gst: Add GstIdStr for holding structure names and field names

This is an efficient string storage for short strings without heap allocations,
and falling back to the heap for bigger allocations. Almost all structure fields
and structure names in use nowadays are short enough to not require a heap
allocation.

As structure names and fields are sometimes dynamically created, storing them in
a GQuark can create a memory leak and potentially a DoS attack by continously
triggering creating of new quarks.

Thanks to Tim for coming up with the name!

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7432>

8 files changed, 968 insertions, 0 deletions

diff --git a/subprojects/gstreamer/gst/gst.h b/subprojects/gstreamer/gst/gst.h
index e599bbe6a5..7cb55a0715 100644
--- a/subprojects/gstreamer/gst/gst.h
+++ b/subprojects/gstreamer/gst/gst.h
@@ -53,6 +53,7 @@
 #include <gst/gsterror.h>
 #include <gst/gstevent.h>
 #include <gst/gstghostpad.h>
+#include <gst/gstidstr.h>
 #include <gst/gstinfo.h>
 #include <gst/gstiterator.h>
 #include <gst/gstmessage.h>
diff --git a/subprojects/gstreamer/gst/gstidstr-private.h b/subprojects/gstreamer/gst/gstidstr-private.h
new file mode 100644
index 0000000000..7b749408de
--- /dev/null
+++ b/subprojects/gstreamer/gst/gstidstr-private.h
@@ -0,0 +1,288 @@
+/* GStreamer
+ *
+ * Copyright (C) 2024 Sebastian Dröge <sebastian@centricular.com>
+ *
+ * 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., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __GST_ID_STR_PRIVATE_H__
+#define __GST_ID_STR_PRIVATE_H__
+
+#include <gst/gstconfig.h>
+#include <gst/gstidstr.h>
+#include <glib-object.h>
+#include <string.h>
+
+G_BEGIN_DECLS
+
+typedef struct {
+  /* < private > */
+  union {
+    struct {
+      guint8 padding[15];
+      // t == 0: Inline-allocated short_string
+      // t == 1: Heap-allocated pointer_string that needs freeing
+      // t == 2: Statically allocated pointer_string that needs no freeing
+      guint8 t;
+    } string_type;
+    struct {
+      gchar s[16];
+      // t == 0 is the NUL terminator
+    } short_string;
+    struct {
+      gchar *s;           // to be freed if t == 1
+      guint32 len;       // Length of the string without NUL-terminator
+#if GLIB_SIZEOF_VOID_P == 8
+      guint8 padding[3]; // always zero
+#elif GLIB_SIZEOF_VOID_P == 4
+      guint8 padding[7]; // always zero
+#else
+  #error "Only 32 bit and 64 bit pointers supported currently"
+#endif
+      guint8 t; // always 1 or 2, see above
+    } pointer_string;
+  } s;
+} GstIdStrPrivate;
+
+static inline void
+_gst_id_str_init_inline (GstIdStr * s)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+  memset (sp, 0, sizeof (*sp));
+}
+
+static inline gsize
+_gst_id_str_get_len (const GstIdStr * s)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+
+  switch (sp->s.string_type.t) {
+    case 0:
+      return strlen (sp->s.short_string.s);
+    case 1:
+    case 2:
+      return sp->s.pointer_string.len;
+    default:
+      g_assert_not_reached ();
+      return 0;
+  }
+}
+
+static inline void
+_gst_id_str_set_with_len_inline (GstIdStr * s, const gchar * value, gsize len)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+
+  g_assert (len <= G_MAXUINT32);
+
+  if (sp->s.string_type.t == 1) {
+    if (sp->s.pointer_string.s == value)
+      return;
+    g_free (sp->s.pointer_string.s);
+  }
+
+  if (len <= 15) {
+    memcpy (sp->s.short_string.s, value, len);
+    memset (&sp->s.short_string.s[len], 0, 16 - len);
+  } else {
+    sp->s.pointer_string.t = 1;
