Audit messages are lost when other side closes (TCP) connection

[jodue]

Sometimes when an (TCP) audit connection is open for a longer period (say 1h) the server side may terminate the connection. In such cases the client side is not informed that the socket is in fact dead. The AuditLogger does implement a reconnect logic but this only works after the first packet could not be delivered. The main problem is that out.flush() does not block until the packet was delivered (ACK) but returns after the packet was entered successfully into the OS network stack. The Socket (and the OutputStream) is only marked as broken and fails with an IOException on the next write operation after the TCP layer gives up the retransmission.

To Reproduce
Steps to reproduce the behavior:

1. Configure an AuditLogger with a TCP connection and send one audit message.
2. Ensure that the server side kills the socket eg. by setting a short IdleTimeout on the server side.
3. Send an audit message
4. Message is dropped silently and not retransmitted

Expected behavior
Audit message should not be lost in case of connection problems when using TCP.

Screenshots
Network dump when the message is retransmitted by TCP logic becaue of missing ACK. After 5 failed attempts the packet is dropped ~6 seconds later. This is not handled in the java code!