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);
      }
  
  }