/* NOTE: this function processes incoming frames and stores flags/data; the TcpStateMachine function processes stored flags, advances the state machine as necessary, and sends out responses */
internal void OnPacketReceived(UInt32 sourceIPAddress, UInt32 destinationIPAddress, byte[] buffer, Int32 index, Int32 count)
{
if (_isDisposed)
{
return;
}
if (count < TCP_HEADER_MIN_LENGTH)
{
return;
}
UInt16 packetHeaderChecksum = (UInt16)((((UInt16)buffer[index + 16]) << 8) + buffer[index + 17]);
// calculate checksum to verify packet integrity.
UInt16 calculateChecksum;
lock (_tcpPseudoHeaderBufferLockObject)
{
// create temporary pseudo header
_tcpPseudoHeaderBuffer[0] = (byte)((sourceIPAddress >> 24) & 0xFF);
_tcpPseudoHeaderBuffer[1] = (byte)((sourceIPAddress >> 16) & 0xFF);
_tcpPseudoHeaderBuffer[2] = (byte)((sourceIPAddress >> 8) & 0xFF);
_tcpPseudoHeaderBuffer[3] = (byte)(sourceIPAddress & 0xFF);
_tcpPseudoHeaderBuffer[4] = (byte)((destinationIPAddress >> 24) & 0xFF);
_tcpPseudoHeaderBuffer[5] = (byte)((destinationIPAddress >> 16) & 0xFF);
_tcpPseudoHeaderBuffer[6] = (byte)((destinationIPAddress >> 8) & 0xFF);
_tcpPseudoHeaderBuffer[7] = (byte)(destinationIPAddress & 0xFF);
_tcpPseudoHeaderBuffer[8] = 0; // ZERO
_tcpPseudoHeaderBuffer[9] = (byte)IPv4Layer.ProtocolType.Tcp; // Protocol Number
_tcpPseudoHeaderBuffer[10] = (byte)((count >> 8) & 0xFF);
_tcpPseudoHeaderBuffer[11] = (byte)(count & 0xFF);
// calculate checksum over entire pseudo-header, TCP header and data
_checksumBufferArray[0] = _tcpPseudoHeaderBuffer;
_checksumOffsetArray[0] = 0;
_checksumCountArray[0] = TCP_PSEUDO_HEADER_LENGTH;
_checksumBufferArray[1] = buffer;
_checksumOffsetArray[1] = index;
_checksumCountArray[1] = count;
calculateChecksum = Utility.CalculateInternetChecksum(_checksumBufferArray, _checksumOffsetArray, _checksumCountArray, 2);
}
if (calculateChecksum != 0x0000)
{
return; // drop packet
}
// find the source and destination port #s for our packet (looking into the packet)
UInt16 sourceIPPort = (UInt16)((((UInt16)buffer[index + 0]) << 8) + buffer[index + 1]);
UInt16 destinationIPPort = (UInt16)((((UInt16)buffer[index + 2]) << 8) + buffer[index + 3]);
TcpSocket socket = null;
for (int i = 0; i < IPv4Layer.MAX_SIMULTANEOUS_SOCKETS; i++)
{
if ((IPv4Layer._sockets[i] != null) &&
(IPv4Layer._sockets[i].ProtocolType == IPv4Layer.ProtocolType.Tcp) &&
(IPv4Layer._sockets[i].SourceIPAddress == destinationIPAddress) &&
(IPv4Layer._sockets[i].SourceIPPort == destinationIPPort) &&
(IPv4Layer._sockets[i].DestinationIPAddress == sourceIPAddress) &&
(IPv4Layer._sockets[i].DestinationIPPort == sourceIPPort))
{
socket = (TcpSocket)IPv4Layer._sockets[i];
socket.OnPacketReceived(sourceIPAddress, destinationIPAddress, buffer, index, count);
break;
}
}
/* TODO: if this packet is a request to connect to a listening port, pass it along now */
if (socket == null)
{
for (int i = 0; i < IPv4Layer.MAX_SIMULTANEOUS_SOCKETS; i++)
{
if ((IPv4Layer._sockets[i] != null) &&
(IPv4Layer._sockets[i].ProtocolType == IPv4Layer.ProtocolType.Tcp) &&
(IPv4Layer._sockets[i].SourceIPAddress == destinationIPAddress) &&
(IPv4Layer._sockets[i].SourceIPPort == destinationIPPort) &&
(((TcpSocket)IPv4Layer._sockets[i]).IsListening == true)
)
{
socket = (TcpSocket)IPv4Layer._sockets[i];
socket.OnPacketReceived(sourceIPAddress, destinationIPAddress, buffer, index, count);
break;
}
}
}
/* if this packet is otherwise invalid, respond a TCP "RESET" packet */
if (socket == null)
{
/* send a TCP "RESET" packet */
UInt32 sequenceNumber =
((UInt32)buffer[index + 4] << 24) +
((UInt32)buffer[index + 5] << 16) +
((UInt32)buffer[index + 6] << 8) +
(UInt32)buffer[index + 7];
UInt32 acknowledgmentNumber =
((UInt32)buffer[index + 8] << 24) +
((UInt32)buffer[index + 9] << 16) +
((UInt32)buffer[index + 10] << 8) +
(UInt32)buffer[index + 11];
SendTcpSegment(destinationIPAddress, sourceIPAddress, destinationIPPort, sourceIPPort,
acknowledgmentNumber, sequenceNumber, 0, false, false, true, false, false, null, new byte[] { }, 0, 0, Int64.MaxValue);
}
}