/**
   * Populates a specific <tt>Request</tt> instance with the headers common to dialog-creating
   * <tt>Request</tt>s and ones sent inside existing dialogs and specific to the general event
   * package subscription functionality that this instance and a specific <tt>Subscription</tt>
   * represent.
   *
   * @param req the <tt>Request</tt> instance to be populated with common headers and ones specific
   *     to the event package of a specific <tt>Subscription</tt>
   * @param subscription the <tt>Subscription</tt> which is to be described in the specified
   *     <tt>Request</tt> i.e. its properties are to be used to populate the specified
   *     <tt>Request</tt>
   * @param expires the subscription duration to be set into the Expires header of the specified
   *     SUBSCRIBE <tt>Request</tt>
   * @throws OperationFailedException if we fail parsing or populating the subscription request.
   */
  protected void populateSubscribeRequest(Request req, Subscription subscription, int expires)
      throws OperationFailedException {
    HeaderFactory headerFactory = protocolProvider.getHeaderFactory();

    // Event
    EventHeader evHeader;
    try {
      evHeader = headerFactory.createEventHeader(eventPackage);

      String eventId = subscription.getEventId();
      if (eventId != null) evHeader.setEventId(eventId);
    } catch (ParseException e) {
      // these two should never happen.
      logger.error("An unexpected error occurred while" + "constructing the EventHeader", e);
      throw new OperationFailedException(
          "An unexpected error occurred while" + "constructing the EventHeader",
          OperationFailedException.INTERNAL_ERROR,
          e);
    }
    req.setHeader(evHeader);

    // Accept
    AcceptHeader accept;
    try {
      accept = headerFactory.createAcceptHeader("application", contentSubType);
    } catch (ParseException e) {
      logger.error("wrong accept header", e);
      throw new OperationFailedException(
          "An unexpected error occurred while" + "constructing the AcceptHeader",
          OperationFailedException.INTERNAL_ERROR,
          e);
    }
    req.setHeader(accept);

    // Expires
    ExpiresHeader expHeader;
    try {
      expHeader = headerFactory.createExpiresHeader(expires);
    } catch (InvalidArgumentException e) {
      logger.error("Invalid expires value: " + expires, e);
      throw new OperationFailedException(
          "An unexpected error occurred while" + "constructing the ExpiresHeader",
          OperationFailedException.INTERNAL_ERROR,
          e);
    }
    req.setHeader(expHeader);
  }
  /**
   * Creates a new SUBSCRIBE request in the form of a <tt>ClientTransaction</tt> with the parameters
   * of a specific <tt>Subscription</tt>.
   *
   * @param subscription the <tt>Subscription</tt> to be described in a SUBSCRIBE request
   * @param expires the subscription duration of the SUBSCRIBE request to be created
   * @return a new <tt>ClientTransaction</tt> initialized with a new SUBSCRIBE request which matches
   *     the parameters of the specified <tt>Subscription</tt>
   * @throws OperationFailedException if the request could not be generated
   */
  private ClientTransaction createSubscription(Subscription subscription, int expires)
      throws OperationFailedException {
    Address toAddress = subscription.getAddress();
    HeaderFactory headerFactory = protocolProvider.getHeaderFactory();

    // Call ID
    CallIdHeader callIdHeader = protocolProvider.getDefaultJainSipProvider().getNewCallId();

    // CSeq
    CSeqHeader cSeqHeader;
    try {
      cSeqHeader = headerFactory.createCSeqHeader(1l, Request.SUBSCRIBE);
    } catch (InvalidArgumentException ex) {
      // Shouldn't happen
      logger.error("An unexpected error occurred while" + "constructing the CSeqHeader", ex);
      throw new OperationFailedException(
          "An unexpected error occurred while" + "constructing the CSeqHeader",
          OperationFailedException.INTERNAL_ERROR,
          ex);
    } catch (ParseException ex) {
      // shouldn't happen
      logger.error("An unexpected error occurred while" + "constructing the CSeqHeader", ex);
      throw new OperationFailedException(
          "An unexpected error occurred while" + "constructing the CSeqHeader",
          OperationFailedException.INTERNAL_ERROR,
          ex);
    }

    // FromHeader and ToHeader
    String localTag = SipMessageFactory.generateLocalTag();
    FromHeader fromHeader;
    ToHeader toHeader;
    try {
      // FromHeader
      fromHeader =
          headerFactory.createFromHeader(protocolProvider.getOurSipAddress(toAddress), localTag);

      // ToHeader
      toHeader = headerFactory.createToHeader(toAddress, null);
    } catch (ParseException ex) {
      // these two should never happen.
      logger.error(
          "An unexpected error occurred while" + "constructing the FromHeader or ToHeader", ex);
      throw new OperationFailedException(
          "An unexpected error occurred while" + "constructing the FromHeader or ToHeader",
          OperationFailedException.INTERNAL_ERROR,
          ex);
    }

    // ViaHeaders
    ArrayList<ViaHeader> viaHeaders = protocolProvider.getLocalViaHeaders(toAddress);

    // MaxForwards
    MaxForwardsHeader maxForwards = protocolProvider.getMaxForwardsHeader();

    Request req;
    try {
      req =
          protocolProvider
              .getMessageFactory()
              .createRequest(
                  toHeader.getAddress().getURI(),
                  Request.SUBSCRIBE,
                  callIdHeader,
                  cSeqHeader,
                  fromHeader,
                  toHeader,
                  viaHeaders,
                  maxForwards);
    } catch (ParseException ex) {
      // shouldn't happen
      logger.error("Failed to create message Request!", ex);
      throw new OperationFailedException(
          "Failed to create message Request!", OperationFailedException.INTERNAL_ERROR, ex);
    }

    populateSubscribeRequest(req, subscription, expires);

    // Transaction
    ClientTransaction subscribeTransaction;
    try {
      subscribeTransaction =
          protocolProvider.getDefaultJainSipProvider().getNewClientTransaction(req);
    } catch (TransactionUnavailableException ex) {
      logger.error(
          "Failed to create subscribe transaction.\n"
              + "This is most probably a network connection error.",
          ex);
      throw new OperationFailedException(
          "Failed to create the subscription transaction",
          OperationFailedException.NETWORK_FAILURE);
    }
    return subscribeTransaction;
  }