cosmopolitan/third_party/lua/lauxlib.c

/*
** $Id: lauxlib.c $
** Auxiliary functions for building Lua libraries
** See Copyright Notice in lua.h
*/

#define lauxlib_c
#define LUA_LIB

#include "libc/calls/calls.h"
#include "libc/errno.h"
#include "third_party/lua/lauxlib.h"
#include "third_party/lua/lprefix.h"
#include "third_party/lua/lua.h"

/* clang-format off */


/**
 * @fileoverview The Auxiliary Library
 *
 * The auxiliary library provides several convenient functions to interface C
 * with Lua. While the basic API provides the primitive functions for all
 * interactions between C and Lua, the auxiliary library provides
 * higher-level functions for some common tasks.
 *
 * All functions and types from the auxiliary library are defined in header
 * file lauxlib.h and have a prefix luaL_.
 *
 * All functions in the auxiliary library are built on top of the basic API,
 * and so they provide nothing that cannot be done with that API.
 * Nevertheless, the use of the auxiliary library ensures more consistency to
 * your code.
 *
 * Several functions in the auxiliary library use internally some extra stack
 * slots. When a function in the auxiliary library uses less than five slots,
 * it does not check the stack size; it simply assumes that there are enough
 * slots.
 *
 * Several functions in the auxiliary library are used to check C function
 * arguments. Because the error message is formatted for arguments (e.g.,
 * "bad argument #1"), you should not use these functions for other stack
 * values.
 *
 * Functions called luaL_check* always raise an error if the check is not
 * satisfied.
 */


#if !defined(MAX_SIZET)
/* maximum value for size_t */
#define MAX_SIZET	((size_t)(~(size_t)0))
#endif


/*
** {======================================================
** Traceback
** =======================================================
*/


#define LEVELS1	10	/* size of the first part of the stack */
#define LEVELS2	11	/* size of the second part of the stack */



/*
** Search for 'objidx' in table at index -1. ('objidx' must be an
** absolute index.) Return 1 + string at top if it found a good name.
*/
static int findfield (lua_State *L, int objidx, int level) {
  if (level == 0 || !lua_istable(L, -1))
    return 0;  /* not found */
  lua_pushnil(L);  /* start 'next' loop */
  while (lua_next(L, -2)) {  /* for each pair in table */
    if (lua_type(L, -2) == LUA_TSTRING) {  /* ignore non-string keys */
      if (lua_rawequal(L, objidx, -1)) {  /* found object? */
        lua_pop(L, 1);  /* remove value (but keep name) */
        return 1;
      }
      else if (findfield(L, objidx, level - 1)) {  /* try recursively */
        /* stack: lib_name, lib_table, field_name (top) */
        lua_pushliteral(L, ".");  /* place '.' between the two names */
        lua_replace(L, -3);  /* (in the slot occupied by table) */
        lua_concat(L, 3);  /* lib_name.field_name */
        return 1;
      }
    }
    lua_pop(L, 1);  /* remove value */
  }
  return 0;  /* not found */
}


/*
** Search for a name for a function in all loaded modules
*/
static int pushglobalfuncname (lua_State *L, lua_Debug *ar) {
  int top = lua_gettop(L);
  lua_getinfo(L, "f", ar);  /* push function */
  lua_getfield(L, LUA_REGISTRYINDEX, LUA_LOADED_TABLE);
  if (findfield(L, top + 1, 2)) {
    const char *name = lua_tostring(L, -1);
    if (strncmp(name, LUA_GNAME ".", 3) == 0) {  /* name start with '_G.'? */
      lua_pushstring(L, name + 3);  /* push name without prefix */
      lua_remove(L, -2);  /* remove original name */
    }
    lua_copy(L, -1, top + 1);  /* copy name to proper place */
    lua_settop(L, top + 1);  /* remove table "loaded" and name copy */
    return 1;
  }
  else {
    lua_settop(L, top);  /* remove function and global table */
    return 0;
  }
}


static void pushfuncname (lua_State *L, lua_Debug *ar) {
  if (pushglobalfuncname(L, ar)) {  /* try first a global name */
    lua_pushfstring(L, "function '%s'", lua_tostring(L, -1));
    lua_remove(L, -2);  /* remove name */
  }
  else if (*ar->namewhat != '\0')  /* is there a name from code? */
    lua_pushfstring(L, "%s '%s'", ar->namewhat, ar->name);  /* use it */
  else if (*ar->what == 'm')  /* main? */
      lua_pushliteral(L, "main chunk");
  else if (*ar->what != 'C')  /* for Lua functions, use <file:line> */
    lua_pushfstring(L, "function <%s:%d>", ar->short_src, ar->linedefined);
  else  /* nothing left... */
    lua_pushliteral(L, "?");
}


static int lastlevel (lua_State *L) {
  lua_Debug ar;
  int li = 1, le = 1;
  /* find an upper bound */
  while (lua_getstack(L, le, &ar)) { li = le; le *= 2; }
  /* do a binary search */
  while (li < le) {
    int m = (li + le)/2;
    if (lua_getstack(L, m, &ar)) li = m + 1;
    else le = m;
  }
  return le - 1;
}


/**
 * luaL_traceback [-0, +1, m]
 *
 * Creates and pushes a traceback of the stack L1. If msg is not NULL, it is
 * appended at the beginning of the traceback. The level parameter tells at
 * which level to start the traceback.
 */
LUALIB_API void luaL_traceback (lua_State *L, lua_State *L1,
                                const char *msg, int level) {
  luaL_Buffer b;
  lua_Debug ar;
  int last = lastlevel(L1);
  int limit2show = (last - level > LEVELS1 + LEVELS2) ? LEVELS1 : -1;
  luaL_buffinit(L, &b);
  if (msg) {
    luaL_addstring(&b, msg);
    luaL_addchar(&b, '\n');
  }
  luaL_addstring(&b, "stack traceback:");
  while (lua_getstack(L1, level++, &ar)) {
    if (limit2show-- == 0) {  /* too many levels? */
      int n = last - level - LEVELS2 + 1;  /* number of levels to skip */
      lua_pushfstring(L, "\n...(skipping %d levels)", n);
      luaL_addvalue(&b);  /* add warning about skip */
      level += n;  /* and skip to last levels */
    }
    else {
      lua_getinfo(L1, "Slnt", &ar);
      if (ar.currentline <= 0)
        lua_pushfstring(L, "\n%s: in ", ar.short_src);
      else
        lua_pushfstring(L, "\n%s:%d: in ", ar.short_src, ar.currentline);
      luaL_addvalue(&b);
      pushfuncname(L, &ar);
      luaL_addvalue(&b);
      if (ar.istailcall)
        luaL_addstring(&b, "\n(...tail calls...)");
    }
  }
  luaL_pushresult(&b);
}


