gvarianttype.c 36.5 KB
Newer Older
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1 2 3 4 5 6 7
/*
 * Copyright © 2007, 2008 Ryan Lortie
 * Copyright © 2009, 2010 Codethink Limited
 *
 * 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
8
 * version 2.1 of the License, or (at your option) any later version.
Allison Karlitskaya's avatar
Allison Karlitskaya committed
9 10 11 12 13 14 15
 *
 * 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
16
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
Allison Karlitskaya's avatar
Allison Karlitskaya committed
17 18 19 20
 *
 * Author: Ryan Lortie <desrt@desrt.ca>
 */

21 22
#include "config.h"

Allison Karlitskaya's avatar
Allison Karlitskaya committed
23 24 25
#include "gvarianttype.h"

#include <glib/gtestutils.h>
26
#include <glib/gstrfuncs.h>
27
#include <glib/gvariant-internal.h>
Allison Karlitskaya's avatar
Allison Karlitskaya committed
28 29 30

#include <string.h>

31
#include "gstrfuncsprivate.h"
Allison Karlitskaya's avatar
Allison Karlitskaya committed
32 33

/**
Johan Dahlin's avatar
Johan Dahlin committed
34
 * SECTION:gvarianttype
Allison Karlitskaya's avatar
Allison Karlitskaya committed
35 36 37 38
 * @title: GVariantType
 * @short_description: introduction to the GVariant type system
 * @see_also: #GVariantType, #GVariant
 *
39 40 41 42 43
 * This section introduces the GVariant type system. It is based, in
 * large part, on the D-Bus type system, with two major changes and
 * some minor lifting of restrictions. The
 * [D-Bus specification](http://dbus.freedesktop.org/doc/dbus-specification.html),
 * therefore, provides a significant amount of
Allison Karlitskaya's avatar
Allison Karlitskaya committed
44 45
 * information that is useful when working with GVariant.
 *
Murray Cumming's avatar
Murray Cumming committed
46
 * The first major change with respect to the D-Bus type system is the
Allison Karlitskaya's avatar
Allison Karlitskaya committed
47 48 49
 * introduction of maybe (or "nullable") types.  Any type in GVariant can be
 * converted to a maybe type, in which case, "nothing" (or "null") becomes a
 * valid value.  Maybe types have been added by introducing the
50
 * character "m" to type strings.
Allison Karlitskaya's avatar
Allison Karlitskaya committed
51 52 53
 *
 * The second major change is that the GVariant type system supports the
 * concept of "indefinite types" -- types that are less specific than
Murray Cumming's avatar
Murray Cumming committed
54 55
 * the normal types found in D-Bus.  For example, it is possible to speak
 * of "an array of any type" in GVariant, where the D-Bus type system
Allison Karlitskaya's avatar
Allison Karlitskaya committed
56 57
 * would require you to speak of "an array of integers" or "an array of
 * strings".  Indefinite types have been added by introducing the
58
 * characters "*", "?" and "r" to type strings.
Allison Karlitskaya's avatar
Allison Karlitskaya committed
59 60 61 62 63
 *
 * Finally, all arbitrary restrictions relating to the complexity of
 * types are lifted along with the restriction that dictionary entries
 * may only appear nested inside of arrays.
 *
Murray Cumming's avatar
Murray Cumming committed
64
 * Just as in D-Bus, GVariant types are described with strings ("type
Allison Karlitskaya's avatar
Allison Karlitskaya committed
65
 * strings").  Subject to the differences mentioned above, these strings
Murray Cumming's avatar
Murray Cumming committed
66
 * are of the same form as those found in DBus.  Note, however: D-Bus
Allison Karlitskaya's avatar
Allison Karlitskaya committed
67 68 69 70 71
 * always works in terms of messages and therefore individual type
 * strings appear nowhere in its interface.  Instead, "signatures"
 * are a concatenation of the strings of the type of each argument in a
 * message.  GVariant deals with single values directly so GVariant type
 * strings always describe the type of exactly one value.  This means
Murray Cumming's avatar
Murray Cumming committed
72
 * that a D-Bus signature string is generally not a valid GVariant type
Allison Karlitskaya's avatar
Allison Karlitskaya committed
73 74 75 76 77 78 79 80
 * string -- except in the case that it is the signature of a message
 * containing exactly one argument.
 *
 * An indefinite type is similar in spirit to what may be called an
 * abstract type in other type systems.  No value can exist that has an
 * indefinite type as its type, but values can exist that have types
 * that are subtypes of indefinite types.  That is to say,
 * g_variant_get_type() will never return an indefinite type, but
Allison Karlitskaya's avatar
Allison Karlitskaya committed
81
 * calling g_variant_is_of_type() with an indefinite type may return
82
 * %TRUE.  For example, you cannot have a value that represents "an
Allison Karlitskaya's avatar
Allison Karlitskaya committed
83 84 85 86
 * array of no particular type", but you can have an "array of integers"
 * which certainly matches the type of "an array of no particular type",
 * since "array of integers" is a subtype of "array of no particular
 * type".
Allison Karlitskaya's avatar
Allison Karlitskaya committed
87 88 89 90 91 92 93 94 95
 *
 * This is similar to how instances of abstract classes may not
 * directly exist in other type systems, but instances of their
 * non-abstract subtypes may.  For example, in GTK, no object that has
 * the type of #GtkBin can exist (since #GtkBin is an abstract class),
 * but a #GtkWindow can certainly be instantiated, and you would say
