/// <summary>
/// Acknowledge the reception of packets which have been sent. The reliability
/// shared context/state is updated when packets are received from the other end
/// of the connection. The other side will update it's ackmask with which packets
/// have been received (starting from last received sequence ID) each time it sends
/// a packet back. This checks the resend timers on each non-acknowledged packet
/// and notifies if it's time to resend yet.
/// </summary>
/// <param name="context">Pipeline context, contains the buffer slices this pipeline connection owns.</param>
/// <returns></returns>
public static unsafe bool ReleaseOrResumePackets(NetworkPipelineContext context)
{
SharedContext *reliable = (SharedContext *)context.internalSharedProcessBuffer.GetUnsafePtr();
Context * ctx = (Context *)context.internalProcessBuffer.GetUnsafePtr();
// Last sequence ID and ackmask we received from the remote peer, these are confirmed delivered packets
var lastReceivedAckMask = reliable->SentPackets.AckMask;
var lastOwnSequenceIdAckedByRemote = (ushort)reliable->SentPackets.Acked;
// To deal with wrapping, chop off the upper half of the sequence ID and multiply by window size, it
// will then never wrap but will map to the correct index in the packet storage, wrapping happens when
// sending low sequence IDs (since it checks sequence IDs backwards in time).
var sequence = (ushort)(reliable->WindowSize * ((1 - lastOwnSequenceIdAckedByRemote) >> 15));
// Check each slot in the window, starting from the sequence ID calculated above (this isn't the
// latest sequence ID though as it was adjusted to avoid wrapping)
for (int i = 0; i < reliable->WindowSize; i++)
{
var info = GetPacketInformation(context.internalProcessBuffer, sequence);
if (info->SequenceId >= 0)
{
// Check the bit for this sequence ID against the ackmask. Bit 0 in the ackmask is the latest
// ackedSeqId, bit 1 latest ackedSeqId - 1 (one older) and so on. If bit X is 1 then ackedSeqId-X is acknowledged
var ackBits = 1 << (lastOwnSequenceIdAckedByRemote - info->SequenceId);
// Release if this seqId has been flipped on in the ackmask (so it's acknowledged)
// Ignore if sequence ID is out of window range of the last acknowledged id
if (SequenceHelpers.AbsDistance((ushort)lastOwnSequenceIdAckedByRemote, (ushort)info->SequenceId) < reliable->WindowSize && (ackBits & lastReceivedAckMask) != 0)
{
Release(context.internalProcessBuffer, info->SequenceId);
info->SendTime = -1;
sequence = (ushort)(sequence - 1);
continue;
}
var timeToResend = CurrentResendTime(context.internalSharedProcessBuffer);
if (context.timestamp > info->SendTime + timeToResend)
{
ctx->Resume = info->SequenceId;
}
}
sequence = (ushort)(sequence - 1);
}
return(ctx->Resume != NullEntry);
}
/// <summary>
/// Read header data and update reliability tracking information in the shared context.
/// - If the packets sequence ID is lower than the last received ID+1, then it's stale
/// - If the packets sequence ID is higher, then we'll process it and update tracking info in the shared context
/// </summary>
/// <param name="context">Pipeline context, the reliability shared state is used here.</param>
/// <param name="header">Packet header of a new received packet.</param>
/// <returns>Sequence ID of the received packet.</returns>
public static unsafe int Read(NetworkPipelineContext context, PacketHeader header)
{
SharedContext *reliable = (SharedContext *)context.internalSharedProcessBuffer.GetUnsafePtr();
reliable->stats.PacketsReceived++;
if (SequenceHelpers.StalePacket(
header.SequenceId,
(ushort)(reliable->ReceivedPackets.Sequence + 1),
(ushort)reliable->WindowSize))
{
reliable->stats.PacketsStale++;
return((int)ErrorCodes.Stale_Packet);
}
var window = reliable->WindowSize - 1;
if (SequenceHelpers.GreaterThan16((ushort)(header.SequenceId + 1), (ushort)reliable->ReceivedPackets.Sequence))
{
int distance = SequenceHelpers.AbsDistance(header.SequenceId, (ushort)reliable->ReceivedPackets.Sequence);
for (var i = 0; i < Math.Min(distance, window); ++i)
{
if ((reliable->ReceivedPackets.AckMask & 1 << (window - i)) == 0)
{
reliable->stats.PacketsDropped++;
}
}
if (distance > window)
{
reliable->stats.PacketsDropped += distance - window;
reliable->ReceivedPackets.AckMask = 1;
}
else
{
reliable->ReceivedPackets.AckMask <<= distance;
reliable->ReceivedPackets.AckMask |= 1;
}
reliable->ReceivedPackets.Sequence = header.SequenceId;
}
else if (SequenceHelpers.LessThan16(header.SequenceId, (ushort)reliable->ReceivedPackets.Sequence))
{
int distance = SequenceHelpers.AbsDistance(header.SequenceId, (ushort)reliable->ReceivedPackets.Sequence);
// If this is a resent packet the distance will seem very big and needs to be calculated again with adjustment for wrapping
if (distance >= ushort.MaxValue - reliable->WindowSize)
{
distance = reliable->ReceivedPackets.Sequence - header.SequenceId;
}
var ackBit = 1 << distance;
if ((ackBit & reliable->ReceivedPackets.AckMask) != 0)
{
reliable->stats.PacketsDuplicated++;
return((int)ErrorCodes.Duplicated_Packet);
}
reliable->stats.PacketsOutOfOrder++;
reliable->ReceivedPackets.AckMask |= (uint)ackBit;
}
// Store receive timestamp for remote sequence ID we just received
StoreRemoteReceiveTimestamp(context.internalSharedProcessBuffer, header.SequenceId, context.timestamp);
ReadAckPacket(context, header);
return(header.SequenceId);
}