transmission/libtransmission/variant.c

/*
 * This file Copyright (C) Mnemosyne LLC
 *
 * This file is licensed by the GPL version 2. Works owned by the
 * Transmission project are granted a special exemption to clause 2 (b)
 * so that the bulk of its code can remain under the MIT license.
 * This exemption does not extend to derived works not owned by
 * the Transmission project.
 *
 * $Id:$
 */

#include <assert.h>
#include <errno.h>
#include <stdio.h> /* rename() */
#include <stdlib.h> /* strtoul(), strtod(), realloc(), qsort(), mkstemp() */
#include <string.h>

#ifdef WIN32 /* tr_mkstemp() */
 #include <fcntl.h>
 #define _S_IREAD 256
 #define _S_IWRITE 128
#endif

#include <locale.h> /* setlocale() */
#include <unistd.h> /* write(), unlink() */

#include <event2/buffer.h>

#define __LIBTRANSMISSION_VARIANT_MODULE___
#include "transmission.h"
#include "ConvertUTF.h"  
#include "fdlimit.h" /* tr_close_file() */
#include "platform.h" /* TR_PATH_MAX */
#include "utils.h" /* tr_new(), tr_free() */
#include "variant.h"
#include "variant-common.h"

/**
***
**/

static bool
tr_variantIsContainer (const tr_variant * v)
{
  return tr_variantIsList (v) || tr_variantIsDict (v);
}

static bool
tr_variantIsSomething (const tr_variant * v)
{
  return tr_variantIsContainer (v)
      || tr_variantIsInt (v)
      || tr_variantIsString (v)
      || tr_variantIsReal (v)
      || tr_variantIsBool (v);
}

void
tr_variantInit (tr_variant * v, char type)
{
  v->type = type;
  memset (&v->val, 0, sizeof(v->val));
}

/***
****
***/

static const struct tr_variant_string STRING_INIT =
{
  .type = TR_STRING_TYPE_QUARK,
  .quark = TR_KEY_NONE,
  .len = 0,
  .str.str = ""
};

static void
tr_variant_string_clear (struct tr_variant_string * str)
{
  if (str->type == TR_STRING_TYPE_HEAP)
    tr_free ((char*)(str->str.str));

  *str = STRING_INIT;
}

/* returns a const pointer to the variant's string */
static const char *
tr_variant_string_get_string (const struct tr_variant_string * str)
{
  const char * ret;

  switch (str->type)
    {
      case TR_STRING_TYPE_BUF: ret = str->str.buf; break;
      case TR_STRING_TYPE_HEAP: ret = str->str.str; break;
      case TR_STRING_TYPE_QUARK: ret = str->str.str; break;
      default: ret = NULL;
    }

  return ret;
}

static void
tr_variant_string_set_quark (struct tr_variant_string  * str,
                             const tr_quark              quark)
{
  tr_variant_string_clear (str);

  str->type = TR_STRING_TYPE_QUARK;
  str->quark = quark;
  str->str.str = tr_quark_get_string (quark, &str->len);
}

static void
tr_variant_string_set_string (struct tr_variant_string  * str,
                              const char                * bytes,
                              int                         len)
{
  tr_variant_string_clear (str);

  if (bytes == NULL)
    len = 0;
  else if (len < 0)
    len = strlen (bytes);

  if ((size_t)len < sizeof(str->str.buf))
    {
      str->type = TR_STRING_TYPE_BUF;
      memcpy (str->str.buf, bytes, len);
      str->str.buf[len] = '\0';
      str->len = len;
    }
  else
    {
      char * tmp = tr_new (char, len+1);
      memcpy (tmp, bytes, len);
      tmp[len] = '\0';
      str->type = TR_STRING_TYPE_HEAP;
      str->str.str = tmp;
      str->len = len;
    }
}