 * that the #GtkWindow is a #GtkBin (since #GtkWindow is a subclass of
 * #GtkBin).
 *
96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
 * ## GVariant Type Strings
 *
 * A GVariant type string can be any of the following:
 *
 * - any basic type string (listed below)
 *
 * - "v", "r" or "*"
 *
 * - one of the characters 'a' or 'm', followed by another type string
 *
 * - the character '(', followed by a concatenation of zero or more other
 *   type strings, followed by the character ')'
 *
 * - the character '{', followed by a basic type string (see below),
 *   followed by another type string, followed by the character '}'
 *
 * A basic type string describes a basic type (as per
 * g_variant_type_is_basic()) and is always a single character in length.
 * The valid basic type strings are "b", "y", "n", "q", "i", "u", "x", "t",
 * "h", "d", "s", "o", "g" and "?".
 *
 * The above definition is recursive to arbitrary depth. "aaaaai" and
 * "(ui(nq((y)))s)" are both valid type strings, as is
119 120 121 122
 * "a(aa(ui)(qna{ya(yd)}))". In order to not hit memory limits, #GVariant
 * imposes a limit on recursion depth of 65 nested containers. This is the
 * limit in the D-Bus specification (64) plus one to allow a #GDBusMessage to
 * be nested in a top-level tuple.
123 124
 *
 * The meaning of each of the characters is as follows:
125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140
 * - `b`: the type string of %G_VARIANT_TYPE_BOOLEAN; a boolean value.
 * - `y`: the type string of %G_VARIANT_TYPE_BYTE; a byte.
 * - `n`: the type string of %G_VARIANT_TYPE_INT16; a signed 16 bit integer.
 * - `q`: the type string of %G_VARIANT_TYPE_UINT16; an unsigned 16 bit integer.
 * - `i`: the type string of %G_VARIANT_TYPE_INT32; a signed 32 bit integer.
 * - `u`: the type string of %G_VARIANT_TYPE_UINT32; an unsigned 32 bit integer.
 * - `x`: the type string of %G_VARIANT_TYPE_INT64; a signed 64 bit integer.
 * - `t`: the type string of %G_VARIANT_TYPE_UINT64; an unsigned 64 bit integer.
 * - `h`: the type string of %G_VARIANT_TYPE_HANDLE; a signed 32 bit value
 *   that, by convention, is used as an index into an array of file
 *   descriptors that are sent alongside a D-Bus message.
 * - `d`: the type string of %G_VARIANT_TYPE_DOUBLE; a double precision
 *   floating point value.
 * - `s`: the type string of %G_VARIANT_TYPE_STRING; a string.
 * - `o`: the type string of %G_VARIANT_TYPE_OBJECT_PATH; a string in the form
 *   of a D-Bus object path.
141
 * - `g`: the type string of %G_VARIANT_TYPE_SIGNATURE; a string in the form of
142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171
 *   a D-Bus type signature.
 * - `?`: the type string of %G_VARIANT_TYPE_BASIC; an indefinite type that
 *   is a supertype of any of the basic types.
 * - `v`: the type string of %G_VARIANT_TYPE_VARIANT; a container type that
 *   contain any other type of value.
 * - `a`: used as a prefix on another type string to mean an array of that
 *   type; the type string "ai", for example, is the type of an array of
 *   signed 32-bit integers.
 * - `m`: used as a prefix on another type string to mean a "maybe", or
 *   "nullable", version of that type; the type string "ms", for example,
 *   is the type of a value that maybe contains a string, or maybe contains
 *   nothing.
 * - `()`: used to enclose zero or more other concatenated type strings to
 *   create a tuple type; the type string "(is)", for example, is the type of
 *   a pair of an integer and a string.
 * - `r`: the type string of %G_VARIANT_TYPE_TUPLE; an indefinite type that is
 *   a supertype of any tuple type, regardless of the number of items.
 * - `{}`: used to enclose a basic type string concatenated with another type
 *   string to create a dictionary entry type, which usually appears inside of
 *   an array to form a dictionary; the type string "a{sd}", for example, is
 *   the type of a dictionary that maps strings to double precision floating
 *   point values.
 *
 *   The first type (the basic type) is the key type and the second type is
 *   the value type. The reason that the first type is restricted to being a
 *   basic type is so that it can easily be hashed.
 * - `*`: the type string of %G_VARIANT_TYPE_ANY; the indefinite type that is
 *   a supertype of all types.  Note that, as with all type strings, this
 *   character represents exactly one type. It cannot be used inside of tuples
 *   to mean "any number of items".
172 173 174 175 176 177 178 179 180 181 182 183 184 185
 *
 * Any type string of a container that contains an indefinite type is,
 * itself, an indefinite type. For example, the type string "a*"
 * (corresponding to %G_VARIANT_TYPE_ARRAY) is an indefinite type
 * that is a supertype of every array type. "(*s)" is a supertype
 * of all tuples that contain exactly two items where the second
 * item is a string.
 *
 * "a{?*}" is an indefinite type that is a supertype of all arrays
 * containing dictionary entries where the key is any basic type and
 * the value is any type at all.  This is, by definition, a dictionary,
 * so this type string corresponds to %G_VARIANT_TYPE_DICTIONARY. Note
 * that, due to the restriction that the key of a dictionary entry must
 * be a basic type, "{**}" is not a valid type string.
Allison Karlitskaya's avatar
Allison Karlitskaya committed
186 187 188 189 190 191 192 193 194
 */


static gboolean
g_variant_type_check (const GVariantType *type)
{
  if (type == NULL)
    return FALSE;

