gststructure.c

/* GStreamer
 * Copyright (C) 2003 David A. Schleef <ds@schleef.org>
 *
 * gststructure.c: lists of { GQuark, GValue } tuples
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/**
 * SECTION:gststructure
 * @short_description: Generic structure containing fields of names and values
 * @see_also: #GstCaps, #GstMessage, #GstEvent, #GstQuery
 *
 * A #GstStructure is a collection of key/value pairs. The keys are expressed
 * as GQuarks and the values can be of any GType.
 *
 * In addition to the key/value pairs, a #GstStructure also has a name. The name
 * starts with a letter and can be folled by letters, numbers and any of "/-_.:".
 *
 * #GstStructure is used by various GStreamer subsystems to store information
 * in a flexible and extensible way. A #GstStructure does not have a refcount
 * because it usually is part of a higher level object such as #GstCaps. It
 * provides a means to enforce mutability using the refcount of the parent
 * with the gst_structure_set_parent_refcount() method.
 *
 * A #GstStructure can be created with gst_structure_new_empty() or
 * gst_structure_new(), which both take a name and an optional set of
 * key/value pairs along with the types of the values.
 *
 * Field values can be changed with gst_structure_set_value() or
 * gst_structure_set().
 *
 * Field values can be retrieved with gst_structure_get_value() or the more
 * convenient gst_structure_get_*() functions.
 *
 * Fields can be removed with gst_structure_remove_field() or
 * gst_structure_remove_fields().
 *
 * Strings in structures must be ASCII or UTF-8 encoded. Other encodings are
 * not allowed. Strings must not be empty either, but may be NULL.
 *
 * Last reviewed on 2009-06-08 (0.10.23)
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <string.h>

#include "gst_private.h"
#include "gstquark.h"
#include <gst/gst.h>
#include <gobject/gvaluecollector.h>

typedef struct _GstStructureField GstStructureField;

struct _GstStructureField
{
  GQuark name;
  GValue value;
};

typedef struct
{
  GstStructure s;

  /* owned by parent structure, NULL if no parent */
  gint *parent_refcount;

  GArray *fields;
} GstStructureImpl;

#define GST_STRUCTURE_REFCOUNT(s) (((GstStructureImpl*)(s))->parent_refcount)
#define GST_STRUCTURE_FIELDS(s) (((GstStructureImpl*)(s))->fields)

#define GST_STRUCTURE_FIELD(structure, index) \
    &g_array_index(GST_STRUCTURE_FIELDS(structure), GstStructureField, (index))

#define IS_MUTABLE(structure) \
    (!GST_STRUCTURE_REFCOUNT(structure) || \
     g_atomic_int_get (GST_STRUCTURE_REFCOUNT(structure)) == 1)

#define IS_TAGLIST(structure) \
    (structure->name == GST_QUARK (TAGLIST))

static void gst_structure_set_field (GstStructure * structure,
    GstStructureField * field);
static GstStructureField *gst_structure_get_field (const GstStructure *
    structure, const gchar * fieldname);
static GstStructureField *gst_structure_id_get_field (const GstStructure *
    structure, GQuark field);
static void gst_structure_transform_to_string (const GValue * src_value,
    GValue * dest_value);
static GstStructure *gst_structure_copy_conditional (const GstStructure *
    structure);
static gboolean gst_structure_parse_value (gchar * str, gchar ** after,
    GValue * value, GType default_type);
static gboolean gst_structure_parse_simple_string (gchar * s, gchar ** end);

GType _gst_structure_type = 0;


G_DEFINE_BOXED_TYPE (GstStructure, gst_structure,
    gst_structure_copy_conditional, gst_structure_free);

void
_priv_gst_structure_initialize (void)
{
  _gst_structure_type = gst_structure_get_type ();

  g_value_register_transform_func (_gst_structure_type, G_TYPE_STRING,
      gst_structure_transform_to_string);
}

static GstStructure *
gst_structure_new_id_empty_with_size (GQuark quark, guint prealloc)
{
  GstStructureImpl *structure;

  structure = g_slice_new (GstStructureImpl);
  ((GstStructure *) structure)->type = _gst_structure_type;
  ((GstStructure *) structure)->name = quark;
  GST_STRUCTURE_REFCOUNT (structure) = NULL;
  GST_STRUCTURE_FIELDS (structure) =
      g_array_sized_new (FALSE, FALSE, sizeof (GstStructureField), prealloc);