/***
****
***/

static inline const char *
getStr (const tr_variant * v)
{
  assert (tr_variantIsString (v));

  return tr_variant_string_get_string (&v->val.s);
}

static int
dictIndexOf (const tr_variant * dict, const tr_quark key)
{
  if (tr_variantIsDict (dict))
    {
      const tr_variant * walk;
      const tr_variant * const begin = dict->val.l.vals;
      const tr_variant * const end = begin + dict->val.l.count;

      for (walk=begin; walk!=end; ++walk)
        if (walk->key == key)
          return walk - begin;
    }

  return -1;
}

tr_variant *
tr_variantDictFind (tr_variant * dict, const tr_quark key)
{
  const int i = dictIndexOf (dict, key);

  return i < 0 ? NULL : dict->val.l.vals+i;
}

static bool
tr_variantDictFindType (tr_variant      * dict,
                        const tr_quark    key,
                        int               type,
                        tr_variant     ** setme)
{
  return tr_variantIsType (*setme = tr_variantDictFind (dict, key), type);
}

size_t
tr_variantListSize (const tr_variant * list)
{
  return tr_variantIsList (list) ? list->val.l.count : 0;
}

tr_variant*
tr_variantListChild (tr_variant * v,
                     size_t    i)
{
  tr_variant * ret = NULL;

  if (tr_variantIsList (v) && (i < v->val.l.count))
    ret = v->val.l.vals + i;

  return ret;
}

bool
tr_variantListRemove (tr_variant * list, size_t i)
{
  bool removed = false;

  if (tr_variantIsList (list) && (i < list->val.l.count))
    {
      removed = true;
      tr_variantFree (&list->val.l.vals[i]);
      tr_removeElementFromArray (list->val.l.vals, i,
                                 sizeof (tr_variant),
                                 list->val.l.count--);
    }

  return removed;
}

bool
tr_variantGetInt (const tr_variant  * v,
                  int64_t           * setme)
{
  bool success = false;

  if (!success && ((success = tr_variantIsInt (v))))
    if (setme)
      *setme = v->val.i;

  if (!success && ((success = tr_variantIsBool (v))))
    if (setme)
      *setme = v->val.b ? 1 : 0;

  return success;
}

bool
tr_variantGetStr (const tr_variant   * v,
                  const char        ** setme,
                  size_t             * len)
{
  const bool success = tr_variantIsString (v);

  if (success)
    *setme = getStr (v);

  if (len != NULL)
    *len = success ? v->val.s.len : 0;

  return success;
}

bool
tr_variantGetRaw (const tr_variant   * v,
                  const uint8_t     ** setme_raw,
                  size_t             * setme_len)
{
  const bool success = tr_variantIsString (v);

  if (success)
    {
      *setme_raw = (uint8_t*) getStr (v);
      *setme_len = v->val.s.len;
    }

  return success;
}

bool
tr_variantGetBool (const tr_variant * v, bool * setme)
{
  const char * str;
  bool success = false;

  if ((success = tr_variantIsBool (v)))
    *setme = v->val.b;

  if (!success && tr_variantIsInt (v))
    if ((success = (v->val.i==0 || v->val.i==1)))
      *setme = v->val.i!=0;

  if (!success && tr_variantGetStr (v, &str, NULL))
    if ((success = (!strcmp (str,"true") || !strcmp (str,"false"))))
      *setme = !strcmp (str,"true");

  return success;
}

bool
tr_variantGetReal (const tr_variant * v, double * setme)
{
  bool success = false;

  if (!success && ((success = tr_variantIsReal (v))))
    *setme = v->val.d;

  if (!success && ((success = tr_variantIsInt (v))))
    *setme = v->val.i;

  if (!success && tr_variantIsString (v))
    {
      char * endptr;
      char locale[128];
      double d;