195 196
#if 0
  return g_variant_type_string_scan ((const gchar *) type, NULL, NULL);
Allison Karlitskaya's avatar
Allison Karlitskaya committed
197 198 199 200 201
#else
  return TRUE;
#endif
}

202 203 204 205 206 207
static gboolean
variant_type_string_scan_internal (const gchar  *string,
                                   const gchar  *limit,
                                   const gchar **endptr,
                                   gsize        *depth,
                                   gsize         depth_limit)
Allison Karlitskaya's avatar
Allison Karlitskaya committed
208
{
209 210
  gsize max_depth = 0, child_depth;

Allison Karlitskaya's avatar
Allison Karlitskaya committed
211 212 213 214 215 216 217 218 219
  g_return_val_if_fail (string != NULL, FALSE);

  if (string == limit || *string == '\0')
    return FALSE;

  switch (*string++)
    {
    case '(':
      while (string == limit || *string != ')')
220 221 222 223 224 225 226 227 228
        {
          if (depth_limit == 0 ||
              !variant_type_string_scan_internal (string, limit, &string,
                                                  &child_depth,
                                                  depth_limit - 1))
            return FALSE;

          max_depth = MAX (max_depth, child_depth + 1);
        }
Allison Karlitskaya's avatar
Allison Karlitskaya committed
229 230 231 232 233

      string++;
      break;

    case '{':
234 235 236 237 238 239
      if (depth_limit == 0 ||
          string == limit || *string == '\0' ||                                  /* { */
          !strchr ("bynqihuxtdsog?", *string++) ||                               /* key */
          !variant_type_string_scan_internal (string, limit, &string,
                                              &child_depth, depth_limit - 1) ||  /* value */
          string == limit || *string++ != '}')                                   /* } */
Allison Karlitskaya's avatar
Allison Karlitskaya committed
240 241
        return FALSE;

242
      max_depth = MAX (max_depth, child_depth + 1);
Allison Karlitskaya's avatar
Allison Karlitskaya committed
243 244 245
      break;

    case 'm': case 'a':
246 247 248 249 250 251 252
      if (depth_limit == 0 ||
          !variant_type_string_scan_internal (string, limit, &string,
                                              &child_depth, depth_limit - 1))
        return FALSE;

      max_depth = MAX (max_depth, child_depth + 1);
      break;
Allison Karlitskaya's avatar
Allison Karlitskaya committed
253 254 255 256

    case 'b': case 'y': case 'n': case 'q': case 'i': case 'u':
    case 'x': case 't': case 'd': case 's': case 'o': case 'g':
    case 'v': case 'r': case '*': case '?': case 'h':
257
      max_depth = MAX (max_depth, 1);
Allison Karlitskaya's avatar
Allison Karlitskaya committed
258 259 260 261 262 263 264 265
      break;

    default:
      return FALSE;
    }

  if (endptr != NULL)
    *endptr = string;
266 267
  if (depth != NULL)
    *depth = max_depth;
Allison Karlitskaya's avatar
Allison Karlitskaya committed
268 269 270 271

  return TRUE;
}

272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333
/**
 * g_variant_type_string_scan:
 * @string: a pointer to any string
 * @limit: (nullable): the end of @string, or %NULL
 * @endptr: (out) (optional): location to store the end pointer, or %NULL
 *
 * Scan for a single complete and valid GVariant type string in @string.
 * The memory pointed to by @limit (or bytes beyond it) is never
 * accessed.
 *
 * If a valid type string is found, @endptr is updated to point to the
 * first character past the end of the string that was found and %TRUE
 * is returned.
 *
 * If there is no valid type string starting at @string, or if the type
 * string does not end before @limit then %FALSE is returned.
 *
 * For the simple case of checking if a string is a valid type string,
 * see g_variant_type_string_is_valid().
 *
 * Returns: %TRUE if a valid type string was found
 *
 * Since: 2.24
 **/
gboolean
g_variant_type_string_scan (const gchar  *string,
                            const gchar  *limit,
                            const gchar **endptr)
{
  return variant_type_string_scan_internal (string, limit, endptr, NULL,
                                            G_VARIANT_MAX_RECURSION_DEPTH);
}

/* < private >
 * g_variant_type_string_get_depth_:
 * @type_string: a pointer to any string
 *
 * Get the maximum depth of the nested types in @type_string. A basic type will
 * return depth 1, and a container type will return a greater value. The depth
 * of a tuple is 1 plus the depth of its deepest child type.
 *
 * If @type_string is not a valid #GVariant type string, 0 will be returned.
 *
 * Returns: depth of @type_string, or 0 on error
 * Since: 2.60
 */
gsize
g_variant_type_string_get_depth_ (const gchar *type_string)
{
  const gchar *endptr;
  gsize depth = 0;

  g_return_val_if_fail (type_string != NULL, 0);

  if (!variant_type_string_scan_internal (type_string, NULL, &endptr, &depth,
                                          G_VARIANT_MAX_RECURSION_DEPTH) ||
      *endptr != '\0')
    return 0;

