#include <pcap.h>
#include <stdio.h>

#define macaddr "08:00:27:e8:9d:d4"

void got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet);

void got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet){
	pcap_t *handle;
	char errbuf[BUFSIZ];
	char *writedev = args;
	int i;

	handle = pcap_open_live(writedev, BUFSIZ, 1, 1000, errbuf);
	if (handle == NULL){
		fprintf(stderr, "Couldn't open device %s: %s\n", writedev, errbuf);
	}

	if((pcap_inject(handle, packet, header->len)) < 0 ){
		fprintf(stderr, "Error: %s\n", pcap_geterr(handle));
	}
	//printf("Wrote %d bytes.\n", bytes_written);

	pcap_close(handle);

}

int usage(void){
	printf("Usage: slitheen-proxy [internal network interface] [NAT interface]\n");
}

int main(int argc, char *argv[]){
	pid_t pid;
	char filter1[33] = "ether src host 08:00:27:e8:9d:d4";
	char filter2[33] = "ether src host 08:00:27:e8:9d:d4";

	char *dev1 = NULL; /* Device that leads to the internal network */
	char *dev2 = NULL; /* Device that leads out to the world */

	if (argc != 3) { 
		usage();
		return(2);
	}
	dev1 = argv[1];
	dev2 = argv[2];

	snprintf(filter1, 33, "ether src host %s", macaddr);
	snprintf(filter2, 33, "ether dst host %s", macaddr);

	pid = fork();
	if (pid < 0) {
		fprintf(stderr, "Fork call failed.\n");
		return(2);
	}
	if (pid == 0) {
		sniff_packets(dev1, dev2, filter1);		
	} else {
		sniff_packets(dev2, dev1, filter2);
	}
	
	return(0);
}

int sniff_packets(char *readdev, char *writedev, char *filter){
	pcap_t *handle;
	char errbuf[BUFSIZ];
	struct bpf_program fp;
	bpf_u_int32 mask;
	bpf_u_int32 net;

	if (pcap_lookupnet(readdev, &net, &mask, errbuf) == -1){
		fprintf(stderr, "Can't get netmask for device %s\n", readdev);
		return(2);
	}

	handle = pcap_open_live(readdev, BUFSIZ, 1, 1000, errbuf);
	if (handle == NULL){
		fprintf(stderr, "Couldn't open device %s: %s\n", readdev, errbuf);
	}

	if(pcap_datalink(handle) != DLT_EN10MB) {
		fprintf(stderr, "Device %s does not provide Ethernet headers - not supported\n", readdev);
		return(2);
	}

	if(pcap_compile(handle, &fp, filter, 0 , net) == -1){
		fprintf(stderr, "Couldn't parse filter %s: %s\n", filter, pcap_geterr(handle));
		return(2);
	}

	if (pcap_setfilter(handle, &fp) == -1) {
		fprintf(stderr, "Couldn't install filter %s: %s\n", filter, pcap_geterr(handle));
		return(2);
	}

	/*callback function*/
	pcap_loop(handle, -1, got_packet, writedev);

	/*Sniff a packet*/
	pcap_close(handle);
	return(0);
}