package org.jscsi.target.connection.stage.fullfeature;

 import java.io.IOException;

 import java.nio.ByteBuffer;

 import java.security.DigestException;

 import org.jscsi.exception.InternetSCSIException;

 import org.jscsi.parser.BasicHeaderSegment;

 import org.jscsi.parser.ProtocolDataUnit;

 import org.jscsi.parser.nop.NOPOutParser;

 import org.jscsi.target.connection.TargetPduFactory;

 import org.jscsi.target.connection.phase.TargetFullFeaturePhase;

 import org.jscsi.target.settings.SettingsException;

 /**

  * A stage for processing NOP-Out PDUs, which are used by the initiator for pinging the target, making sure that the

  * connection is still up.

  * <p>

  * The {@link #execute(ProtocolDataUnit)} method will process these ping messages and send a NOP-In PDU as ping echo,

  * containing a copy of the NOP-Out PDU's data segment.

  * <p>

  * If either the NOP-OUT PDU's initiator or target transfer tag equals the reserved value of 0xffffffff, then no reply

  * will be sent, since the PDU is only supposed to acknowledge a changed ExpCmdSN, or serve as an echo to a NOP-IN ping

  * sent by the target.

  * 

  * @author Andreas Ergenzinger

  */

 public class PingStage extends TargetFullFeatureStage {

     private static final int RESERVED_TAG_VALUE = 0xffffffff;

     public PingStage (TargetFullFeaturePhase targetFullFeaturePhase) {

         super(targetFullFeaturePhase);

     }

     @Override

     public void execute (final ProtocolDataUnit pdu) throws IOException , InterruptedException , InternetSCSIException , DigestException , SettingsException {

         final BasicHeaderSegment bhs = pdu.getBasicHeaderSegment();

         final NOPOutParser parser = (NOPOutParser) bhs.getParser();

         if (parser.getTargetTransferTag() != RESERVED_TAG_VALUE) {

             /*

              * This is an error. The jSCSI Target does not send NOP-In ping messages, which would be the only legal

              * reason for the initiator sending a NOP-Out with the TargetTransferTag equal to 0xffffffff. And even if

              * the jSCSI Target was sending pings, the echo would be processed in a dedicated stage. Therefore, we treat

              * this as an error. Close the connection.

              */

             throw new InternetSCSIException("NOP-Out PDU TargetTransferTag = " + parser.getTargetTransferTag() + " in PingStage");

         }

         // decide whether or not response is necessary

         if (bhs.getInitiatorTaskTag() == RESERVED_TAG_VALUE) return;// send no response

         // else

         // prepare response data segment (copy up to initiator's

         // MaxRecvDataSegmentLength)

         final int dataSegmentLength = Math.min(pdu.getDataSegment().capacity(), settings.getMaxRecvDataSegmentLength());

         final ByteBuffer responseDataSegment = ByteBuffer.allocate(dataSegmentLength);

         responseDataSegment.put(pdu.getDataSegment().array(),// source array,

                 0,// offset within the array of the first byte to be read

                 dataSegmentLength);// length

         // send response

         final ProtocolDataUnit responsePdu = TargetPduFactory.createNopInPDU(0,// logicalUnitNumber,

                                                                                // reserved

                 bhs.getInitiatorTaskTag(),// initiatorTaskTag

                 RESERVED_TAG_VALUE,// targetTransferTag

                 responseDataSegment, parser.getExpectedStatusSequenceNumber());

         connection.sendPdu(responsePdu);

     }

 }