text: /************************************************************************
  * lsqlite3                                                              *
  * Copyright (C) 2002-2007 Tiago Dionizio, Doug Currie                   *
  * All rights reserved.                                                  *
  * Author    : Tiago Dionizio <tiago.dionizio@ist.utl.pt>                *
  * Author    : Doug Currie <doug.currie@alum.mit.edu>                    *
  * Library   : lsqlite3 - a SQLite 3 database binding for Lua 5          *
  *                                                                       *
  * Permission is hereby granted, free of charge, to any person obtaining *
  * a copy of this software and associated documentation files (the       *
  * "Software"), to deal in the Software without restriction, including   *
  * without limitation the rights to use, copy, modify, merge, publish,   *
  * distribute, sublicense, and/or sell copies of the Software, and to    *
  * permit persons to whom the Software is furnished to do so, subject to *
  * the following conditions:                                             *
  *                                                                       *
  * The above copyright notice and this permission notice shall be        *
  * included in all copies or substantial portions of the Software.       *
  *                                                                       *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       *
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    *
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*
  * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  *
  * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  *
  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     *
  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                *
  ************************************************************************/
  
  #include <stdlib.h>
  #include <string.h>
  #include <assert.h>
  
  #define LUA_LIB
  #include "lua.h"
  #include "lauxlib.h"
  
  #include "sqlite3.h"
  
  /* compile time features */
  #if !defined(SQLITE_OMIT_PROGRESS_CALLBACK)
      #define SQLITE_OMIT_PROGRESS_CALLBACK 0
  #endif
  
  typedef struct sdb sdb;
  typedef struct sdb_vm sdb_vm;
  typedef struct sdb_func sdb_func;
  
  /* to use as C user data so i know what function sqlite is calling */
  struct sdb_func {
      /* references to associated lua values */
      int fn_step;
      int fn_finalize;
      int udata;
  
      sdb *db;
      char aggregate;
  
      sdb_func *next;
  };
  
  /* information about database */
  struct sdb {
      /* associated lua state */
      lua_State *L;
      /* sqlite database handle */
      sqlite3 *db;
  
      /* sql functions stack usage */
      sdb_func *func;         /* top SQL function being called */
  
      /* references */
      int busy_cb;        /* busy callback */
      int busy_udata;
  
      int progress_cb;    /* progress handler */
      int progress_udata;
  
      int trace_cb;       /* trace callback */
      int trace_udata;
  };
  
  static const char *sqlite_meta      = ":sqlite3";
  static const char *sqlite_vm_meta   = ":sqlite3:vm";
  static const char *sqlite_ctx_meta  = ":sqlite3:ctx";
  static int sqlite_ctx_meta_ref;
  
  /*
  ** =======================================================
  ** Database Virtual Machine Operations
  ** =======================================================
  */
  
  static void vm_push_column(lua_State *L, sqlite3_stmt *vm, int idx) {
      switch (sqlite3_column_type(vm, idx)) {
          case SQLITE_INTEGER:
              {
                  sqlite_int64 i64 = sqlite3_column_int64(vm, idx);
                  lua_Number n = (lua_Number)i64;
                  if (n == i64)
                      lua_pushnumber(L, n);
                  else
                      lua_pushlstring(L, (const char*)sqlite3_column_text(vm, idx), sqlite3_column_bytes(vm, idx));
              }
              break;
          case SQLITE_FLOAT:
              lua_pushnumber(L, sqlite3_column_double(vm, idx));
              break;
          case SQLITE_TEXT:
              lua_pushlstring(L, (const char*)sqlite3_column_text(vm, idx), sqlite3_column_bytes(vm, idx));
              break;
          case SQLITE_BLOB:
              lua_pushlstring(L, sqlite3_column_blob(vm, idx), sqlite3_column_bytes(vm, idx));
              break;
          case SQLITE_NULL:
              lua_pushnil(L);
              break;
          default:
              lua_pushnil(L);
              break;
      }
  }
  
  /* virtual machine information */
  struct sdb_vm {
      sdb *db;                /* associated database handle */
      sqlite3_stmt *vm;       /* virtual machine */
  
      /* sqlite3_step info */
      int columns;            /* number of columns in result */
      char has_values;        /* true when step succeeds */
  
      char temp;              /* temporary vm used in db:rows */
  };
  
  /* called with sql text on the lua stack */
  static sdb_vm *newvm(lua_State *L, sdb *db) {
      sdb_vm *svm = (sdb_vm*)lua_newuserdata(L, sizeof(sdb_vm));
  
      luaL_getmetatable(L, sqlite_vm_meta);
      lua_setmetatable(L, -2);        /* set metatable */
  
      svm->db = db;
      svm->columns = 0;
      svm->has_values = 0;
      svm->vm = NULL;
      svm->temp = 0;
  
      /* add an entry on the database table: svm -> sql text */
      lua_pushlightuserdata(L, db);
      lua_rawget(L, LUA_REGISTRYINDEX);
      lua_pushlightuserdata(L, svm);
      lua_pushvalue(L, -4); /* the sql text */
      lua_rawset(L, -3);
      lua_pop(L, 1);
  
      return svm;
  }
  
  static int cleanupvm(lua_State *L, sdb_vm *svm) {
      /* remove entry in database table - no harm if not present in the table */
      lua_pushlightuserdata(L, svm->db);
      lua_rawget(L, LUA_REGISTRYINDEX);
      lua_pushlightuserdata(L, svm);
      lua_pushnil(L);
      lua_rawset(L, -3);
      lua_pop(L, 1);
  
      svm->columns = 0;
      svm->has_values = 0;
  
      if (!svm->vm) return 0;
  
      lua_pushnumber(L, sqlite3_finalize(svm->vm));
      svm->vm = NULL;
      return 1;
  }
  
  static int stepvm(lua_State *L, sdb_vm *svm) {
      int result;
      int loop_limit = 3;
      while ( loop_limit-- ) {
          result = sqlite3_step(svm->vm);
          if ( result==SQLITE_ERROR ) {
            result = sqlite3_reset (svm->vm);
          }
          if ( result==SQLITE_SCHEMA ) {
              sqlite3_stmt *vn;
              const char *sql;
              /* recover sql text */
              lua_pushlightuserdata(L, svm->db);
              lua_rawget(L, LUA_REGISTRYINDEX);
              lua_pushlightuserdata(L, svm);
              lua_rawget(L, -2); /* sql text */
              sql = luaL_checkstring(L, -1);
              /* re-prepare */
              result = sqlite3_prepare(svm->db->db, sql, -1, &vn, NULL);
              if (result != SQLITE_OK) break;
              sqlite3_transfer_bindings(svm->vm, vn);
              sqlite3_finalize(svm->vm);
              svm->vm = vn;
              lua_pop(L,2);
          } else {
            break;
          }
      }
      return result;
  }
  
  static sdb_vm *lsqlite_getvm(lua_State *L, int index) {
      sdb_vm *svm = (sdb_vm*)luaL_checkudata(L, index, sqlite_vm_meta);
      if (svm == NULL) luaL_argerror(L, index, "bad sqlite virtual machine");
      return svm;
  }
  
  static sdb_vm *lsqlite_checkvm(lua_State *L, int index) {
      sdb_vm *svm = lsqlite_getvm(L, index);
      if (svm->vm == NULL) luaL_argerror(L, index, "attempt to use closed sqlite virtual machine");
      return svm;
  }
  
  static int dbvm_isopen(lua_State *L) {
      sdb_vm *svm = lsqlite_getvm(L, 1);
      lua_pushboolean(L, svm->vm != NULL ? 1 : 0);
      return 1;
  }
  