/**
 * Improved Lua traceback.
 * @see https://luyuhuang.tech/2020/12/01/lua-traceback-with-parameters.html
 * @author Luyu Huang
 */
LUALIB_API void luaL_traceback2(lua_State *L, lua_State *L1, const char *msg,
                                int level) {
  lua_Debug ar;
  int top = lua_gettop(L);
  int last = lastlevel(L1);
  int n1 = (last - level > LEVELS1 + LEVELS2) ? LEVELS1 : -1;
  if (msg) lua_pushfstring(L, "%s\n", msg);
  luaL_checkstack(L, 10, NULL);
  lua_pushliteral(L, "stack traceback:");
  while (lua_getstack(L1, level++, &ar)) {
    if (n1-- == 0) {                 /* too many levels? */
      lua_pushliteral(L, "\n\t..."); /* add a '...' */
      level = last - LEVELS2 + 1;    /* and skip to last ones */
    } else {
      lua_getinfo(L1, "Slntu", &ar);
      lua_pushfstring(L, "\n\t%s:", ar.short_src);
      if (ar.currentline > 0)
        lua_pushfstring(L, "%d:", ar.currentline);
      lua_pushliteral(L, " in ");
      pushfuncname(L, &ar);
      if (ar.nparams > 0)
        lua_pushliteral(L, ", params:");
      for (int i = 1; i <= ar.nparams; ++i) {
        const char *name = lua_getlocal(L1, &ar, i);
        if (name) {
          lua_xmove(L1, L, 1);                            // -3
          const char *val = luaL_tolstring(L, -1, NULL);  // -2
          lua_pushfstring(L, " %s = %s;", name, val);     // -1
          lua_insert(L, -3);
          lua_pop(L, 2);
        }
      }
      if (ar.istailcall) lua_pushliteral(L, "\n\t(...tail calls...)");
      lua_concat(L, lua_gettop(L) - top);
    }
  }
  lua_concat(L, lua_gettop(L) - top);
}


/* }====================================================== */


/*
** {======================================================
** Error-report functions
** =======================================================
*/

/**
 * luaL_argerror [-0, +0, v]
 *
 * Raises an error reporting a problem with argument arg of the C function
 * that called it, using a standard message that includes extramsg as a
 * comment:
 *
 * bad argument #arg to 'funcname' (extramsg)
 *
 * This function never returns.
 */
LUALIB_API int luaL_argerror (lua_State *L, int arg, const char *extramsg) {
  lua_Debug ar;
  if (!lua_getstack(L, 0, &ar))  /* no stack frame? */
    return luaL_error(L, "bad argument #%d (%s)", arg, extramsg);
  lua_getinfo(L, "n", &ar);
  if (strcmp(ar.namewhat, "method") == 0) {
    arg--;  /* do not count 'self' */
    if (arg == 0)  /* error is in the self argument itself? */
      return luaL_error(L, "calling '%s' on bad self (%s)",
                           ar.name, extramsg);
  }
  if (ar.name == NULL)
    ar.name = (pushglobalfuncname(L, &ar)) ? lua_tostring(L, -1) : "?";
  return luaL_error(L, "bad argument #%d to '%s' (%s)",
                        arg, ar.name, extramsg);
}

/**
 * luaL_typeerror [-0, +0, v]
 *
 * Raises a type error for the argument arg of the C function that called it,
 * using a standard message; tname is a "name" for the expected type. This
 * function never returns.
 */
LUALIB_API int luaL_typeerror (lua_State *L, int arg, const char *tname) {
  const char *msg;
  const char *typearg;  /* name for the type of the actual argument */
  if (luaL_getmetafield(L, arg, "__name") == LUA_TSTRING)
    typearg = lua_tostring(L, -1);  /* use the given type name */
  else if (lua_type(L, arg) == LUA_TLIGHTUSERDATA)
    typearg = "light userdata";  /* special name for messages */
  else
    typearg = luaL_typename(L, arg);  /* standard name */
  msg = lua_pushfstring(L, "%s expected, got %s", tname, typearg);
  return luaL_argerror(L, arg, msg);
}


static void tag_error (lua_State *L, int arg, int tag) {
  luaL_typeerror(L, arg, lua_typename(L, tag));
}

/**
 * luaL_where [-0, +1, m]
 *
 * Pushes onto the stack a string identifying the current position of the
 * control at level lvl in the call stack. Typically this string has the
 * following format:
 */
LUALIB_API void luaL_where (lua_State *L, int level) {
  /*
  ** The use of 'lua_pushfstring' ensures this function does not
  ** need reserved stack space when called.
  */
  lua_Debug ar;
  if (lua_getstack(L, level, &ar)) {  /* check function at level */
    lua_getinfo(L, "Sl", &ar);  /* get info about it */
    if (ar.currentline > 0) {  /* is there info? */
      lua_pushfstring(L, "%s:%d: ", ar.short_src, ar.currentline);
      return;
    }
  }
  lua_pushfstring(L, "");  /* else, no information available... */
}

/**
 * luaL_error [-0, +0, v]
 *
 * Raises an error. The error message format is given by fmt plus any extra
 * arguments, following the same rules of lua_pushfstring. It also adds at
 * the beginning of the message the file name and the line number where the
 * error occurred, if this information is available.
 *
 * This function never returns, but it is an idiom to use it in C functions
 * as return luaL_error(args).
 */
LUALIB_API int luaL_error (lua_State *L, const char *fmt, ...) {
  /*
  ** Again, the use of 'lua_pushvfstring' ensures this function does
  ** not need reserved stack space when called. (At worst, it generates
  ** an error with "stack overflow" instead of the given message.)
  */
  va_list argp;
  va_start(argp, fmt);
  luaL_where(L, 1);
  lua_pushvfstring(L, fmt, argp);
  va_end(argp);
  lua_concat(L, 2);
  return lua_error(L);
}