      /* the json spec requires a '.' decimal point regardless of locale */
      tr_strlcpy (locale, setlocale (LC_NUMERIC, NULL), sizeof (locale));
      setlocale (LC_NUMERIC, "POSIX");
      d  = strtod (getStr (v), &endptr);
      setlocale (LC_NUMERIC, locale);

      if ((success = (getStr (v) != endptr) && !*endptr))
        *setme = d;
    }

  return success;
}

bool
tr_variantDictFindInt (tr_variant      * dict,
                       const tr_quark    key,
                       int64_t         * setme)
{
  tr_variant * child = tr_variantDictFind (dict, key);
  return tr_variantGetInt (child, setme);
}

bool
tr_variantDictFindBool (tr_variant      * dict,
                        const tr_quark    key,
                        bool            * setme)
{
  tr_variant * child = tr_variantDictFind (dict, key);
  return tr_variantGetBool (child, setme);
}

bool
tr_variantDictFindReal (tr_variant      * dict,
                        const tr_quark    key,
                        double          * setme)
{
  tr_variant * child = tr_variantDictFind (dict, key);
  return tr_variantGetReal (child, setme);
}

bool
tr_variantDictFindStr (tr_variant       * dict,
                        const tr_quark    key,
                        const char     ** setme,
                        size_t          * len)
{
  tr_variant * child = tr_variantDictFind (dict, key);
  return tr_variantGetStr (child, setme, len);
}

bool
tr_variantDictFindList (tr_variant       * dict,
                        const tr_quark     key,
                        tr_variant      ** setme)
{
  return tr_variantDictFindType (dict, key, TR_VARIANT_TYPE_LIST, setme);
}

bool
tr_variantDictFindDict (tr_variant       * dict,
                        const tr_quark     key,
                        tr_variant      ** setme)
{
  return tr_variantDictFindType (dict, key, TR_VARIANT_TYPE_DICT, setme);
}

bool
tr_variantDictFindRaw (tr_variant      * dict,
                       const tr_quark    key,
                       const uint8_t  ** setme_raw,
                       size_t          * setme_len)
{
  tr_variant * child = tr_variantDictFind (dict, key);
  return tr_variantGetRaw (child, setme_raw, setme_len);
}

/***
****
***/

void
tr_variantInitRaw (tr_variant * v, const void * src, size_t byteCount)
{
  tr_variantInit (v, TR_VARIANT_TYPE_STR);
  tr_variant_string_set_string (&v->val.s, src, byteCount);
}

void
tr_variantInitQuark (tr_variant * v, const tr_quark q)
{
  tr_variantInit (v, TR_VARIANT_TYPE_STR);
  tr_variant_string_set_quark (&v->val.s, q);
}

void
tr_variantInitStr (tr_variant * v, const void * str, int len)
{
  tr_variantInit (v, TR_VARIANT_TYPE_STR);
  tr_variant_string_set_string (&v->val.s, str, len);
}

void
tr_variantInitBool (tr_variant * v, bool value)
{
  tr_variantInit (v, TR_VARIANT_TYPE_BOOL);
  v->val.b = value != 0;
}

void
tr_variantInitReal (tr_variant * v, double value)
{
  tr_variantInit (v, TR_VARIANT_TYPE_REAL);
  v->val.d = value;
}

void
tr_variantInitInt (tr_variant * v, int64_t value)
{
  tr_variantInit (v, TR_VARIANT_TYPE_INT);
  v->val.i = value;
}

void
tr_variantInitList (tr_variant * v, size_t reserve_count)
{
  tr_variantInit (v, TR_VARIANT_TYPE_LIST);
  tr_variantListReserve (v, reserve_count);
}

static void
containerReserve (tr_variant * v, size_t count)
{
  const size_t needed = v->val.l.count + count;

  assert (tr_variantIsContainer (v));

  if (needed > v->val.l.alloc)
    {
      /* scale the alloc size in powers-of-2 */
      size_t n = v->val.l.alloc ? v->val.l.alloc : 8;
      while (n < needed)
        n *= 2u;

      v->val.l.vals = tr_renew (tr_variant, v->val.l.vals, n);
      v->val.l.alloc = n;
    }
}

void
tr_variantListReserve (tr_variant * list, size_t count)
{
  assert (tr_variantIsList (list));
  containerReserve (list, count);
}

void
tr_variantInitDict (tr_variant * v, size_t reserve_count)
{
  tr_variantInit (v, TR_VARIANT_TYPE_DICT);
  tr_variantDictReserve (v, reserve_count);
}