  return depth;
}

Allison Karlitskaya's avatar
Allison Karlitskaya committed
334 335 336 337 338 339 340 341
/**
 * g_variant_type_string_is_valid:
 * @type_string: a pointer to any string
 *
 * Checks if @type_string is a valid GVariant type string.  This call is
 * equivalent to calling g_variant_type_string_scan() and confirming
 * that the following character is a nul terminator.
 *
342 343
 * Returns: %TRUE if @type_string is exactly one valid type string
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
344 345 346 347 348
 * Since 2.24
 **/
gboolean
g_variant_type_string_is_valid (const gchar *type_string)
{
349
  const gchar *endptr;
Allison Karlitskaya's avatar
Allison Karlitskaya committed
350 351 352 353 354 355 356 357 358 359 360

  g_return_val_if_fail (type_string != NULL, FALSE);

  if (!g_variant_type_string_scan (type_string, NULL, &endptr))
    return FALSE;

  return *endptr == '\0';
}

/**
 * g_variant_type_free:
361
 * @type: (nullable): a #GVariantType, or %NULL
Allison Karlitskaya's avatar
Allison Karlitskaya committed
362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385
 *
 * Frees a #GVariantType that was allocated with
 * g_variant_type_copy(), g_variant_type_new() or one of the container
 * type constructor functions.
 *
 * In the case that @type is %NULL, this function does nothing.
 *
 * Since 2.24
 **/
void
g_variant_type_free (GVariantType *type)
{
  g_return_if_fail (type == NULL || g_variant_type_check (type));

  g_free (type);
}

/**
 * g_variant_type_copy:
 * @type: a #GVariantType
 *
 * Makes a copy of a #GVariantType.  It is appropriate to call
 * g_variant_type_free() on the return value.  @type may not be %NULL.
 *
386 387
 * Returns: (transfer full): a new #GVariantType
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416
 * Since 2.24
 **/
GVariantType *
g_variant_type_copy (const GVariantType *type)
{
  gsize length;
  gchar *new;

  g_return_val_if_fail (g_variant_type_check (type), NULL);

  length = g_variant_type_get_string_length (type);
  new = g_malloc (length + 1);

  memcpy (new, type, length);
  new[length] = '\0';

  return (GVariantType *) new;
}

/**
 * g_variant_type_new:
 * @type_string: a valid GVariant type string
 *
 * Creates a new #GVariantType corresponding to the type string given
 * by @type_string.  It is appropriate to call g_variant_type_free() on
 * the return value.
 *
 * It is a programmer error to call this function with an invalid type
 * string.  Use g_variant_type_string_is_valid() if you are unsure.
417
 *
418 419
 * Returns: (transfer full): a new #GVariantType
 *
420
 * Since: 2.24
Allison Karlitskaya's avatar
Allison Karlitskaya committed
421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437
 */
GVariantType *
g_variant_type_new (const gchar *type_string)
{
  g_return_val_if_fail (type_string != NULL, NULL);

  return g_variant_type_copy (G_VARIANT_TYPE (type_string));
}

/**
 * g_variant_type_get_string_length:
 * @type: a #GVariantType
 *
 * Returns the length of the type string corresponding to the given
 * @type.  This function must be used to determine the valid extent of
 * the memory region returned by g_variant_type_peek_string().
 *
438 439
 * Returns: the length of the corresponding type string
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468
 * Since 2.24
 **/
gsize
g_variant_type_get_string_length (const GVariantType *type)
{
  const gchar *type_string = (const gchar *) type;
  gint brackets = 0;
  gsize index = 0;

  g_return_val_if_fail (g_variant_type_check (type), 0);

  do
    {
      while (type_string[index] == 'a' || type_string[index] == 'm')
        index++;

      if (type_string[index] == '(' || type_string[index] == '{')
        brackets++;

      else if (type_string[index] == ')' || type_string[index] == '}')
        brackets--;

      index++;
    }
  while (brackets);

  return index;
}

469 470 471 472
/*
  This function is not introspectable, it returns something that
  is not an array and neither a string
*/
Allison Karlitskaya's avatar
Allison Karlitskaya committed
473
/**
474
 * g_variant_type_peek_string: (skip)
Allison Karlitskaya's avatar
Allison Karlitskaya committed
475 476 477 478 479 480 481 482
 * @type: a #GVariantType
 *
 * Returns the type string corresponding to the given @type.  The
 * result is not nul-terminated; in order to determine its length you
 * must call g_variant_type_get_string_length().
 *
 * To get a nul-terminated string, see g_variant_type_dup_string().
 *
483 484
 * Returns: the corresponding type string (not nul-terminated)
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502
 * Since 2.24
 **/
const gchar *
g_variant_type_peek_string (const GVariantType *type)
{
  g_return_val_if_fail (g_variant_type_check (type), NULL);

  return (const gchar *) type;
}

/**
 * g_variant_type_dup_string:
 * @type: a #GVariantType
 *
 * Returns a newly-allocated copy of the type string corresponding to
 * @type.  The returned string is nul-terminated.  It is appropriate to
 * call g_free() on the return value.
 *
503 504
 * Returns: (transfer full): the corresponding type string
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530
 * Since 2.24
 **/
gchar *
g_variant_type_dup_string (const GVariantType *type)
{
  g_return_val_if_fail (g_variant_type_check (type), NULL);

  return g_strndup (g_variant_type_peek_string (type),
                    g_variant_type_get_string_length (type));
}

