tcp.c

伪tcp代码的实现

#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <netinet/if_ether.h>
#include <string.h>
#include <netinet/tcp.h>
#include <unistd.h>
#include <fcntl.h>
#include <pthread.h>
#define SRCPORT 3000
#define HEADER_LEN 36 
#define PORTS 1024
int i_index;
struct thread_d
	{
		int syn;
		u_int32_t saddr;
		u_int32_t daddr;
		u_int32_t seq;
	};
struct t_tcphdr
	{
		struct tcphdr thdr;
		u_int8_t opt_name;
		u_int8_t opt_len;
		u_int16_t opt;
	};
u_int16_t in_chksum(u_short *addr,int len)
{
	u_int32_t sum=0;
	u_int16_t *ad=addr,result;
	while(len>1)
		{
			sum+=*ad++;
			len-=2;
		}
	if(len==1)
		{
			result=0;
			*((u_char*)&result)=*(u_char*)ad;
			sum+=result;
		}
	sum=(sum>>16)+(sum&0xffff);
	sum+=(sum>>16);
	result=~sum;
	return(result);
	}
u_int32_t localIP(int sock)
{
	struct ifreq ifr;
	struct sockaddr_in *sa;
	strcpy(ifr.ifr_name,"eth0");
	if(ioctl(sock,SIOCGIFADDR,&ifr)<0)
		{
			perror("ioctl siogifaddr");
			exit(-1);
		}
	sa=(struct sockaddr_in*)&ifr.ifr_addr;
	return sa->sin_addr.s_addr;
}
void *getresponse(void *arg)
{
	struct thread_d *arg_r=(struct thread_d*)arg;
	u_char ports[PORTS],packet[1024];
	fd_set rfd;
	struct sockaddr_in sa;
	struct in_addr sa_in;
	struct iphdr *i_hdr;
	struct tcphdr *thdr;
	int sock_pck,len,n,i;
	u_int32_t seq;
	struct timeval tv;
	char pchdest[20];
	seq=arg_r->seq;
	sa_in.s_addr=arg_r->daddr;
	strncpy(pchdest,inet_ntoa(sa_in),16);
	if((sock_pck=socket(PF_PACKET,SOCK_RAW,htons(ETH_P_IP)))<0)
		{
			perror("socket packet");
			exit(-1);
		}
	if(!arg_r->syn)
		bzero(ports,sizeof(ports));
	while(1)
		{
			bzero(packet,sizeof(packet));
			FD_ZERO(&rfd);
			FD_SET(sock_pck,&rfd);
			tv.tv_sec=0;
			tc.tv_usec=500;
			if(select(sock_pck+1,&rfd,NULL,NULL,&tv)==0)
				if(i_index=(PORTS-1))
					break;
				else
					continue;

				if(n=recvfrom(sock_pck,packet,1024,0,&sa,&len)<54)
					continue;
				i_hdr=(struct iphdr*)(packet+sizeof(struct ethhdr));
				if(i_hdr->daddr==arg_r->saddr&&i_hdr->saddr==arg_r->daddr)
					{
						thdr=(struct tcphdr*)(packet+sizeof(struct ehhhdr)+sizeof(struct iphdr));
						if(arg_r->syn&&thdr->ack==1&&thdr->ack_seq==htonl(seq+1)&&thdr->dest==htons(SRCPORT))
							{
								if(thdr->rst==0)
									printf("%s's port %4d is on service\n",pchdest,ntohl(thdr->source));
								else if(!arg_r->syn&&thdr->window==0&&(ntohl(thdr->ack_seq)>=seq||ntohl(thdr->ack_seq)<=seq+32120)&&thdr->dest==htons(SRCPORT))
									if(thdr->rst==1)
										ports[ntohs(thdr->source)]=1;
							}
					}
				if(!arg_r->syn)
					for(i=1;i<PORTS;i++)
						if(ports[i]==0)
							printf("%s's port %4d is on service\n",pchdest,i);
						return NULL;
		}
}
int main(int argc,char *argv[])
{
	