void
tr_variantDictReserve (tr_variant  * dict,
                       size_t        reserve_count)
{
  assert (tr_variantIsDict (dict));
  containerReserve (dict, reserve_count);
}

tr_variant *
tr_variantListAdd (tr_variant * list)
{
  tr_variant * child;

  assert (tr_variantIsList (list));

  containerReserve (list, 1);
  child = &list->val.l.vals[list->val.l.count++];
  child->key = 0;
  tr_variantInit (child, TR_VARIANT_TYPE_INT);

  return child;
}

tr_variant *
tr_variantListAddInt (tr_variant  * list,
                      int64_t       val)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitInt (child, val);
  return child;
}

tr_variant *
tr_variantListAddReal (tr_variant  * list,
                       double        val)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitReal (child, val);
  return child;
}

tr_variant *
tr_variantListAddBool (tr_variant  * list,
                       bool          val)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitBool (child, val);
  return child;
}

tr_variant *
tr_variantListAddStr (tr_variant  * list,
                      const char  * val)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitStr (child, val, -1);
  return child;
}

tr_variant *
tr_variantListAddQuark (tr_variant     * list,
                        const tr_quark   val)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitQuark (child, val);
  return child;
}

tr_variant *
tr_variantListAddRaw (tr_variant  * list,
                      const void  * val,
                      size_t        len)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitRaw (child, val, len);
  return child;
}

tr_variant*
tr_variantListAddList (tr_variant  * list,
                       size_t        reserve_count)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitList (child, reserve_count);
  return child;
}

tr_variant*
tr_variantListAddDict (tr_variant  * list,
                       size_t        reserve_count)
{
  tr_variant * child = tr_variantListAdd (list);
  tr_variantInitDict (child, reserve_count);
  return child;
}

tr_variant *
tr_variantDictAdd (tr_variant      * dict,
                   const tr_quark    key)
{
  tr_variant * val;

  assert (tr_variantIsDict (dict));

  containerReserve (dict, 1);

  val = dict->val.l.vals + dict->val.l.count++;
  tr_variantInit (val, TR_VARIANT_TYPE_INT);
  val->key = key;
  return val;
}

static tr_variant*
dictFindOrAdd (tr_variant * dict, const tr_quark key, int type)
{
  tr_variant * child;

  /* see if it already exists, and if so, try to reuse it */
  if ((child = tr_variantDictFind (dict, key)))
    {
      if (!tr_variantIsType (child, type))
        {
          tr_variantDictRemove (dict, key);
          child = NULL;
        }
      else if (child->type == TR_VARIANT_TYPE_STR)
        {
          tr_variant_string_clear (&child->val.s);
        }
    }

  /* if it doesn't exist, create it */
  if (child == NULL)
    child = tr_variantDictAdd (dict, key);

  return child;
}

tr_variant*
tr_variantDictAddInt (tr_variant      * dict,
                      const tr_quark    key,
                      int64_t           val)
{
  tr_variant * child = dictFindOrAdd (dict, key, TR_VARIANT_TYPE_INT);
  tr_variantInitInt (child, val);
  return child;
}

tr_variant*
tr_variantDictAddBool (tr_variant      * dict,
                       const tr_quark    key,
                       bool              val)
{
  tr_variant * child = dictFindOrAdd (dict, key, TR_VARIANT_TYPE_BOOL);
  tr_variantInitBool (child, val);
  return child;
}

tr_variant*
tr_variantDictAddReal (tr_variant      * dict,
                       const tr_quark    key,
                       double            val)
{
  tr_variant * child = dictFindOrAdd (dict, key, TR_VARIANT_TYPE_REAL);
  tr_variantInitReal (child, val);
  return child;
}

tr_variant*
tr_variantDictAddQuark (tr_variant      * dict,
                        const tr_quark    key,
                        const tr_quark    val)
{
  tr_variant * child = dictFindOrAdd (dict, key, TR_VARIANT_TYPE_STR);
  tr_variantInitQuark (child, val);
  return child;
}