/**
 * g_variant_type_is_definite:
 * @type: a #GVariantType
 *
 * Determines if the given @type is definite (ie: not indefinite).
 *
 * A type is definite if its type string does not contain any indefinite
 * type characters ('*', '?', or 'r').
 *
 * A #GVariant instance may not have an indefinite type, so calling
 * this function on the result of g_variant_get_type() will always
 * result in %TRUE being returned.  Calling this function on an
 * indefinite type like %G_VARIANT_TYPE_ARRAY, however, will result in
 * %FALSE being returned.
 *
531 532
 * Returns: %TRUE if @type is definite
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568
 * Since 2.24
 **/
gboolean
g_variant_type_is_definite (const GVariantType *type)
{
  const gchar *type_string;
  gsize type_length;
  gsize i;

  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  type_length = g_variant_type_get_string_length (type);
  type_string = g_variant_type_peek_string (type);

  for (i = 0; i < type_length; i++)
    if (type_string[i] == '*' ||
        type_string[i] == '?' ||
        type_string[i] == 'r')
      return FALSE;

  return TRUE;
}

/**
 * g_variant_type_is_container:
 * @type: a #GVariantType
 *
 * Determines if the given @type is a container type.
 *
 * Container types are any array, maybe, tuple, or dictionary
 * entry types plus the variant type.
 *
 * This function returns %TRUE for any indefinite type for which every
 * definite subtype is a container -- %G_VARIANT_TYPE_ARRAY, for
 * example.
 *
569 570
 * Returns: %TRUE if @type is a container type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609
 * Since 2.24
 **/
gboolean
g_variant_type_is_container (const GVariantType *type)
{
  gchar first_char;

  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  first_char = g_variant_type_peek_string (type)[0];
  switch (first_char)
  {
    case 'a':
    case 'm':
    case 'r':
    case '(':
    case '{':
    case 'v':
      return TRUE;

    default:
      return FALSE;
  }
}

/**
 * g_variant_type_is_basic:
 * @type: a #GVariantType
 *
 * Determines if the given @type is a basic type.
 *
 * Basic types are booleans, bytes, integers, doubles, strings, object
 * paths and signatures.
 *
 * Only a basic type may be used as the key of a dictionary entry.
 *
 * This function returns %FALSE for all indefinite types except
 * %G_VARIANT_TYPE_BASIC.
 *
610 611
 * Returns: %TRUE if @type is a basic type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655
 * Since 2.24
 **/
gboolean
g_variant_type_is_basic (const GVariantType *type)
{
  gchar first_char;

  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  first_char = g_variant_type_peek_string (type)[0];
  switch (first_char)
  {
    case 'b':
    case 'y':
    case 'n':
    case 'q':
    case 'i':
    case 'h':
    case 'u':
    case 't':
    case 'x':
    case 'd':
    case 's':
    case 'o':
    case 'g':
    case '?':
      return TRUE;

    default:
      return FALSE;
  }
}

/**
 * g_variant_type_is_maybe:
 * @type: a #GVariantType
 *
 * Determines if the given @type is a maybe type.  This is true if the
 * type string for @type starts with an 'm'.
 *
 * This function returns %TRUE for any indefinite type for which every
 * definite subtype is a maybe type -- %G_VARIANT_TYPE_MAYBE, for
 * example.
 *
656 657
 * Returns: %TRUE if @type is a maybe type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678
 * Since 2.24
 **/
gboolean
g_variant_type_is_maybe (const GVariantType *type)
{
  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  return g_variant_type_peek_string (type)[0] == 'm';
}

/**
 * g_variant_type_is_array:
 * @type: a #GVariantType
 *
 * Determines if the given @type is an array type.  This is true if the
 * type string for @type starts with an 'a'.
 *
 * This function returns %TRUE for any indefinite type for which every
 * definite subtype is an array type -- %G_VARIANT_TYPE_ARRAY, for
 * example.
 *
679 680
 * Returns: %TRUE if @type is an array type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702
 * Since 2.24
 **/
gboolean
g_variant_type_is_array (const GVariantType *type)
{
  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  return g_variant_type_peek_string (type)[0] == 'a';
}

/**
 * g_variant_type_is_tuple:
 * @type: a #GVariantType
 *
 * Determines if the given @type is a tuple type.  This is true if the
 * type string for @type starts with a '(' or if @type is
 * %G_VARIANT_TYPE_TUPLE.
 *
 * This function returns %TRUE for any indefinite type for which every
 * definite subtype is a tuple type -- %G_VARIANT_TYPE_TUPLE, for
 * example.
 *
703 704
 * Returns: %TRUE if @type is a tuple type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728
 * Since 2.24
 **/
gboolean
g_variant_type_is_tuple (const GVariantType *type)
{
  gchar type_char;

  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  type_char = g_variant_type_peek_string (type)[0];
  return type_char == 'r' || type_char == '(';
}

/**
 * g_variant_type_is_dict_entry:
 * @type: a #GVariantType
 *
 * Determines if the given @type is a dictionary entry type.  This is
 * true if the type string for @type starts with a '{'.
 *
 * This function returns %TRUE for any indefinite type for which every
 * definite subtype is a dictionary entry type --
 * %G_VARIANT_TYPE_DICT_ENTRY, for example.
 *
729 730
 * Returns: %TRUE if @type is a dictionary entry type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
731 732 733 734 735 736 737 738 739 740
 * Since 2.24
 **/
gboolean
g_variant_type_is_dict_entry (const GVariantType *type)
{
  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  return g_variant_type_peek_string (type)[0] == '{';
}

