#19096 introduced a generic TCPTransport base class so we can have multiple TCP based transport implementation. These implementations can vary in how they respond internally to situations where we concurrently send, receive and handle disconnects and can have different exceptions. However, disconnects are important events for the rest of the code base and should be distinguished from other errors (for example, it signals TransportMasterAction that it needs to retry and wait for the a (new) master to come back). Therefore, we should make sure that all the implementations do the proper translation from their internal exceptions into ConnectTransportException which is used externally.
Similarly we should make sure that the transport implementation properly recognize errors that were caused by a disconnect as such and deal with them correctly. This was, for example, the source of a build failure at https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+multijob-intake/1080 , where a concurrency issue cause SocketException to bubble out of MockTcpTransport.
This PR adds a tests which concurrently simulates connects, disconnects, sending and receiving and makes sure the above holds. It also fixes anything (not much!) that was found it.
bd574d92ae