#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/types.h>
#include <sys/sysctl.h>


/*
 * Supplied string can contain up to 32 hex chars.  If it contains less, the
 * rest are assumed to be zero.
 */
int
str_to_key(uint8_t *key, const char *str)
{
	unsigned int len, i;
	unsigned int byte_num;
	unsigned int nibble_num;
	char c;
	uint8_t val;
	
	len = strlen(str);
	if (len > 32)
		return (0);


	memset(key, 0, 16);
	
	byte_num = 0;
	nibble_num = 0;
	for (i = 0; i < len; i++) {
		c = tolower(str[i]);
		if (c >= '0' && c <= '9')
			val = c - '0';
		else if (c >= 'a' && c <= 'f')
			val = c - 'a' + 10;
		else
			return (0);

		key[byte_num] |= val << ((1 - nibble_num) * 4);
		nibble_num = (nibble_num + 1) % 2;
		if (nibble_num == 0)
			byte_num++;
	}

	return (1);
}


int
main(int argc, char **argv)
{
	int i;
	int set_psk;
	uint8_t key[16];
	const char *which_sysctl;
	
	if (!(((argc == 3) && (strcmp(argv[1], "-p") == 0)) || (argc == 2))) {
		printf("usage: %s [-p] <key>\n", argv[0]);
		printf("    -p     Set pre-shared key, otherwise set server key\n");
		printf("    <key>  Up to 32 hex digits\n");
		return (1);
	}

	set_psk = (argc == 3);
	
	if (!str_to_key(key, argv[argc - 1])) {
		printf("Bad key format\n");
		return (1);
	}

	which_sysctl = set_psk ? "net.inet.tcp.fastopen.setpsk" : "net.inet.tcp.fastopen.setkey";
	printf("Setting %s to ", which_sysctl);
	for (i = 0; i < 16; i++)
		printf("%02x", key[i]);
	printf("\n");
	if (-1 == sysctlbyname(which_sysctl, NULL, NULL, key, sizeof(key))) {
		perror("Setting key failed");
		return (1);
	}
	
	return (0);
}