741 742 743 744 745 746
/**
 * g_variant_type_is_variant:
 * @type: a #GVariantType
 *
 * Determines if the given @type is the variant type.
 *
747 748
 * Returns: %TRUE if @type is the variant type
 *
749 750 751 752 753 754 755 756 757 758
 * Since 2.24
 **/
gboolean
g_variant_type_is_variant (const GVariantType *type)
{
  g_return_val_if_fail (g_variant_type_check (type), FALSE);

  return g_variant_type_peek_string (type)[0] == 'v';
}

Allison Karlitskaya's avatar
Allison Karlitskaya committed
759 760
/**
 * g_variant_type_hash:
761
 * @type: (type GVariantType): a #GVariantType
Allison Karlitskaya's avatar
Allison Karlitskaya committed
762 763 764 765 766 767 768
 *
 * Hashes @type.
 *
 * The argument type of @type is only #gconstpointer to allow use with
 * #GHashTable without function pointer casting.  A valid
 * #GVariantType must be provided.
 *
769 770
 * Returns: the hash value
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793
 * Since 2.24
 **/
guint
g_variant_type_hash (gconstpointer type)
{
  const gchar *type_string;
  guint value = 0;
  gsize length;
  gsize i;

  g_return_val_if_fail (g_variant_type_check (type), 0);

  type_string = g_variant_type_peek_string (type);
  length = g_variant_type_get_string_length (type);

  for (i = 0; i < length; i++)
    value = (value << 5) - value + type_string[i];

  return value;
}

/**
 * g_variant_type_equal:
794 795
 * @type1: (type GVariantType): a #GVariantType
 * @type2: (type GVariantType): a #GVariantType
Allison Karlitskaya's avatar
Allison Karlitskaya committed
796 797 798 799 800 801 802 803 804 805 806 807
 *
 * Compares @type1 and @type2 for equality.
 *
 * Only returns %TRUE if the types are exactly equal.  Even if one type
 * is an indefinite type and the other is a subtype of it, %FALSE will
 * be returned if they are not exactly equal.  If you want to check for
 * subtypes, use g_variant_type_is_subtype_of().
 *
 * The argument types of @type1 and @type2 are only #gconstpointer to
 * allow use with #GHashTable without function pointer casting.  For
 * both arguments, a valid #GVariantType must be provided.
 *
808 809
 * Returns: %TRUE if @type1 and @type2 are exactly equal
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847
 * Since 2.24
 **/
gboolean
g_variant_type_equal (gconstpointer type1,
                      gconstpointer type2)
{
  const gchar *string1, *string2;
  gsize size1, size2;

  g_return_val_if_fail (g_variant_type_check (type1), FALSE);
  g_return_val_if_fail (g_variant_type_check (type2), FALSE);

  if (type1 == type2)
    return TRUE;

  size1 = g_variant_type_get_string_length (type1);
  size2 = g_variant_type_get_string_length (type2);

  if (size1 != size2)
    return FALSE;

  string1 = g_variant_type_peek_string (type1);
  string2 = g_variant_type_peek_string (type2);

  return memcmp (string1, string2, size1) == 0;
}

/**
 * g_variant_type_is_subtype_of:
 * @type: a #GVariantType
 * @supertype: a #GVariantType
 *
 * Checks if @type is a subtype of @supertype.
 *
 * This function returns %TRUE if @type is a subtype of @supertype.  All
 * types are considered to be subtypes of themselves.  Aside from that,
 * only indefinite types can have subtypes.
 *
848 849
 * Returns: %TRUE if @type is a subtype of @supertype
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919
 * Since 2.24
 **/
gboolean
g_variant_type_is_subtype_of (const GVariantType *type,
                              const GVariantType *supertype)
{
  const gchar *supertype_string;
  const gchar *supertype_end;
  const gchar *type_string;

  g_return_val_if_fail (g_variant_type_check (type), FALSE);
  g_return_val_if_fail (g_variant_type_check (supertype), FALSE);

  supertype_string = g_variant_type_peek_string (supertype);
  type_string = g_variant_type_peek_string (type);

  supertype_end = supertype_string +
                  g_variant_type_get_string_length (supertype);

  /* we know that type and supertype are both well-formed, so it's
   * safe to treat this merely as a text processing problem.
   */
  while (supertype_string < supertype_end)
    {
      char supertype_char = *supertype_string++;

      if (supertype_char == *type_string)
        type_string++;

      else if (*type_string == ')')
        return FALSE;

      else
        {
          const GVariantType *target_type = (GVariantType *) type_string;

          switch (supertype_char)
            {
            case 'r':
              if (!g_variant_type_is_tuple (target_type))
                return FALSE;
              break;

            case '*':
              break;

            case '?':
              if (!g_variant_type_is_basic (target_type))
                return FALSE;
              break;

            default:
              return FALSE;
            }

          type_string += g_variant_type_get_string_length (target_type);
        }
    }

  return TRUE;
}

/**
 * g_variant_type_element:
 * @type: an array or maybe #GVariantType
 *
 * Determines the element type of an array or maybe type.
 *
 * This function may only be used with array or maybe types.
 *
920 921
 * Returns: (transfer none): the element type of @type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956
 * Since 2.24
 **/
const GVariantType *
g_variant_type_element (const GVariantType *type)
{
  const gchar *type_string;