  static int dbvm_tostring(lua_State *L) {
      char buff[39];
      sdb_vm *svm = lsqlite_getvm(L, 1);
      if (svm->vm == NULL)
          strcpy(buff, "closed");
      else
          sprintf(buff, "%p", svm);
      lua_pushfstring(L, "sqlite virtual machine (%s)", buff);
      return 1;
  }
  
  static int dbvm_gc(lua_State *L) {
      sdb_vm *svm = lsqlite_getvm(L, 1);
      if (svm->vm != NULL)  /* ignore closed vms */
          cleanupvm(L, svm);
      return 0;
  }
  
  static int dbvm_step(lua_State *L) {
      int result;
      sdb_vm *svm = lsqlite_checkvm(L, 1);
  
      result = stepvm(L, svm);
      svm->has_values = result == SQLITE_ROW ? 1 : 0;
      svm->columns = sqlite3_data_count(svm->vm);
  
      lua_pushnumber(L, result);
      return 1;
  }
  
  static int dbvm_finalize(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      return cleanupvm(L, svm);
  }
  
  static int dbvm_reset(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_reset(svm->vm);
      lua_pushnumber(L, sqlite3_errcode(svm->db->db));
      return 1;
  }
  
  static void dbvm_check_contents(lua_State *L, sdb_vm *svm) {
      if (!svm->has_values) {
          luaL_error(L, "misuse of function");
      }
  }
  
  static void dbvm_check_index(lua_State *L, sdb_vm *svm, int index) {
      if (index < 0 || index >= svm->columns) {
          luaL_error(L, "index out of range [0..%d]", svm->columns - 1);
      }
  }
  
  static void dbvm_check_bind_index(lua_State *L, sdb_vm *svm, int index) {
      if (index < 1 || index > sqlite3_bind_parameter_count(svm->vm)) {
          luaL_error(L, "bind index out of range [1..%d]", sqlite3_bind_parameter_count(svm->vm));
      }
  }
  
  /*
  ** =======================================================
  ** Virtual Machine - generic info
  ** =======================================================
  */
  static int dbvm_columns(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      lua_pushnumber(L, sqlite3_column_count(svm->vm));
      return 1;
  }
  
  /*
  ** =======================================================
  ** Virtual Machine - getters
  ** =======================================================
  */
  
  static int dbvm_get_value(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      int index = luaL_checkint(L, 2);
      dbvm_check_contents(L, svm);
      dbvm_check_index(L, svm, index);
      vm_push_column(L, svm->vm, index);
      return 1;
  }
  
  static int dbvm_get_name(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      int index = luaL_checknumber(L, 2);
      dbvm_check_index(L, svm, index);
      lua_pushstring(L, sqlite3_column_name(svm->vm, index));
      return 1;
  }
  
  static int dbvm_get_type(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      int index = luaL_checknumber(L, 2);
      dbvm_check_index(L, svm, index);
      lua_pushstring(L, sqlite3_column_decltype(svm->vm, index));
      return 1;
  }
  
  static int dbvm_get_values(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = svm->columns;
      int n;
      dbvm_check_contents(L, svm);
  
      lua_newtable(L);
      for (n = 0; n < columns;) {
          vm_push_column(L, vm, n++);
          lua_rawseti(L, -2, n);
      }
      return 1;
  }
  
  static int dbvm_get_names(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = sqlite3_column_count(vm); /* valid as soon as statement prepared */
      int n;
  
      lua_newtable(L);
      for (n = 0; n < columns;) {
          lua_pushstring(L, sqlite3_column_name(vm, n++));
          lua_rawseti(L, -2, n);
      }
      return 1;
  }
  
  static int dbvm_get_types(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = sqlite3_column_count(vm); /* valid as soon as statement prepared */
      int n;
  
      lua_newtable(L);
      for (n = 0; n < columns;) {
          lua_pushstring(L, sqlite3_column_decltype(vm, n++));
          lua_rawseti(L, -2, n);
      }
      return 1;
  }
  
  static int dbvm_get_uvalues(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = svm->columns;
      int n;
      dbvm_check_contents(L, svm);
  
      lua_checkstack(L, columns);
      for (n = 0; n < columns; ++n)
          vm_push_column(L, vm, n);
      return columns;
  }
  
  static int dbvm_get_unames(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = sqlite3_column_count(vm); /* valid as soon as statement prepared */
      int n;
  
      lua_checkstack(L, columns);
      for (n = 0; n < columns; ++n)
          lua_pushstring(L, sqlite3_column_name(vm, n));
      return columns;
  }
  
  static int dbvm_get_utypes(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = sqlite3_column_count(vm); /* valid as soon as statement prepared */
      int n;
  
      lua_checkstack(L, columns);
      for (n = 0; n < columns; ++n)
          lua_pushstring(L, sqlite3_column_decltype(vm, n));
      return columns;
  }
  
  static int dbvm_get_named_values(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = svm->columns;
      int n;
      dbvm_check_contents(L, svm);
  
      lua_newtable(L);
      for (n = 0; n < columns; ++n) {
          lua_pushstring(L, sqlite3_column_name(vm, n));
          vm_push_column(L, vm, n);
          lua_rawset(L, -3);
      }
      return 1;
  }
  
  static int dbvm_get_named_types(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int columns = sqlite3_column_count(vm);
      int n;
  
      lua_newtable(L);
      for (n = 0; n < columns; ++n) {
          lua_pushstring(L, sqlite3_column_name(vm, n));
          lua_pushstring(L, sqlite3_column_decltype(vm, n));
          lua_rawset(L, -3);
      }
      return 1;
  }
  
  /*
  ** =======================================================
  ** Virtual Machine - Bind
  ** =======================================================
  */
  
  static int dbvm_bind_index(lua_State *L, sqlite3_stmt *vm, int index, int lindex) {
      switch (lua_type(L, lindex)) {
          case LUA_TSTRING:
              return sqlite3_bind_text(vm, index, lua_tostring(L, lindex), lua_strlen(L, lindex), SQLITE_TRANSIENT);
          case LUA_TNUMBER:
              return sqlite3_bind_double(vm, index, lua_tonumber(L, lindex));
          case LUA_TBOOLEAN:
              return sqlite3_bind_int(vm, index, lua_toboolean(L, lindex) ? 1 : 0);
          case LUA_TNONE:
          case LUA_TNIL:
              return sqlite3_bind_null(vm, index);
          default:
              luaL_error(L, "index (%d) - invalid data type for bind (%s)", index, lua_typename(L, lua_type(L, lindex)));
              return SQLITE_MISUSE; /*!*/
      }
  }
  
  
  static int dbvm_bind_parameter_count(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      lua_pushnumber(L, sqlite3_bind_parameter_count(svm->vm));
      return 1;
  }
  
  static int dbvm_bind_parameter_name(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      int index = luaL_checknumber(L, 2);
      dbvm_check_bind_index(L, svm, index);
      lua_pushstring(L, sqlite3_bind_parameter_name(svm->vm, index));
      return 1;
  }
  
  static int dbvm_bind(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int index = luaL_checkint(L, 2);
      int result;
  
      dbvm_check_bind_index(L, svm, index);
      result = dbvm_bind_index(L, vm, index, 3);
  
      lua_pushnumber(L, result);
      return 1;
  }
  
  static int dbvm_bind_blob(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      int index = luaL_checkint(L, 2);
      const char *value = luaL_checkstring(L, 3);
      int len = lua_strlen(L, 3);
  