+    sp->s.pointer_string.len = len;
+    sp->s.pointer_string.s = (gchar *) g_malloc (len + 1);
+    memcpy (sp->s.pointer_string.s, value, len);
+    sp->s.pointer_string.s[len] = '\0';
+  }
+}
+
+static inline void
+_gst_id_str_set_inline (GstIdStr * s, const gchar * value)
+{
+  gsize len = strlen (value);
+  _gst_id_str_set_with_len_inline (s, value, len);
+}
+
+static inline void
+_gst_id_str_set_static_str_with_len_inline (GstIdStr * s, const gchar * value, gsize len)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+
+  g_assert (len <= G_MAXUINT32);
+
+  if (sp->s.string_type.t == 1)
+    g_free (sp->s.pointer_string.s);
+
+  if (len <= 15) {
+    memcpy (sp->s.short_string.s, value, len);
+    memset (&sp->s.short_string.s[len], 0, 16 - len);
+  } else {
+    sp->s.pointer_string.t = 2;
+    sp->s.pointer_string.len = len;
+    sp->s.pointer_string.s = (gchar *) value;
+  }
+}
+
+static inline void
+_gst_id_str_set_static_str_inline (GstIdStr * s, const gchar * value)
+{
+  gsize len = strlen (value);
+  _gst_id_str_set_static_str_with_len_inline (s, value, len);
+}
+
+static inline void
+_gst_id_str_clear_inline (GstIdStr * s)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+
+  if (sp->s.string_type.t == 1) {
+    g_free (sp->s.pointer_string.s);
+  }
+  memset (sp, 0, sizeof (*sp));
+}
+
+static inline void
+_gst_id_str_copy_into_inline (GstIdStr * d,
+    const GstIdStr * s)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+  GstIdStrPrivate *dp = (GstIdStrPrivate *) d;
+
+  _gst_id_str_clear_inline (d);
+
+  *dp = *sp;
+  if (dp->s.string_type.t == 1) {
+#if GLIB_CHECK_VERSION (2, 68, 0)
+      dp->s.pointer_string.s = (gchar *) g_memdup2 (dp->s.pointer_string.s, dp->s.pointer_string.len + 1);
+#else
+      dp->s.pointer_string.s = (gchar *) g_memdup (dp->s.pointer_string.s, dp->s.pointer_string.len + 1);
+#endif
+  }
+}
+
+static inline void
+_gst_id_str_move_inline (GstIdStr * d,
+    GstIdStr * s)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+  GstIdStrPrivate *dp = (GstIdStrPrivate *) d;
+
+  _gst_id_str_clear_inline (d);
+
+  memcpy (dp, s, sizeof (*sp));
+  memset (sp, 0, sizeof (*sp));
+}
+
+static inline GstIdStr *
+_gst_id_str_new_inline (void)
+{
+  return (GstIdStr *) g_new0 (GstIdStrPrivate, 1);
+}
+
+static inline GstIdStr *
+_gst_id_str_copy_inline (const GstIdStr * s)
+{
+  GstIdStr *copy = _gst_id_str_new_inline ();
+
+  _gst_id_str_copy_into_inline (copy, s);
+
+  return copy;
+}
+
+static inline void
+_gst_id_str_free_inline (GstIdStr * s)
+{
+  _gst_id_str_clear_inline (s);
+  g_free (s);
+}
+
+static inline const gchar *
+_gst_id_str_as_str_inline (const GstIdStr * s)
+{
+  GstIdStrPrivate *sp = (GstIdStrPrivate *) s;
+
+  switch (sp->s.string_type.t) {
+    case 0:
+      return sp->s.short_string.s;
+    case 1:
+    case 2:
+      return sp->s.pointer_string.s;
+    default:
+      g_assert_not_reached ();
+      return NULL;
+  }
+}
+
+static inline gboolean
+_gst_id_str_is_equal_inline (const GstIdStr * s1,
+    const GstIdStr * s2)
+{
+  GstIdStrPrivate *sp1 = (GstIdStrPrivate *) s1;
+  GstIdStrPrivate *sp2 = (GstIdStrPrivate *) s2;
+
+  // Covers the short_string case and equal pointer_string pointers
+  if (sp1 == sp2 || memcmp (sp1, sp2, sizeof (*sp1)) == 0)
+    return TRUE;
+
+  // If one of the strings is a short_string then they can't be equal at this
+  // point: either they're both short_strings and not the same, or one is a
+  // short_string and the other a pointer_string which would mean that they have
+  // different lengths.