  GST_TRACE ("created structure %p", structure);

  return GST_STRUCTURE_CAST (structure);
}

/**
 * gst_structure_new_id_empty:
 * @quark: name of new structure
 *
 * Creates a new, empty #GstStructure with the given name as a GQuark.
 *
 * Free-function: gst_structure_free
 *
 * Returns: (transfer full): a new, empty #GstStructure
 */
GstStructure *
gst_structure_new_id_empty (GQuark quark)
{
  g_return_val_if_fail (quark != 0, NULL);

  return gst_structure_new_id_empty_with_size (quark, 0);
}

#ifndef G_DISABLE_CHECKS
static gboolean
gst_structure_validate_name (const gchar * name)
{
  const gchar *s;

  g_return_val_if_fail (name != NULL, FALSE);

  if (G_UNLIKELY (!g_ascii_isalpha (*name))) {
    GST_WARNING ("Invalid character '%c' at offset 0 in structure name: %s",
        *name, name);
    return FALSE;
  }

  /* FIXME: test name string more */
  s = &name[1];
  while (*s && (g_ascii_isalnum (*s) || strchr ("/-_.:+", *s) != NULL))
    s++;
  if (G_UNLIKELY (*s != '\0')) {
    GST_WARNING ("Invalid character '%c' at offset %" G_GUINTPTR_FORMAT " in"
        " structure name: %s", *s, ((guintptr) s - (guintptr) name), name);
    return FALSE;
  }

  if (strncmp (name, "video/x-raw-", 12) == 0) {
    g_warning ("0.10-style raw video caps are being created. Should be "
        "video/x-raw,format=(string).. now.");
  } else if (strncmp (name, "audio/x-raw-", 12) == 0) {
    g_warning ("0.10-style raw audio caps are being created. Should be "
        "audio/x-raw,format=(string).. now.");
  }

  return TRUE;
}
#endif

/**
 * gst_structure_new_empty:
 * @name: name of new structure
 *
 * Creates a new, empty #GstStructure with the given @name.
 *
 * See gst_structure_set_name() for constraints on the @name parameter.
 *
 * Free-function: gst_structure_free
 *
 * Returns: (transfer full): a new, empty #GstStructure
 */
GstStructure *
gst_structure_new_empty (const gchar * name)
{
  g_return_val_if_fail (gst_structure_validate_name (name), NULL);

  return gst_structure_new_id_empty_with_size (g_quark_from_string (name), 0);
}

/**
 * gst_structure_new:
 * @name: name of new structure
 * @firstfield: name of first field to set
 * @...: additional arguments
 *
 * Creates a new #GstStructure with the given name.  Parses the
 * list of variable arguments and sets fields to the values listed.
 * Variable arguments should be passed as field name, field type,
 * and value.  Last variable argument should be NULL.
 *
 * Free-function: gst_structure_free
 *
 * Returns: (transfer full): a new #GstStructure
 */
GstStructure *
gst_structure_new (const gchar * name, const gchar * firstfield, ...)
{
  GstStructure *structure;
  va_list varargs;

  va_start (varargs, firstfield);
  structure = gst_structure_new_valist (name, firstfield, varargs);
  va_end (varargs);

  return structure;
}

/**
 * gst_structure_new_valist:
 * @name: name of new structure
 * @firstfield: name of first field to set
 * @varargs: variable argument list
 *
 * Creates a new #GstStructure with the given @name.  Structure fields
 * are set according to the varargs in a manner similar to
 * gst_structure_new().
 *
 * See gst_structure_set_name() for constraints on the @name parameter.
 *
 * Free-function: gst_structure_free
 *
 * Returns: (transfer full): a new #GstStructure
 */
GstStructure *
gst_structure_new_valist (const gchar * name,
    const gchar * firstfield, va_list varargs)
{
  GstStructure *structure;

  structure = gst_structure_new_empty (name);

  if (structure)
    gst_structure_set_valist (structure, firstfield, varargs);

  return structure;
}

/**
 * gst_structure_set_parent_refcount:
 * @structure: a #GstStructure
 * @refcount: (in): a pointer to the parent's refcount
 *
 * Sets the parent_refcount field of #GstStructure. This field is used to
 * determine whether a structure is mutable or not. This function should only be
 * called by code implementing parent objects of #GstStructure, as described in
 * the MT Refcounting section of the design documents.
 *
 * Returns: %TRUE if the parent refcount could be set.
 */
gboolean
gst_structure_set_parent_refcount (GstStructure * structure, gint * refcount)
{
  g_return_val_if_fail (structure != NULL, FALSE);