      lua_pushnumber(L, sqlite3_bind_blob(svm->vm, index, value, len, SQLITE_TRANSIENT));
      return 1;
  }
  
  static int dbvm_bind_values(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int top = lua_gettop(L);
      int result, n;
  
      if (top - 1 != sqlite3_bind_parameter_count(vm))
          luaL_error(L,
              "incorrect number of parameters to bind (%d given, %d to bind)",
              top - 1,
              sqlite3_bind_parameter_count(vm)
          );
  
      for (n = 2; n <= top; ++n) {
          if ((result = dbvm_bind_index(L, vm, n - 1, n)) != SQLITE_OK) {
              lua_pushnumber(L, result);
              return 1;
          }
      }
  
      lua_pushnumber(L, SQLITE_OK);
      return 1;
  }
  
  static int dbvm_bind_names(lua_State *L) {
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm = svm->vm;
      int count = sqlite3_bind_parameter_count(vm);
      const char *name;
      int result, n;
      luaL_checktype(L, 2, LUA_TTABLE);
  
      for (n = 1; n <= count; ++n) {
          name = sqlite3_bind_parameter_name(vm, n);
          if (name && (name[0] == ':' || name[0] == '$')) {
              lua_pushstring(L, ++name);
              lua_gettable(L, 2);
              result = dbvm_bind_index(L, vm, n, -1);
              lua_pop(L, 1);
          }
          else {
              lua_pushnumber(L, n);
              lua_gettable(L, 2);
              result = dbvm_bind_index(L, vm, n, -1);
              lua_pop(L, 1);
          }
  
          if (result != SQLITE_OK) {
              lua_pushnumber(L, result);
              return 1;
          }
      }
  
      lua_pushnumber(L, SQLITE_OK);
      return 1;
  }
  
  /*
  ** =======================================================
  ** Database (internal management)
  ** =======================================================
  */
  
  /*
  ** When creating database handles, always creates a `closed' database handle
  ** before opening the actual database; so, if there is a memory error, the
  ** database is not left opened.
  **
  ** Creates a new 'table' and leaves it in the stack
  */
  static sdb *newdb (lua_State *L) {
      sdb *db = (sdb*)lua_newuserdata(L, sizeof(sdb));
      db->L = L;
      db->db = NULL;  /* database handle is currently `closed' */
      db->func = NULL;
  
      db->busy_cb =
      db->busy_udata =
      db->progress_cb =
      db->progress_udata =
      db->trace_cb =
      db->trace_udata = LUA_NOREF;
  
      luaL_getmetatable(L, sqlite_meta);
      lua_setmetatable(L, -2);        /* set metatable */
  
      /* to keep track of 'open' virtual machines */
      lua_pushlightuserdata(L, db);
      lua_newtable(L);
      lua_rawset(L, LUA_REGISTRYINDEX);
  
      return db;
  }
  
  static int cleanupdb(lua_State *L, sdb *db) {
      sdb_func *func;
      sdb_func *func_next;
      int top;
      int result;
  
      /* free associated virtual machines */
      lua_pushlightuserdata(L, db);
      lua_rawget(L, LUA_REGISTRYINDEX);
  
      /* close all used handles */
      top = lua_gettop(L);
      lua_pushnil(L);
      while (lua_next(L, -2)) {
          sdb_vm *svm = lua_touserdata(L, -2); /* key: vm; val: sql text */
          cleanupvm(L, svm);
  
          lua_settop(L, top);
          lua_pushnil(L);
      }
  
      lua_pop(L, 1); /* pop vm table */
  
      /* remove entry in lua registry table */
      lua_pushlightuserdata(L, db);
      lua_pushnil(L);
      lua_rawset(L, LUA_REGISTRYINDEX);
  
      /* 'free' all references */
      luaL_unref(L, LUA_REGISTRYINDEX, db->busy_cb);
      luaL_unref(L, LUA_REGISTRYINDEX, db->busy_udata);
      luaL_unref(L, LUA_REGISTRYINDEX, db->progress_cb);
      luaL_unref(L, LUA_REGISTRYINDEX, db->progress_udata);
      luaL_unref(L, LUA_REGISTRYINDEX, db->trace_cb);
      luaL_unref(L, LUA_REGISTRYINDEX, db->trace_udata);
  
      /* close database */
      result = sqlite3_close(db->db);
      db->db = NULL;
  
      /* free associated memory with created functions */
      func = db->func;
      while (func) {
          func_next = func->next;
          luaL_unref(L, LUA_REGISTRYINDEX, func->fn_step);
          luaL_unref(L, LUA_REGISTRYINDEX, func->fn_finalize);
          luaL_unref(L, LUA_REGISTRYINDEX, func->udata);
          free(func);
          func = func_next;
      }
      db->func = NULL;
      return result;
  }
  
  static sdb *lsqlite_getdb(lua_State *L, int index) {
      sdb *db = (sdb*)luaL_checkudata(L, index, sqlite_meta);
      if (db == NULL) luaL_typerror(L, index, "sqlite database");
      return db;
  }
  
  static sdb *lsqlite_checkdb(lua_State *L, int index) {
      sdb *db = lsqlite_getdb(L, index);
      if (db->db == NULL) luaL_argerror(L, index, "attempt to use closed sqlite database");
      return db;
  }
  
  
  /*
  ** =======================================================
  ** User Defined Functions - Context Methods
  ** =======================================================
  */
  typedef struct {
      sqlite3_context *ctx;
      int ud;
  } lcontext;
  
  static lcontext *lsqlite_make_context(lua_State *L) {
      lcontext *ctx = (lcontext*)lua_newuserdata(L, sizeof(lcontext));
      lua_rawgeti(L, LUA_REGISTRYINDEX, sqlite_ctx_meta_ref);
      lua_setmetatable(L, -2);
      ctx->ctx = NULL;
      ctx->ud = LUA_NOREF;
      return ctx;
  }
  
  static lcontext *lsqlite_getcontext(lua_State *L, int index) {
      lcontext *ctx = (lcontext*)luaL_checkudata(L, index, sqlite_ctx_meta);
      if (ctx == NULL) luaL_typerror(L, index, "sqlite context");
      return ctx;
  }
  
  static lcontext *lsqlite_checkcontext(lua_State *L, int index) {
      lcontext *ctx = lsqlite_getcontext(L, index);
      if (ctx->ctx == NULL) luaL_argerror(L, index, "invalid sqlite context");
      return ctx;
  }
  
  static int lcontext_tostring(lua_State *L) {
      char buff[39];
      lcontext *ctx = lsqlite_getcontext(L, 1);
      if (ctx->ctx == NULL)
          strcpy(buff, "closed");
      else
          sprintf(buff, "%p", ctx->ctx);
      lua_pushfstring(L, "sqlite function context (%s)", buff);
      return 1;
  }
  
  static void lcontext_check_aggregate(lua_State *L, lcontext *ctx) {
      sdb_func *func = (sdb_func*)sqlite3_user_data(ctx->ctx);
      if (!func->aggregate) {
          luaL_error(L, "attempt to call aggregate method from scalar function");
      }
  }
  
  static int lcontext_user_data(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      sdb_func *func = (sdb_func*)sqlite3_user_data(ctx->ctx);
      lua_rawgeti(L, LUA_REGISTRYINDEX, func->udata);
      return 1;
  }
  
  static int lcontext_get_aggregate_context(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      lcontext_check_aggregate(L, ctx);
      lua_rawgeti(L, LUA_REGISTRYINDEX, ctx->ud);
      return 1;
  }
  
  static int lcontext_set_aggregate_context(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      lcontext_check_aggregate(L, ctx);
      lua_settop(L, 2);
      luaL_unref(L, LUA_REGISTRYINDEX, ctx->ud);
      ctx->ud = luaL_ref(L, LUA_REGISTRYINDEX);
      return 0;
  }
  
  static int lcontext_aggregate_count(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      lcontext_check_aggregate(L, ctx);
      lua_pushnumber(L, sqlite3_aggregate_count(ctx->ctx));
      return 1;
  }
  