+  if (sp1->s.string_type.t == 0 || sp2->s.string_type.t == 0)
+    return FALSE;
+
+  // Otherwise they're both pointer_strings
+  if (sp1->s.pointer_string.len != sp2->s.pointer_string.len)
+    return FALSE;
+  return memcmp (sp1->s.pointer_string.s, sp2->s.pointer_string.s, sp1->s.pointer_string.len) == 0;
+}
+
+static inline gboolean
+_gst_id_str_is_equal_to_str_inline (const GstIdStr * s1,
+    const gchar * s2)
+{
+  return strcmp (_gst_id_str_as_str_inline (s1), s2) == 0;
+}
+
+static inline gboolean
+_gst_id_str_is_equal_to_str_with_len_inline (const GstIdStr * s1,
+    const gchar * s2, gsize len)
+{
+  GstIdStr s2_int = GST_ID_STR_INIT;
+
+  _gst_id_str_set_static_str_with_len_inline (&s2_int, s2, len);
+  return _gst_id_str_is_equal_inline (s1, &s2_int);
+}
+
+#ifndef GST_ID_STR_DISABLE_INLINES
+#define gst_id_str_init(s) _gst_id_str_init_inline(s)
+#define gst_id_str_get_len(s) _gst_id_str_get_len(s)
+#define gst_id_str_set(s, value) _gst_id_str_set_inline(s, value)
+#define gst_id_str_set_with_len(s, value, len) _gst_id_str_set_with_len_inline(s, value, len)
+#define gst_id_str_set_static_str(s, value) _gst_id_str_set_static_str_inline(s, value)
+#define gst_id_str_set_static_str_with_len(s, value, len) _gst_id_str_set_static_str_with_len_inline(s, value, len)
+#define gst_id_str_clear(s) _gst_id_str_clear_inline(s)
+#define gst_id_str_copy(s) _gst_id_str_copy_inline(s)
+#define gst_id_str_new() _gst_id_str_new_inline()
+#define gst_id_str_free(s) _gst_id_str_free_inline(s)
+#define gst_id_str_copy_into(d, s) _gst_id_str_copy_into_inline(d, s)
+#define gst_id_str_move(d, s) _gst_id_str_move_inline(d, s)
+#define gst_id_str_is_equal(s1, s2) _gst_id_str_is_equal_inline(s1, s2)
+#define gst_id_str_is_equal_to_str(s1, s2) _gst_id_str_is_equal_to_str_inline(s1, s2)
+#define gst_id_str_is_equal_to_str_with_len(s1, s2, len) _gst_id_str_is_equal_to_str_with_len_inline(s1, s2, len)
+#define gst_id_str_as_str(s) _gst_id_str_as_str_inline(s)
+#endif
+
+G_END_DECLS
+
+#endif
diff --git a/subprojects/gstreamer/gst/gstidstr.c b/subprojects/gstreamer/gst/gstidstr.c
new file mode 100644
index 0000000000..9e3674aa34
--- /dev/null
+++ b/subprojects/gstreamer/gst/gstidstr.c
@@ -0,0 +1,331 @@
+/* GStreamer
+ *
+ * Copyright (C) 2024 Sebastian Dröge <sebastian@centricular.com>
+ *
+ * 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., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+/**
+ * SECTION:gstidstr
+ * @title: GstIdStr
+ * @short_description: String type optimized for short strings
+ * @see_also: #GstStructure
+ *
+ * A #GstIdStr is string type optimized for short strings and used for structure
+ * names, structure field names and in other places.
+ *
+ * Strings up to 16 bytes (including NUL terminator) are stored inline, other
+ * strings are stored on the heap.