  /* if we have a parent_refcount already, we can only clear
   * if with a NULL refcount */
  if (GST_STRUCTURE_REFCOUNT (structure)) {
    if (refcount != NULL) {
      g_return_val_if_fail (refcount == NULL, FALSE);
      return FALSE;
    }
  } else {
    if (refcount == NULL) {
      g_return_val_if_fail (refcount != NULL, FALSE);
      return FALSE;
    }
  }

  GST_STRUCTURE_REFCOUNT (structure) = refcount;

  return TRUE;
}

/**
 * gst_structure_copy:
 * @structure: a #GstStructure to duplicate
 *
 * Duplicates a #GstStructure and all its fields and values.
 *
 * Free-function: gst_structure_free
 *
 * Returns: (transfer none): a new #GstStructure.
 */
GstStructure *
gst_structure_copy (const GstStructure * structure)
{
  GstStructure *new_structure;
  GstStructureField *field;
  guint i, len;

  g_return_val_if_fail (structure != NULL, NULL);

  len = GST_STRUCTURE_FIELDS (structure)->len;
  new_structure = gst_structure_new_id_empty_with_size (structure->name, len);

  for (i = 0; i < len; i++) {
    GstStructureField new_field = { 0 };

    field = GST_STRUCTURE_FIELD (structure, i);

    new_field.name = field->name;
    gst_value_init_and_copy (&new_field.value, &field->value);
    g_array_append_val (GST_STRUCTURE_FIELDS (new_structure), new_field);
  }
  GST_CAT_TRACE (GST_CAT_PERFORMANCE, "doing copy %p -> %p",
      structure, new_structure);

  return new_structure;
}

/**
 * gst_structure_free:
 * @structure: (in) (transfer full): the #GstStructure to free
 *
 * Frees a #GstStructure and all its fields and values. The structure must not
 * have a parent when this function is called.
 */
void
gst_structure_free (GstStructure * structure)
{
  GstStructureField *field;
  guint i, len;

  g_return_if_fail (structure != NULL);
  g_return_if_fail (GST_STRUCTURE_REFCOUNT (structure) == NULL);

  len = GST_STRUCTURE_FIELDS (structure)->len;
  for (i = 0; i < len; i++) {
    field = GST_STRUCTURE_FIELD (structure, i);

    if (G_IS_VALUE (&field->value)) {
      g_value_unset (&field->value);
    }
  }
  g_array_free (GST_STRUCTURE_FIELDS (structure), TRUE);
#ifdef USE_POISONING
  memset (structure, 0xff, sizeof (GstStructure));
#endif
  GST_TRACE ("free structure %p", structure);

  g_slice_free1 (sizeof (GstStructureImpl), structure);
}

/**
 * gst_structure_get_name:
 * @structure: a #GstStructure
 *
 * Get the name of @structure as a string.
 *
 * Returns: the name of the structure.
 */
const gchar *
gst_structure_get_name (const GstStructure * structure)
{
  g_return_val_if_fail (structure != NULL, NULL);

  return g_quark_to_string (structure->name);
}

/**
 * gst_structure_has_name:
 * @structure: a #GstStructure
 * @name: structure name to check for
 *
 * Checks if the structure has the given name
 *
 * Returns: TRUE if @name matches the name of the structure.
 */
gboolean
gst_structure_has_name (const GstStructure * structure, const gchar * name)
{
  const gchar *structure_name;

  g_return_val_if_fail (structure != NULL, FALSE);
  g_return_val_if_fail (name != NULL, FALSE);