  #if 0
  void *sqlite3_get_auxdata(sqlite3_context*, int);
  void sqlite3_set_auxdata(sqlite3_context*, int, void*, void (*)(void*));
  #endif
  
  static int lcontext_result(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      switch (lua_type(L, 2)) {
          case LUA_TNUMBER:
              sqlite3_result_double(ctx->ctx, luaL_checknumber(L, 2));
              break;
          case LUA_TSTRING:
              sqlite3_result_text(ctx->ctx, luaL_checkstring(L, 2), lua_strlen(L, 2), SQLITE_TRANSIENT);
              break;
          case LUA_TNIL:
          case LUA_TNONE:
              sqlite3_result_null(ctx->ctx);
              break;
          default:
              luaL_error(L, "invalid result type %s", lua_typename(L, 2));
              break;
      }
  
      return 0;
  }
  
  static int lcontext_result_blob(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      const char *blob = luaL_checkstring(L, 2);
      int size = lua_strlen(L, 2);
      sqlite3_result_blob(ctx->ctx, (const void*)blob, size, SQLITE_TRANSIENT);
      return 0;
  }
  
  static int lcontext_result_double(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      double d = luaL_checknumber(L, 2);
      sqlite3_result_double(ctx->ctx, d);
      return 0;
  }
  
  static int lcontext_result_error(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      const char *err = luaL_checkstring(L, 2);
      int size = lua_strlen(L, 2);
      sqlite3_result_error(ctx->ctx, err, size);
      return 0;
  }
  
  static int lcontext_result_int(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      int i = luaL_checkint(L, 2);
      sqlite3_result_int(ctx->ctx, i);
      return 0;
  }
  
  static int lcontext_result_null(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      sqlite3_result_null(ctx->ctx);
      return 0;
  }
  
  static int lcontext_result_text(lua_State *L) {
      lcontext *ctx = lsqlite_checkcontext(L, 1);
      const char *text = luaL_checkstring(L, 2);
      int size = lua_strlen(L, 2);
      sqlite3_result_text(ctx->ctx, text, size, SQLITE_TRANSIENT);
      return 0;
  }
  
  /*
  ** =======================================================
  ** Database Methods
  ** =======================================================
  */
  
  static int db_isopen(lua_State *L) {
      sdb *db = lsqlite_getdb(L, 1);
      lua_pushboolean(L, db->db != NULL ? 1 : 0);
      return 1;
  }
  
  static int db_last_insert_rowid(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      /* conversion warning: int64 -> luaNumber */
      sqlite_int64 rowid = sqlite3_last_insert_rowid(db->db);
      lua_Number n = (lua_Number)rowid;
      if (n == rowid)
          lua_pushnumber(L, n);
      else
          lua_pushfstring(L, "%ll", rowid);
      return 1;
  }
  
  static int db_changes(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      lua_pushnumber(L, sqlite3_changes(db->db));
      return 1;
  }
  
  static int db_total_changes(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      lua_pushnumber(L, sqlite3_total_changes(db->db));
      return 1;
  }
  
  static int db_errcode(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      lua_pushnumber(L, sqlite3_errcode(db->db));
      return 1;
  }
  
  static int db_errmsg(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      lua_pushstring(L, sqlite3_errmsg(db->db));
      return 1;
  }
  
  static int db_interrupt(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      sqlite3_interrupt(db->db);
      return 0;
  }
  
  /*
  ** Registering SQL functions:
  */
  
  static void db_push_value(lua_State *L, sqlite3_value *value) {
      switch (sqlite3_value_type(value)) {
          case SQLITE_TEXT:
              lua_pushlstring(L, (const char*)sqlite3_value_text(value), sqlite3_value_bytes(value));
              break;
  
          case SQLITE_INTEGER:
              {
                  sqlite_int64 i64 = sqlite3_value_int64(value);
                  lua_Number n = (lua_Number)i64;
                  if (n == i64)
                      lua_pushnumber(L, n);
                  else
                      lua_pushlstring(L, (const char*)sqlite3_value_text(value), sqlite3_value_bytes(value));
              }
              break;
  
          case SQLITE_FLOAT:
              lua_pushnumber(L, sqlite3_value_double(value));
              break;
  
          case SQLITE_BLOB:
              lua_pushlstring(L, sqlite3_value_blob(value), sqlite3_value_bytes(value));
              break;
  
          case SQLITE_NULL:
              lua_pushnil(L);
              break;
  
          default:
              /* things done properly (SQLite + Lua SQLite)
              ** this should never happen */
              lua_pushnil(L);
              break;
      }
  }
  
  /*
  ** callback functions used when calling registered sql functions
  */
  
  /* scalar function to be called
  ** callback params: context, values... */
  static void db_sql_normal_function(sqlite3_context *context, int argc, sqlite3_value **argv) {
      sdb_func *func = (sdb_func*)sqlite3_user_data(context);
      lua_State *L = func->db->L;
      int n;
      lcontext *ctx;
  
      int top = lua_gettop(L);
  
      /* ensure there is enough space in the stack */
      lua_checkstack(L, argc + 3);
  
      lua_rawgeti(L, LUA_REGISTRYINDEX, func->fn_step);   /* function to call */
  
      if (!func->aggregate) {
          ctx = lsqlite_make_context(L); /* push context - used to set results */
      }
      else {
          /* reuse context userdata value */
          void *p = sqlite3_aggregate_context(context, 1);
          /* i think it is OK to use assume that using a light user data
          ** as an entry on LUA REGISTRY table will be unique */
          lua_pushlightuserdata(L, p);
          lua_rawget(L, LUA_REGISTRYINDEX);       /* context table */
  
          if (lua_isnil(L, -1)) { /* not yet created? */
              lua_pop(L, 1);
              ctx = lsqlite_make_context(L);
              lua_pushlightuserdata(L, p);
              lua_pushvalue(L, -2);
              lua_rawset(L, LUA_REGISTRYINDEX);
          }
          else
              ctx = lsqlite_getcontext(L, -1);
      }
  
      /* push params */
      for (n = 0; n < argc; ++n) {
          db_push_value(L, argv[n]);
      }
  
      /* set context */
      ctx->ctx = context;
  
      if (lua_pcall(L, argc + 1, 0, 0)) {
          const char *errmsg = lua_tostring(L, -1);
          int size = lua_strlen(L, -1);
          sqlite3_result_error(context, errmsg, size);
      }
  
