | Traceback (most recent call last):
File "/Users/blai/projects/ait-dsn/ait/dsn/cfdp/cfdp.py", line 287, in read_pdus_from_socket
pdu = make_pdu_from_bytes(pdu_bytes)
File "/Users/blai/projects/ait-dsn/ait/dsn/cfdp/pdu/util.py", line 62, in make_pdu_from_bytes
directive_code = FileDirective(pdu_body[0])
File "/Users/blai/.virtualenvs/p2/lib/python2.7/site-packages/enum/init.py", line 347, in call
return cls.new(cls, value)
File "/Users/blai/.virtualenvs/p2/lib/python2.7/site-packages/enum/init.py", line 662, in new
raise ValueError("%s is not a valid %s" % (value, cls.name))
ValueError: 105 is not a valid FileDirective

2019-11-06T09:56:13.507 | INFO | Receiver 2: Received FILE DATA PDU event
2019-11-06T09:56:13.508 | INFO | Writing file data to file /Users/blai/projects/ait-core/ait/dsn/cfdp/datasink/tempfiles/tmp_transfer_2_1 with offset 28672
2019-11-06T09:56:13.604 | WARNING | EXCEPTION: pdu header should be at least 4 bytes long
2019-11-06T09:56:13.604 | WARNING | Traceback (most recent call last):
File "/Users/blai/projects/ait-dsn/ait/dsn/cfdp/cfdp.py", line 287, in read_pdus_from_socket
pdu = make_pdu_from_bytes(pdu_bytes)
File "/Users/blai/projects/ait-dsn/ait/dsn/cfdp/pdu/util.py", line 58, in make_pdu_from_bytes
header = Header.to_object(pdu_bytes)
File "/Users/blai/projects/ait-dsn/ait/dsn/cfdp/pdu/header.py", line 230, in to_object
raise ValueError('pdu header should be at least 4 bytes long')
ValueError: pdu header should be at least 4 bytes long