// set the checksum field, totalSize covers all the fields for
// which the checksum is calculated
// offset is points to the beginning of the IP header (!!!)
// Should be called after the UDP header + data have been written
public static void SetUdpChecksum(byte[] !packet,
int ipOffset,
ref UdpHeader udpHeader)
{
// sum IP pseudo
ushort ipPayloadSize = 0;
ushort headerSum = IPFormat.SumPseudoHeader(packet, ipOffset,
ref ipPayloadSize);
Debug.Assert(((ushort)udpHeader.length) == ipPayloadSize);
// now add it to the udp header + data
int ipHeaderSize = (packet[ipOffset] & 0xf) * 4;
int udpOffset = ipOffset + ipHeaderSize;
Debug.Assert(packet[udpOffset + 6] == 0);
Debug.Assert(packet[udpOffset + 7] == 0);
ushort payloadSum = IPFormat.SumShortValues(packet, udpOffset,
ipPayloadSize);
udpHeader.checksum = IPFormat.ComplementAndFixZeroChecksum(
IPFormat.SumShortValues(headerSum, payloadSum));
packet[udpOffset + 6] = (byte)(udpHeader.checksum >> 8);
packet[udpOffset + 7] = (byte)(udpHeader.checksum & 0xff);
}
// set the checksum field
// offset points to the beginning of the IP header (!!!)
// Should be called after the TCP header + data have been written
public static void SetTcpChecksum(byte[] !packet,
int ipOffset,
ref TcpHeader tcpHeader)
{
// sum IP pseudo
ushort ipPayloadLength = 0;
ushort headerSum =
IPFormat.SumPseudoHeader(packet, ipOffset,
ref ipPayloadLength);
int ipHeaderSize = (packet[ipOffset] & 0xf) * 4;
int tcpOffset = ipOffset + ipHeaderSize;
Debug.Assert(packet[tcpOffset + 16] == 0);
Debug.Assert(packet[tcpOffset + 17] == 0);
// now add it to the TCP header + data
ushort payloadSum = IPFormat.SumShortValues(packet, tcpOffset,
ipPayloadLength);
tcpHeader.checksum = (ushort)
~(IPFormat.SumShortValues(headerSum, payloadSum));
// Complement and change +0 to -0 if needed.
ushort tcpChecksum = IPFormat.ComplementAndFixZeroChecksum(
(IPFormat.SumShortValues(headerSum, payloadSum)));
tcpHeader.checksum = tcpChecksum;
unchecked {
packet[tcpOffset + 16] = (byte)(tcpChecksum >> 8);
packet[tcpOffset + 17] = (byte)(tcpChecksum >> 0);
}
}
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);
}
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);
}