      /* invalidate context */
      ctx->ctx = NULL;
  
      if (!func->aggregate) {
          luaL_unref(L, LUA_REGISTRYINDEX, ctx->ud);
      }
  
      lua_settop(L, top);
  }
  
  static void db_sql_finalize_function(sqlite3_context *context) {
      sdb_func *func = (sdb_func*)sqlite3_user_data(context);
      lua_State *L = func->db->L;
      void *p = sqlite3_aggregate_context(context, 1); /* minimal mem usage */
      lcontext *ctx;
      int top = lua_gettop(L);
  
      lua_rawgeti(L, LUA_REGISTRYINDEX, func->fn_finalize);   /* function to call */
  
      /* i think it is OK to use assume that using a light user data
      ** as an entry on LUA REGISTRY table will be unique */
      lua_pushlightuserdata(L, p);
      lua_rawget(L, LUA_REGISTRYINDEX);       /* context table */
  
      if (lua_isnil(L, -1)) { /* not yet created? - shouldn't happen in finalize function */
          lua_pop(L, 1);
          ctx = lsqlite_make_context(L);
          lua_pushlightuserdata(L, p);
          lua_pushvalue(L, -2);
          lua_rawset(L, LUA_REGISTRYINDEX);
      }
      else
          ctx = lsqlite_getcontext(L, -1);
  
      /* set context */
      ctx->ctx = context;
  
      if (lua_pcall(L, 1, 0, 0)) {
          sqlite3_result_error(context, lua_tostring(L, -1), -1);
      }
  
      /* invalidate context */
      ctx->ctx = NULL;
  
      /* cleanup context */
      luaL_unref(L, LUA_REGISTRYINDEX, ctx->ud);
      /* remove it from registry */
      lua_pushlightuserdata(L, p);
      lua_pushnil(L);
      lua_rawset(L, LUA_REGISTRYINDEX);
  
      lua_settop(L, top);
  }
  
  /*
  ** Register a normal function
  ** Params: db, function name, number arguments, [ callback | step, finalize], user data
  ** Returns: true on sucess
  **
  ** Normal function:
  ** Params: context, params
  **
  ** Aggregate function:
  ** Params of step: context, params
  ** Params of finalize: context
  */
  static int db_register_function(lua_State *L, int aggregate) {
      sdb *db = lsqlite_checkdb(L, 1);
      const char *name;
      int args;
      int result;
      sdb_func *func;
  
      /* safety measure */
      if (aggregate) aggregate = 1;
  
      name = luaL_checkstring(L, 2);
      args = luaL_checkint(L, 3);
      luaL_checktype(L, 4, LUA_TFUNCTION);
      if (aggregate) luaL_checktype(L, 5, LUA_TFUNCTION);
  
      /* maybe an alternative way to allocate memory should be used/avoided */
      func = (sdb_func*)malloc(sizeof(sdb_func));
      if (func == NULL) {
          luaL_error(L, "out of memory");
      }
  
      result = sqlite3_create_function(
          db->db, name, args, SQLITE_UTF8, func,
          aggregate ? NULL : db_sql_normal_function,
          aggregate ? db_sql_normal_function : NULL,
          aggregate ? db_sql_finalize_function : NULL
      );
  
      if (result == SQLITE_OK) {
          /* safety measures for userdata field to be present in the stack */
          lua_settop(L, 5 + aggregate);
  
          /* save registered function in db function list */
          func->db = db;
          func->aggregate = aggregate;
          func->next = db->func;
          db->func = func;
  
          /* save the setp/normal function callback */
          lua_pushvalue(L, 4);
          func->fn_step = luaL_ref(L, LUA_REGISTRYINDEX);
          /* save user data */
          lua_pushvalue(L, 5+aggregate);
          func->udata = luaL_ref(L, LUA_REGISTRYINDEX);
  
          if (aggregate) {
              lua_pushvalue(L, 5);
              func->fn_finalize = luaL_ref(L, LUA_REGISTRYINDEX);
          }
          else
              func->fn_finalize = LUA_NOREF;
      }
      else {
          /* free allocated memory */
          free(func);
      }
  
      lua_pushboolean(L, result == SQLITE_OK ? 1 : 0);
      return 1;
  }
  
  static int db_create_function(lua_State *L) {
      return db_register_function(L, 0);
  }
  
  static int db_create_aggregate(lua_State *L) {
      return db_register_function(L, 1);
  }
  
  /* create_collation; contributed by Thomas Lauer
  */
  
  typedef struct {
      lua_State *L;
      int ref;
  } scc;
  
  static int collwrapper(scc *co,int l1,const void *p1,
                          int l2,const void *p2) {
      int res=0;
      lua_State *L=co->L;
      lua_rawgeti(L,LUA_REGISTRYINDEX,co->ref);
      lua_pushlstring(L,p1,l1);
      lua_pushlstring(L,p2,l2);
      if (lua_pcall(L,2,1,0)==0) res=(int)lua_tonumber(L,-1);
      lua_pop(L,1);
      return res;
  }
  
  static void collfree(scc *co) {
      if (co) {
          luaL_unref(co->L,LUA_REGISTRYINDEX,co->ref);
          free(co);
      }
  }
  
  static int db_create_collation(lua_State *L) {
      sdb *db=lsqlite_checkdb(L,1);
      const char *collname=luaL_checkstring(L,2);
      scc *co=NULL;
      int (*collfunc)(scc *,int,const void *,int,const void *)=NULL;
      lua_settop(L,3); /* default args to nil, and exclude extras */
      if (lua_isfunction(L,3)) collfunc=collwrapper;
      else if (!lua_isnil(L,3))
          luaL_error(L,"create_collation: function or nil expected");
      if (collfunc != NULL) {
          co=(scc *)malloc(sizeof(scc)); /* userdata is a no-no as it
                                            will be garbage-collected */
          if (co) {
              co->L=L;
              /* lua_settop(L,3) above means we don't need: lua_pushvalue(L,3); */
              co->ref=luaL_ref(L,LUA_REGISTRYINDEX);
          }
          else luaL_error(L,"create_collation: could not allocate callback");
      }
      sqlite3_create_collation_v2(db->db, collname, SQLITE_UTF8,
          (void *)co,
          (int(*)(void*,int,const void*,int,const void*))collfunc,
          (void(*)(void*))collfree);
      return 0;
  }
  
  /*
  ** trace callback:
  ** Params: database, callback function, userdata
  **
  ** callback function:
  ** Params: userdata, sql
  */
  static void db_trace_callback(void *user, const char *sql) {
      sdb *db = (sdb*)user;
      lua_State *L = db->L;
      int top = lua_gettop(L);
  
      /* setup lua callback call */
      lua_rawgeti(L, LUA_REGISTRYINDEX, db->trace_cb);    /* get callback */
      lua_rawgeti(L, LUA_REGISTRYINDEX, db->trace_udata); /* get callback user data */
      lua_pushstring(L, sql); /* traced sql statement */
  
      /* call lua function */
      lua_pcall(L, 2, 0, 0);
      /* ignore any error generated by this function */
  
      lua_settop(L, top);
  }
  
  static int db_trace(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
  
      if (lua_gettop(L) < 2 || lua_isnil(L, 2)) {
          luaL_unref(L, LUA_REGISTRYINDEX, db->trace_cb);
          luaL_unref(L, LUA_REGISTRYINDEX, db->trace_udata);
  
          db->trace_cb =
          db->trace_udata = LUA_NOREF;
  
          /* clear busy handler */
          sqlite3_trace(db->db, NULL, NULL);
      }
      else {
          luaL_checktype(L, 2, LUA_TFUNCTION);
  
          /* make sure we have an userdata field (even if nil) */
          lua_settop(L, 3);
  
          luaL_unref(L, LUA_REGISTRYINDEX, db->trace_cb);
          luaL_unref(L, LUA_REGISTRYINDEX, db->trace_udata);
  
          db->trace_udata = luaL_ref(L, LUA_REGISTRYINDEX);
          db->trace_cb = luaL_ref(L, LUA_REGISTRYINDEX);
  