tr_variant*
tr_variantDictAddStr (tr_variant      * dict,
                      const tr_quark    key,
                      const char      * val)
{
  tr_variant * child = dictFindOrAdd (dict, key, TR_VARIANT_TYPE_STR);
  tr_variantInitStr (child, val, -1);
  return child;
}

tr_variant*
tr_variantDictAddRaw (tr_variant      * dict,
                      const tr_quark    key,
                      const void      * src,
                      size_t            len)
{
  tr_variant * child = dictFindOrAdd (dict, key, TR_VARIANT_TYPE_STR);
  tr_variantInitRaw (child, src, len);
  return child;
}

tr_variant*
tr_variantDictAddList (tr_variant     * dict,
                       const tr_quark   key,
                       size_t           reserve_count)
{
  tr_variant * child = tr_variantDictAdd (dict, key);
  tr_variantInitList (child, reserve_count);
  return child;
}

tr_variant*
tr_variantDictAddDict (tr_variant     * dict,
                       const tr_quark   key,
                       size_t           reserve_count)
{
  tr_variant * child = tr_variantDictAdd (dict, key);
  tr_variantInitDict (child, reserve_count);
  return child;
}

bool
tr_variantDictRemove (tr_variant     * dict,
                      const tr_quark   key)
{
  bool removed = false;
  const int i = dictIndexOf (dict, key);

  if (i >= 0)
    {
      const int last = dict->val.l.count - 1;

      tr_variantFree (&dict->val.l.vals[i]);

      if (i != last)
        dict->val.l.vals[i] = dict->val.l.vals[last];

      --dict->val.l.count;

       removed = true;
    }

  return removed;
}

/***
****  BENC WALKING
***/

struct KeyIndex
{
  const char * keystr;
  tr_variant * val;
};

static int
compareKeyIndex (const void * va, const void * vb)
{
  const struct KeyIndex * a = va;
  const struct KeyIndex * b = vb;

  return strcmp (a->keystr, b->keystr);
}

struct SaveNode
{
  const tr_variant * v;
  tr_variant sorted;
  size_t childIndex;
  bool isVisited;
};

static void
nodeConstruct (struct SaveNode   * node,
               const tr_variant  * v,
               bool                sort_dicts)
{
  node->isVisited = false;
  node->childIndex = 0;

  if (sort_dicts && tr_variantIsDict(v))
    {
      /* make node->sorted a sorted version of this dictionary */

      size_t i;
      const size_t n = v->val.l.count;
      struct KeyIndex * tmp = tr_new (struct KeyIndex, n);

      for (i=0; i<n; i++)
        {
          tmp[i].val = v->val.l.vals+i;
          tmp[i].keystr = tr_quark_get_string (tmp[i].val->key, NULL);
        }

      qsort (tmp, n, sizeof (struct KeyIndex), compareKeyIndex);

      tr_variantInitDict (&node->sorted, n);
      for (i=0; i<n; ++i)
        node->sorted.val.l.vals[i] = *tmp[i].val;
      node->sorted.val.l.count = n;

      tr_free (tmp);

      node->v = &node->sorted;
    }
  else
    {
      node->v = v;
    }
}

static void
nodeDestruct (struct SaveNode * node)
{
  if (node->v == &node->sorted)
    tr_free (node->sorted.val.l.vals);
}

/**
 * This function's previous recursive implementation was
 * easier to read, but was vulnerable to a smash-stacking
 * attack via maliciously-crafted data. (#667)
 */
void
tr_variantWalk (const tr_variant               * v,
                const struct VariantWalkFuncs  * walkFuncs,
                void                           * user_data,
                bool                             sort_dicts)
{
  int stackSize = 0;
  int stackAlloc = 64;
  char lc_numeric[128];
  struct SaveNode * stack = tr_new (struct SaveNode, stackAlloc);

