/* Prosody IM

-- Copyright (C) 2008-2017 Matthew Wild

-- Copyright (C) 2008-2017 Waqas Hussain

-- Copyright (C) 2016-2017 Kim Alvefur

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

*/

/*

* crand.c

* C PRNG interface

*

* The purpose of this module is to provide access to a PRNG in

* environments without /dev/urandom

*

* Caution! This has not been extensively tested.

*

*/

#define _DEFAULT_SOURCE

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include "lualib.h"

#include "lauxlib.h"

#if defined(WITH_GETRANDOM)

#ifndef __GLIBC_PREREQ

/* Not compiled with glibc at all */

#define __GLIBC_PREREQ(a,b) 0

#endif

#if ! __GLIBC_PREREQ(2,25)

/* Not compiled with a glibc that provides getrandom() */

#include <unistd.h>

#include <sys/syscall.h>

#ifndef SYS_getrandom

#error getrandom() requires Linux 3.17 or later

#endif

/* This wasn't present before glibc 2.25 */

int getrandom(void *buf, size_t buflen, unsigned int flags) {

	return syscall(SYS_getrandom, buf, buflen, flags);

}

#else

#include <sys/random.h>

#endif

#elif defined(WITH_OPENSSL)

#include <openssl/rand.h>

#elif defined(WITH_ARC4RANDOM)

#ifdef __linux__

#include <bsd/stdlib.h>

#endif

#else

#error util.crand compiled without a random source

#endif

#ifndef SMALLBUFSIZ

#define SMALLBUFSIZ 32

#endif

int Lrandom(lua_State *L) {

	char smallbuf[SMALLBUFSIZ];

	char *buf = &smallbuf[0];

	const lua_Integer l = luaL_checkinteger(L, 1);

	const size_t len = l;

	luaL_argcheck(L, l >= 0, 1, "must be > 0");

	if(len == 0) {

		lua_pushliteral(L, "");

		return 1;

	}

	if(len > SMALLBUFSIZ) {

		buf = lua_newuserdata(L, len);

	}

#if defined(WITH_GETRANDOM)

	/*

	 * This acts like a read from /dev/urandom with the exception that it

	 * *does* block if the entropy pool is not yet initialized.

	 */

	int left = len;

	char *p = buf;

	do {

		int ret = getrandom(p, left, 0);

		if(ret < 0) {

			lua_pushstring(L, strerror(errno));

			return lua_error(L);

		}

		p += ret;

		left -= ret;

	} while(left > 0);

#elif defined(WITH_ARC4RANDOM)

	arc4random_buf(buf, len);

#elif defined(WITH_OPENSSL)

	if(!RAND_status()) {

		lua_pushliteral(L, "OpenSSL PRNG not seeded");

		return lua_error(L);

	}

	if(RAND_bytes((unsigned char *)buf, len) != 1) {

		/* TODO ERR_get_error() */

		lua_pushstring(L, "RAND_bytes() failed");

		return lua_error(L);

	}

#endif

	lua_pushlstring(L, buf, len);

	return 1;

}

int luaopen_util_crand(lua_State *L) {

#if (LUA_VERSION_NUM > 501)

	luaL_checkversion(L);

#endif

	lua_createtable(L, 0, 2);

	lua_pushcfunction(L, Lrandom);

	lua_setfield(L, -2, "bytes");

#if defined(WITH_GETRANDOM)

	lua_pushstring(L, "Linux");

#elif defined(WITH_ARC4RANDOM)

	lua_pushstring(L, "arc4random()");

#elif defined(WITH_OPENSSL)

	lua_pushstring(L, "OpenSSL");

#endif

	lua_setfield(L, -2, "_source");

	return 1;

}