/**
* Retrieves acknowledgement information for a given outbound (and inbound) sequence
*
* @param outboundSequenceId outbound sequence identifier
* @return acknowledgement information for a given outbound sequence
* @throws UnknownSequenceException if no such sequence exits for a given sequence identifier
*/
public AcknowledgementData getAcknowledgementData(String outboundSequenceId)
throws UnknownSequenceException {
assert sequenceManager != null;
AcknowledgementData.Builder ackDataBuilder = AcknowledgementData.getBuilder();
Sequence inboundSequence = sequenceManager.getBoundSequence(outboundSequenceId);
if (inboundSequence != null) {
/**
* If inbound sequence exists, we are not checking if inboundSequence.isAckRequested() is
* true. Instead, we are allways attaching inbound sequence acknowledegements (even if not
* requested by the other side) This is to avoid potential locks in InOrder
* delivery/redelivery scenarios.
*
* <p>For example, following could happen on the client side with InOrder enabled if we
* strictly checked for inboundSequence.isAckRequested() to be true:
*
* <p>0. response to a previous client request arrives, endpoint is waiting for an
* acknowledgement 1. client request is put to delivery queue 2. acknowledgements are attached
* to the client request and ackRequested flag is cleared on inbound sequence 3. client
* request gets lost. 4. client request is scheduled for a resend 5. client request is put to
* delivery queue 6. this time, ackRequested flag is clear, so we will not append any
* acknowledgements 7. client request is processed on the endpoint and response is put to the
* endpoint's source delivery queue 8. since there was no acknowledgement of the previous
* response, the new response is blocekd in the delivery queue forever
*
* <p>After step 8., communication between client and endpoint might freeze in a deadlock
* unless another means of communicating the sequence acknowledgements from client to the
* endpoint are established.
*/
ackDataBuilder.acknowledgements(
inboundSequence.getId(),
inboundSequence.getAcknowledgedMessageNumbers(),
inboundSequence.isClosed());
inboundSequence.clearAckRequestedFlag();
}
// outbound sequence ack requested flag
final Sequence outboundSequence = sequenceManager.getSequence(outboundSequenceId);
if (outboundSequence.hasUnacknowledgedMessages()) {
ackDataBuilder.ackReqestedSequenceId(outboundSequenceId);
outboundSequence.updateLastAcknowledgementRequestTime();
}
final AcknowledgementData acknowledgementData = ackDataBuilder.build();
return acknowledgementData;
}