  /* always use a '.' decimal point s.t. locale-hopping doesn't bite us */
  tr_strlcpy (lc_numeric, setlocale (LC_NUMERIC, NULL), sizeof (lc_numeric));
  setlocale (LC_NUMERIC, "POSIX");

  nodeConstruct (&stack[stackSize++], v, sort_dicts);

  while (stackSize > 0)
    {
      struct SaveNode * node = &stack[stackSize-1];
      const tr_variant * v;

      if (!node->isVisited)
        {
          v = node->v;
          node->isVisited = true;
        }
      else if (tr_variantIsContainer(node->v) && (node->childIndex < node->v->val.l.count))
        {
          const int index = node->childIndex++;
          v = node->v->val.l.vals + index;

          if (tr_variantIsDict (node->v))
            {
              tr_variant tmp;
              tr_variantInitQuark (&tmp, v->key);
              walkFuncs->stringFunc (&tmp, user_data);
            }
        }
      else /* done with this node */
        {
          if (tr_variantIsContainer (node->v))
            walkFuncs->containerEndFunc (node->v, user_data);
          --stackSize;
          nodeDestruct (node);
          continue;
        }

      if (v) switch (v->type)
        {
          case TR_VARIANT_TYPE_INT:
            walkFuncs->intFunc (v, user_data);
            break;

          case TR_VARIANT_TYPE_BOOL:
            walkFuncs->boolFunc (v, user_data);
            break;

          case TR_VARIANT_TYPE_REAL:
            walkFuncs->realFunc (v, user_data);
            break;

          case TR_VARIANT_TYPE_STR:
            walkFuncs->stringFunc (v, user_data);
            break;

          case TR_VARIANT_TYPE_LIST:
            if (v == node->v)
              {
                walkFuncs->listBeginFunc (v, user_data);
              }
            else
              {
                if (stackAlloc == stackSize)
                  {
                    stackAlloc *= 2;
                    stack = tr_renew (struct SaveNode, stack, stackAlloc);
                  }
                nodeConstruct (&stack[stackSize++], v, sort_dicts);
              }
            break;

          case TR_VARIANT_TYPE_DICT:
            if (v == node->v)
              {
                walkFuncs->dictBeginFunc (v, user_data);
              }
            else
              {
                if (stackAlloc == stackSize)
                  {
                    stackAlloc *= 2;
                    stack = tr_renew (struct SaveNode, stack, stackAlloc);
                  }
                nodeConstruct (&stack[stackSize++], v, sort_dicts);
              }
            break;

          default:
            /* did caller give us an uninitialized val? */
            tr_err ("%s", _("Invalid metadata"));
            break;
        }
    }

  /* restore the locale... */
  setlocale (LC_NUMERIC, lc_numeric);

  tr_free (stack);
}

/****
*****
****/

static void
freeDummyFunc (const tr_variant * v UNUSED, void * buf UNUSED)
{}

static void
freeStringFunc (const tr_variant * v, void * unused UNUSED)
{
  tr_variant_string_clear (&((tr_variant*)v)->val.s);
}

static void
freeContainerEndFunc (const tr_variant * v, void * unused UNUSED)
{
  tr_free (v->val.l.vals);
}

static const struct VariantWalkFuncs freeWalkFuncs = { freeDummyFunc,
                                                       freeDummyFunc,
                                                       freeDummyFunc,
                                                       freeStringFunc,
                                                       freeDummyFunc,
                                                       freeDummyFunc,
                                                       freeContainerEndFunc };

void
tr_variantFree (tr_variant * v)
{
  if (tr_variantIsSomething (v))
    tr_variantWalk (v, &freeWalkFuncs, NULL, false);
}

/***
****
***/

static void
tr_variantListCopy (tr_variant * target, const tr_variant * src)
{
  int i = 0;
  const tr_variant * val;

  while ((val = tr_variantListChild ((tr_variant*)src, i++)))
    {
      if (tr_variantIsBool (val))
       {
          bool boolVal = 0;
          tr_variantGetBool (val, &boolVal);
          tr_variantListAddBool (target, boolVal);
       }
     else if (tr_variantIsReal (val))
       {
         double realVal = 0;
         tr_variantGetReal (val, &realVal);
         tr_variantListAddReal (target, realVal);
       }
     else if (tr_variantIsInt (val))
       {
         int64_t intVal = 0;
         tr_variantGetInt (val, &intVal);
         tr_variantListAddInt (target, intVal);
       }
     else if (tr_variantIsString (val))
       {
         size_t len;
         const char * str;
         tr_variantGetStr (val, &str, &len);
         tr_variantListAddRaw (target, str, len);
       }
     else if (tr_variantIsDict (val))
       {
         tr_variantMergeDicts (tr_variantListAddDict (target, 0), val);
       }
     else if (tr_variantIsList (val))
       {
         tr_variantListCopy (tr_variantListAddList (target, 0), val);
       }
     else
       {
         tr_err ("tr_variantListCopy skipping item");
       }
   }
}