  g_return_val_if_fail (g_variant_type_check (type), NULL);

  type_string = g_variant_type_peek_string (type);

  g_assert (type_string[0] == 'a' || type_string[0] == 'm');

  return (const GVariantType *) &type_string[1];
}

/**
 * g_variant_type_first:
 * @type: a tuple or dictionary entry #GVariantType
 *
 * Determines the first item type of a tuple or dictionary entry
 * type.
 *
 * This function may only be used with tuple or dictionary entry types,
 * but must not be used with the generic tuple type
 * %G_VARIANT_TYPE_TUPLE.
 *
 * In the case of a dictionary entry type, this returns the type of
 * the key.
 *
 * %NULL is returned in case of @type being %G_VARIANT_TYPE_UNIT.
 *
 * This call, together with g_variant_type_next() provides an iterator
 * interface over tuple and dictionary entry types.
 *
957 958
 * Returns: (transfer none): the first item type of @type, or %NULL
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992
 * Since 2.24
 **/
const GVariantType *
g_variant_type_first (const GVariantType *type)
{
  const gchar *type_string;

  g_return_val_if_fail (g_variant_type_check (type), NULL);

  type_string = g_variant_type_peek_string (type);
  g_assert (type_string[0] == '(' || type_string[0] == '{');

  if (type_string[1] == ')')
    return NULL;

  return (const GVariantType *) &type_string[1];
}

/**
 * g_variant_type_next:
 * @type: a #GVariantType from a previous call
 *
 * Determines the next item type of a tuple or dictionary entry
 * type.
 *
 * @type must be the result of a previous call to
 * g_variant_type_first() or g_variant_type_next().
 *
 * If called on the key type of a dictionary entry then this call
 * returns the value type.  If called on the value type of a dictionary
 * entry then this call returns %NULL.
 *
 * For tuples, %NULL is returned when @type is the last item in a tuple.
 *
993 994
 * Returns: (transfer none): the next #GVariantType after @type, or %NULL
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026
 * Since 2.24
 **/
const GVariantType *
g_variant_type_next (const GVariantType *type)
{
  const gchar *type_string;

  g_return_val_if_fail (g_variant_type_check (type), NULL);

  type_string = g_variant_type_peek_string (type);
  type_string += g_variant_type_get_string_length (type);

  if (*type_string == ')' || *type_string == '}')
    return NULL;

  return (const GVariantType *) type_string;
}

/**
 * g_variant_type_n_items:
 * @type: a tuple or dictionary entry #GVariantType
 *
 * Determines the number of items contained in a tuple or
 * dictionary entry type.
 *
 * This function may only be used with tuple or dictionary entry types,
 * but must not be used with the generic tuple type
 * %G_VARIANT_TYPE_TUPLE.
 *
 * In the case of a dictionary entry type, this function will always
 * return 2.
 *
1027 1028
 * Returns: the number of items in @type
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055
 * Since 2.24
 **/
gsize
g_variant_type_n_items (const GVariantType *type)
{
  gsize count = 0;

  g_return_val_if_fail (g_variant_type_check (type), 0);

  for (type = g_variant_type_first (type);
       type;
       type = g_variant_type_next (type))
    count++;

  return count;
}

/**
 * g_variant_type_key:
 * @type: a dictionary entry #GVariantType
 *
 * Determines the key type of a dictionary entry type.
 *
 * This function may only be used with a dictionary entry type.  Other
 * than the additional restriction, this call is equivalent to
 * g_variant_type_first().
 *
1056 1057
 * Returns: (transfer none): the key type of the dictionary entry
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080
 * Since 2.24
 **/
const GVariantType *
g_variant_type_key (const GVariantType *type)
{
  const gchar *type_string;

  g_return_val_if_fail (g_variant_type_check (type), NULL);

  type_string = g_variant_type_peek_string (type);
  g_assert (type_string[0] == '{');

  return (const GVariantType *) &type_string[1];
}

/**
 * g_variant_type_value:
 * @type: a dictionary entry #GVariantType
 *
 * Determines the value type of a dictionary entry type.
 *
 * This function may only be used with a dictionary entry type.
 *
1081 1082
 * Returns: (transfer none): the value type of the dictionary entry
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1083 1084 1085 1086 1087
 * Since 2.24
 **/
const GVariantType *
g_variant_type_value (const GVariantType *type)
{
1088
#ifndef G_DISABLE_ASSERT
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1089
  const gchar *type_string;
1090
#endif
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1091 1092 1093

  g_return_val_if_fail (g_variant_type_check (type), NULL);

1094
#ifndef G_DISABLE_ASSERT
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1095 1096
  type_string = g_variant_type_peek_string (type);
  g_assert (type_string[0] == '{');
1097
#endif
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1098 1099 1100 1101 1102 1103

  return g_variant_type_next (g_variant_type_key (type));
}

/**
 * g_variant_type_new_tuple:
1104
 * @items: (array length=length): an array of #GVariantTypes, one for each item
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1105 1106 1107 1108 1109 1110 1111 1112 1113
 * @length: the length of @items, or -1
 *
 * Constructs a new tuple type, from @items.
 *
 * @length is the number of items in @items, or -1 to indicate that
 * @items is %NULL-terminated.
 *
 * It is appropriate to call g_variant_type_free() on the return value.
 *
1114 1115
 * Returns: (transfer full): a new tuple #GVariantType
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1116 1117 1118 1119 1120 1121 1122 1123
 * Since 2.24
 **/
static GVariantType *
g_variant_type_new_tuple_slow (const GVariantType * const *items,
                               gint                        length)
{
  /* the "slow" version is needed in case the static buffer of 1024
   * bytes is exceeded when running the normal version.  this will
1124
   * happen only with very unusually large types, so it can be slow.
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1125 1126
   */
  GString *string;
1127
  gint i;
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152