/**
 * luaL_fileresult [-0, +(1|3), m]
 *
 * This function produces the return values for file-related functions in the
 * standard library (io.open, os.rename, file:seek, etc.).
 */
LUALIB_API int luaL_fileresult (lua_State *L, int stat, const char *fname) {
  int en = errno;  /* calls to Lua API may change this value */
  if (stat) {
    lua_pushboolean(L, 1);
    return 1;
  }
  else {
    luaL_pushfail(L);
    if (fname)
      lua_pushfstring(L, "%s: %s", fname, strerror(en));
    else
      lua_pushstring(L, strerror(en));
    lua_pushinteger(L, en);
    return 3;
  }
}


#if !defined(l_inspectstat)	/* { */

#if defined(LUA_USE_POSIX)

/*
** use appropriate macros to interpret 'pclose' return status
*/
#define l_inspectstat(stat,what)  \
   if (WIFEXITED(stat)) { stat = WEXITSTATUS(stat); } \
   else if (WIFSIGNALED(stat)) { stat = WTERMSIG(stat); what = "signal"; }

#else

#define l_inspectstat(stat,what)  /* no op */

#endif

#endif				/* } */


/**
 * luaL_execresult [-0, +3, m]
 *
 * This function produces the return values for process-related functions in
 * the standard library (os.execute and io.close).
 */
LUALIB_API int luaL_execresult (lua_State *L, int stat) {
  if (stat != 0 && errno != 0)  /* error with an 'errno'? */
    return luaL_fileresult(L, 0, NULL);
  else {
    const char *what = "exit";  /* type of termination */
    l_inspectstat(stat, what);  /* interpret result */
    if (*what == 'e' && stat == 0)  /* successful termination? */
      lua_pushboolean(L, 1);
    else
      luaL_pushfail(L);
    lua_pushstring(L, what);
    lua_pushinteger(L, stat);
    return 3;  /* return true/fail,what,code */
  }
}

/* }====================================================== */



/*
** {======================================================
** Userdata's metatable manipulation
** =======================================================
*/

/**
 * luaL_newmetatable [-0, +1, m]
 *
 * If the registry already has the key tname, returns 0. Otherwise, creates a
 * new table to be used as a metatable for userdata, adds to this new table
 * the pair __name = tname, adds to the registry the pair [tname] = new
 * table, and returns 1.
 *
 * In both cases, the function pushes onto the stack the final value
 * associated with tname in the registry.
 */
LUALIB_API int luaL_newmetatable (lua_State *L, const char *tname) {
  if (luaL_getmetatable(L, tname) != LUA_TNIL)  /* name already in use? */
    return 0;  /* leave previous value on top, but return 0 */
  lua_pop(L, 1);
  lua_createtable(L, 0, 2);  /* create metatable */
  lua_pushstring(L, tname);
  lua_setfield(L, -2, "__name");  /* metatable.__name = tname */
  lua_pushvalue(L, -1);
  lua_setfield(L, LUA_REGISTRYINDEX, tname);  /* registry.name = metatable */
  return 1;
}

/**
 * luaL_setmetatable [-0, +0, –]
 *
 * Sets the metatable of the object on the top of the stack as the metatable
 * associated with name tname in the registry (see luaL_newmetatable).
 */
LUALIB_API void luaL_setmetatable (lua_State *L, const char *tname) {
  luaL_getmetatable(L, tname);
  lua_setmetatable(L, -2);
}

/**
 * luaL_testudata [-0, +0, m]
 *
 * This function works like luaL_checkudata, except that, when the test
 * fails, it returns NULL instead of raising an error.
 */
LUALIB_API void *luaL_testudata (lua_State *L, int ud, const char *tname) {
  void *p = lua_touserdata(L, ud);
  if (p != NULL) {  /* value is a userdata? */
    if (lua_getmetatable(L, ud)) {  /* does it have a metatable? */
      luaL_getmetatable(L, tname);  /* get correct metatable */
      if (!lua_rawequal(L, -1, -2))  /* not the same? */
        p = NULL;  /* value is a userdata with wrong metatable */
      lua_pop(L, 2);  /* remove both metatables */
      return p;
    }
  }
  return NULL;  /* value is not a userdata with a metatable */
}

/**
 * luaL_checkudata [-0, +0, v]
 *
 * Checks whether the function argument arg is a userdata of the type tname
 * (see luaL_newmetatable) and returns the userdata's memory-block address
 * (see lua_touserdata).
 */
LUALIB_API void *luaL_checkudata (lua_State *L, int ud, const char *tname) {
  void *p = luaL_testudata(L, ud, tname);
  luaL_argexpected(L, p != NULL, ud, tname);
  return p;
}

/* }====================================================== */


/*
** {======================================================
** Argument check functions
** =======================================================
*/

/**
 * luaL_checkoption [-0, +0, v]
 *
 * Checks whether the function argument arg is a string and searches for this
 * string in the array lst (which must be NULL-terminated). Returns the index
 * in the array where the string was found. Raises an error if the argument
 * is not a string or if the string cannot be found.
 *
 * If def is not NULL, the function uses def as a default value when there is
 * no argument arg or when this argument is nil.
 *
 * This is a useful function for mapping strings to C enums. (The usual
 * convention in Lua libraries is to use strings instead of numbers to select
 * options.)
 */
LUALIB_API int luaL_checkoption (lua_State *L, int arg, const char *def,
                                 const char *const lst[]) {
  const char *name = (def) ? luaL_optstring(L, arg, def) :
                             luaL_checkstring(L, arg);
  int i;
  for (i=0; lst[i]; i++)
    if (strcmp(lst[i], name) == 0)
      return i;
  return luaL_argerror(L, arg,
                       lua_pushfstring(L, "invalid option '%s'", name));
}


