//#ETH/TCP/CAT IPV6 EDITION - MEOW!!
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>
#include <unistd.h>
#include <net/if.h>
#include <sys/socket.h>
#include <sys/random.h>
#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <net/ethernet.h>
#define PACKET_SIZE 2048
#define MTU 1280
void fixpacket(uint8_t *packet){
	//clearing
	memset(packet+14+40+16,0,2);
	
	uint8_t pseudopacket[PACKET_SIZE]={0};
	memcpy(pseudopacket,14+packet+8,32);
	memcpy(pseudopacket+34,14+packet+4,2);
	pseudopacket[39]=6;
	memcpy(pseudopacket+40,14+packet+40,MTU);
	uint32_t sum = 0;
	int pseudolength = ((pseudopacket[34]<<8) | (pseudopacket[35])) + 40;
	if(pseudolength&1){pseudolength++;}
	for(int i = 0;pseudolength>i;i+=2){
		sum += (pseudopacket[i]<<8)|(pseudopacket[i+1]);
	}
	while(sum>>16){
		sum=(sum&0xFFFF)+(sum>>16);
	}
	sum=~sum;
	//printf("c:%d %d\n",packet[14+40+16],packet[14+40+16+1]);
	packet[14+40+16]=sum>>8;
	packet[14+40+16+1]=sum&255;
}
int main(int argc,char* argv[]){
	if(argc!=5){
			fprintf(stderr,"Invalid argument count:%d\n\nUsage:\tethtcpcat [IFACE] [SRC_V6_ADDR] [TARGET_V6_ADDR] [TARGET_TCP_PORT]\n\nThis is a generic netcat-like TCP client using its own network stack\n\n",argc);
			return 1;
	}
	uint16_t dport=atoi(argv[4]);
	int s = socket(AF_PACKET,SOCK_RAW,htons(ETH_P_ALL));
	struct sockaddr_ll sa = {.sll_family=AF_PACKET,.sll_protocol=htons(ETH_P_ALL),.sll_ifindex=if_nametoindex(argv[1])};
	bind(s,(void*)&sa,sizeof sa);
	uint8_t packet[PACKET_SIZE] = {
			[12]=0x86,0xdd, //Ethertype IPv6
			0x60,0,0,0,	//Version 6,class and flowlabel 0
			0,20,6,64,	//Length 20, TCP, TTL 64
			[14+40+2]=dport>>8,dport&255, // Source and destination port
			[14+40+12]=0x50,0x02,5,0	// Dataoffset 5, Flag SYN, window 1280
	};
	getrandom(packet+14+40+4,4,GRND_RANDOM);
	getrandom(packet+14+40,2,GRND_RANDOM);
	{
		char macfilepath[256];
		snprintf(macfilepath,256,"/sys/class/net/%s/address",argv[1]);
		FILE *fp;
		char c=0;
		int i=0;
		fp=fopen(macfilepath,"r");
		while(  12>i && (c=fgetc(fp))!=EOF  ){
				if(c!=':'){
					packet[6+(i>>1)]<<=4;
					packet[6+(i>>1)]|=(c>'9')?(10+c-'a'):(c-'0');
					i++;
				}
		}
		fclose(fp);
	}
	{
		FILE *fp;
		char c=0;
		int i=0;
		fp=fopen("/proc/net/arp","r");
		fseek(fp,120,SEEK_CUR);
		while(  12>i && (c=fgetc(fp))!=EOF  ){
				if(c!=':'){
					packet[(i>>1)]<<=4;
					packet[(i>>1)]|=(c>'9')?(10+c-'a'):(c-'0');
					i++;
				}
		}
		fclose(fp);	
		
	}
	inet_pton(AF_INET6,argv[2],packet+14+8);
	inet_pton(AF_INET6,argv[3],packet+14+24);
	
	
	//We send  SYN!!!
	fixpacket(packet);
	write(s,packet,60+14);
	////////////////////////
	//We receive SYNACK
	int rxlen=0;
	uint8_t rxbuf[PACKET_SIZE]={0};
	packet[14+40+7]++;
	for(;;){
		rxlen = read(s,rxbuf,MTU);
		if(!memcmp(rxbuf+14+40+8,packet+14+40+4,4)){
			break;
		}
	}

	
	memcpy(packet+14+40+8,rxbuf+14+40+4,4);
	/////ACK///////
	packet[14+40+13]=16;
	packet[14+40+11]++;
	
	//We send ACK!!
	fixpacket(packet);
	write(s,packet,60+14);
	
	//We send real data!!
	uint16_t payloadlen = 20+read(0,packet+14+40+20,MTU);
	packet[14+4]=payloadlen>>8;
	packet[14+5]=payloadlen&255;
	
	fixpacket(packet);
	write(s,packet,40+14+payloadlen);
	
	
	//We receive reply
	for(;;){
		rxlen = read(s,rxbuf,MTU);
		if((rxbuf[14+40]==packet[14+40+2])&&(rxbuf[14+40+1]==packet[14+40+3])&&(rxlen!=14+40+20)){
			break;
		}
	}
	write(1,rxbuf+14+40+20,rxlen-(14+40+20));
	
	
	return 0;
}