/// <summary>
/// Writes the layer to the buffer.
/// </summary>
/// <param name="buffer">The buffer to write the layer to.</param>
/// <param name="offset">The offset in the buffer to start writing the layer at.</param>
/// <param name="payloadLength">The length of the layer's payload (the number of bytes after the layer in the packet).</param>
/// <param name="previousLayer">The layer that comes before this layer. null if this is the first layer.</param>
/// <param name="nextLayer">The layer that comes after this layer. null if this is the last layer.</param>
public override void Write(byte[] buffer, int offset, int payloadLength, ILayer previousLayer, ILayer nextLayer)
{
IpV4Protocol protocol;
if (Protocol == null)
{
if (nextLayer == null)
{
throw new ArgumentException("Can't determine protocol automatically from next layer because there is no next layer");
}
IIpNextLayer ipNextLayer = nextLayer as IIpNextLayer;
if (ipNextLayer == null)
{
throw new ArgumentException("Can't determine protocol automatically from next layer (" + nextLayer.GetType() + ")");
}
protocol = ipNextLayer.PreviousLayerProtocol;
}
else
{
protocol = Protocol.Value;
}
IpV4Datagram.WriteHeader(buffer, offset,
TypeOfService, Identification, Fragmentation,
Ttl, protocol, HeaderChecksum,
Source, CurrentDestination,
Options, payloadLength);
}
/// <summary>
/// Finalizes the layer data in the buffer.
/// Used for fields that must be calculated according to the layer's payload (like checksum).
/// </summary>
/// <param name="buffer">The buffer to finalize the layer in.</param>
/// <param name="offset">The offset in the buffer the layer starts.</param>
/// <param name="payloadLength">The length of the layer's payload (the number of bytes after the layer in the packet).</param>
/// <param name="nextLayer">The layer that comes after this layer. null if this is the last layer.</param>
public override void Finalize(byte[] buffer, int offset, int payloadLength, ILayer nextLayer)
{
IIpNextTransportLayer nextTransportLayer = nextLayer as IIpNextTransportLayer;
if (nextTransportLayer == null || !nextTransportLayer.CalculateChecksum)
{
return;
}
IpV4Datagram.WriteTransportChecksum(buffer, offset, Length, (ushort)payloadLength,
nextTransportLayer.ChecksumOffset, nextTransportLayer.IsChecksumOptional,
nextTransportLayer.Checksum, Destination);
}