/*
** Ensures the stack has at least 'space' extra slots, raising an error
** if it cannot fulfill the request. (The error handling needs a few
** extra slots to format the error message. In case of an error without
** this extra space, Lua will generate the same 'stack overflow' error,
** but without 'msg'.)
*/
LUALIB_API void luaL_checkstack (lua_State *L, int space, const char *msg) {
  if (l_unlikely(!lua_checkstack(L, space))) {
    if (msg)
      luaL_error(L, "stack overflow (%s)", msg);
    else
      luaL_error(L, "stack overflow");
  }
}


/**
 * luaL_checktype [-0, +0, v]
 *
 * Checks whether the function argument arg has type t. See lua_type for the
 * encoding of types for t.
 */
LUALIB_API void luaL_checktype (lua_State *L, int arg, int t) {
  if (l_unlikely(lua_type(L, arg) != t))
    tag_error(L, arg, t);
}


/**
 * luaL_checkany [-0, +0, v]
 *
 * Checks whether the function has an argument of any type (including nil) at
 * position arg.
 */
LUALIB_API void luaL_checkany (lua_State *L, int arg) {
  if (l_unlikely(lua_type(L, arg) == LUA_TNONE))
    luaL_argerror(L, arg, "value expected");
}


/**
 * luaL_checklstring [-0, +0, v]
 *
 * Checks whether the function argument arg is a string and returns this
 * string; if l is not NULL fills its referent with the string's length.
 *
 * This function uses lua_tolstring to get its result, so all conversions and
 * caveats of that function apply here.
 */
LUALIB_API const char *luaL_checklstring (lua_State *L, int arg, size_t *len) {
  const char *s = lua_tolstring(L, arg, len);
  if (l_unlikely(!s)) tag_error(L, arg, LUA_TSTRING);
  return s;
}


/**
 * luaL_optlstring [-0, +0, v]
 *
 * If the function argument arg is a string, returns this string. If this
 * argument is absent or is nil, returns d. Otherwise, raises an error.
 *
 * If l is not NULL, fills its referent with the result's length. If the
 * result is NULL (only possible when returning d and d == NULL), its length
 * is considered zero.
 *
 * This function uses lua_tolstring to get its result, so all conversions and
 * caveats of that function apply here.
 */
LUALIB_API const char *luaL_optlstring (lua_State *L, int arg,
                                        const char *def, size_t *len) {
  if (lua_isnoneornil(L, arg)) {
    if (len)
      *len = (def ? strlen(def) : 0);
    return def;
  }
  else return luaL_checklstring(L, arg, len);
}


/**
 * luaL_checknumber [-0, +0, v]
 *
 * Checks whether the function argument arg is a number and returns this
 * number converted to a lua_Number.
 */
LUALIB_API lua_Number luaL_checknumber (lua_State *L, int arg) {
  int isnum;
  lua_Number d = lua_tonumberx(L, arg, &isnum);
  if (l_unlikely(!isnum))
    tag_error(L, arg, LUA_TNUMBER);
  return d;
}


/**
 * luaL_optnumber [-0, +0, v]
 *
 * If the function argument arg is a number, returns this number as a
 * lua_Number. If this argument is absent or is nil, returns d. Otherwise,
 * raises an error.
 */
LUALIB_API lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number def) {
  return luaL_opt(L, luaL_checknumber, arg, def);
}


static void interror (lua_State *L, int arg) {
  if (lua_isnumber(L, arg))
    luaL_argerror(L, arg, "number has no integer representation");
  else
    tag_error(L, arg, LUA_TNUMBER);
}


/**
 * luaL_checkinteger [-0, +0, v]
 *
 * Checks whether the function argument arg is an integer (or can be
 * converted to an integer) and returns this integer.
 */
LUALIB_API lua_Integer luaL_checkinteger (lua_State *L, int arg) {
  int isnum;
  lua_Integer d = lua_tointegerx(L, arg, &isnum);
  if (l_unlikely(!isnum)) {
    interror(L, arg);
  }
  return d;
}


/**
 * luaL_optinteger [-0, +0, v]
 *
 * If the function argument arg is an integer (or it is convertible to an
 * integer), returns this integer. If this argument is absent or is nil,
 * returns d. Otherwise, raises an error.
 */
LUALIB_API lua_Integer luaL_optinteger (lua_State *L, int arg,
                                                      lua_Integer def) {
  return luaL_opt(L, luaL_checkinteger, arg, def);
}

/* }====================================================== */


/*
** {======================================================
** Generic Buffer manipulation
** =======================================================
*/

/* userdata to box arbitrary data */
typedef struct UBox {
  void *box;
  size_t bsize;
} UBox;


static void *resizebox (lua_State *L, int idx, size_t newsize) {
  void *ud;
  lua_Alloc allocf = lua_getallocf(L, &ud);
  UBox *box = (UBox *)lua_touserdata(L, idx);
  void *temp = allocf(ud, box->box, box->bsize, newsize);
  if (l_unlikely(temp == NULL && newsize > 0)) {  /* allocation error? */
    lua_pushliteral(L, "not enough memory");
    lua_error(L);  /* raise a memory error */
  }
  box->box = temp;
  box->bsize = newsize;
  return temp;
}


static int boxgc (lua_State *L) {
  resizebox(L, 1, 0);
  return 0;
}


static const luaL_Reg boxmt[] = {  /* box metamethods */
  {"__gc", boxgc},
  {"__close", boxgc},
  {NULL, NULL}
};


static void newbox (lua_State *L) {
  UBox *box = (UBox *)lua_newuserdatauv(L, sizeof(UBox), 0);
  box->box = NULL;
  box->bsize = 0;
  if (luaL_newmetatable(L, "_UBOX*"))  /* creating metatable? */
    luaL_setfuncs(L, boxmt, 0);  /* set its metamethods */
  lua_setmetatable(L, -2);
}


/*
** check whether buffer is using a userdata on the stack as a temporary
** buffer
*/
#define buffonstack(B)	((B)->b != (B)->init.b)


/*
** Whenever buffer is accessed, slot 'idx' must either be a box (which
** cannot be NULL) or it is a placeholder for the buffer.
*/
#define checkbufferlevel(B,idx)  \
  lua_assert(buffonstack(B) ? lua_touserdata(B->L, idx) != NULL  \
                            : lua_touserdata(B->L, idx) == (void*)B)