  /* getting the string is cheap and comparing short strings is too
   * should be faster than getting the quark for name and comparing the quarks
   */
  structure_name = g_quark_to_string (structure->name);

  return (structure_name && strcmp (structure_name, name) == 0);
}

/**
 * gst_structure_get_name_id:
 * @structure: a #GstStructure
 *
 * Get the name of @structure as a GQuark.
 *
 * Returns: the quark representing the name of the structure.
 */
GQuark
gst_structure_get_name_id (const GstStructure * structure)
{
  g_return_val_if_fail (structure != NULL, 0);

  return structure->name;
}

/**
 * gst_structure_set_name:
 * @structure: a #GstStructure
 * @name: the new name of the structure
 *
 * Sets the name of the structure to the given @name.  The string
 * provided is copied before being used. It must not be empty, start with a
 * letter and can be followed by letters, numbers and any of "/-_.:".
 */
void
gst_structure_set_name (GstStructure * structure, const gchar * name)
{
  g_return_if_fail (structure != NULL);
  g_return_if_fail (IS_MUTABLE (structure));
  g_return_if_fail (gst_structure_validate_name (name));

  structure->name = g_quark_from_string (name);
}

static inline void
gst_structure_id_set_value_internal (GstStructure * structure, GQuark field,
    const GValue * value)
{
  GstStructureField gsfield = { 0, {0,} };

  gsfield.name = field;
  gst_value_init_and_copy (&gsfield.value, value);

  gst_structure_set_field (structure, &gsfield);
}

/**
 * gst_structure_id_set_value:
 * @structure: a #GstStructure
 * @field: a #GQuark representing a field
 * @value: the new value of the field
 *
 * Sets the field with the given GQuark @field to @value.  If the field
 * does not exist, it is created.  If the field exists, the previous
 * value is replaced and freed.
 */
void
gst_structure_id_set_value (GstStructure * structure,
    GQuark field, const GValue * value)
{

  g_return_if_fail (structure != NULL);
  g_return_if_fail (G_IS_VALUE (value));
  g_return_if_fail (IS_MUTABLE (structure));

  gst_structure_id_set_value_internal (structure, field, value);
}

/**
 * gst_structure_set_value:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to set
 * @value: the new value of the field
 *
 * Sets the field with the given name @field to @value.  If the field
 * does not exist, it is created.  If the field exists, the previous
 * value is replaced and freed.
 */
void
gst_structure_set_value (GstStructure * structure,
    const gchar * fieldname, const GValue * value)
{
  g_return_if_fail (structure != NULL);
  g_return_if_fail (fieldname != NULL);
  g_return_if_fail (G_IS_VALUE (value));
  g_return_if_fail (IS_MUTABLE (structure));

  gst_structure_id_set_value_internal (structure,
      g_quark_from_string (fieldname), value);
}

static inline void
gst_structure_id_take_value_internal (GstStructure * structure, GQuark field,
    GValue * value)
{
  GstStructureField gsfield = { 0, {0,} };

  gsfield.name = field;
  gsfield.value = *value;

  gst_structure_set_field (structure, &gsfield);

  /* we took ownership */
#ifdef USE_POISONING
  memset (value, 0, sizeof (GValue));
#else
  value->g_type = G_TYPE_INVALID;
#endif
}

/**
 * gst_structure_id_take_value:
 * @structure: a #GstStructure
 * @field: a #GQuark representing a field
 * @value: (transfer full): the new value of the field
 *
 * Sets the field with the given GQuark @field to @value.  If the field
 * does not exist, it is created.  If the field exists, the previous
 * value is replaced and freed.
 *
 * Since: 0.10.31
 */
void
gst_structure_id_take_value (GstStructure * structure, GQuark field,
    GValue * value)
{
  g_return_if_fail (structure != NULL);
  g_return_if_fail (G_IS_VALUE (value));
  g_return_if_fail (IS_MUTABLE (structure));

  gst_structure_id_take_value_internal (structure, field, value);
}

/**
 * gst_structure_take_value:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to set
 * @value: (transfer full): the new value of the field
 *
 * Sets the field with the given name @field to @value.  If the field
 * does not exist, it is created.  If the field exists, the previous
 * value is replaced and freed. The function will take ownership of @value.
 *
 * Since: 0.10.31
 */
void
gst_structure_take_value (GstStructure * structure, const gchar * fieldname,
    GValue * value)
{
  g_return_if_fail (structure != NULL);
  g_return_if_fail (fieldname != NULL);
  g_return_if_fail (G_IS_VALUE (value));
  g_return_if_fail (IS_MUTABLE (structure));

  gst_structure_id_take_value_internal (structure,
      g_quark_from_string (fieldname), value);
}

static void
gst_structure_set_valist_internal (GstStructure * structure,
    const gchar * fieldname, va_list varargs)
{
  gchar *err = NULL;
  GType type;

  while (fieldname) {
    GstStructureField field = { 0 };

    field.name = g_quark_from_string (fieldname);

    type = va_arg (varargs, GType);