  string = g_string_new ("(");
  for (i = 0; i < length; i++)
    {
      const GVariantType *type;
      gsize size;

      g_return_val_if_fail (g_variant_type_check (items[i]), NULL);

      type = items[i];
      size = g_variant_type_get_string_length (type);
      g_string_append_len (string, (const gchar *) type, size);
    }
  g_string_append_c (string, ')');

  return (GVariantType *) g_string_free (string, FALSE);
}

GVariantType *
g_variant_type_new_tuple (const GVariantType * const *items,
                          gint                        length)
{
  char buffer[1024];
  gsize offset;
  gsize i;
1153
  gsize length_unsigned;
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1154 1155 1156 1157

  g_return_val_if_fail (length == 0 || items != NULL, NULL);

  if (length < 0)
1158 1159 1160
    for (length_unsigned = 0; items[length_unsigned] != NULL; length_unsigned++);
  else
    length_unsigned = (gsize) length;
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1161 1162 1163 1164

  offset = 0;
  buffer[offset++] = '(';

1165
  for (i = 0; i < length_unsigned; i++)
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1166 1167 1168 1169 1170 1171 1172 1173 1174 1175
    {
      const GVariantType *type;
      gsize size;

      g_return_val_if_fail (g_variant_type_check (items[i]), NULL);

      type = items[i];
      size = g_variant_type_get_string_length (type);

      if (offset + size >= sizeof buffer) /* leave room for ')' */
1176
        return g_variant_type_new_tuple_slow (items, length_unsigned);
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1177 1178 1179 1180 1181 1182 1183 1184

      memcpy (&buffer[offset], type, size);
      offset += size;
    }

  g_assert (offset < sizeof buffer);
  buffer[offset++] = ')';

1185
  return (GVariantType *) g_memdup2 (buffer, offset);
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1186 1187 1188
}

/**
1189
 * g_variant_type_new_array: (constructor)
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1190 1191 1192 1193 1194 1195 1196
 * @element: a #GVariantType
 *
 * Constructs the type corresponding to an array of elements of the
 * type @type.
 *
 * It is appropriate to call g_variant_type_free() on the return value.
 *
1197 1198
 * Returns: (transfer full): a new array #GVariantType
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218
 * Since 2.24
 **/
GVariantType *
g_variant_type_new_array (const GVariantType *element)
{
  gsize size;
  gchar *new;

  g_return_val_if_fail (g_variant_type_check (element), NULL);

  size = g_variant_type_get_string_length (element);
  new = g_malloc (size + 1);

  new[0] = 'a';
  memcpy (new + 1, element, size);

  return (GVariantType *) new;
}

/**
1219
 * g_variant_type_new_maybe: (constructor)
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1220 1221 1222 1223 1224 1225 1226
 * @element: a #GVariantType
 *
 * Constructs the type corresponding to a maybe instance containing
 * type @type or Nothing.
 *
 * It is appropriate to call g_variant_type_free() on the return value.
 *
1227 1228
 * Returns: (transfer full): a new maybe #GVariantType
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248
 * Since 2.24
 **/
GVariantType *
g_variant_type_new_maybe (const GVariantType *element)
{
  gsize size;
  gchar *new;

  g_return_val_if_fail (g_variant_type_check (element), NULL);

  size = g_variant_type_get_string_length (element);
  new = g_malloc (size + 1);

  new[0] = 'm';
  memcpy (new + 1, element, size);

  return (GVariantType *) new;
}

/**
1249
 * g_variant_type_new_dict_entry: (constructor)
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1250 1251 1252 1253 1254 1255 1256 1257
 * @key: a basic #GVariantType
 * @value: a #GVariantType
 *
 * Constructs the type corresponding to a dictionary entry with a key
 * of type @key and a value of type @value.
 *
 * It is appropriate to call g_variant_type_free() on the return value.
 *
1258 1259
 * Returns: (transfer full): a new dictionary entry #GVariantType
 *
Allison Karlitskaya's avatar
Allison Karlitskaya committed
1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291
 * Since 2.24
 **/
GVariantType *
g_variant_type_new_dict_entry (const GVariantType *key,
                               const GVariantType *value)
{
  gsize keysize, valsize;
  gchar *new;

  g_return_val_if_fail (g_variant_type_check (key), NULL);
  g_return_val_if_fail (g_variant_type_check (value), NULL);

  keysize = g_variant_type_get_string_length (key);
  valsize = g_variant_type_get_string_length (value);

  new = g_malloc (1 + keysize + valsize + 1);

  new[0] = '{';
  memcpy (new + 1, key, keysize);
  memcpy (new + 1 + keysize, value, valsize);
  new[1 + keysize + valsize] = '}';

  return (GVariantType *) new;
}

/* private */
const GVariantType *
g_variant_type_checked_ (const gchar *type_string)
{
  g_return_val_if_fail (g_variant_type_string_is_valid (type_string), NULL);
  return (const GVariantType *) type_string;
}