/*
** Compute new size for buffer 'B', enough to accommodate extra 'sz'
** bytes.
*/
static size_t newbuffsize (luaL_Buffer *B, size_t sz) {
  size_t newsize = B->size * 2;  /* double buffer size */
  if (l_unlikely(MAX_SIZET - sz < B->n))  /* overflow in (B->n + sz)? */
    return luaL_error(B->L, "buffer too large");
  if (newsize < B->n + sz)  /* double is not big enough? */
    newsize = B->n + sz;
  return newsize;
}


/*
** Returns a pointer to a free area with at least 'sz' bytes in buffer
** 'B'. 'boxidx' is the relative position in the stack where is the
** buffer's box or its placeholder.
*/
static char *prepbuffsize (luaL_Buffer *B, size_t sz, int boxidx) {
  checkbufferlevel(B, boxidx);
  if (B->size - B->n >= sz)  /* enough space? */
    return B->b + B->n;
  else {
    lua_State *L = B->L;
    char *newbuff;
    size_t newsize = newbuffsize(B, sz);
    /* create larger buffer */
    if (buffonstack(B))  /* buffer already has a box? */
      newbuff = (char *)resizebox(L, boxidx, newsize);  /* resize it */
    else {  /* no box yet */
      lua_remove(L, boxidx);  /* remove placeholder */
      newbox(L);  /* create a new box */
      lua_insert(L, boxidx);  /* move box to its intended position */
      lua_toclose(L, boxidx);
      newbuff = (char *)resizebox(L, boxidx, newsize);
      memcpy(newbuff, B->b, B->n * sizeof(char));  /* copy original content */
    }
    B->b = newbuff;
    B->size = newsize;
    return newbuff + B->n;
  }
}

/*
** returns a pointer to a free area with at least 'sz' bytes
*/
LUALIB_API char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz) {
  return prepbuffsize(B, sz, -1);
}


/**
 * luaL_addlstring [-?, +?, m]
 *
 * Adds the string pointed to by s with length l to the buffer B (see
 * luaL_Buffer). The string can contain embedded zeros.
 */
LUALIB_API void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l) {
  if (l > 0) {  /* avoid 'memcpy' when 's' can be NULL */
    char *b = prepbuffsize(B, l, -1);
    memcpy(b, s, l * sizeof(char));
    luaL_addsize(B, l);
  }
}


/**
 * luaL_addstring [-?, +?, m]
 *
 * Adds the zero-terminated string pointed to by s to the buffer B (see
 * luaL_Buffer).
 */
LUALIB_API void luaL_addstring (luaL_Buffer *B, const char *s) {
  luaL_addlstring(B, s, strlen(s));
}


/**
 * luaL_pushresult [-?, +1, m]
 *
 * Finishes the use of buffer B leaving the final string on the top of the
 * stack.
 */
LUALIB_API void luaL_pushresult (luaL_Buffer *B) {
  lua_State *L = B->L;
  checkbufferlevel(B, -1);
  lua_pushlstring(L, B->b, B->n);
  if (buffonstack(B))
    lua_closeslot(L, -2);  /* close the box */
  lua_remove(L, -2);  /* remove box or placeholder from the stack */
}


/**
 * luaL_pushresultsize [-?, +1, m]
 *
 * Equivalent to the sequence luaL_addsize, luaL_pushresult.
 */
LUALIB_API void luaL_pushresultsize (luaL_Buffer *B, size_t sz) {
  luaL_addsize(B, sz);
  luaL_pushresult(B);
}


/*
** 'luaL_addvalue' is the only function in the Buffer system where the
** box (if existent) is not on the top of the stack. So, instead of
** calling 'luaL_addlstring', it replicates the code using -2 as the
** last argument to 'prepbuffsize', signaling that the box is (or will
** be) bellow the string being added to the buffer. (Box creation can
** trigger an emergency GC, so we should not remove the string from the
** stack before we have the space guaranteed.)
*/
LUALIB_API void luaL_addvalue (luaL_Buffer *B) {
  lua_State *L = B->L;
  size_t len;
  const char *s = lua_tolstring(L, -1, &len);
  char *b = prepbuffsize(B, len, -2);
  memcpy(b, s, len * sizeof(char));
  luaL_addsize(B, len);
  lua_pop(L, 1);  /* pop string */
}


/**
 * luaL_buffinit [-0, +0, –]
 *
 * Initializes a buffer B (see luaL_Buffer). This function does not allocate
 * any space; the buffer must be declared as a variable.
 */
LUALIB_API void luaL_buffinit (lua_State *L, luaL_Buffer *B) {
  B->L = L;
  B->b = B->init.b;
  B->n = 0;
  B->size = LUAL_BUFFERSIZE;
  lua_pushlightuserdata(L, (void*)B);  /* push placeholder */
}


/**
 * luaL_buffinitsize [-?, +?, m]
 *
 * Equivalent to the sequence luaL_buffinit, luaL_prepbuffsize.
 */
LUALIB_API char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz) {
  luaL_buffinit(L, B);
  return prepbuffsize(B, sz, -1);
}

/* }====================================================== */


/*
** {======================================================
** Reference system
** =======================================================
*/

/* index of free-list header (after the predefined values) */
#define freelist	(LUA_RIDX_LAST + 1)

/*
** The previously freed references form a linked list:
** t[freelist] is the index of a first free index, or zero if list is
** empty; t[t[freelist]] is the index of the second element; etc.
*/
LUALIB_API int luaL_ref (lua_State *L, int t) {
  int ref;
  if (lua_isnil(L, -1)) {
    lua_pop(L, 1);  /* remove from stack */
    return LUA_REFNIL;  /* 'nil' has a unique fixed reference */
  }
  t = lua_absindex(L, t);
  if (lua_rawgeti(L, t, freelist) == LUA_TNIL) {  /* first access? */
    ref = 0;  /* list is empty */
    lua_pushinteger(L, 0);  /* initialize as an empty list */
    lua_rawseti(L, t, freelist);  /* ref = t[freelist] = 0 */
  }
  else {  /* already initialized */
    lua_assert(lua_isinteger(L, -1));
    ref = (int)lua_tointeger(L, -1);  /* ref = t[freelist] */
  }
  lua_pop(L, 1);  /* remove element from stack */
  if (ref != 0) {  /* any free element? */
    lua_rawgeti(L, t, ref);  /* remove it from list */
    lua_rawseti(L, t, freelist);  /* (t[freelist] = t[ref]) */
  }
  else  /* no free elements */
    ref = (int)lua_rawlen(L, t) + 1;  /* get a new reference */
  lua_rawseti(L, t, ref);
  return ref;
}