          /* set busy handler */
          sqlite3_trace(db->db, db_trace_callback, db);
      }
  
      return 0;
  }
  
  
  #if !defined(SQLITE_OMIT_PROGRESS_CALLBACK) || !SQLITE_OMIT_PROGRESS_CALLBACK
  
  /*
  ** progress handler:
  ** Params: database, number of opcodes, callback function, userdata
  **
  ** callback function:
  ** Params: userdata
  ** returns: 0 to return immediatly and return SQLITE_ABORT, non-zero to continue
  */
  static int db_progress_callback(void *user) {
      int result = 1; /* abort by default */
      sdb *db = (sdb*)user;
      lua_State *L = db->L;
      int top = lua_gettop(L);
  
      lua_rawgeti(L, LUA_REGISTRYINDEX, db->progress_cb);
      lua_rawgeti(L, LUA_REGISTRYINDEX, db->progress_udata);
  
      /* call lua function */
      if (!lua_pcall(L, 1, 1, 0))
          result = lua_toboolean(L, -1);
  
      lua_settop(L, top);
      return result;
  }
  
  static int db_progress_handler(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
  
      if (lua_gettop(L) < 2 || lua_isnil(L, 2)) {
          luaL_unref(L, LUA_REGISTRYINDEX, db->progress_cb);
          luaL_unref(L, LUA_REGISTRYINDEX, db->progress_udata);
  
          db->progress_cb =
          db->progress_udata = LUA_NOREF;
  
          /* clear busy handler */
          sqlite3_progress_handler(db->db, 0, NULL, NULL);
      }
      else {
          int nop = luaL_checkint(L, 2);  /* number of opcodes */
          luaL_checktype(L, 3, LUA_TFUNCTION);
  
          /* make sure we have an userdata field (even if nil) */
          lua_settop(L, 4);
  
          luaL_unref(L, LUA_REGISTRYINDEX, db->progress_cb);
          luaL_unref(L, LUA_REGISTRYINDEX, db->progress_udata);
  
          db->progress_udata = luaL_ref(L, LUA_REGISTRYINDEX);
          db->progress_cb = luaL_ref(L, LUA_REGISTRYINDEX);
  
          /* set progress callback */
          sqlite3_progress_handler(db->db, nop, db_progress_callback, db);
      }
  
      return 0;
  }
  
  #else /* #if !defined(SQLITE_OMIT_PROGRESS_CALLBACK) || !SQLITE_OMIT_PROGRESS_CALLBACK */
  
  static int db_progress_handler(lua_State *L) {
      lua_pushliteral(L, "progress callback support disabled at compile time");
      lua_error(L);
      return 0;
  }
  
  #endif /* #if !defined(SQLITE_OMIT_PROGRESS_CALLBACK) || !SQLITE_OMIT_PROGRESS_CALLBACK */
  
  /*
  ** busy handler:
  ** Params: database, callback function, userdata
  **
  ** callback function:
  ** Params: userdata, number of tries
  ** returns: 0 to return immediatly and return SQLITE_BUSY, non-zero to try again
  */
  static int db_busy_callback(void *user, int tries) {
      int retry = 0; /* abort by default */
      sdb *db = (sdb*)user;
      lua_State *L = db->L;
      int top = lua_gettop(L);
  
      lua_rawgeti(L, LUA_REGISTRYINDEX, db->busy_cb);
      lua_rawgeti(L, LUA_REGISTRYINDEX, db->busy_udata);
      lua_pushnumber(L, tries);
  
      /* call lua function */
      if (!lua_pcall(L, 2, 1, 0))
          retry = lua_toboolean(L, -1);
  
      lua_settop(L, top);
      return retry;
  }
  
  static int db_busy_handler(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
  
      if (lua_gettop(L) < 2 || lua_isnil(L, 2)) {
          luaL_unref(L, LUA_REGISTRYINDEX, db->busy_cb);
          luaL_unref(L, LUA_REGISTRYINDEX, db->busy_udata);
  
          db->busy_cb =
          db->busy_udata = LUA_NOREF;
  
          /* clear busy handler */
          sqlite3_busy_handler(db->db, NULL, NULL);
      }
      else {
          luaL_checktype(L, 2, LUA_TFUNCTION);
          /* make sure we have an userdata field (even if nil) */
          lua_settop(L, 3);
  
          luaL_unref(L, LUA_REGISTRYINDEX, db->busy_cb);
          luaL_unref(L, LUA_REGISTRYINDEX, db->busy_udata);
  
          db->busy_udata = luaL_ref(L, LUA_REGISTRYINDEX);
          db->busy_cb = luaL_ref(L, LUA_REGISTRYINDEX);
  
          /* set busy handler */
          sqlite3_busy_handler(db->db, db_busy_callback, db);
      }
  
      return 0;
  }
  
  static int db_busy_timeout(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      int timeout = luaL_checkint(L, 2);
      sqlite3_busy_timeout(db->db, timeout);
  
      /* if there was a timeout callback registered, it is now
      ** invalid/useless. free any references we may have */
      luaL_unref(L, LUA_REGISTRYINDEX, db->busy_cb);
      luaL_unref(L, LUA_REGISTRYINDEX, db->busy_udata);
      db->busy_cb =
      db->busy_udata = LUA_NOREF;
  
      return 0;
  }
  
  /*
  ** Params: db, sql, callback, user
  ** returns: code [, errmsg]
  **
  ** Callback:
  ** Params: user, number of columns, values, names
  ** Returns: 0 to continue, other value will cause abort
  */
  static int db_exec_callback(void* user, int columns, char **data, char **names) {
      int result = SQLITE_ABORT; /* abort by default */
      lua_State *L = (lua_State*)user;
      int n;
  
      int top = lua_gettop(L);
  
      lua_pushvalue(L, 3); /* function to call */
      lua_pushvalue(L, 4); /* user data */
      lua_pushnumber(L, columns); /* total number of rows in result */
  
      /* column values */
      lua_pushvalue(L, 6);
      for (n = 0; n < columns;) {
          lua_pushstring(L, data[n++]);
          lua_rawseti(L, -2, n);
      }
  
      /* columns names */
      lua_pushvalue(L, 5);
      if (lua_isnil(L, -1)) {
          lua_pop(L, 1);
          lua_newtable(L);
          lua_pushvalue(L, -1);
          lua_replace(L, 5);
          for (n = 0; n < columns;) {
              lua_pushstring(L, names[n++]);
              lua_rawseti(L, -2, n);
          }
      }
  
      /* call lua function */
      if (!lua_pcall(L, 4, 1, 0)) {
          if (lua_isnumber(L, -1))
              result = lua_tonumber(L, -1);
      }
  
      lua_settop(L, top);
      return result;
  }
  
  static int db_exec(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      const char *sql = luaL_checkstring(L, 2);
      int result;
  
      if (!lua_isnoneornil(L, 3)) {
          /* stack:
          **  3: callback function
          **  4: userdata
          **  5: column names
          **  6: reusable column values
          */
          luaL_checktype(L, 3, LUA_TFUNCTION);
          lua_settop(L, 4);   /* 'trap' userdata - nil extra parameters */
          lua_pushnil(L);     /* column names not known at this point */
          lua_newtable(L);    /* column values table */
  
          result = sqlite3_exec(db->db, sql, db_exec_callback, L, NULL);
      }
      else {
          /* no callbacks */
          result = sqlite3_exec(db->db, sql, NULL, NULL, NULL);
      }
  
      lua_pushnumber(L, result);
      return 1;
  }
  
  /*
  ** Params: db, sql
  ** returns: code, compiled length or error message
  */
  static int db_prepare(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      const char *sql = luaL_checkstring(L, 2);
      int sql_len = lua_strlen(L, 2);
      const char *sqltail;
      sdb_vm *svm;
      lua_settop(L,2); /* sql is on top of stack for call to newvm */
      svm = newvm(L, db);
  
      if (sqlite3_prepare(db->db, sql, sql_len, &svm->vm, &sqltail) != SQLITE_OK) {
          cleanupvm(L, svm);
  
          lua_pushnil(L);
          lua_pushnumber(L, sqlite3_errcode(db->db));
          return 2;
      }
  