+ *
+ * ```cpp
+ * GstIdStr s = GST_ID_STR_INIT;
+ *
+ * gst_id_str_set (&s, "Hello, World!");
+ * g_print ("%s\n", gst_id_str_as_str (&s));
+ *
+ * gst_id_str_clear (&s);
+ * ```
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#define GST_ID_STR_DISABLE_INLINES
+
+#include "gstidstr.h"
+#include "gstidstr-private.h"
+
+G_DEFINE_BOXED_TYPE (GstIdStr, gst_id_str, gst_id_str_copy, gst_id_str_free);
+
+// Make sure the string type fields are in the same place for each variant
+// See https://developercommunity.visualstudio.com/t/C-offsetof-an-array-item-is-accepted-by/10736612
+#ifndef _MSC_VER
+G_STATIC_ASSERT (G_STRUCT_OFFSET (GstIdStrPrivate,
+        s.string_type.t) == G_STRUCT_OFFSET (GstIdStrPrivate,
+        s.short_string.s[15]));
+#endif
+G_STATIC_ASSERT (G_STRUCT_OFFSET (GstIdStrPrivate,
+        s.string_type.t) == G_STRUCT_OFFSET (GstIdStrPrivate,
+        s.pointer_string.t));
+// The overall struct should be 16 bytes large and at least pointer aligned
+G_STATIC_ASSERT (sizeof (GstIdStrPrivate) == 16);
+// See https://developercommunity.visualstudio.com/t/C-offsetof-an-array-item-is-accepted-by/10736612
+#ifndef _MSC_VER
+G_STATIC_ASSERT (G_ALIGNOF (GstIdStrPrivate) >= G_ALIGNOF (gpointer));
+// Alignment and size of the private and public type must be the same
+G_STATIC_ASSERT (G_ALIGNOF (GstIdStrPrivate) == G_ALIGNOF (GstIdStr));
+#endif
+G_STATIC_ASSERT (sizeof (GstIdStrPrivate) == sizeof (GstIdStr));
+
+/**
+ * gst_id_str_init:
+ * @s: A %GstIdStr
+ *
+ * Initializes a (usually stack-allocated) id string @s. The newly-initialized
+ * id string will contain an empty string by default as value.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_init (GstIdStr * s)
+{
+  _gst_id_str_init_inline (s);
+}
+
+/**
+ * gst_id_str_get_len:
+ * @s: A %GstIdStr
+ *
+ * Returns the length of @s, exluding the NUL-terminator. This is equivalent to
+ * calling `strcmp()` but potentially faster.
+ *
+ * Since: 1.26
+ */
+gsize
+gst_id_str_get_len (const GstIdStr * s)
+{
+  return _gst_id_str_get_len (s);
+}
+
+/**
+ * gst_id_str_set:
+ * @s: A %GstIdStr
+ * @value: A NUL-terminated string
+ *
+ * Sets @s to the string @value.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_set (GstIdStr * s, const gchar * value)
+{
+  _gst_id_str_set_inline (s, value);
+}
+
+/**
+ * gst_id_str_set_with_len:
+ * @s: A %GstIdStr
+ * @value: A string
+ * @len: Length of the string
+ *
+ * Sets @s to the string @value of length @len. @value does not have to be
+ * NUL-terminated and @len should not include the NUL-terminator.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_set_with_len (GstIdStr * s, const gchar * value, gsize len)
+{
+  _gst_id_str_set_with_len_inline (s, value, len);
+}
+
+/**
+ * gst_id_str_set_static_str:
+ * @s: A %GstIdStr
+ * @value: A NUL-terminated string
+ *
+ * Sets @s to the string @value. @value needs to be valid for the remaining
+ * lifetime of the process, e.g. has to be a static string.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_set_static_str (GstIdStr * s, const gchar * value)
+{
+  _gst_id_str_set_static_str_inline (s, value);
+}
+
+/**
+ * gst_id_str_set_static_str_with_len:
+ * @s: A %GstIdStr
+ * @value: A string
+ * @len: Length of the string
+ *
+ * Sets @s to the string @value of length @len. @value needs to be valid for the
+ * remaining lifetime of the process, e.g. has to be a static string.
+ *
+ * @value does not have to be NUL-terminated and @len should not include the
+ * NUL-terminator.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_set_static_str_with_len (GstIdStr * s, const gchar * value,
+    gsize len)
+{
+  _gst_id_str_set_static_str_with_len_inline (s, value, len);
+}
+
+/**
+ * gst_id_str_clear:
+ * @s: A %GstIdStr
+ *
+ * Clears @s and sets it to the empty string.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_clear (GstIdStr * s)
+{
+  _gst_id_str_clear_inline (s);
+}
+
+/**
+ * gst_id_str_copy:
+ * @s: A %GstIdStr
+ *
+ * Copies @s into newly allocated heap memory.
+ *
+ * Returns: (transfer full): A heap-allocated copy of @s.
+ *
+ * Since: 1.26
+ */
+GstIdStr *
+gst_id_str_copy (const GstIdStr * s)
+{
+  return _gst_id_str_copy_inline (s);
+}
+
+/**
+ * gst_id_str_new:
+ *
+ * Returns a newly heap allocated empty string.
+ *
+ * Returns: (transfer full): A heap-allocated string.