/**
 * luaL_unref [-0, +0, –]
 *
 * Releases the reference ref from the table at index t (see luaL_ref). The
 * entry is removed from the table, so that the referred object can be
 * collected. The reference ref is also freed to be used again.
 *
 * If ref is LUA_NOREF or LUA_REFNIL, luaL_unref does nothing.
 */
LUALIB_API void luaL_unref (lua_State *L, int t, int ref) {
  if (ref >= 0) {
    t = lua_absindex(L, t);
    lua_rawgeti(L, t, freelist);
    lua_assert(lua_isinteger(L, -1));
    lua_rawseti(L, t, ref);  /* t[ref] = t[freelist] */
    lua_pushinteger(L, ref);
    lua_rawseti(L, t, freelist);  /* t[freelist] = ref */
  }
}

/* }====================================================== */


/*
** {======================================================
** Load functions
** =======================================================
*/

typedef struct LoadF {
  int n;  /* number of pre-read characters */
  FILE *f;  /* file being read */
  char buff[BUFSIZ];  /* area for reading file */
} LoadF;


static const char *getF (lua_State *L, void *ud, size_t *size) {
  LoadF *lf = (LoadF *)ud;
  (void)L;  /* not used */
  if (lf->n > 0) {  /* are there pre-read characters to be read? */
    *size = lf->n;  /* return them (chars already in buffer) */
    lf->n = 0;  /* no more pre-read characters */
  }
  else {  /* read a block from file */
    /* 'fread' can return > 0 *and* set the EOF flag. If next call to
       'getF' called 'fread', it might still wait for user input.
       The next check avoids this problem. */
    if (feof(lf->f)) return NULL;
    *size = fread(lf->buff, 1, sizeof(lf->buff), lf->f);  /* read block */
  }
  return lf->buff;
}


static int errfile (lua_State *L, const char *what, int fnameindex) {
  const char *serr = strerror(errno);
  const char *filename = lua_tostring(L, fnameindex) + 1;
  lua_pushfstring(L, "cannot %s %s: %s", what, filename, serr);
  lua_remove(L, fnameindex);
  return LUA_ERRFILE;
}


static int skipBOM (LoadF *lf) {
  const char *p = "\xEF\xBB\xBF";  /* UTF-8 BOM mark */
  int c;
  lf->n = 0;
  do {
    c = getc(lf->f);
    if (c == EOF || c != *(const unsigned char *)p++) return c;
    lf->buff[lf->n++] = c;  /* to be read by the parser */
  } while (*p != '\0');
  lf->n = 0;  /* prefix matched; discard it */
  return getc(lf->f);  /* return next character */
}


/*
** reads the first character of file 'f' and skips an optional BOM mark
** in its beginning plus its first line if it starts with '#'. Returns
** true if it skipped the first line.  In any case, '*cp' has the
** first "valid" character of the file (after the optional BOM and
** a first-line comment).
*/
static int skipcomment (LoadF *lf, int *cp) {
  int c = *cp = skipBOM(lf);
  if (c == '#') {  /* first line is a comment (Unix exec. file)? */
    do {  /* skip first line */
      c = getc(lf->f);
    } while (c != EOF && c != '\n');
    *cp = getc(lf->f);  /* skip end-of-line, if present */
    return 1;  /* there was a comment */
  }
  else return 0;  /* no comment */
}


/**
 * luaL_loadfilex [-0, +1, m]
 *
 * Loads a file as a Lua chunk. This function uses lua_load to load the chunk
 * in the file named filename. If filename is NULL, then it loads from the
 * standard input. The first line in the file is ignored if it starts with a
 * #.
 *
 * The string mode works as in the function lua_load.
 *
 * This function returns the same results as lua_load or LUA_ERRFILE for
 * file-related errors.
 *
 * As lua_load, this function only loads the chunk; it does not run it.
 */
LUALIB_API int luaL_loadfilex (lua_State *L, const char *filename,
                                             const char *mode) {
  LoadF lf;
  int status, readstatus;
  int c;
  int fnameindex = lua_gettop(L) + 1;  /* index of filename on the stack */
  if (filename == NULL) {
    lua_pushliteral(L, "=stdin");
    lf.f = stdin;
  }
  else {
    lua_pushfstring(L, "@%s", filename);
    lf.f = fopen(filename, "r");
    if (lf.f == NULL) return errfile(L, "open", fnameindex);
  }
  if (skipcomment(&lf, &c))  /* read initial portion */
    lf.buff[lf.n++] = '\n';  /* add line to correct line numbers */
  if (c == LUA_SIGNATURE[0] && filename) {  /* binary file? */
    lf.f = freopen(filename, "rb", lf.f);  /* reopen in binary mode */
    if (lf.f == NULL) return errfile(L, "reopen", fnameindex);
    skipcomment(&lf, &c);  /* re-read initial portion */
  }
  if (c != EOF)
    lf.buff[lf.n++] = c;  /* 'c' is the first character of the stream */
  status = lua_load(L, getF, &lf, lua_tostring(L, -1), mode);
  readstatus = ferror(lf.f);
  if (filename) fclose(lf.f);  /* close file (even in case of errors) */
  if (readstatus) {
    lua_settop(L, fnameindex);  /* ignore results from 'lua_load' */
    return errfile(L, "read", fnameindex);
  }
  lua_remove(L, fnameindex);
  return status;
}


typedef struct LoadS {
  const char *s;
  size_t size;
} LoadS;


static const char *getS (lua_State *L, void *ud, size_t *size) {
  LoadS *ls = (LoadS *)ud;
  (void)L;  /* not used */
  if (ls->size == 0) return NULL;
  *size = ls->size;
  ls->size = 0;
  return ls->s;
}


