Description of problem:
I have two CentOS 7 hosts: one acting as the sigul bridge, the other as the sigul server.  My workstation (the sigul client) is running Fedora 24.  It seems that any attempt to use the sigul client results in an error like this:

$ sigul list-users
Administrator's password:
2016-09-19 11:12:16,660 WARNING: (child) Exception in child
Traceback (most recent call last):
  File "/usr/share/sigul/double_tls.py", line 777, in __child
    _ForwardingBuffer.forward_two_way(buf_1, buf_2)
  File "/usr/share/sigul/double_tls.py", line 177, in forward_two_way
    buf_1._receive(poll_descs)
  File "/usr/share/sigul/double_tls.py", line 335, in _receive
    r1 = self.__receive_inner(poll_descs)
  File "/usr/share/sigul/double_tls.py", line 277, in __receive_inner
    data = self.__inner_src.recv(self._BUFFER_LEN - len(self.__buffer))
ValueError: I/O operation on closed socket


Version-Release number of selected component (if applicable):
bridge & sever: sigul-0.101-1.el7.noarch
client:         sigul-0.102-3.fc24.noarch

How reproducible:
always


Actual results:

In addition to the error shown above for the client, the bridge logs:

2016-09-19 11:32:28,316 INFO: Client with CN 'd13677' connected
2016-09-19 11:32:28,319 INFO: Unexpected EOF: EOFError('Unexpected EOF on _DoubleTLS',)
2016-09-19 11:32:28,319 DEBUG: Request handling finished
2016-09-19 11:32:28,319 DEBUG: Waiting for the server to connect
2016-09-19 11:32:28,366 DEBUG: Waiting for the client to connect

and the server logs:

2016-09-19 11:32:28,319 DEBUG: (child) NSPR error: Connection reset
2016-09-19 11:32:28,321 DEBUG: Child exited with status 256
2016-09-19 11:32:28,322 INFO: Unexpected EOF
2016-09-19 11:32:28,322 DEBUG: Request handling finished
2016-09-19 11:32:28,363 DEBUG: Waiting for a request


Expected results:
Normal functionality, or a more helpful error message if there's some incompatibility boundary being crossed here.

Additional info:

This occurred while I was attempting to rebuild an old Fedora 21 setup.  At first I thought the problem was with the new CentOS 7-based server and bridge until I went back for a sanity check and attempted my example "sigul list-users" against the old F21 setup.  Interestingly, I get the same errors on the client and older bridge.   The older server merely logs:

2016-09-19 11:38:45,007 INFO: Unexpected EOF


Since my $HOME (and consequently ~/.sigul/) is on NFS and usable from both my workstation and the bridge, I am to log into the bridge and run sigul commands there successfully as workaround.  This also confirms that there's likely no problems in the configuration of my new bridge and server.