Question

怎么用C/C++编写发送tcp/ip协议中的syn包

求代码，最好能有一点注释的
要Windows下的

Answer 1

要先装pcap，用Winpcap构造 SYN的数据包

#include <iostream>
using namespace std;
#include <pcap/pcap.h>
#pragma comment(lib,"wpcap.lib") //要先装pcap，用Winpcap构造 SYN的数据包

#include <winsock2.h>
#pragma comment(lib,"ws2_32.lib")

#include "Packet_Header.h"

#define MSG_MAXLEN 58

USHORT checksum(USHORT *buf,int size)
{
	ULONG cksum = 0;
	while(size > 1)
	{
		cksum += *buf++;
		size -= sizeof(USHORT);
	}
	if(size)
	{
		cksum += *(USHORT*)buf;
	}
	cksum = (cksum >> 16) + (cksum & 0xffff);
	cksum += (cksum >> 16);

	return (USHORT)(~cksum);
}

int main()
{
	pcap_if_t *alldevs;
	char errbuf[PCAP_ERRBUF_SIZE] = {};
	
	if(-1 == pcap_findalldevs(&alldevs,errbuf))
	{
		cout<<"Get dev list error"<<endl;
		return -1;
	}

	for(pcap_if_t *d = alldevs;NULL != d;d = d->next)
	{
		cout<<d->description<<endl;
	}

	pcap_t *pt = pcap_open_live(alldevs->name,65536,true,20,errbuf);
	if(NULL == pt)
	{
		cout<<"Open dev error"<<endl;
		return -1;
	}

	UCHAR SendMsg[MSG_MAXLEN] = {0};

	PETHERHDR pethhdr = (PETHERHDR)SendMsg;
	pethhdr->ethDst[0] = 0x00;//mac
	pethhdr->ethDst[1] = 0x21;
	pethhdr->ethDst[2] = 0x85;
	pethhdr->ethDst[3] = 0x02;
	pethhdr->ethDst[4] = 0x30;
	pethhdr->ethDst[5] = 0x4e;
	
	pethhdr->ethSrc[0] = 0x00;
	pethhdr->ethSrc[1] = 0x23;
	pethhdr->ethSrc[2] = 0x8b;
	pethhdr->ethSrc[3] = 0xb6;
	pethhdr->ethSrc[4] = 0xbd;
	pethhdr->ethSrc[5] = 0xd7;

	pethhdr->ethtype = htons(0x0800);

	/*IP header*/
	PIPHDR piphdr = (PIPHDR)(SendMsg + sizeof(ETHERHDR));
	piphdr->ipv_l = (4<<4 | (sizeof(IPHDR)/sizeof(ULONG)));
	piphdr->iptos = 0;
	piphdr->iplen = htons(sizeof(SendMsg)-sizeof(ETHERHDR));
	//piphdr->ipID = htons(0x1234);//0xede6
	piphdr->ipTTL = 58;
	piphdr->ipCheckSum = 0;
	piphdr->ipProtocol = IPPROTO_TCP;
	piphdr->ipSrc = inet_addr("192.168.0.183");
	piphdr->ipDst = inet_addr("119.75.217.109");//119.75.217.109 
	//发送给百度(ip 119.75.217.109：80)
	piphdr->ipCheckSum = checksum((USHORT*)piphdr,sizeof(IPHDR));

	/*TCP header*/
	PTCPHDR ptcphdr = (PTCPHDR)(SendMsg + sizeof(ETHERHDR) + sizeof(IPHDR));
	ptcphdr->tcpSrcPort = htons(44523);
	ptcphdr->tcpDstPort = htons(80);
	ptcphdr->tcpSeq = htonl(0x7d2cb526);//0x7d2cb526 
	ptcphdr->tcpAck = htonl(0);
	ptcphdr->tcpl_r = ((sizeof(TCPHDR)/sizeof(ULONG))<<4 | 0);
	ptcphdr->tcpFlags = 2;
	ptcphdr->tcpWnd = htons(2048);
	ptcphdr->tcpChkSum = 0;
	ptcphdr->tcpUrp = 0;

	UCHAR *tmpbuf = new UCHAR[sizeof(SendMsg) - sizeof(ETHERHDR) - sizeof(IPHDR) + sizeof(PSDHDR)];
	memset(tmpbuf,0,sizeof(TCPHDR)+sizeof(PSDHDR));
	PPSDHDR ppsdhdr = (PPSDHDR)tmpbuf;
	ppsdhdr->psdSrcAddr = piphdr->ipSrc;
	ppsdhdr->psdDstAddr = piphdr->ipDst;
	ppsdhdr->psdzero = 0;
	ppsdhdr->psdProto = IPPROTO_TCP;
	ppsdhdr->psdPackLen = htons(sizeof(SendMsg) - sizeof(ETHERHDR) - sizeof(IPHDR));

	memcpy(tmpbuf+sizeof(PSDHDR),SendMsg+sizeof(ETHERHDR)+sizeof(IPHDR),sizeof(tmpbuf+sizeof(PSDHDR)));

	ptcphdr->tcpChkSum = checksum((USHORT*)tmpbuf,sizeof(SendMsg)-sizeof(ETHERHDR)-sizeof(IPHDR));

	if(0 !=pcap_sendpacket(pt,SendMsg,sizeof(SendMsg)))
	{
		cout<<"Error"<<endl;
	}

	system("pause");
	return 0;
}