+ *
+ * Since: 1.26
+ */
+GstIdStr *
+gst_id_str_new (void)
+{
+  return _gst_id_str_new_inline ();
+}
+
+/**
+ * gst_id_str_free:
+ * @s: A heap allocated %GstIdStr
+ *
+ * Frees @s. This should only be called for heap-allocated #GstIdStr.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_free (GstIdStr * s)
+{
+  _gst_id_str_free_inline (s);
+}
+
+/**
+ * gst_id_str_copy_into:
+ * @d: The destination %GstIdStr
+ * @s: The source %GstIdStr
+ *
+ * Copies @s into @d.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_copy_into (GstIdStr * d, const GstIdStr * s)
+{
+  _gst_id_str_copy_into_inline (d, s);
+}
+
+/**
+ * gst_id_str_move:
+ * @d: The destination %GstIdStr
+ * @s: The source %GstIdStr
+ *
+ * Moves @s into @d and resets @s.
+ *
+ * Since: 1.26
+ */
+void
+gst_id_str_move (GstIdStr * d, GstIdStr * s)
+{
+  _gst_id_str_move_inline (d, s);
+}
+
+/**
+ * gst_id_str_is_equal:
+ * @s1: A %GstIdStr
+ * @s2: A %GstIdStr
+ *
+ * Compares @s1 and @s2 for equality.
+ *
+ * Returns: %TRUE if @s1 and @s2 are equal.
+ *
+ * Since: 1.26
+ */
+gboolean
+gst_id_str_is_equal (const GstIdStr * s1, const GstIdStr * s2)
+{
+  return _gst_id_str_is_equal_inline (s1, s2);
+}
+
+/**
+ * gst_id_str_is_equal_to_str:
+ * @s1: A %GstIdStr
+ * @s2: A string
+ *
+ * Compares @s1 and @s2 for equality.
+ *
+ * Returns: %TRUE if @s1 and @s2 are equal.
+ *
+ * Since: 1.26
+ */
+gboolean
+gst_id_str_is_equal_to_str (const GstIdStr * s1, const gchar * s2)
+{
+  return _gst_id_str_is_equal_to_str_inline (s1, s2);
+}
+
+/**
+ * gst_id_str_is_equal_to_str_with_len:
+ * @s1: A %GstIdStr
+ * @s2: A string
+ * @len: Length of @s2.
+ *
+ * Compares @s1 and @s2 with length @len for equality. @s2 does not have to be
+ * NUL-terminated and @len should not include the NUL-terminator.
+ *
+ * This is generally faster than gst_id_str_is_equal_to_str() if the length is
+ * already known.
+ *
+ * Returns: %TRUE if @s1 and @s2 are equal.
+ *
+ * Since: 1.26
+ */
+gboolean
+gst_id_str_is_equal_to_str_with_len (const GstIdStr * s1, const gchar * s2,
+    gsize len)
+{
+  return _gst_id_str_is_equal_to_str_with_len_inline (s1, s2, len);
+}
+
+/**
+ * gst_id_str_as_str:
+ * @s: A %GstIdStr
+ *
+ * Returns: the NUL-terminated string representation of @s.
+ *
+ * Since: 1.26
+ */
+const gchar *
+gst_id_str_as_str (const GstIdStr * s)
+{
+  return _gst_id_str_as_str_inline (s);
+}
diff --git a/subprojects/gstreamer/gst/gstidstr.h b/subprojects/gstreamer/gst/gstidstr.h
new file mode 100644
index 0000000000..1bf951e52c
--- /dev/null
+++ b/subprojects/gstreamer/gst/gstidstr.h
@@ -0,0 +1,114 @@
+/* GStreamer
+ *
+ * Copyright (C) 2024 Sebastian Dröge <sebastian@centricular.com>
+ *
+ * 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., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __GST_ID_STR_H__
+#define __GST_ID_STR_H__
+
+#include <gst/gstconfig.h>
+#include <glib-object.h>
+
+G_BEGIN_DECLS
+
+/**
+ * GstIdStr:
+ *
+ * String type optimized for short strings.
+ *
+ * Strings are usually stack- or inline-allocated, and for short strings smaller
+ * than 16 bytes (including NUL terminator) no heap allocations are performed.
+ *
+ * Since: 1.26
+ */
+typedef struct {
+  /* < private > */
+  gpointer pointer;
+#if GLIB_SIZEOF_VOID_P == 8
+  guint8 padding[8];
+#elif GLIB_SIZEOF_VOID_P == 4
+  guint8 padding[12];
+#else
+  #error "Only 32 bit and 64 bit pointers supported currently"
+#endif
+} GstIdStr;
+
+/**
+ * GST_ID_STR_INIT:
+ *
+ * Initializer for #GstIdStr.
