/// <summary>
/// Gets the fragment or if no fragment is available registers the callback which
/// gets called once a fragment is available. These 2 steps are performed in a
/// synchronized way.
///
/// While getting a fragment the following algorithm is used:
/// 1. If this is the first time or if the last fragment read is an EndFragment,
/// then a new set of fragments is chosen based on the implicit priority.
/// PromptResponse is higher in priority order than default.
/// 2. If last fragment read is not an EndFragment, then next fragment is chosen from
/// the priority collection as the last fragment. This will ensure fragments
/// are sent in order.
/// </summary>
/// <param name="callback">
/// Callback to call once data is available. (This will be used if no data is currently
/// available).
/// </param>
/// <param name="priorityType">
/// Priority stream to which the returned object belongs to, if any.
/// If the call does not return any data, the value of this "out" parameter
/// is undefined.
/// </param>
/// <returns>
/// A FragmentRemoteObject if available, otherwise null.
/// </returns>
internal byte[] ReadOrRegisterCallback(OnDataAvailableCallback callback,
out DataPriorityType priorityType)
{
lock (_readSyncObject)
{
priorityType = DataPriorityType.Default;
// Send data from which ever stream that has data directly.
byte[] result = null;
SerializedDataStream promptDataToBeSent = _dataToBeSent[(int)DataPriorityType.PromptResponse];
if (promptDataToBeSent is not null)
{
result = promptDataToBeSent.ReadOrRegisterCallback(_onSendCollectionDataAvailable);
priorityType = DataPriorityType.PromptResponse;
}
if (result == null)
{
SerializedDataStream defaultDataToBeSent = _dataToBeSent[(int)DataPriorityType.Default];
if (defaultDataToBeSent is not null)
{
result = defaultDataToBeSent.ReadOrRegisterCallback(_onSendCollectionDataAvailable);
priorityType = DataPriorityType.Default;
}
}
// No data to return..so register the callback.
if (result == null)
{
// Register callback.
_onDataAvailableCallback = callback;
}
return(result);
}
}