计算udp校验和例子_UDP 包校验和计算

可以参考一下我的代码：

//校验

USHORT checksum(USHORT* buff, INT size)

{

ULONG cksum = 0;

while(size>1)

{

cksum += *buff++;

size -= sizeof(USHORT);

}

// 是奇数

if(size)

{

cksum += *(UCHAR*)buff;

}

// 将位的chsum高位和低位相加，然后取反

cksum = (cksum >> 16) + (cksum & 0xffff);

cksum += (cksum >> 16);

return (USHORT)(~cksum);

}

//修改数包窗口大小,以及清除标志位

void ModifyPacketWndSize(PVOID pPacketContent,INT iPacketSize)

{

//定义数据包tcp/ip结构指针

int            nLeavingLen;

PETHeader    pEtherHdr=NULL;

PIPHeader    pIpHdr=NULL;

PTCPHeader    pTcpHdr=NULL;

PUDPHeader    pUdpHdr=NULL;

CHAR        *pData=NULL;

//基本判断

if (pPacketContent==NULL)

{

return FALSE;

}

//获得以太帧头,过滤协议，过滤ip协议，放行其他协议

nLeavingLen=iPacketSize;

if(nLeavingLen < sizeof(ETHeader))

{

return NDIS_STATUS_SUCCESS;

}

nLeavingLen -= sizeof(ETHeader);

pEtherHdr = (PETHeader)pPacketContent;

if(pEtherHdr->type != 0x8) // 如果不是IP协议，则不处理

return;

//获得ip头

pIpHdr = (PIPHeader)(pEtherHdr + 1);

// 验证剩余数据长度，防止发生内核非法访问

if(nLeavingLen < sizeof(IPHeader))

return;

nLeavingLen -= sizeof(IPHeader);

// 检查版本信息，我们仅处理IPv4

if(((pIpHdr->iphVerLen >> 4) & 0x0f) == 6)

{

return;

}

// 如果是TCP封包，修改窗口大小

if(pIpHdr->ipProtocol == 6)

{

//TCP伪数据包头指针

PSDHEADER *pPsdHeader=NULL;

//数据包校验缓存大小

INT iTcpCheckoutBufSize;

NDIS_PHYSICAL_ADDRESS phyaddr = {-1};

NDIS_STATUS Status;

//修改窗口大小

pTcpHdr = (PTCPHeader)(pIpHdr + 1);

pTcpHdr->windows=200;

KdPrint(("改变窗口大小!n"));

//pTcpHdr->flags=0;

//Tcp数据校验

iTcpCheckoutBufSize=sizeof(PSDHEADER)+nLeavingLen;

Status=NdisAllocateMemory(&pPsdHeader,iTcpCheckoutBufSize,0,phyaddr);

if (Status==NDIS_STATUS_SUCCESS)

{

NdisZeroMemory(pPsdHeader,iTcpCheckoutBufSize);

//填充伪TCP头

pPsdHeader->daddr=pIpHdr->ipSource;

pPsdHeader->saddr=pIpHdr->ipDestination;

pPsdHeader->mbz=0;

pPsdHeader->ptcl=0x06;

pPsdHeader->tcpl=htons(nLeavingLen);

计算TCP校验和

pTcpHdr->checksum=0;

NdisMoveMemory((PCHAR)pPsdHeader+sizeof(PSDHEADER),pTcpHdr,nLeavingLen);

pTcpHdr->checksum=checksum((PUSHORT)pPsdHeader,iTcpCheckoutBufSize);

NdisFreeMemory(pPsdHeader,iTcpCheckoutBufSize,0);

}

}

return;

}