+ *
+ * Since: 1.26
+ */
+#define GST_ID_STR_INIT { .pointer = NULL, .padding = {0, } }
+
+GST_API
+GType gst_id_str_get_type (void);
+
+GST_API
+gsize gst_id_str_get_len (const GstIdStr *s) G_GNUC_PURE;
+
+GST_API
+void gst_id_str_set (GstIdStr *s, const gchar *value);
+
+GST_API
+void gst_id_str_set_with_len (GstIdStr *s, const gchar *value, gsize len);
+
+GST_API
+void gst_id_str_set_static_str (GstIdStr *s, const gchar *value);
+
+GST_API
+void gst_id_str_set_static_str_with_len (GstIdStr *s, const gchar *value, gsize len);
+
+GST_API
+void gst_id_str_init (GstIdStr *s);
+
+GST_API
+void gst_id_str_clear (GstIdStr *s);
+
+GST_API
+GstIdStr * gst_id_str_new (void) G_GNUC_MALLOC;
+
+GST_API
+GstIdStr * gst_id_str_copy (const GstIdStr *s) G_GNUC_MALLOC;
+
+GST_API
+void gst_id_str_free (GstIdStr *s);
+
+GST_API
+void gst_id_str_copy_into (GstIdStr *d, const GstIdStr *s);
+
+GST_API
+void gst_id_str_move (GstIdStr *d, GstIdStr *s);
+
+GST_API
+const gchar * gst_id_str_as_str (const GstIdStr *s) G_GNUC_PURE;
+
+GST_API
+gboolean gst_id_str_is_equal (const GstIdStr *s1, const GstIdStr *s2) G_GNUC_PURE;
+
+GST_API
+gboolean gst_id_str_is_equal_to_str (const GstIdStr *s1, const gchar *s2) G_GNUC_PURE;
+
+GST_API
+gboolean gst_id_str_is_equal_to_str_with_len (const GstIdStr *s1, const gchar *s2, gsize len) G_GNUC_PURE;
+
+G_END_DECLS
+
+#endif
+
diff --git a/subprojects/gstreamer/gst/meson.build b/subprojects/gstreamer/gst/meson.build
index bc77e50a20..15dbf3a004 100644
--- a/subprojects/gstreamer/gst/meson.build
+++ b/subprojects/gstreamer/gst/meson.build
@@ -27,6 +27,7 @@ gst_sources = files(
   'gstformat.c',
   'gstghostpad.c',
   'gstdevicemonitor.c',
+  'gstidstr.c',
   'gstinfo.c',
   'gstiterator.c',
   'gstatomicqueue.c',
@@ -106,6 +107,7 @@ gst_headers = files(
   'gstformat.h',
   'gstghostpad.h',
   'gstdevicemonitor.h',
+  'gstidstr.h',
   'gstinfo.h',
   'gstiterator.h',
   'gstatomicqueue.h',
diff --git a/subprojects/gstreamer/tests/check/gst/gstidstr-noinline.c b/subprojects/gstreamer/tests/check/gst/gstidstr-noinline.c
new file mode 100644
index 0000000000..5a221f10f6
--- /dev/null
+++ b/subprojects/gstreamer/tests/check/gst/gstidstr-noinline.c
@@ -0,0 +1,22 @@
+/* GStreamer
+ *
+ * Copyright (C) 2024 Sebastian Dröge <sebastian@centricular.com>
+ *
+ * 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., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#define GST_ID_STR_DISABLE_INLINES
+#include "gstidstr.c"
diff --git a/subprojects/gstreamer/tests/check/gst/gstidstr.c b/subprojects/gstreamer/tests/check/gst/gstidstr.c
new file mode 100644
index 0000000000..b902c70d62
--- /dev/null
+++ b/subprojects/gstreamer/tests/check/gst/gstidstr.c
@@ -0,0 +1,208 @@
+/* GStreamer
+ *
+ * unit test for GstIdStr
+ *
+ * Copyright (C) 2024 Sebastian Dröge <sebastian@centricular.com>
+ *
+ * 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., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/gst.h>
+#include <gst/check/gstcheck.h>
+#include "gst/gstidstr-private.h"
+
+#define GST_ID_STR_PRIVATE(s) ((GstIdStrPrivate *)s)
+
+GST_START_TEST (test_init)
+{
+  GstIdStr s = GST_ID_STR_INIT;
+  GstIdStr s2 = GST_ID_STR_INIT;
+  const gchar short_without_nul[] =
+      { 'H', 'e', 'l', 'l', 'o', ',', ' ', 'W', 'o', 'r', 'l', 'd', '!' };
+  const gchar long_without_nul[] =
+      { 'H', 'e', 'l', 'l', 'o', ',', ' ', 'W', 'o', 'r', 'l', 'd', '!', ' ',
+    'G', 'o', 'o', 'd', 'b', 'y', 'e', ',', ' ', 'W', 'o', 'r', 'l', 'd',
+    '!'
