internal static void WriteHeader(byte[] buffer, int offset,
byte typeOfService, ushort identification,
IpV4Fragmentation fragmentation,
byte ttl, IpV4Protocol protocol, ushort?headerChecksum,
IpV4Address source, IpV4Address destination,
IpV4Options options, int payloadLength)
{
int headerLength = HeaderMinimumLength + options.BytesLength;
buffer[offset + Offset.VersionAndHeaderLength] = (byte)((DefaultVersion << 4) + headerLength / 4);
buffer[offset + Offset.TypeOfService] = typeOfService;
buffer.Write(offset + Offset.TotalLength, (ushort)(headerLength + payloadLength), Endianity.Big);
buffer.Write(offset + Offset.Identification, identification, Endianity.Big);
fragmentation.Write(buffer, offset + Offset.Fragmentation);
buffer[offset + Offset.Ttl] = ttl;
buffer[offset + Offset.Protocol] = (byte)protocol;
buffer.Write(offset + Offset.Source, source, Endianity.Big);
buffer.Write(offset + Offset.Destination, destination, Endianity.Big);
options.Write(buffer, offset + Offset.Options);
ushort headerChecksumValue =
headerChecksum == null
? Sum16BitsToChecksum(Sum16Bits(buffer, offset, headerLength))
: headerChecksum.Value;
buffer.Write(offset + Offset.HeaderChecksum, headerChecksumValue, Endianity.Big);
}
internal static IpV4Address CalculateDestination(IpV4Address currentDestination, IpV4Options options)
{
if (options == null)
{
return(currentDestination);
}
IpV4OptionRoute destinationControllerRouteOption =
(IpV4OptionRoute)options.OptionsCollection.FirstOrDefault(option => option.OptionType == IpV4OptionType.LooseSourceRouting ||
option.OptionType == IpV4OptionType.StrictSourceRouting);
if (destinationControllerRouteOption != null)
{
ReadOnlyCollection <IpV4Address> route = destinationControllerRouteOption.Route;
if (destinationControllerRouteOption.PointedAddressIndex < route.Count)
{
return(route[route.Count - 1]);
}
}
return(currentDestination);
}