BID for MySQL (9-byte, time based ID generator)

bid.c

/*
 * Copyright (c) 2017, Brian Leishman
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * USAGE INSTRUCTIONS:
 * 
 * make sure libmysqlclient-dev is installed:
 * apt-get install libmysqlclient-dev
 * 
 * Replace "/usr/lib/mysql/plugin" with your MySQL plugins directory (can be found by running "select @@plugin_dir;")
 * gcc -I/usr/include/mysql -o bid.so -shared bid.c -fPIC && cp bid.so /usr/lib/mysql/plugin/bid.so
 * 
 * Then, on the server:
 * create function`bid`returns string soname'bid.so';
 * 
 * And use/test like:
 * select `bid`();
 * 
 * Also, make sure to store in a "BINARY(9)" column type
 * 
 * Yeet!
 *  
 */

#ifdef STANDARD
/* STANDARD is defined, don't use any mysql functions */
#include <string.h>
#ifdef __WIN__
typedef unsigned __int64 ulonglong; /* Microsofts 64 bit types */
typedef __int64 longlong;
#else
typedef unsigned long long ulonglong;
typedef long long longlong;
#endif /*__WIN__*/
#else
#include <my_global.h>
#include <my_sys.h>
#if defined(MYSQL_SERVER)
#include <m_string.h>
#else
/* when compiled as standalone */
#include <string.h>
#endif
#endif
#include <mysql.h>
#include <ctype.h>

#include <stdint.h>
#include <time.h>

#ifdef HAVE_DLOPEN

int randint(int n) {
	//https://stackoverflow.com/a/822361/728236
	if ((n - 1) == RAND_MAX) {
		return rand();
	} else {
		// Chop off all of the values that would cause skew...
		long end = RAND_MAX / n; // truncate skew
		assert(end > 0L);
		end *= n;

		// ... and ignore results from rand() that fall above that limit.
		// (Worst case the loop condition should succeed 50% of the time,
		// so we can expect to bail out of this loop pretty quickly.)
		int r;
		while ((r = rand()) >= end);

		return r % n;
	}
}

my_bool bid_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
void bid_deinit(UDF_INIT *initid);
char *bid(UDF_INIT *initid __attribute__ ((unused)), UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *message __attribute__ ((unused)));

my_bool bid_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
	initid->maybe_null = 0;

	return 0;
}

char *bid(UDF_INIT *initid __attribute__ ((unused)), UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *message __attribute__ ((unused))) {
	struct timespec ts;
	unsigned char *bytes = malloc(sizeof (char) * (9));

	timespec_get(&ts, TIME_UTC);
	uint64_t Timestamp = ts.tv_sec * 1000000000 + ts.tv_nsec;

	bytes[0] = (Timestamp >> 56) & 0xFF;
	bytes[1] = (Timestamp >> 48) & 0xFF;
	bytes[2] = (Timestamp >> 40) & 0xFF;
	bytes[3] = (Timestamp >> 32) & 0xFF;
	bytes[4] = (Timestamp >> 24) & 0xFF;
	bytes[5] = (Timestamp >> 16) & 0xFF;
	bytes[6] = (Timestamp >> 8) & 0xFF;
	bytes[7] = Timestamp & 0xFF;
	bytes[8] = randint(256) & 0xFF;

	*length = 9;
	return bytes;
}

#endif /* HAVE_DLOPEN */