      /* vm already in the stack */
      lua_pushstring(L, sqltail);
      return 2;
  }
  
  static int db_do_next_row(lua_State *L, int packed) {
      int result;
      sdb_vm *svm = lsqlite_checkvm(L, 1);
      sqlite3_stmt *vm;
      int columns;
      int i;
  
      result = stepvm(L, svm);
      vm = svm->vm; /* stepvm may change svm->vm if re-prepare is needed */
      svm->has_values = result == SQLITE_ROW ? 1 : 0;
      svm->columns = columns = sqlite3_data_count(vm);
  
      if (result == SQLITE_ROW) {
          if (packed) {
              lua_newtable(L);
              if (packed == 1) {
                  for (i = 0; i < columns;) {
                      vm_push_column(L, vm, i);
                      lua_rawseti(L, -2, ++i);
                  }
              }
              else {
                  for (i = 0; i < columns; ++i) {
                      lua_pushstring(L, sqlite3_column_name(vm, i));
                      vm_push_column(L, vm, i);
                      lua_rawset(L, -3);
                  }
              }
              return 1;
          }
          else {
              lua_checkstack(L, columns);
              for (i = 0; i < columns; ++i)
                  vm_push_column(L, vm, i);
              return svm->columns;
          }
      }
  
      if (svm->temp) {
          /* finalize and check for errors */
          result = sqlite3_finalize(vm);
          svm->vm = NULL;
          cleanupvm(L, svm);
      }
      else if (result == SQLITE_DONE) {
          result = sqlite3_reset(vm);
      }
  
      if (result != SQLITE_OK) {
          lua_pushstring(L, sqlite3_errmsg(svm->db->db));
          lua_error(L);
      }
      return 0;
  }
  
  static int db_next_row(lua_State *L) {
      return db_do_next_row(L, 0);
  }
  
  static int db_next_packed_row(lua_State *L) {
      return db_do_next_row(L, 1);
  }
  
  static int db_next_named_row(lua_State *L) {
      return db_do_next_row(L, 2);
  }
  
  static int dbvm_do_rows(lua_State *L, int(*f)(lua_State *)) {
      /* sdb_vm *svm =  */
      lsqlite_checkvm(L, 1);
      lua_pushvalue(L,1);
      lua_pushcfunction(L, f);
      lua_insert(L, -2);
      return 2;
  }
  
  static int dbvm_rows(lua_State *L) {
      return dbvm_do_rows(L, db_next_packed_row);
  }
  
  static int dbvm_nrows(lua_State *L) {
      return dbvm_do_rows(L, db_next_named_row);
  }
  
  static int dbvm_urows(lua_State *L) {
      return dbvm_do_rows(L, db_next_row);
  }
  
  static int db_do_rows(lua_State *L, int(*f)(lua_State *)) {
      sdb *db = lsqlite_checkdb(L, 1);
      const char *sql = luaL_checkstring(L, 2);
      sdb_vm *svm;
      lua_settop(L,2); /* sql is on top of stack for call to newvm */
      svm = newvm(L, db);
      svm->temp = 1;
  
      if (sqlite3_prepare(db->db, sql, -1, &svm->vm, NULL) != SQLITE_OK) {
          cleanupvm(L, svm);
  
          lua_pushstring(L, sqlite3_errmsg(svm->db->db));
          lua_error(L);
      }
  
      lua_pushcfunction(L, f);
      lua_insert(L, -2);
      return 2;
  }
  
  static int db_rows(lua_State *L) {
      return db_do_rows(L, db_next_packed_row);
  }
  
  static int db_nrows(lua_State *L) {
      return db_do_rows(L, db_next_named_row);
  }
  
  /* unpacked version of db:rows */
  static int db_urows(lua_State *L) {
      return db_do_rows(L, db_next_row);
  }
  
  static int db_tostring(lua_State *L) {
      char buff[32];
      sdb *db = lsqlite_getdb(L, 1);
      if (db->db == NULL)
          strcpy(buff, "closed");
      else
          sprintf(buff, "%p", lua_touserdata(L, 1));
      lua_pushfstring(L, "sqlite database (%s)", buff);
      return 1;
  }
  
  static int db_close(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      lua_pushnumber(L, cleanupdb(L, db));
      return 1;
  }
  
  static int db_close_vm(lua_State *L) {
      sdb *db = lsqlite_checkdb(L, 1);
      /* cleanup temporary only tables? */
      int temp = lua_toboolean(L, 2);
  
      /* free associated virtual machines */
      lua_pushlightuserdata(L, db);
      lua_rawget(L, LUA_REGISTRYINDEX);
  
      /* close all used handles */
      lua_pushnil(L);
      while (lua_next(L, -2)) {
          sdb_vm *svm = lua_touserdata(L, -2); /* key: vm; val: sql text */
  
          if ((!temp || svm->temp) && svm->vm)
          {
              sqlite3_finalize(svm->vm);
              svm->vm = NULL;
          }
  
          /* leave key in the stack */
          lua_pop(L, 1);
      }
      return 0;
  }
  
  static int db_gc(lua_State *L) {
      sdb *db = lsqlite_getdb(L, 1);
      if (db->db != NULL)  /* ignore closed databases */
          cleanupdb(L, db);
      return 0;
  }
  
  /*
  ** =======================================================
  ** General library functions
  ** =======================================================
  */
  
  static int lsqlite_version(lua_State *L) {
      lua_pushstring(L, sqlite3_libversion());
      return 1;
  }
  
  static int lsqlite_complete(lua_State *L) {
      const char *sql = luaL_checkstring(L, 1);
      lua_pushboolean(L, sqlite3_complete(sql));
      return 1;
  }
  
  #ifndef WIN32
  static int lsqlite_temp_directory(lua_State *L) {
      const char *oldtemp = sqlite3_temp_directory;
  
      if (!lua_isnone(L, 1)) {
          const char *temp = luaL_optstring(L, 1, NULL);
          if (sqlite3_temp_directory) {
              sqlite3_free((char*)sqlite3_temp_directory);
          }
          if (temp) {
              sqlite3_temp_directory = sqlite3_mprintf("%s", temp);
          }
          else {
              sqlite3_temp_directory = NULL;
          }
      }
      lua_pushstring(L, oldtemp);
      return 1;
  }
  #endif
  
  static int lsqlite_do_open(lua_State *L, const char *filename) {
      sdb *db = newdb(L); /* create and leave in stack */
  
      if (sqlite3_open(filename, &db->db) == SQLITE_OK) {
          /* database handle already in the stack - return it */
          return 1;
      }
  
      /* failed to open database */
      lua_pushnil(L);                             /* push nil */
      lua_pushnumber(L, sqlite3_errcode(db->db));
      lua_pushstring(L, sqlite3_errmsg(db->db));  /* push error message */
  
      /* clean things up */
      cleanupdb(L, db);
  
