protected internal virtual byte[] AttachPseudoIPHeader(byte[] origHeader)
{
bool odd = origHeader.Length % 2 != 0;
int headerSize = 12 + origHeader.Length;
if (odd)
{
headerSize++;
}
byte[] headerForChecksum = new byte[headerSize];
// 0-7: ip src+dest addr
Array.Copy(_bytes, _ethOffset + IPFields_Fields.IP_SRC_POS, headerForChecksum, 0, 8);
// 8: always zero
headerForChecksum[8] = 0;
// 9: ip protocol
headerForChecksum[9] = (byte)IPProtocol;
// 10-11: header+data length
ArrayHelper.insertLong(headerForChecksum, origHeader.Length, 10, 2);
// prefix the pseudoHeader to the header+data
Array.Copy(origHeader, 0, headerForChecksum, 12, origHeader.Length);
//if not even length, pad with a zero
if (odd)
{
headerForChecksum[headerForChecksum.Length - 1] = 0;
}
return(headerForChecksum);
}
/*
* taken from TCP/IP Illustrated Vol. 2(1995) by Gary R. Wright and W.
* Richard Stevens. Page 236
*/
/// <summary> Computes the IP checksum, optionally updating the IP checksum header.
///
/// </summary>
/// <param name="update">Specifies whether or not to update the IP checksum
/// header after computing the checksum. A value of true indicates
/// the header should be updated, a value of false indicates it
/// should not be updated.
/// </param>
/// <returns> The computed IP checksum.
/// </returns>
public int ComputeIPChecksum(bool update)
{
//copy the ip header
byte[] ip = ArrayHelper.copy(_bytes, _ethOffset, IpHeaderLength);
//reset the checksum field (checksum is calculated when this field is zeroed)
ArrayHelper.insertLong(ip, 0, IPFields_Fields.IP_CSUM_POS, 2);
//compute the one's complement sum of the ip header
int cs = _OnesCompSum(ip, 0, ip.Length);
if (update)
{
IPChecksum = cs;
}
return(cs);
}
/// <summary> Computes the UDP checksum, optionally updating the UDP checksum header.
///
/// </summary>
/// <param name="update">Specifies whether or not to update the UDP checksum header
/// after computing the checksum. A value of true indicates the
/// header should be updated, a value of false indicates it should
/// not be updated.
/// </param>
/// <returns> The computed UDP checksum.
/// </returns>
public int ComputeUDPChecksum(bool update)
{
// copy the udp section with data
byte[] udp = IPData;
// reset the checksum field (checksum is calculated when this field is
// zeroed)
ArrayHelper.insertLong(udp, 0, UDPFields_Fields.UDP_CSUM_POS, UDPFields_Fields.UDP_CSUM_LEN);
//pseudo ip header should be attached to the udp+data
udp = AttachPseudoIPHeader(udp);
// compute the one's complement sum of the udp header
int cs = _OnesCompSum(udp);
if (update)
{
UDPChecksum = cs;
}
return(cs);
}
public int ComputeTransportLayerChecksum(int checksumOffset, bool update, bool pseudoIPHeader)
{
// copy the tcp section with data
byte[] dataToChecksum = IPData;
// reset the checksum field (checksum is calculated when this field is
// zeroed)
ArrayHelper.insertLong(dataToChecksum, 0, checksumOffset, 2);
if (pseudoIPHeader)
{
dataToChecksum = AttachPseudoIPHeader(dataToChecksum);
}
// compute the one's complement sum of the tcp header
int cs = _OnesCompSum(dataToChecksum);
if (update)
{
SetTransportLayerChecksum(cs, checksumOffset);
}
return(cs);
}
/// <summary> Sets the hardware destination address.</summary>
public virtual void setARPTargetHwAddress(long addr)
{
ArrayHelper.insertLong(_bytes, addr, _ethOffset + ARPFields_Fields.ARP_T_HW_ADDR_POS, 6);
}
/// <summary> Sets the IP header checksum.</summary>
protected internal virtual void SetChecksum(int cs, int checkSumOffset)
{
ArrayHelper.insertLong(_bytes, cs, checkSumOffset, 2);
}