+  };
+
+  fail_unless_equals_string (gst_id_str_as_str (&s), "");
+  fail_unless_equals_int (gst_id_str_get_len (&s), 0);
+
+  // Should be stack allocated
+  gst_id_str_set (&s, "Hello, World!");
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (&s)->s.string_type.t, 0);
+  fail_unless_equals_string (gst_id_str_as_str (&s), "Hello, World!");
+  fail_unless_equals_int (gst_id_str_get_len (&s), 13);
+
+  gst_id_str_set_with_len (&s2, short_without_nul, sizeof (short_without_nul));
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (&s2)->s.string_type.t, 0);
+  fail_unless_equals_string (gst_id_str_as_str (&s2), "Hello, World!");
+  fail_unless (gst_id_str_is_equal (&s, &s2));
+  fail_unless_equals_int (gst_id_str_get_len (&s2), 13);
+
+  // Should become the empty string again
+  gst_id_str_clear (&s);
+  fail_unless_equals_string (gst_id_str_as_str (&s), "");
+  fail_unless_equals_int (gst_id_str_get_len (&s), 0);
+
+  // Should be heap allocated
+  gst_id_str_set (&s, "Hello, World! Goodbye, World!");
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (&s)->s.string_type.t, 1);
+  fail_unless_equals_string (gst_id_str_as_str (&s),
+      "Hello, World! Goodbye, World!");
+  fail_unless_equals_int (gst_id_str_get_len (&s), 29);
+
+  gst_id_str_set_with_len (&s2, long_without_nul, sizeof (long_without_nul));
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (&s2)->s.string_type.t, 1);
+  fail_unless_equals_string (gst_id_str_as_str (&s2),
+      "Hello, World! Goodbye, World!");
+  fail_unless (gst_id_str_is_equal (&s, &s2));
+  fail_unless_equals_int (gst_id_str_get_len (&s2), 29);
+
+  // Should become the empty string again
+  gst_id_str_clear (&s);
+  fail_unless_equals_string (gst_id_str_as_str (&s), "");
+  fail_unless_equals_int (gst_id_str_get_len (&s), 0);
+  gst_id_str_clear (&s2);
+  fail_unless_equals_string (gst_id_str_as_str (&s2), "");
+  fail_unless_equals_int (gst_id_str_get_len (&s2), 0);
+}
+
+GST_END_TEST;
+
+GST_START_TEST (test_alloc)
+{
+  GstIdStr *s = gst_id_str_new ();
+  GstIdStr *copy;
+
+  fail_unless_equals_string (gst_id_str_as_str (s), "");
+
+  // Should be stack allocated
+  gst_id_str_set (s, "Hello, World!");
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (s)->s.string_type.t, 0);
+  fail_unless_equals_string (gst_id_str_as_str (s), "Hello, World!");
+
+  // Should be a full copy
+  copy = gst_id_str_copy (s);
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (copy)->s.string_type.t, 0);
+  fail_unless_equals_string (gst_id_str_as_str (copy), "Hello, World!");
+  // Strings are the same, but pointers should be different because the strings should be inlined
+  fail_unless_equals_string (gst_id_str_as_str (s), gst_id_str_as_str (copy));
+  fail_unless (gst_id_str_as_str (s) != gst_id_str_as_str (copy));
+  gst_id_str_free (copy);
+
+  // Should become the empty string again
+  gst_id_str_clear (s);
+  fail_unless_equals_string (gst_id_str_as_str (s), "");
+
+  // Should be heap allocated
+  gst_id_str_set (s, "Hello, World! Goodbye, World!");
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (s)->s.string_type.t, 1);
+  fail_unless_equals_string (gst_id_str_as_str (s),
+      "Hello, World! Goodbye, World!");
+
+  // Should be a full copy
+  copy = gst_id_str_copy (s);
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (copy)->s.string_type.t, 1);
