A few MP/jsocket issues, conspiring to cause spurious socket closure / MP link down exceptions.
This has mainly gone unnoticed, until
HPCC-10917 was merged.
Some of the problems :
1) non-MP clients connecting to the MP port are not ignore early enough if invalid (e.g. if invalid MP connect packet length sent, or invalid host/remote ep sent)
2) IpAddress::setNetAddress, set invalid 'null' ip if null IPv4 provided.
3) InterCommunicator received all closed sockets as exceptions (since
HPCC-10917 change) - need to ignore all but specific one listening to.
4) Communicator - needed similar change to ignore all close sockets from outside of group.
5) Thor watchdog thread, needs to handle closed socket from group (prior to
HPCC-10917 they were ignored at MP level)