    G_VALUE_COLLECT_INIT (&field.value, type, varargs, 0, &err);
    if (G_UNLIKELY (err)) {
      g_critical ("%s", err);
      return;
    }
    gst_structure_set_field (structure, &field);

    fieldname = va_arg (varargs, gchar *);
  }
}

/**
 * gst_structure_set:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to set
 * @...: variable arguments
 *
 * Parses the variable arguments and sets fields accordingly.
 * Variable arguments should be in the form field name, field type
 * (as a GType), value(s).  The last variable argument should be NULL.
 */
void
gst_structure_set (GstStructure * structure, const gchar * field, ...)
{
  va_list varargs;

  g_return_if_fail (structure != NULL);
  g_return_if_fail (IS_MUTABLE (structure) || field == NULL);

  va_start (varargs, field);
  gst_structure_set_valist_internal (structure, field, varargs);
  va_end (varargs);
}

/**
 * gst_structure_set_valist:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to set
 * @varargs: variable arguments
 *
 * va_list form of gst_structure_set().
 */
void
gst_structure_set_valist (GstStructure * structure,
    const gchar * fieldname, va_list varargs)
{
  g_return_if_fail (structure != NULL);
  g_return_if_fail (IS_MUTABLE (structure));

  gst_structure_set_valist_internal (structure, fieldname, varargs);
}

static void
gst_structure_id_set_valist_internal (GstStructure * structure,
    GQuark fieldname, va_list varargs)
{
  gchar *err = NULL;
  GType type;

  while (fieldname) {
    GstStructureField field = { 0 };

    field.name = fieldname;

    type = va_arg (varargs, GType);

#ifndef G_VALUE_COLLECT_INIT
    g_value_init (&field.value, type);
    G_VALUE_COLLECT (&field.value, varargs, 0, &err);
#else
    G_VALUE_COLLECT_INIT (&field.value, type, varargs, 0, &err);
#endif
    if (G_UNLIKELY (err)) {
      g_critical ("%s", err);
      return;
    }
    gst_structure_set_field (structure, &field);

    fieldname = va_arg (varargs, GQuark);
  }
}

/**
 * gst_structure_id_set:
 * @structure: a #GstStructure
 * @fieldname: the GQuark for the name of the field to set
 * @...: variable arguments
 *
 * Identical to gst_structure_set, except that field names are
 * passed using the GQuark for the field name. This allows more efficient
 * setting of the structure if the caller already knows the associated
 * quark values.
 * The last variable argument must be NULL.
 *
 * Since: 0.10.10
 */
void
gst_structure_id_set (GstStructure * structure, GQuark field, ...)
{
  va_list varargs;

  g_return_if_fail (structure != NULL);

  va_start (varargs, field);
  gst_structure_id_set_valist_internal (structure, field, varargs);
  va_end (varargs);
}

/**
 * gst_structure_id_set_valist:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to set
 * @varargs: variable arguments
 *
 * va_list form of gst_structure_id_set().
 *
 * Since: 0.10.10
 */
void
gst_structure_id_set_valist (GstStructure * structure,
    GQuark fieldname, va_list varargs)
{
  g_return_if_fail (structure != NULL);
  g_return_if_fail (IS_MUTABLE (structure));

  gst_structure_id_set_valist_internal (structure, fieldname, varargs);
}

/**
 * gst_structure_new_id:
 * @name_quark: name of new structure
 * @field_quark: the GQuark for the name of the field to set
 * @...: variable arguments
 *
 * Creates a new #GstStructure with the given name as a GQuark, followed by
 * fieldname quark, GType, argument(s) "triplets" in the same format as
 * gst_structure_id_set(). Basically a convenience wrapper around
 * gst_structure_new_id_empty() and gst_structure_id_set().
 *
 * The last variable argument must be NULL (or 0).
 *
 * Free-function: gst_structure_free
 *
 * Returns: (transfer full): a new #GstStructure
 *
 * Since: 0.10.24
 */
GstStructure *
gst_structure_new_id (GQuark name_quark, GQuark field_quark, ...)
{
  GstStructure *s;
  va_list varargs;

  g_return_val_if_fail (name_quark != 0, NULL);
  g_return_val_if_fail (field_quark != 0, NULL);

  s = gst_structure_new_id_empty (name_quark);

  va_start (varargs, field_quark);
  gst_structure_id_set_valist_internal (s, field_quark, varargs);
  va_end (varargs);

  return s;
}

#if GST_VERSION_NANO == 1
#define GIT_G_WARNING g_warning
#else
#define GIT_G_WARNING GST_WARNING
#endif

