letmein.c

#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <unistd.h>
#include <fcntl.h>

/*
 * 0x00 - strange char
 * 0x01 ^a - seems to do nothing, except after ^r
 * 0x02 - 0x0E ^b - ^n - strange chars
 * 0x0F ^o - clear the screen
 * 0x10 ^p + <char> - seems to move the cursor
 * 0x11 ^q - same as space
 * 0x12 ^r - kills output then ^a fixes it
 * 0x13 - 0x1A ^s - ^z - same as space
 * 0x1B - 0x1F - same as space
 *
 * 0x10 0x00 - col 0 row 0 home cursor
 *      0x01 - col 1 row 0
 *      ...
 *      0x17 - col 23 row 0
 *      0x18 - off the screen (sometimes?)
 *      0x18 - col 0 row 1
 *      0x19 - col 1 row 1
 *      ...
 *      0x2F - col 23 row 0
 *      0x30 - off the screen (for real this time)
 */

void reset_screen(void)
{
	putchar(0x0F);
}

void move_cursor(int row, int col)
{
	if(row < 0 || row > 1)
		return;
	if(col < 0 || col > 23)
		return;
	putchar(0x10);
	putchar(row * 24 + col);
}

char get(void)
{
	char ch;

	read(0, &ch, 1);
	if(ch == 'q')
		execl("/sbin/init", "/sbin/init", (char *)NULL);
	return ch;
}

void wait_for_key(void)
{
	get();
}

int main(void)
{
	char code[5] = "31337";
	char input[5];
	int i;
	struct termios t;

	/*
	if(fcntl(0, F_SETFL, O_DIRECT) == -1)
	{
		perror("fcntl failed");
		return -1;
	}
	if(setvbuf(stdin, NULL, _IONBF, 0) != 0)
	{
		perror("setbuf for stdin failed");
		return -1;
	}
	*/
	if(setvbuf(stdout, NULL, _IONBF, 0) != 0)
	{
		perror("setbuf on stdout failed");
		return -1;
	}
	if(tcgetattr(0, &t) == -1)
	{
		perror("tcgetattr failed");
		return -1;
	}
	cfmakeraw(&t);
	if(tcsetattr(0, TCSAFLUSH, &t) == -1)
	{
		perror("tcsetattr failed");
		return -1;
	}
	while(1)
	{
		reset_screen();
		/* Wait for a keystroke to display message */
		/* We don't want to burn the screen do we? */
		wait_for_key();
		printf("You are at a keypad:");
		move_cursor(1, 0);
		/* Give them a hint at how many keys to press */
		for(i = 0; i < sizeof(code); i++)
			putchar('_');
		move_cursor(1, 0);
		/* Read in keys */
		for(i = 0; i < sizeof(input); i++)
		{
			input[i] = get();
			putchar('*');
		}
		if(memcmp(input, code, sizeof(code)) == 0)
		{
			printf("good!");
			wait_for_key();
		}
	}
	return 0;
}