env.c

/********************************************
*
* Copyright 2009 by Sean Conner.  All Rights Reserved.
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 3 of the License, or (at your
* option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, see <http://www.gnu.org/licenses/>.
*
* Comments, questions and criticisms can be sent to: sean@conman.org
*
* ---------------------------------------------------------------------
*
* This module is nothing more than an array of the environmental variables
* of the current process.  There's not much more to say about this than
*
        env = require "org.conman.env"
        print(env.LUA_PATH)
        print(env['LUA_CPATH'])
        
*
*********************************************/

#include <stddef.h>
#include <string.h>

#include <lua.h>
#include <lauxlib.h>

#if !defined(LUA_VERSION_NUM) || LUA_VERSION_NUM < 501
#  error You need to compile against Lua 5.1 or higher
#endif

int luaopen_org_conman_env(lua_State *L)
{
  extern char const **environ;
  int i;
  
#if LUA_VERSION_NUM == 501
  static struct luaL_Reg const env[] =
  {
    { NULL , NULL }
  };
  
  luaL_register(L,"org.conman.env",env);
#else
  lua_createtable(L,0,0);
#endif

  for (i = 0 ; environ[i] != NULL ; i++)
  {
    char const *value = strchr(environ[i],'=');
    size_t      len;
    int         type;
    
    if (value != NULL)
    {
      len = (size_t)(value - environ[i]);
      value++;
    }
    else
    {
      len   = strlen(environ[i]);
      value = "";
    }
    
    /*---------------------------------------------------------------------
    ; http://lwn.net/Articles/678148/
    ;
    ; The gist---if two environment variables exist with the same name,
    ; getenv() will return the first one, while languages like Perl and Lua,
    ; which dump everythinig into hash, will typically return the second
    ; value, which could be exploited.  So we duplicate the behavior of
    ; getenv() and only save the environment variable if it already hasn't
    ; been set.
    ;----------------------------------------------------------------------*/
    
    lua_pushlstring(L,environ[i],len);
    lua_gettable(L,-2);
    type = lua_type(L,-1);
    lua_pop(L,1);
    
    if (type == LUA_TNIL)
    {
      lua_pushlstring(L,environ[i],len);
      lua_pushstring(L,value);
      lua_settable(L,-3);
    }
  }
  
  return 1;
}