/* If the structure currently contains a field with the same name, it is
 * replaced with the provided field. Otherwise, the field is added to the
 * structure. The field's value is not deeply copied.
 */
static void
gst_structure_set_field (GstStructure * structure, GstStructureField * field)
{
  GstStructureField *f;
  guint i, len = GST_STRUCTURE_FIELDS (structure)->len;

  if (G_UNLIKELY (G_VALUE_HOLDS_STRING (&field->value))) {
    const gchar *s;

    s = g_value_get_string (&field->value);
    /* only check for NULL strings in taglists, as they are allowed in message
     * structs, e.g. error message debug strings */
    if (G_UNLIKELY (IS_TAGLIST (structure) && (s == NULL || *s == '\0'))) {
      if (s == NULL) {
        GIT_G_WARNING ("Trying to set NULL string on field '%s' on taglist. "
            "Please file a bug.", g_quark_to_string (field->name));
        g_value_unset (&field->value);
        return;
      } else {
        /* empty strings never make sense */
        GIT_G_WARNING ("Trying to set empty string on taglist field '%s'. "
            "Please file a bug.", g_quark_to_string (field->name));
        g_value_unset (&field->value);
        return;
      }
    } else if (G_UNLIKELY (s != NULL && !g_utf8_validate (s, -1, NULL))) {
      g_warning ("Trying to set string on %s field '%s', but string is not "
          "valid UTF-8. Please file a bug.",
          IS_TAGLIST (structure) ? "taglist" : "structure",
          g_quark_to_string (field->name));
      g_value_unset (&field->value);
      return;
    }
  } else if (G_UNLIKELY (G_VALUE_HOLDS (&field->value, G_TYPE_DATE))) {
    const GDate *d;

    d = g_value_get_boxed (&field->value);
    /* only check for NULL GDates in taglists, as they might make sense
     * in other, generic structs */
    if (G_UNLIKELY ((IS_TAGLIST (structure) && d == NULL))) {
      GIT_G_WARNING ("Trying to set NULL GDate on field '%s' on taglist. "
          "Please file a bug.", g_quark_to_string (field->name));
      g_value_unset (&field->value);
      return;
    } else if (G_UNLIKELY (d != NULL && !g_date_valid (d))) {
      g_warning
          ("Trying to set invalid GDate on %s field '%s'. Please file a bug.",
          IS_TAGLIST (structure) ? "taglist" : "structure",
          g_quark_to_string (field->name));
      g_value_unset (&field->value);
      return;
    }
  }

  for (i = 0; i < len; i++) {
    f = GST_STRUCTURE_FIELD (structure, i);

    if (G_UNLIKELY (f->name == field->name)) {
      g_value_unset (&f->value);
      memcpy (f, field, sizeof (GstStructureField));
      return;
    }
  }

  g_array_append_val (GST_STRUCTURE_FIELDS (structure), *field);
}

/* If there is no field with the given ID, NULL is returned.
 */
static GstStructureField *
gst_structure_id_get_field (const GstStructure * structure, GQuark field_id)
{
  GstStructureField *field;
  guint i, len;

  len = GST_STRUCTURE_FIELDS (structure)->len;

  for (i = 0; i < len; i++) {
    field = GST_STRUCTURE_FIELD (structure, i);

    if (G_UNLIKELY (field->name == field_id))
      return field;
  }

  return NULL;
}

/* If there is no field with the given ID, NULL is returned.
 */
static GstStructureField *
gst_structure_get_field (const GstStructure * structure,
    const gchar * fieldname)
{
  g_return_val_if_fail (structure != NULL, NULL);
  g_return_val_if_fail (fieldname != NULL, NULL);

  return gst_structure_id_get_field (structure,
      g_quark_from_string (fieldname));
}

