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/// @module system
/// Random.
// @section random
#include <lua.h>
#include <lauxlib.h>
#include "compat.h"
#include <fcntl.h>
#ifdef _WIN32
#include "windows.h"
#include "wincrypt.h"
#else
#include <errno.h>
#include <unistd.h>
#include <string.h>
#endif
/***
Generate random bytes.
This uses `CryptGenRandom()` on Windows, and `/dev/urandom` on other platforms. It will return the
requested number of bytes, or an error, never a partial result.
@function random
@tparam[opt=1] int length number of bytes to get
@treturn[1] string string of random bytes
@treturn[2] nil
@treturn[2] string error message
*/
static int lua_get_random_bytes(lua_State* L) {
int num_bytes = luaL_optinteger(L, 1, 1); // Number of bytes, default to 1 if not provided
if (num_bytes <= 0) {
if (num_bytes == 0) {
lua_pushliteral(L, "");
return 1;
}
lua_pushnil(L);
lua_pushstring(L, "invalid number of bytes, must not be less than 0");
return 2;
}
unsigned char* buffer = (unsigned char*)lua_newuserdata(L, num_bytes);
if (buffer == NULL) {
lua_pushnil(L);
lua_pushstring(L, "failed to allocate memory for random buffer");
return 2;
}
ssize_t n;
ssize_t total_read = 0;
#ifdef _WIN32
HCRYPTPROV hCryptProv;
if (!CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {
DWORD error = GetLastError();
lua_pushnil(L);
lua_pushfstring(L, "failed to acquire cryptographic context: %lu", error);
return 2;
}
if (!CryptGenRandom(hCryptProv, num_bytes, buffer)) {
DWORD error = GetLastError();
lua_pushnil(L);
lua_pushfstring(L, "failed to get random data: %lu", error);
CryptReleaseContext(hCryptProv, 0);
return 2;
}
CryptReleaseContext(hCryptProv, 0);
#else
// for macOS/unixes use /dev/urandom for non-blocking
int fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
if (fd < 0) {
lua_pushnil(L);
lua_pushstring(L, "failed opening /dev/urandom");
return 2;
}
while (total_read < num_bytes) {
n = read(fd, buffer + total_read, num_bytes - total_read);
if (n < 0) {
if (errno == EINTR) {
continue; // Interrupted, retry
} else {
lua_pushnil(L);
lua_pushfstring(L, "failed reading /dev/urandom: %s", strerror(errno));
close(fd);
return 2;
}
}
total_read += n;
}
close(fd);
#endif
lua_pushlstring(L, (const char*)buffer, num_bytes);
return 1;
}
static luaL_Reg func[] = {
{ "random", lua_get_random_bytes },
{ NULL, NULL }
};
/*-------------------------------------------------------------------------
* Initializes module
*-------------------------------------------------------------------------*/
void random_open(lua_State *L) {
luaL_setfuncs(L, func, 0);
}
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