public static bool IsChecksumValid(IPFormat.IPHeader !ipHeader,
TcpHeader tcpHeader,
NetPacket !payload)
{
// Compute partial checksums of headers
ushort checksum = IPFormat.SumPseudoHeader(ipHeader);
checksum = IPFormat.SumShortValues(checksum,
SumHeader(tcpHeader));
// Checksum payload (without potential odd byte)
int length = payload.Available;
int end = length & ~1;
int i = 0;
uint payloadChecksum = 0;
while (i != end)
{
byte b0 = payload.PeekAvailable(i++);
byte b1 = payload.PeekAvailable(i++);
payloadChecksum += ((((uint)b0) << 8) + (uint)b1);
}
// Handle odd byte.
if (i != length)
{
payloadChecksum += (((uint)payload.PeekAvailable(i++)) << 8);
}
// Merge bits from payload checksum
checksum = IPFormat.SumUInt16AndUInt32Values(checksum, payloadChecksum);
// Complement and change +0 to -0 if needed.
checksum = IPFormat.ComplementAndFixZeroChecksum(checksum);
// Check for match.
bool checksumMatch = (tcpHeader.checksum == checksum);
// If checksum error, unconditionally output message to debugger.
if (checksumMatch == false)
{
DebugStub.WriteLine("Bad TCP checksum {0:x4} != {1:x4}: SEQ {2:x8} ACK {3:x8}",
__arglist(tcpHeader.checksum, checksum,
tcpHeader.seq,
tcpHeader.ackSeq
));
}
// IsValid is a Match.
return(checksumMatch);
}
/// <summary>
/// Write IP and UDP headers and payload data into a
/// byte array.
/// </summary>
/// <param name="pkt">Array of bytes representing
/// packet to be sent.</param>
/// <param name="offset">Offset of IP Header within
/// packet.</param>
/// <param name="ipHeader">IP header to be written
/// to packet.</param>
/// <param name="udpHeader">UDP header to be written
/// to packet.</param>
/// <param name="payload">Payload of UDP Packet.</param>
/// <param name="payloadOffset">The offset of start
/// of the payload data within the payload
/// array.</param>
/// <param name="payloadLength">The size of the payload data.</param>
public static void WriteUdpPacket(byte[] !pkt,
int offset,
IPFormat.IPHeader !ipHeader,
ref UdpHeader udpHeader,
byte[] payload,
int payloadOffset,
int payloadLength)
{
int udpStart = IPFormat.WriteIPHeader(pkt, offset, ipHeader);
int udpEnd = WriteUdpHeader(pkt, udpStart, ref udpHeader);
if (pkt != payload || udpEnd != payloadOffset)
{
Array.Copy(payload, payloadOffset,
pkt, udpEnd, payloadLength);
}
SetUdpChecksum(pkt, offset, ref udpHeader);
}
public static bool IsChecksumValid(IPFormat.IPHeader !ipHeader,
UdpHeader udpHeader,
NetPacket !payload)
{
// Compute partial checksums of headers
ushort checksum = IPFormat.SumPseudoHeader(ipHeader);
checksum = IPFormat.SumShortValues(checksum,
UdpFormat.SumHeader(udpHeader));
// Checksum payload
int length = payload.Available;
int end = length & ~1;
int i = 0;
while (i != end)
{
int x = ((((int)payload.PeekAvailable(i++)) << 8) +
(int)payload.PeekAvailable(i++));
checksum = IPFormat.SumShortValues(checksum, (ushort)x);
}
if (i != length)
{
int x = (((int)payload.PeekAvailable(i++)) << 8);
checksum = IPFormat.SumShortValues(checksum, (ushort)x);
}
checksum = IPFormat.ComplementAndFixZeroChecksum(checksum);
if (udpHeader.checksum != checksum)
{
DebugStub.WriteLine("Bad UDP checksum {0:x4} != {1:x4}",
__arglist(udpHeader.checksum, checksum));
}
return(udpHeader.checksum == checksum);
}
public static void WriteUdpPacket(byte[] !pkt,
int offset,
IPFormat.IPHeader !ipHeader,
ref UdpHeader udpHeader,
byte[] !in ExHeap payload,
// a helper method to write the TCP segment (without data)
public static void WriteTcpSegment(byte[] !pktData,
ushort localPort,
ushort destPort,
uint ackSeq,
uint seq,
ushort wnd,
IPv4 sIP,
IPv4 dIP,
ushort dataLen,
bool isAck,
bool isSyn,
bool isRst,
bool isFin,
bool withOptions)
{
// now create the IP,TCP headers!
int start = EthernetFormat.Size;
// prepare it...
TcpFormat.TcpHeader tcpHeader = new TcpFormat.TcpHeader();
tcpHeader.sourcePort = localPort;
tcpHeader.destPort = destPort;
if (withOptions)
{
tcpHeader.off_res1 = 0x60;
}
else
{
tcpHeader.off_res1 = 0x50;
}
tcpHeader.ackSeq = ackSeq;
tcpHeader.seq = seq;
tcpHeader.window = wnd;
if (isFin)
{
TcpFormat.SetFIN(ref tcpHeader);
}
if (isSyn)
{
TcpFormat.SetSYN(ref tcpHeader);
}
if (isAck)
{
TcpFormat.SetACK(ref tcpHeader);
}
if (isRst)
{
TcpFormat.SetReset(ref tcpHeader);
}
IPFormat.IPHeader ipHeader = new IPFormat.IPHeader();
ipHeader.SetDefaults(IPFormat.Protocol.TCP);
ipHeader.totalLength = (ushort)(IPFormat.Size + TcpFormat.Size + dataLen);
ipHeader.srcAddr = sIP;
ipHeader.destAddr = dIP;
IPFormat.SetDontFragBit(ipHeader);
// write the ip header + ip checksum
start = IPFormat.WriteIPHeader(pktData, start, ipHeader);
// write TCP header, no checksum
start = TcpFormat.WriteTcpHeader(pktData, start, ref tcpHeader);
// calc the checksum...
TcpFormat.SetTcpChecksum(pktData, EthernetFormat.Size, ref tcpHeader);
}
