//这个地方必须保证不为奇数长度
//这个地方在于求和要按照网络字节序
//求出的结果是按照本机字节序解释的，写入还要转换
//假如是校验的话，结果是零的话不论字节序如何应该都一样？
static uint AddSpanBytesSum(Span <byte> buffer)
{
var vs = MemoryMarshal.Cast <byte, ushort>(buffer);
uint sum = 0;
foreach (var item in vs)
{
sum += Meth.AsBigEndian(item);
}
if ((buffer.Length % sizeof(ushort)) != 0)
{
uint n = buffer[buffer.Length - 1];
sum += n << 8;
}
return(sum);
}
public static void Set(
ref TCPHeader header,
IPv4Address sourceAddress,
ushort sourcePort,
IPv4Address desAddress,
ushort desPort,
Span <byte> headerAndData)
{
header._SourcePort = Meth.AsBigEndian(sourcePort);
header._DesPort = Meth.AsBigEndian(desPort);
var ph = new PseudoHeader(
sourceAddress,
desAddress,
Protocol.TCP,
(ushort)headerAndData.Length);
header._Checksum = 0;
header._Checksum = Meth.AsBigEndian(Meth.CalculationHeaderChecksum(ph, headerAndData));
}
public static void Set(
ref TCPHeader header,
IPv4Address sourceAddress,
ushort sourcePort,
IPv4Address desAddress,
ushort desPort,
TCPFlag tcpFlag,
ushort windowSize,
uint sequenceNumber,
uint acknowledgmentNumber,
Span <byte> headerAndData)
{
header = new TCPHeader();
header._SourcePort = Meth.AsBigEndian(sourcePort);
header._DesPort = Meth.AsBigEndian(desPort);
header._SequenceNumber = Meth.AsBigEndian(sequenceNumber);
header._AcknowledgmentNumber = Meth.AsBigEndian(acknowledgmentNumber);
header._WindowSize = Meth.AsBigEndian(windowSize);
header._TCPHeader12_14._Byte_0 = (byte)(5 << 4);
header._TCPHeader12_14._Byte_1 = (byte)tcpFlag;
var ph = new PseudoHeader(
sourceAddress,
desAddress,
Protocol.TCP,
(ushort)headerAndData.Length);
header._Checksum = Meth.AsBigEndian(Meth.CalculationHeaderChecksum(ph, headerAndData));
}
public void CalculationHeaderChecksum()
{
_IPHeader64_96._HeaderChecksum = 0;
_IPHeader64_96._HeaderChecksum = Meth.AsBigEndian(Meth.CalculationHeaderChecksum(ref this));
}