static size_t
tr_variantDictSize (const tr_variant * dict)
{
  return tr_variantIsDict (dict) ? dict->val.l.count : 0;
}

bool
tr_variantDictChild (tr_variant   * dict,
                     size_t         n,
                     tr_quark     * key,
                     tr_variant  ** val)
{
  bool success = 0;

  assert (tr_variantIsDict (dict));

  if (tr_variantIsDict (dict) && (n<dict->val.l.count))
    {
      *key = dict->val.l.vals[n].key;
      *val = dict->val.l.vals+n;
      success = true;
    }

  return success;
}

void
tr_variantMergeDicts (tr_variant * target, const tr_variant * source)
{
  size_t i;
  const size_t sourceCount = tr_variantDictSize (source);

  assert (tr_variantIsDict (target));
  assert (tr_variantIsDict (source));

  tr_variantDictReserve (target, sourceCount + tr_variantDictSize(target));

  for (i=0; i<sourceCount; ++i)
    {
      tr_quark key;
      tr_variant * val;
      tr_variant * t;

      if (tr_variantDictChild ((tr_variant*)source, i, &key, &val))
        {
          if (tr_variantIsBool (val))
            {
              bool boolVal;
              tr_variantGetBool (val, &boolVal);
              tr_variantDictAddBool (target, key, boolVal);
            }
          else if (tr_variantIsReal (val))
            {
              double realVal = 0;
              tr_variantGetReal (val, &realVal);
              tr_variantDictAddReal (target, key, realVal);
            }
          else if (tr_variantIsInt (val))
            {
              int64_t intVal = 0;
              tr_variantGetInt (val, &intVal);
              tr_variantDictAddInt (target, key, intVal);
            }
          else if (tr_variantIsString (val))
            {
              size_t len;
              const char * str;
              tr_variantGetStr (val, &str, &len);
              tr_variantDictAddRaw (target, key, str, len);
            }
          else if (tr_variantIsDict (val) && tr_variantDictFindDict (target, key, &t))
            {
              tr_variantMergeDicts (t, val);
            }
          else if (tr_variantIsList (val))
            {
              if (tr_variantDictFind (target, key) == NULL)
                tr_variantListCopy (tr_variantDictAddList (target, key, tr_variantListSize (val)), val);
            }
          else if (tr_variantIsDict (val))
            {
              tr_variant * target_dict = tr_variantDictFind (target, key);

              if (target_dict == NULL)
                target_dict = tr_variantDictAddDict (target, key, tr_variantDictSize (val));

              if (tr_variantIsDict (target_dict))
                tr_variantMergeDicts (target_dict, val);
            }
          else
            {
              tr_dbg ("tr_variantMergeDicts skipping \"%s\"", tr_quark_get_string(key,NULL));
            }
        }
    }
}

/***
****
***/

struct evbuffer *
tr_variantToBuf (const tr_variant * v, tr_variant_fmt fmt)
{
  struct evbuffer * buf = evbuffer_new();

  evbuffer_expand (buf, 4096); /* alloc a little memory to start off with */

  switch (fmt)
    {
      case TR_VARIANT_FMT_BENC:
        tr_variantToBufBenc (v, buf);
        break;

      case TR_VARIANT_FMT_JSON:
        tr_variantToBufJson (v, buf, false);
        break;

      case TR_VARIANT_FMT_JSON_LEAN:
        tr_variantToBufJson (v, buf, true);
        break;
    }

  return buf;
}

char*
tr_variantToStr (const tr_variant * v, tr_variant_fmt fmt, int * len)
{
  struct evbuffer * buf = tr_variantToBuf (v, fmt);
  const size_t n = evbuffer_get_length (buf);
  char * ret = evbuffer_free_to_str (buf);
  if (len != NULL)
    *len = (int) n;
  return ret;
}