+  fail_unless_equals_string (gst_id_str_as_str (copy),
+      "Hello, World! Goodbye, World!");
+  gst_id_str_free (copy);
+
+  // Should be stored by pointer but not heap allocated
+  gst_id_str_set_static_str (s, "Hello, World! Goodbye, World!");
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (s)->s.string_type.t, 2);
+  fail_unless_equals_string (gst_id_str_as_str (s),
+      "Hello, World! Goodbye, World!");
+
+  // Should be a shallow copy because it's a static string
+  copy = gst_id_str_copy (s);
+  fail_unless_equals_int (GST_ID_STR_PRIVATE (copy)->s.string_type.t, 2);
+  fail_unless_equals_string (gst_id_str_as_str (copy),
+      "Hello, World! Goodbye, World!");
+  fail_unless_equals_pointer (GST_ID_STR_PRIVATE (copy)->s.pointer_string.s,
+      GST_ID_STR_PRIVATE (s)->s.pointer_string.s);
+  gst_id_str_free (copy);
+
+  // Should become the empty string again
+  gst_id_str_clear (s);
+  fail_unless_equals_string (gst_id_str_as_str (s), "");
+
+  gst_id_str_free (s);
+}
+
+GST_END_TEST;
+
+GST_START_TEST (test_compare)
+{
+  GstIdStr s1 = GST_ID_STR_INIT;
+  GstIdStr s2 = GST_ID_STR_INIT;
+
+  fail_unless (gst_id_str_is_equal (&s1, &s2));
+  fail_unless (gst_id_str_is_equal (&s1, &s1));
+  fail_unless (gst_id_str_is_equal_to_str (&s1, ""));
+  fail_if (gst_id_str_is_equal_to_str (&s1, "Hello, World!"));
+
+  // Should be stack allocated
+  gst_id_str_set (&s1, "Hello, World!");
+
+  fail_if (gst_id_str_is_equal (&s1, &s2));
+  fail_unless (gst_id_str_is_equal (&s1, &s1));
+  fail_unless (gst_id_str_is_equal_to_str (&s1, "Hello, World!"));
+  fail_if (gst_id_str_is_equal_to_str (&s1, "Hello, World?"));
+  fail_if (gst_id_str_is_equal_to_str (&s1, ""));
+
+  // Should be heap allocated
+  gst_id_str_set (&s1, "Hello, World! Goodbye, World!");
+
+  fail_if (gst_id_str_is_equal (&s1, &s2));
+  fail_unless (gst_id_str_is_equal (&s1, &s1));
+  fail_unless (gst_id_str_is_equal_to_str (&s1,
+          "Hello, World! Goodbye, World!"));
+  fail_if (gst_id_str_is_equal_to_str (&s1, ""));
+  fail_if (gst_id_str_is_equal_to_str (&s1, "Hello, World? Goodbye, World!"));
+
+  gst_id_str_set (&s2, "Hello, World!");
+  fail_if (gst_id_str_is_equal (&s1, &s2));
+
+  gst_id_str_set (&s1, "Hello, World!");
+  fail_unless (gst_id_str_is_equal (&s1, &s2));
+
+  gst_id_str_clear (&s1);
+  gst_id_str_clear (&s2);
+}
+
+GST_END_TEST;
+
+static Suite *
+gst_id_str_suite (void)
+{
+  Suite *s = suite_create ("GstIdStr");
+  TCase *tc_chain = tcase_create ("general");
+
+  suite_add_tcase (s, tc_chain);
+
+  tcase_add_test (tc_chain, test_init);
+  tcase_add_test (tc_chain, test_alloc);
+  tcase_add_test (tc_chain, test_compare);
+
+  return s;
+}
+
+GST_CHECK_MAIN (gst_id_str);
diff --git a/subprojects/gstreamer/tests/check/meson.build b/subprojects/gstreamer/tests/check/meson.build
index 48bb37c08d..e8419fc435 100644
--- a/subprojects/gstreamer/tests/check/meson.build
+++ b/subprojects/gstreamer/tests/check/meson.build
@@ -20,6 +20,8 @@ core_tests = [
   [ 'gst/gstelement.c', not gst_registry or not gst_parse],
   [ 'gst/gstelementfactory.c', not gst_registry ],
   [ 'gst/gstghostpad.c', not gst_registry ],
+  [ 'gst/gstidstr.c' ],
+  [ 'gst/gstidstr-noinline.c' ],
   [ 'gst/gstinfo.c' ],
   [ 'gst/gstiterator.c' ],
   [ 'gst/gstmessage.c' ],