      /* return */
      return 3;
  }
  
  static int lsqlite_open(lua_State *L) {
      const char *filename = luaL_checkstring(L, 1);
      return lsqlite_do_open(L, filename);
  }
  
  static int lsqlite_open_memory(lua_State *L) {
      return lsqlite_do_open(L, ":memory:");
  }
  
  static int lsqlite_newindex(lua_State *L) {
      lua_pushliteral(L, "attempt to change readonly table");
      lua_error(L);
      return 0;
  }
  
  /*
  ** =======================================================
  ** Register functions
  ** =======================================================
  */
  
  #define SC(s)   { #s, SQLITE_ ## s },
  #define LSC(s)  { #s, LSQLITE_ ## s },
  
  static const struct {
      const char* name;
      int value;
  } sqlite_constants[] = {
      /* error codes */
      SC(OK)          SC(ERROR)       SC(INTERNAL)    SC(PERM)
      SC(ABORT)       SC(BUSY)        SC(LOCKED)      SC(NOMEM)
      SC(READONLY)    SC(INTERRUPT)   SC(IOERR)       SC(CORRUPT)
      SC(NOTFOUND)    SC(FULL)        SC(CANTOPEN)    SC(PROTOCOL)
      SC(EMPTY)       SC(SCHEMA)      SC(TOOBIG)      SC(CONSTRAINT)
      SC(MISMATCH)    SC(MISUSE)      SC(NOLFS)
      SC(FORMAT)      SC(NOTADB)
  
      /* sqlite_step specific return values */
      SC(RANGE)       SC(ROW)         SC(DONE)
  
      /* column types */
      SC(INTEGER)     SC(FLOAT)       SC(TEXT)        SC(BLOB)
      SC(NULL)
  
      /* terminator */
      { NULL, 0 }
  };
  
  /* ======================================================= */
  
  static const luaL_Reg dblib[] = {
      {"isopen",              db_isopen               },
      {"last_insert_rowid",   db_last_insert_rowid    },
      {"changes",             db_changes              },
      {"total_changes",       db_total_changes        },
      {"errcode",             db_errcode              },
      {"error_code",          db_errcode              },
      {"errmsg",              db_errmsg               },
      {"error_message",       db_errmsg               },
      {"interrupt",           db_interrupt            },
  
      {"create_function",     db_create_function      },
      {"create_aggregate",    db_create_aggregate     },
      {"create_collation",    db_create_collation     },
  
      {"trace",               db_trace                },
      {"progress_handler",    db_progress_handler     },
      {"busy_timeout",        db_busy_timeout         },
      {"busy_handler",        db_busy_handler         },
  
      {"prepare",             db_prepare              },
      {"rows",                db_rows                 },
      {"urows",               db_urows                },
      {"nrows",               db_nrows                },
  
      {"exec",                db_exec                 },
      {"execute",             db_exec                 },
      {"close",               db_close                },
      {"close_vm",            db_close_vm             },
  
      {"__tostring",          db_tostring             },
      {"__gc",                db_gc                   },
  
      {NULL, NULL}
  };
  
  static const luaL_Reg vmlib[] = {
      {"isopen",              dbvm_isopen             },
  
      {"step",                dbvm_step               },
      {"reset",               dbvm_reset              },
      {"finalize",            dbvm_finalize           },
  
      {"columns",             dbvm_columns            },
  
      {"bind",                dbvm_bind               },
      {"bind_values",         dbvm_bind_values        },
      {"bind_names",          dbvm_bind_names         },
      {"bind_blob",           dbvm_bind_blob          },
      {"bind_parameter_count",dbvm_bind_parameter_count},
      {"bind_parameter_name", dbvm_bind_parameter_name},
  
      {"get_value",           dbvm_get_value          },
      {"get_values",          dbvm_get_values         },
      {"get_name",            dbvm_get_name           },
      {"get_names",           dbvm_get_names          },
      {"get_type",            dbvm_get_type           },
      {"get_types",           dbvm_get_types          },
      {"get_uvalues",         dbvm_get_uvalues        },
      {"get_unames",          dbvm_get_unames         },
      {"get_utypes",          dbvm_get_utypes         },
  
      {"get_named_values",    dbvm_get_named_values   },
      {"get_named_types",     dbvm_get_named_types    },
  
      {"rows",                dbvm_rows               },
      {"urows",               dbvm_urows              },
      {"nrows",               dbvm_nrows              },
  
      /* compatibility names (added by request) */
      {"idata",               dbvm_get_values         },
      {"inames",              dbvm_get_names          },
      {"itypes",              dbvm_get_types          },
      {"data",                dbvm_get_named_values   },
      {"type",                dbvm_get_named_types    },
  
      {"__tostring",          dbvm_tostring           },
      {"__gc",                dbvm_gc                 },
  
      { NULL, NULL }
  };
  
  static const luaL_Reg ctxlib[] = {
      {"user_data",               lcontext_user_data              },
  
      {"get_aggregate_data",      lcontext_get_aggregate_context  },
      {"set_aggregate_data",      lcontext_set_aggregate_context  },
      {"aggregate_count",         lcontext_aggregate_count        },
  
      {"result",                  lcontext_result                 },
      {"result_null",             lcontext_result_null            },
      {"result_number",           lcontext_result_double          },
      {"result_double",           lcontext_result_double          },
      {"result_int",              lcontext_result_int             },
      {"result_text",             lcontext_result_text            },
      {"result_blob",             lcontext_result_blob            },
      {"result_error",            lcontext_result_error           },
  
      {"__tostring",              lcontext_tostring               },
      {NULL, NULL}
  };
  
  static const luaL_Reg sqlitelib[] = {
      {"version",         lsqlite_version         },
      {"complete",        lsqlite_complete        },
  #ifndef WIN32
      {"temp_directory",  lsqlite_temp_directory  },
  #endif
      {"open",            lsqlite_open            },
      {"open_memory",     lsqlite_open_memory     },
  
      {"__newindex",      lsqlite_newindex        },
      {NULL, NULL}
  };
  
  static void create_meta(lua_State *L, const char *name, const luaL_Reg *lib) {
      luaL_newmetatable(L, name);
      lua_pushstring(L, "__index");
      lua_pushvalue(L, -2);               /* push metatable */
      lua_rawset(L, -3);                  /* metatable.__index = metatable */
  
      /* register metatable functions */
      luaL_openlib(L, NULL, lib, 0);
  
      /* remove metatable from stack */
      lua_pop(L, 1);
  }
  
  LUALIB_API int luaopen_lsqlite3(lua_State *L) {
      create_meta(L, sqlite_meta, dblib);
      create_meta(L, sqlite_vm_meta, vmlib);
      create_meta(L, sqlite_ctx_meta, ctxlib);
  
      luaL_getmetatable(L, sqlite_ctx_meta);
      sqlite_ctx_meta_ref = luaL_ref(L, LUA_REGISTRYINDEX);
  
      /* register (local) sqlite metatable */
  //    luaL_register(L, "sqlite3", sqlitelib);
      lua_newtable(L);
      luaL_register(L, 0, sqlitelib);
  
      {
          int i = 0;
          /* add constants to global table */
          while (sqlite_constants[i].name) {
              lua_pushstring(L, sqlite_constants[i].name);
              lua_pushnumber(L, sqlite_constants[i].value);
              lua_rawset(L, -3);
              ++i;
          }
      }
  
      /* set sqlite's metatable to itself - set as readonly (__newindex) */
      lua_pushvalue(L, -1);
      lua_setmetatable(L, -2);
  
      return 1;
  }
  