#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define _perror(s) perror(s); errno = 0
#define _probably_perror(s) if (errno) { perror(s); errno = 0; }

unsigned short portfrom, portto;
int sock, client, server, peer_size;
struct sockaddr_in *local, *peer, *remote;
char *buffer;

int main(int argc, char **argv) {
	buffer    = malloc(65537);
	remote    = malloc(sizeof(struct sockaddr_in));
	local     = malloc(sizeof(struct sockaddr_in));
	peer      = malloc(sizeof(struct sockaddr_in));
	peer_size = sizeof(struct sockaddr_in);
	portfrom  = 26;
	portto    = 25;

	if (argc >= 3) {
		portfrom = (short)(atol(argv[1]) & 0xFFFF);
		portto   = (short)(atol(argv[2]) & 0xFFFF);
	}

	local->sin_family       = AF_INET;
	local->sin_port         = htons(portfrom);
	local->sin_addr.s_addr  = htonl(INADDR_ANY);

	remote->sin_family      = AF_INET;
	remote->sin_port        = htons(portto);
	remote->sin_addr.s_addr = inet_addr("192.168.1.1");

	printf("Target address: %i.%i.%i.%i:%i\n",
	       remote->sin_addr.s_addr & 0xFF,
	       (remote->sin_addr.s_addr >> 8) & 0xFF,
	       (remote->sin_addr.s_addr >> 16) & 0xFF,
	       (remote->sin_addr.s_addr >> 24) & 0xFF,
	       ntohs(remote->sin_port));

	sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (sock == -1) {
		_perror("socket (controller)");
		exit(1);
	}
	if (bind(sock, (struct sockaddr *)local,
		 sizeof(struct sockaddr_in)) < 0) {
		_perror("bind");
		exit(1);
	}
	if (listen(sock, 10) < 0) {
		_perror("listen");
		exit(1);
	}
	while ((client = accept(sock, (struct sockaddr *)peer,
				&peer_size)) >= 0) {
		unsigned long s;
		int in_recvq, overhead = 0, nr_loops = 0;

		for (s = 0; s < 65536; s++)
			buffer[s] = 0;

		printf("Connection from %s:%i\n",
		       inet_ntoa(peer->sin_addr),
		       ntohs(peer->sin_port));

		server = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
		if (server == -1) {
			_perror("socket (server)");
			exit(1);
		}
		if (connect(server, (struct sockaddr *)remote,
			    sizeof(struct sockaddr_in)) < 0) {
			_perror("connect (server)");
			goto out;
		}

		printf("Server connection is up.\n");
		usleep(100);

		if (ioctl(server, TIOCINQ, &in_recvq) != 0) {
			_perror("TIOCINQ (server)");
			goto out;
		}

	data_waiting:
		if (overhead - nr_loops >= 100)
			goto out;

		while (in_recvq) {
			nr_loops++;
			overhead = nr_loops;
			for (s = 0; s < 65536; s++)
				buffer[s] = 0;

			if (recv(server,buffer, 65535, 0) < 0) {
				_perror("recv (server)");
				goto out;
			}
			printf("%s", buffer);
			if (send(client, buffer, strlen(buffer), 0) < 0) {
				_perror("send (server)");
				goto out;
			}
			if (ioctl(server, TIOCINQ, &in_recvq) != 0) {
				_perror("TIOCINQ (server)");
				goto out;
			}
		}

		if (ioctl(client, TIOCINQ, &in_recvq) != 0) {
			_perror("TIOCINQ (client)");
			goto out;
		}

		while (in_recvq) {
			nr_loops++;
			overhead = nr_loops;
			for (s = 0; s < 65536; s++)
				buffer[s] = 0;

			if (recv(client, buffer, 65535, 0) < 0) {
				_perror("recv (client)");
				goto out;
			}
			printf("%s", buffer);
			if (send(server, buffer, strlen(buffer), 0) < 0) {
				_perror("send (server)");
				goto out;
			}
			if (ioctl(client, TIOCINQ, &in_recvq) != 0) {
				_perror("TIOCINQ (client)");
				goto out;
			}
		}

		if (ioctl(server, TIOCINQ, &in_recvq) != 0) {
			_perror("TIOCINQ (server)");
			goto out;
		}

		overhead++;

		usleep(100);
		goto data_waiting;
	out:
		printf("Connection closing.\n");
		shutdown(client, SHUT_RDWR);
		_probably_perror("shutdown (client)");
		shutdown(server, SHUT_RDWR);
		_probably_perror("shutdown (server)");
		close(client);
		_probably_perror("close (client)");
		close(server);
		_probably_perror("close (server)");
	}

	if (close(sock)) {
		_perror("close (controller)");
	}

	exit(0);
}

/*
 * Local variables:
 *  compile-command: "gcc -W -Wall -Os -o pf portforwarder.c"
 *  c-basic-offset: 8
 * End:
 */