/**
 * gst_structure_get_value:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to get
 *
 * Get the value of the field with name @fieldname.
 *
 * Returns: the #GValue corresponding to the field with the given name.
 */
const GValue *
gst_structure_get_value (const GstStructure * structure,
    const gchar * fieldname)
{
  GstStructureField *field;

  g_return_val_if_fail (structure != NULL, NULL);
  g_return_val_if_fail (fieldname != NULL, NULL);

  field = gst_structure_get_field (structure, fieldname);
  if (field == NULL)
    return NULL;

  return &field->value;
}

/**
 * gst_structure_id_get_value:
 * @structure: a #GstStructure
 * @field: the #GQuark of the field to get
 *
 * Get the value of the field with GQuark @field.
 *
 * Returns: the #GValue corresponding to the field with the given name
 *          identifier.
 */
const GValue *
gst_structure_id_get_value (const GstStructure * structure, GQuark field)
{
  GstStructureField *gsfield;

  g_return_val_if_fail (structure != NULL, NULL);

  gsfield = gst_structure_id_get_field (structure, field);
  if (gsfield == NULL)
    return NULL;

  return &gsfield->value;
}

/**
 * gst_structure_remove_field:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to remove
 *
 * Removes the field with the given name.  If the field with the given
 * name does not exist, the structure is unchanged.
 */
void
gst_structure_remove_field (GstStructure * structure, const gchar * fieldname)
{
  GstStructureField *field;
  GQuark id;
  guint i, len;

  g_return_if_fail (structure != NULL);
  g_return_if_fail (fieldname != NULL);
  g_return_if_fail (IS_MUTABLE (structure));

  id = g_quark_from_string (fieldname);
  len = GST_STRUCTURE_FIELDS (structure)->len;

  for (i = 0; i < len; i++) {
    field = GST_STRUCTURE_FIELD (structure, i);

    if (field->name == id) {
      if (G_IS_VALUE (&field->value)) {
        g_value_unset (&field->value);
      }
      GST_STRUCTURE_FIELDS (structure) =
          g_array_remove_index (GST_STRUCTURE_FIELDS (structure), i);
      return;
    }
  }
}

/**
 * gst_structure_remove_fields:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to remove
 * @...: NULL-terminated list of more fieldnames to remove
 *
 * Removes the fields with the given names. If a field does not exist, the
 * argument is ignored.
 */
void
gst_structure_remove_fields (GstStructure * structure,
    const gchar * fieldname, ...)
{
  va_list varargs;

  g_return_if_fail (structure != NULL);
  g_return_if_fail (fieldname != NULL);
  /* mutability checked in remove_field */

  va_start (varargs, fieldname);
  gst_structure_remove_fields_valist (structure, fieldname, varargs);
  va_end (varargs);
}

/**
 * gst_structure_remove_fields_valist:
 * @structure: a #GstStructure
 * @fieldname: the name of the field to remove
 * @varargs: NULL-terminated list of more fieldnames to remove
 *
 * va_list form of gst_structure_remove_fields().
 */
void
gst_structure_remove_fields_valist (GstStructure * structure,
    const gchar * fieldname, va_list varargs)
{
  gchar *field = (gchar *) fieldname;

  g_return_if_fail (structure != NULL);
  g_return_if_fail (fieldname != NULL);
  /* mutability checked in remove_field */

  while (field) {
    gst_structure_remove_field (structure, field);
    field = va_arg (varargs, char *);
  }
}

/**
 * gst_structure_remove_all_fields:
 * @structure: a #GstStructure
 *
 * Removes all fields in a GstStructure.
 */
void
gst_structure_remove_all_fields (GstStructure * structure)
{
  GstStructureField *field;
  int i;

  g_return_if_fail (structure != NULL);
  g_return_if_fail (IS_MUTABLE (structure));

  for (i = GST_STRUCTURE_FIELDS (structure)->len - 1; i >= 0; i--) {
    field = GST_STRUCTURE_FIELD (structure, i);

    if (G_IS_VALUE (&field->value)) {
      g_value_unset (&field->value);
    }
    GST_STRUCTURE_FIELDS (structure) =
        g_array_remove_index (GST_STRUCTURE_FIELDS (structure), i);
  }
}

/**
 * gst_structure_get_field_type:
 * @structure: a #GstStructure
 * @fieldname: the name of the field
 *
 * Finds the field with the given name, and returns the type of the
 * value it contains.  If the field is not found, G_TYPE_INVALID is
 * returned.
 *
 * Returns: the #GValue of the field
 */
GType
gst_structure_get_field_type (const GstStructure * structure,
    const gchar * fieldname)
{
  GstStructureField *field;

  g_return_val_if_fail (structure != NULL, G_TYPE_INVALID);
  g_return_val_if_fail (fieldname != NULL, G_TYPE_INVALID);