/* portability wrapper for mkstemp(). */
static int
tr_mkstemp (char * template)
{
#ifdef WIN32
  const int flags = O_RDWR | O_BINARY | O_CREAT | O_EXCL | _O_SHORT_LIVED;
  const mode_t mode = _S_IREAD | _S_IWRITE;
  mktemp (template);
  return open (template, flags, mode);
#else
  return mkstemp (template);
#endif
}

int
tr_variantToFile (const tr_variant  * v,
                  tr_variant_fmt      fmt,
                  const char        * filename)
{
  char * tmp;
  int fd;
  int err = 0;
  char buf[TR_PATH_MAX];

  /* follow symlinks to find the "real" file, to make sure the temporary
   * we build with tr_mkstemp() is created on the right partition */
  if (tr_realpath (filename, buf) != NULL)
    filename = buf;

  /* if the file already exists, try to move it out of the way & keep it as a backup */
  tmp = tr_strdup_printf ("%s.tmp.XXXXXX", filename);
  fd = tr_mkstemp (tmp);
  tr_set_file_for_single_pass (fd);
  if (fd >= 0)
    {
      int nleft;

      /* save the variant to a temporary file */
      {
        struct evbuffer * buf = tr_variantToBuf (v, fmt);
        const char * walk = (const char *) evbuffer_pullup (buf, -1);
        nleft = evbuffer_get_length (buf);

        while (nleft > 0)
          {
            const int n = write (fd, walk, nleft);
            if (n >= 0)
              {
                nleft -= n;
                walk += n;
              }
            else if (errno != EAGAIN)
              {
                err = errno;
                break;
              }
          }

        evbuffer_free (buf);
      }

      if (nleft > 0)
        {
          tr_err (_("Couldn't save temporary file \"%1$s\": %2$s"), tmp, tr_strerror (err));
          tr_close_file (fd);
          unlink (tmp);
        }
      else
        {
          tr_close_file (fd);

#ifdef WIN32
          if (MoveFileEx (tmp, filename, MOVEFILE_REPLACE_EXISTING))
#else
          if (!rename (tmp, filename))
#endif
            {
              tr_inf (_("Saved \"%s\""), filename);
            }
          else
            {
              err = errno;
              tr_err (_("Couldn't save file \"%1$s\": %2$s"), filename, tr_strerror (err));
              unlink (tmp);
            }
        }
    }
  else
    {
      err = errno;
      tr_err (_("Couldn't save temporary file \"%1$s\": %2$s"), tmp, tr_strerror (err));
    }

  tr_free (tmp);
  return err;
}

/***
****
***/

int
tr_variantFromFile (tr_variant      * setme,
                    tr_variant_fmt    fmt,
                    const char      * filename)
{
  int err;
  size_t buflen;
  uint8_t * buf;
  const int old_errno = errno;

  errno = 0;
  buf = tr_loadFile (filename, &buflen);

  if (errno)
    err = errno;
  else
    err = tr_variantFromBuf (setme, fmt, buf, buflen, filename, NULL);

  tr_free (buf);
  errno = old_errno;
  return err;
}

int
tr_variantFromBuf (tr_variant      * setme,
                   tr_variant_fmt    fmt,
                   const void      * buf,
                   size_t            buflen,
                   const char      * optional_source,
                   const char     ** setme_end)
{
  int err;

  switch (fmt)
    {
      case TR_VARIANT_FMT_JSON:
      case TR_VARIANT_FMT_JSON_LEAN:
        err = tr_jsonParse (optional_source, buf, buflen, setme, setme_end);
        break;

      case TR_VARIANT_FMT_BENC:
        err = tr_variantParseBenc (buf, ((const char*)buf)+buflen, setme, setme_end);
        break;
    }

  return err;
}