GwySerializable

GwySerializable — Abstract interface for serializable objects

Functions

Types and Values

Object Hierarchy

    GInterface
    ╰── GwySerializable

Prerequisites

GwySerializable requires GObject.

Known Implementations

GwySerializable is implemented by GwyContainer, GwySIUnit and GwyStringList.

Includes

#include <libgwyddion/gwyddion.h>

Description

GwySerializable is an abstract interface for data-like object that can be serialized and deserialized. You can serialize any object implementing this interface with gwy_serializable_serialize() and the restore (deserialize) it with gwy_serializable_deserialize(). It is also posible it duplicate any such object with gwy_serializable_duplicate() and transform one object to copy of another with gwy_serializable_clone().

Note all GwySerializable methods work with object `value', whatever it means for a particular type. Beside that, objects also have their identity which is unique and can't be subject of cloning. It consists of properties like memory address or references held by object users. Two important properties related to identity (and thus NOT retained) are: signals connected to a particular object and user data set with g_object_set_data() or g_object_set_qdata().

You can implement serialization and deserialization in your classes with gwy_serialize_pack_object_struct() and gwy_serialize_unpack_object_struct() or with gwy_serialize_object_items() and gwy_deserialize_object_hash(). The former two are useful for struct-like objects (most objects are of this kind), the latter two for hash-like objects, i.e., objects that can contain components of arbitrary name and type. Serialized size calculations can be in most cases performed by gwy_serialize_get_struct_size() and gwy_serialize_get_items_size() helper functions.

Functions

GwySerializeFunc ()

GByteArray *
(*GwySerializeFunc) (GObject *serializable,
                     GByteArray *buffer);

The type of serialization method, see gwy_serializable_serialize() for description.

Parameters

Returns

buffer with serialized object appended.

GwyDeserializeFunc ()

GObject *
(*GwyDeserializeFunc) (const guchar *buffer,
                       gsize size,
                       gsize *position);

The type of deserialization method, see gwy_serializable_deserialize() for description.

Parameters

Returns

A newly created (restored) object.

gwy_serializable_serialize ()

GByteArray *
gwy_serializable_serialize (GObject *serializable,
                            GByteArray *buffer);

Serializes an object to byte buffer.

This is a high-level method. Do not use it for implementation of child object serialization (should you ever need to do it manually), it would lead to repeated required buffer size calculations.

Parameters

Returns

buffer or a newly allocated GByteArray with serialized object appended.

gwy_serializable_deserialize ()

GObject *
gwy_serializable_deserialize (const guchar *buffer,
                              gsize size,
                              gsize *position);

Restores a serialized object from byte buffer.

The newly created object has reference count according to its nature, thus a GtkObject will have a floating reference, a GObject will have a refcount of 1, etc.

Parameters

Returns

A newly created object.

gwy_serializable_duplicate ()

GObject *
gwy_serializable_duplicate (GObject *object);

Creates a copy of an object.

If the object doesn't support duplication natively, it's brute-force serialized and then deserialized, this may be quite inefficient, namely for large objects.

You can duplicate a NULL, too, but you are discouraged from doing it.

Parameters

Returns

The newly created object copy. However if the object is a singleton, object itself (with incremented reference count) can be returned, too.

gwy_serializable_clone ()

void
gwy_serializable_clone (GObject *source,
                        GObject *copy);

Makes an object identical to another object of the same type.

More precisely, source may be subclass of copy (the extra information is lost then).

Parameters

gwy_serializable_clone_with_type ()

void
gwy_serializable_clone_with_type (GObject *source,
                                  GObject *copy,
                                  GType type);

Makes an object identical to another object of the same type, with explicit type checking.

This function is the same as gwy_serializable_clone(), except it asserts the object type, which must be type .

Since 2.52

Parameters

gwy_serializable_get_size ()

gsize
gwy_serializable_get_size (GObject *serializable);

Calculates the expected size of serialized object.

Parameters

Returns

The expected size of serialized serializable .

gwy_serialize_get_struct_size ()

gsize
gwy_serialize_get_struct_size (const guchar *object_name,
                               gsize nspec,
                               const GwySerializeSpec *spec);

Calculates serialized object size for struct-like objects.

The component specification is the same as in gwy_serialize_pack_object_struct().