/**
 * luaL_loadbufferx [-0, +1, –]
 *
 * Loads a buffer as a Lua chunk. This function uses lua_load to load the
 * chunk in the buffer pointed to by buff with size sz.
 *
 * This function returns the same results as lua_load. name is the chunk
 * name, used for debug information and error messages. The string mode works
 * as in the function lua_load.
 */
LUALIB_API int luaL_loadbufferx (lua_State *L, const char *buff, size_t size,
                                 const char *name, const char *mode) {
  LoadS ls;
  ls.s = buff;
  ls.size = size;
  return lua_load(L, getS, &ls, name, mode);
}


/**
 * luaL_loadstring [-0, +1, –]
 *
 * Loads a string as a Lua chunk. This function uses lua_load to load the
 * chunk in the zero-terminated string s.
 *
 * This function returns the same results as lua_load.
 *
 * Also as lua_load, this function only loads the chunk; it does not run it.
 */
LUALIB_API int luaL_loadstring (lua_State *L, const char *s) {
  return luaL_loadbuffer(L, s, strlen(s), s);
}

/* }====================================================== */



/**
 * luaL_getmetafield [-0, +(0|1), m]
 *
 * Pushes onto the stack the field e from the metatable of the object at
 * index obj and returns the type of the pushed value. If the object does not
 * have a metatable, or if the metatable does not have this field, pushes
 * nothing and returns LUA_TNIL.
 */
LUALIB_API int luaL_getmetafield (lua_State *L, int obj, const char *event) {
  if (!lua_getmetatable(L, obj))  /* no metatable? */
    return LUA_TNIL;
  else {
    int tt;
    lua_pushstring(L, event);
    tt = lua_rawget(L, -2);
    if (tt == LUA_TNIL)  /* is metafield nil? */
      lua_pop(L, 2);  /* remove metatable and metafield */
    else
      lua_remove(L, -2);  /* remove only metatable */
    return tt;  /* return metafield type */
  }
}


/**
 * luaL_callmeta [-0, +(0|1), e]
 *
 * Calls a metamethod.
 *
 * If the object at index obj has a metatable and this metatable has a field
 * e, this function calls this field passing the object as its only argument.
 * In this case this function returns true and pushes onto the stack the
 * value returned by the call. If there is no metatable or no metamethod,
 * this function returns false without pushing any value on the stack.
 */
LUALIB_API int luaL_callmeta (lua_State *L, int obj, const char *event) {
  obj = lua_absindex(L, obj);
  if (luaL_getmetafield(L, obj, event) == LUA_TNIL)  /* no metafield? */
    return 0;
  lua_pushvalue(L, obj);
  lua_call(L, 1, 1);
  return 1;
}


/**
 * luaL_len [-0, +0, e]
 *
 * Returns the "length" of the value at the given index as a number; it is
 * equivalent to the '#' operator in Lua (see §3.4.7). Raises an error if the
 * result of the operation is not an integer. (This case can only happen
 * through metamethods.)
 */
LUALIB_API lua_Integer luaL_len (lua_State *L, int idx) {
  lua_Integer l;
  int isnum;
  lua_len(L, idx);
  l = lua_tointegerx(L, -1, &isnum);
  if (l_unlikely(!isnum))
    luaL_error(L, "object length is not an integer");
  lua_pop(L, 1);  /* remove object */
  return l;
}


/**
 * luaL_tolstring [-0, +1, e]
 *
 * Converts any Lua value at the given index to a C string in a reasonable
 * format. The resulting string is pushed onto the stack and also returned by
 * the function (see §4.1.3). If len is not NULL, the function also sets *len
 * with the string length.
 *
 * If the value has a metatable with a __tostring field, then luaL_tolstring
 * calls the corresponding metamethod with the value as argument, and uses
 * the result of the call as its result.
 */
LUALIB_API const char *luaL_tolstring (lua_State *L, int idx, size_t *len) {
  if (luaL_callmeta(L, idx, "__tostring")) {  /* metafield? */
    if (!lua_isstring(L, -1))
      luaL_error(L, "'__tostring' must return a string");
  }
  else {
    switch (lua_type(L, idx)) {
      case LUA_TNUMBER: {
        if (lua_isinteger(L, idx))
          lua_pushfstring(L, "%I", (LUAI_UACINT)lua_tointeger(L, idx));
        else
          lua_pushfstring(L, "%f", (LUAI_UACNUMBER)lua_tonumber(L, idx));
        break;
      }
      case LUA_TSTRING:
        lua_pushvalue(L, idx);
        break;
      case LUA_TBOOLEAN:
        lua_pushstring(L, (lua_toboolean(L, idx) ? "true" : "false"));
        break;
      case LUA_TNIL:
        lua_pushliteral(L, "nil");
        break;
      default: {
        int tt = luaL_getmetafield(L, idx, "__name");  /* try name */
        const char *kind = (tt == LUA_TSTRING) ? lua_tostring(L, -1) :
                                                 luaL_typename(L, idx);
        lua_pushfstring(L, "%s: %p", kind, lua_topointer(L, idx));
        if (tt != LUA_TNIL)
          lua_remove(L, -2);  /* remove '__name' */
        break;
      }
    }
  }
  return lua_tolstring(L, -1, len);
}


/*
** set functions from list 'l' into table at top - 'nup'; each
** function gets the 'nup' elements at the top as upvalues.
** Returns with only the table at the stack.
*/
LUALIB_API void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup) {
  luaL_checkstack(L, nup, "too many upvalues");
  for (; l->name != NULL; l++) {  /* fill the table with given functions */
    if (l->func == NULL)  /* place holder? */
      lua_pushboolean(L, 0);
    else {
      int i;
      for (i = 0; i < nup; i++)  /* copy upvalues to the top */
        lua_pushvalue(L, -nup);
      lua_pushcclosure(L, l->func, nup);  /* closure with those upvalues */
    }
    lua_setfield(L, -(nup + 2), l->name);
  }
  lua_pop(L, nup);  /* remove upvalues */
}


/*
** ensure that stack[idx][fname] has a table and push that table
** into the stack
*/
LUALIB_API int luaL_getsubtable (lua_State *L, int idx, const char *fname) {
  if (lua_getfield(L, idx, fname) == LUA_TTABLE)
    return 1;  /* table already there */
  else {
    lua_pop(L, 1);  /* remove previous result */
    idx = lua_absindex(L, idx);
    lua_newtable(L);
    lua_pushvalue(L, -1);  /* copy to be left at top */
    lua_setfield(L, idx, fname);  /* assign new table to field */
    return 0;  /* false, because did not find table there */
  }
}


