/* $Id: socksfwd.c,v 1.1 2007-07-24 07:29:41 gophi Exp $ */

#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/select.h>
#include <sys/types.h>

#define TIMEOUT 900

extern int errno, h_errno;

#define die(...) do { \
	int se = errno; \
	fprintf(stderr, "socksfwd: line %d: ", __LINE__); \
	errno = se; \
	fprintf(stderr, __VA_ARGS__); \
	fprintf(stderr, "\n"); \
	exit(EXIT_FAILURE); \
} while (0)

static volatile int flag_alrm = 0;

static void sigalrm(int signo)
{
	flag_alrm = 1;
	signal(signo, sigalrm);
}

static int create_socket(void)
{
	int fd;

	fd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (fd == -1)
		die("socket(): %s", strerror(errno));

	return fd;
}

static int create_listening(int port)
{
	struct hostent *hent;
	int fd, sv;
	struct sockaddr_in sa;

	hent = gethostbyname("127.0.0.1");
	if (!hent)
		die("internal error");

	fd = create_socket();

	memset(&sa, 0, sizeof(sa));
	memcpy(&sa.sin_addr, hent->h_addr, sizeof(sa.sin_addr));
	sa.sin_family = AF_INET;
	sa.sin_port = htons(port);

	sv = 1;
	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &sv, sizeof(sv)) == -1)
		die("setsockopt(): %s", strerror(errno));

	if (bind(fd, (struct sockaddr *) &sa, sizeof(sa)) == -1)
		die("bind(): %s", strerror(errno));

	if (listen(fd, 10) == -1)
		die("listen(): %s", strerror(errno));

	return fd;
}

static int create_connected(struct sockaddr_in *sa)
{
	int fd = create_socket();

	/* moze tez alrm? */
	if (connect(fd, (struct sockaddr *) sa, sizeof(*sa)) == -1)
		die("connect(): %s", strerror(errno));

	return fd;
}

static size_t timeout_recv(int fd, char *buf, size_t sz)
{
	alarm(TIMEOUT);
	flag_alrm = 0;

	while (!flag_alrm) {
		ssize_t rs = read(fd, buf, sz);
		if (rs == -1) {
			if (errno == EAGAIN || errno == EINTR)
				continue;

			die("read(): %s", strerror(errno));
		} else if (!rs)
			exit(EXIT_SUCCESS);

		alarm(0);
		return rs;
	}

	alarm(0);
	if (flag_alrm)
		die("read(): timeout");

	/* NOTREACHED */

	return 0;
}

static void atomic_recv(int fd, char *buf, size_t sz)
{
	while (sz) {
		ssize_t rs = timeout_recv(fd, buf, sz);
		buf += rs;
		sz -= rs;
	}
}

static void atomic_send(int fd, char *buf, size_t sz)
{
	alarm(TIMEOUT);
	flag_alrm = 0;

	while (sz && !flag_alrm) {
		ssize_t rs = write(fd, buf, sz);
		if (rs == -1) {
			if (errno == EAGAIN || errno == EINTR)
				continue;

			die("write(): %s", strerror(errno));
		} else if (!rs)
			die("write(): returned nonsense");

		buf += rs;
		sz -= rs;
	}

	alarm(0);
	if (flag_alrm)
		die("write(): timeout");
}

static void do_tunnel(int src, int dst)
{
	char buf[1024];
	size_t rs;

	rs = timeout_recv(src, buf, sizeof(buf));
	atomic_send(dst, buf, rs);
}

static void tunnel(int fd1, int fd2)
{
	fd_set fds;
	int max = ((fd1 > fd2) ? fd1 : fd2) + 1;

	for (;;) {
		int rs;

		FD_ZERO(&fds);
		FD_SET(fd1, &fds);
		FD_SET(fd2, &fds);

		alarm(TIMEOUT);
		rs = select(max, &fds, NULL, NULL, NULL);
		alarm(0);

		if (rs == 0)
			continue;

		if (rs == -1 && (errno == EAGAIN || errno == EINTR)) {
			if (flag_alrm)
				die("timeout");

			continue;
		}

		if (FD_ISSET(fd1, &fds))
			do_tunnel(fd1, fd2);

		if (FD_ISSET(fd2, &fds))
			do_tunnel(fd2, fd1);
	}
}

static void handle(int fd)
{
	unsigned char buf[256];
	size_t i, methods;
	struct sockaddr_in sa;
	socklen_t len;
	int nfd;

	alarm(0);
	signal(SIGALRM, sigalrm);

	/* version, nmethods */
	atomic_recv(fd, buf, 2);
	if (buf[0] != 5)
		die("invalid socks version in preauth (%d)", buf[0]);

	methods = buf[1];
	atomic_recv(fd, buf, methods);

	for (i = 0; i < methods; ++i)
		if (buf[i] == 0)
			break;
		else if (buf[i] == 0xFF)
			die("no acceptable auth methods");

	if (i == methods)
		die("disable authorization");

	buf[0] = 5;	// version
	buf[1] = 0;	// no auth
	atomic_send(fd, buf, 2);

	atomic_recv(fd, buf, 4);
	if (buf[0] != 5)
		die("invalid socks version in request (%d)", buf[0]);
	if (buf[1] != 1)
		die("invalid request (%d)", buf[1]);
	if (buf[3] != 1 && buf[3] != 3)
		die("invalid address type (%d)", buf[3]);

	memset(&sa, 0, sizeof(sa));
	sa.sin_family = AF_INET;

	if (buf[3] == 1) {	// inet
		atomic_recv(fd, buf, 4);
		memcpy(&sa.sin_addr, buf, 4);
	} else {	// hostname
		struct hostent *hent;
		size_t sz;

		atomic_recv(fd, buf, 1);
		sz = buf[0];

		atomic_recv(fd, buf, sz);
		buf[sz] = 0;

		hent = gethostbyname(buf);
		if (!hent)
			die("cannot resolve %s: %s", buf, hstrerror(h_errno));

		memcpy(&sa.sin_addr, hent->h_addr, sizeof(sa.sin_addr));
	}

	atomic_recv(fd, buf, 2);
	memcpy(&sa.sin_port, buf, 2);

	nfd = create_connected(&sa);

	len = sizeof(sa);
	if (getsockname(nfd, (struct sockaddr *) &sa, &len) == -1)
		die("getsockname(): %s", strerror(errno));

	buf[0] = 5;	// ver
	buf[1] = 0;	// success
	buf[2] = 0;	// reserved
	buf[3] = 1;	// ipv4
	memcpy(&buf + 4, &sa.sin_addr, 4);
	memcpy(&buf + 8, &sa.sin_port, 2);
	atomic_send(fd, buf, 10);

	tunnel(fd, nfd);
	close(nfd);
}

int main(int ac, char * const av[])
{
	int port, fd;

	if (ac < 2)
		die("must specify port");

	port = atoi(av[1]);
	if (!port)
		die("invalid port");

	fd = create_listening(port);
	signal(SIGCHLD, SIG_IGN);

	for (;;) {
		int nfd;
		pid_t pid;

		nfd = accept(fd, NULL, NULL);
		if (nfd == -1) {
			if (errno == EAGAIN || errno == EINTR)
				continue;

			die("accept(): %s", strerror(errno));
		}

		pid = fork();
		if (pid == -1)
			die("fork(): %s", strerror(errno));
		else if (!pid) {
			close(fd);
			handle(nfd);
			close(nfd);
			exit(EXIT_SUCCESS);
		}

		close(nfd);
	}

	/* NOTREACHED */

	close(fd);
	return EXIT_SUCCESS;
}