	struct sockaddr_in sa_to,sa_fr,sa;
	struct t_tcphdr *t_hdr;
	struct tcphdr *thdr;
	struct iphdr *i_hdr;
	int syn=0,sock_raw,sock_pck,i,flag,len;
	u_char *pseudo,psedoHead[HEADER_LEN],packet[1024];
	u_int16_t tcp_len;
	u_int32_t seq=getpid()|0x40000000;
	const int on=1;
	pthread_t tid;
	struct thread_d arg;
	if(argc!=3)
		{
			printf("usage:%s[-s -f] remoteIP\n",argv[0]);
			exit(-1);
		}
	if(strcmp(argv[1],"-s")&&strcmp(argv[2],"-f"))
		{
			printf("usage:%s[-s -f] remoteIP\n",argv[0]);
			exit(-1);
		}
	else if(!strcmp(argv[1],"-s"))
		syn=1;

	bzero(&sa_to,sizeof(sa_to));
	sa_to.sin_family=AF_INET;
	if(inet_aton(argv[2],&sa_to.sin_addr)<0)
		{
			perror("inet_aton");
			exit(-1);
		}
	if((sock_raw=socket(AF_INET,SOCK_RAW,IPPROTO_RAW))<0)
		{
			perror("socket raw");
			exit(-1);
		}
	bzeor(&sa_fr,sizeof(sa_fr));
	sa_fr.sin_family=AF_INET;
	sa_fr.sin_addr.s_addr=localIP(sock_raw);
	arg.syn=syn;
	arg.saddr=sa_fr.sin_addr.s_addr;
	arg.daddr=sa_to.sin_addr.s_addr;
	arg.seq=seq;
	pthread_create(&tid,NULL,getresponse,&arg);
	if(setsockopt(sock_raw,IPPROTO_IP,IP_HDRINCL,&on,sizeof(int))<0)
		{
			perror("setsockopt ipproto_ip");
			exit(-1);
		}
	if((flag=fcntl(sock_raw,F_GETFL))<0)
		{
			perror("fcntl F_GETFL");
			exit(-1);
		}
	usleep(50);
	for(i=1;i<PORTS;i++)
		{
			bzero(packet,sizeof(packet));
			i_hdr=(struct iphdr*)packet;
			i_hdr->ihl=5;
			i_hdr->version=4;
			i_hdr->frag_off=htons(IP_DF);
			i_hdr->ttl=64;
			i_hdr->protocol=IPPROTO_TCP;
			i_hdr->daddr=sa_to.sin_addr.s_addr;
			i_hdr->saddr=sa_fr.sin_addr.s_addr;
			t_hdr=(struct t_tcphdr*)(packet+sizeof(struct iphdr));
			t_hdr->thdr.source=htons(SRCPORT);
			t_hdr->thdr.dest=htons(i);
			t_hdr->thdr.seq=htons(seq);
			t_hdr->thdr.ack_seq=0;
			t_hdr->thdr.doff=5+syn;
			t_hdr->thdr.fin=1-syn;
			t_hdr->thdr.syn=syn;
			t_hdr->thdr.ack=0;
			t_hdr->thdr.window=htons(32120);
			bzero(pseudoHead,HEADER_LEN);
			pseudo=pseudoHead;
			memcpy(pseudo,&(i_hdr->saddr),8);
			pseudo+=9;
			memcpy(pseudo,&(i_hdr->protocol,1);
			pseudo++;
			usleep(10);
			i_index=i;
			if(!syn)
				{
					tcp_len=htons(sizeof(struct tcphdr));
					memcpy(pseudo,&tcp_len,2);
					pseudo+=2;
					memcpy(pseudo,t_hdr,sizeof(struct tcphdr));
					t_hdr->thdr.check=in_chksum(u_short*)pseudoHead,HEADER_LEN-4);
					if(sendto(sock_raw,packet,sizeof(struct tcphdr)+sizeof(struct iphdr),0,&sa_to,sizeof(sa_to))<0)
						perror(sendto);
				}
			else 
				{
					t_hdr->opt_name=2;
					t_hdr->opt_len=4;
					t_hdr->opt=htons(1460);
					tcp_len=htons(sizeof(struct t_tcphdr));
					memcpy(pseudo,&tcp_len,2);
					pseudo+=2;
					memcpy(pseudo,t_hdr,sizeof(struct t_tcphdr));
					t_hdr->thdr.check=in_chksum((u_short*)pseudoHead,HEADER_LEN);
					if(sendto(sock_raw,packet,sizeof(struct iphdr)+sizeof(struct t_tcphdr),0,&sa_to,sizeof(sa_to))<0)
						perror("sendto");
				}
			
				}
	printf("sending ended!/n");
	pthread_join(tid,NULL);
	return 0;
				}
		}
}