/*
** Stripped-down 'require': After checking "loaded" table, calls 'openf'
** to open a module, registers the result in 'package.loaded' table and,
** if 'glb' is true, also registers the result in the global table.
** Leaves resulting module on the top.
*/
LUALIB_API void luaL_requiref (lua_State *L, const char *modname,
                               lua_CFunction openf, int glb) {
  luaL_getsubtable(L, LUA_REGISTRYINDEX, LUA_LOADED_TABLE);
  lua_getfield(L, -1, modname);  /* LOADED[modname] */
  if (!lua_toboolean(L, -1)) {  /* package not already loaded? */
    lua_pop(L, 1);  /* remove field */
    lua_pushcfunction(L, openf);
    lua_pushstring(L, modname);  /* argument to open function */
    lua_call(L, 1, 1);  /* call 'openf' to open module */
    lua_pushvalue(L, -1);  /* make copy of module (call result) */
    lua_setfield(L, -3, modname);  /* LOADED[modname] = module */
  }
  lua_remove(L, -2);  /* remove LOADED table */
  if (glb) {
    lua_pushvalue(L, -1);  /* copy of module */
    lua_setglobal(L, modname);  /* _G[modname] = module */
  }
}


/**
 * luaL_addgsub [-0, +0, m]
 *
 * Adds a copy of the string s to the buffer B (see luaL_Buffer), replacing
 * any occurrence of the string p with the string r.
 */
LUALIB_API void luaL_addgsub (luaL_Buffer *b, const char *s,
                                     const char *p, const char *r) {
  const char *wild;
  size_t l = strlen(p);
  while ((wild = strstr(s, p)) != NULL) {
    luaL_addlstring(b, s, wild - s);  /* push prefix */
    luaL_addstring(b, r);  /* push replacement in place of pattern */
    s = wild + l;  /* continue after 'p' */
  }
  luaL_addstring(b, s);  /* push last suffix */
}


/**
 * luaL_gsub [-0, +1, m]
 *
 * Creates a copy of string s, replacing any occurrence of the string p with
 * the string r. Pushes the resulting string on the stack and returns it.
 */
LUALIB_API const char *luaL_gsub (lua_State *L, const char *s,
                                  const char *p, const char *r) {
  luaL_Buffer b;
  luaL_buffinit(L, &b);
  luaL_addgsub(&b, s, p, r);
  luaL_pushresult(&b);
  return lua_tostring(L, -1);
}


static void *l_alloc (void *ud, void *ptr, size_t osize, size_t nsize) {
  (void)ud; (void)osize;  /* not used */
  if (nsize == 0) {
    free(ptr);
    return NULL;
  }
  else
    return realloc(ptr, nsize);
}


static int panic (lua_State *L) {
  const char *msg = lua_tostring(L, -1);
  if (msg == NULL) msg = "error object is not a string";
  lua_writestringerror("PANIC: unprotected error in call to Lua API (%s)\n",
                        msg);
  return 0;  /* return to Lua to abort */
}


/*
** Warning functions:
** warnfoff: warning system is off
** warnfon: ready to start a new message
** warnfcont: previous message is to be continued
*/
static void warnfoff (void *ud, const char *message, int tocont);
static void warnfon (void *ud, const char *message, int tocont);
static void warnfcont (void *ud, const char *message, int tocont);


/*
** Check whether message is a control message. If so, execute the
** control or ignore it if unknown.
*/
static int checkcontrol (lua_State *L, const char *message, int tocont) {
  if (tocont || *(message++) != '@')  /* not a control message? */
    return 0;
  else {
    if (strcmp(message, "off") == 0)
      lua_setwarnf(L, warnfoff, L);  /* turn warnings off */
    else if (strcmp(message, "on") == 0)
      lua_setwarnf(L, warnfon, L);   /* turn warnings on */
    return 1;  /* it was a control message */
  }
}


static void warnfoff (void *ud, const char *message, int tocont) {
  checkcontrol((lua_State *)ud, message, tocont);
}


/*
** Writes the message and handle 'tocont', finishing the message
** if needed and setting the next warn function.
*/
static void warnfcont (void *ud, const char *message, int tocont) {
  lua_State *L = (lua_State *)ud;
  lua_writestringerror("%s", message);  /* write message */
  if (tocont)  /* not the last part? */
    lua_setwarnf(L, warnfcont, L);  /* to be continued */
  else {  /* last part */
    lua_writestringerror("%s", "\n");  /* finish message with end-of-line */
    lua_setwarnf(L, warnfon, L);  /* next call is a new message */
  }
}


static void warnfon (void *ud, const char *message, int tocont) {
  if (checkcontrol((lua_State *)ud, message, tocont))  /* control message? */
    return;  /* nothing else to be done */
  lua_writestringerror("%s", "Lua warning: ");  /* start a new warning */
  warnfcont(ud, message, tocont);  /* finish processing */
}


/**
 * luaL_newstate [-0, +0, –]
 *
 * Creates a new Lua state. It calls lua_newstate with an allocator based on
 * the standard C allocation functions and then sets a warning function and a
 * panic function (see §4.4) that print messages to the standard error
 * output.
 *
 * Returns the new state, or NULL if there is a memory allocation error.
 */
LUALIB_API lua_State *luaL_newstate (void) {
  lua_State *L = lua_newstate(l_alloc, NULL);
  if (l_likely(L)) {
    lua_atpanic(L, &panic);
    lua_setwarnf(L, warnfoff, L);  /* default is warnings off */
  }
  return L;
}


LUALIB_API void luaL_checkversion_ (lua_State *L, lua_Number ver, size_t sz) {
  lua_Number v = lua_version(L);
  if (sz != LUAL_NUMSIZES)  /* check numeric types */
    luaL_error(L, "core and library have incompatible numeric types");
  else if (v != ver)
    luaL_error(L, "version mismatch: app. needs %f, Lua core provides %f",
                  (LUAI_UACNUMBER)ver, (LUAI_UACNUMBER)v);
}