Parameters

Returns

Serialized object size, it included space for object name and size. The value is exact unless some components are objects that do not return exact size estimate themselves.

gwy_serialize_get_items_size ()

gsize
gwy_serialize_get_items_size (const guchar *object_name,
                              gsize nitems,
                              const GwySerializeItem *items);

Calculates serialized object size for hash-like objects.

The component specification is the same as in gwy_serialize_object_items().

Parameters

Returns

Serialized object size, it included space for object name and size. The value is exact unless some components are objects that do not return exact size estimate themselves.

gwy_serialize_pack_object_struct ()

GByteArray *
gwy_serialize_pack_object_struct (GByteArray *buffer,
                                  const guchar *object_name,
                                  gsize nspec,
                                  const GwySerializeSpec *spec);

Appends serialization of object with g_type_name() object_name and components described by spec to buffer in gwy-file format.

Here's how a serialization method of a simple object whose state is described by a single real number foo could look (without error checking):

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static guchar*
my_object_serialize(GObject *obj,
                    guchar *buffer,
                    gsize *size)
{
    MyObject *my_object = MY_OBJECT(obj);
    GwySerializeSpec spec[] = {
        { 'd', "foo", &my_object->foo, NULL, },
    };

    return gwy_serialize_pack_object_struct(buffer, size,
                                            "MyObject",
                                            G_N_ELEMENTS(spec), spec);
}

Parameters

Returns

The buffer with serialization of spec components appended.

gwy_serialize_unpack_object_struct ()

gboolean
gwy_serialize_unpack_object_struct (const guchar *buffer,
                                    gsize size,
                                    gsize *position,
                                    const guchar *object_name,
                                    gsize nspec,
                                    GwySerializeSpec *spec);

Deserializes an object with named components packed into gwy-file format by gwy_serialize_pack_object_struct().

Extra components are ignored (but cause a warning), components of different type than expected cause failure, missing components are not detected.

It is safe to pass pointers to existing non-atomic objects (strings, arrays, objects) in spec values, they will be dereferenced and freed as necessary when an unpacked value is about to replace them. For the same reason it is an error to pass pointers to unintialized memory there, always initialize non-atomic spec values to NULL pointers, at least.

Caller is responsible for use/clean-up of these values if deserialization succeeds or not.

Here's how a deserialization method of a simple object whose state is described by a single real number foo could look (without error checking):

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static GObject*
my_object_deserialize(const guchar *buffer,
                      gsize size,
                      gsize *position)
{
    double foo = 1.0;
    GwySerializeSpec spec[] = {
        { 'd', "foo", &foo, NULL, },
    };
    MyObject *my_object;

    gwy_serialize_unpack_object_struct(buffer, size, position,
                                       "MyObject",
                                       G_N_ELEMENTS(spec), spec);
    return my_object_new(foo);
}

Parameters

Returns

Whether the unpacking succeeded (see description body for definition of success and failure).

gwy_serialize_check_string ()

gsize
gwy_serialize_check_string (const guchar *buffer,
                            gsize size,
                            gsize position,
                            const guchar *compare_to);

Check whether size bytes of memory in buffer can be interpreted as a NUL-terminated string, and eventually whether it's equal to compare_to .

When compare_to is NULL, the comparsion is not performed.

Parameters

Returns

The length of the NUL-terminated string including the NUL character; zero otherwise.

gwy_serialize_object_items ()

GByteArray *
gwy_serialize_object_items (GByteArray *buffer,
                            const guchar *object_name,
                            gsize nitems,
                            const GwySerializeItem *items);

Serializes an object to buffer in gwy-file format.

More precisely, it appends serialization of object with g_type_name() object_name with components described by items to buffer .

Parameters

Returns

buffer or a newly allocated GByteArray with serialization of items components appended.

gwy_deserialize_object_hash ()

GwySerializeItem *
gwy_deserialize_object_hash (const guchar *buffer,
                             gsize size,
                             gsize *position,
                             const guchar *object_name,
                             gsize *nitems);

Deserializes an object with arbitrary components from gwy-file format.

This function works like gwy_serialize_unpack_object_struct(), except that it does not use any a priori knowledge of what the object contains. So instead of filling values in supplied GwySerializeSpec's, it constructs GwySerializeItem's completely from what is found in buffer . It does considerably less sanity checks and even allows several components of the same name.

Parameters

Returns

A newly allocated array of deserialized components. Note the name fields of GwySerializeSpec's point to buffer and thus are valid only as long as buffer is; any arrays or strings are newly allocated and must be reused or freed by caller.

GWY_SERIALIZABLE_GET_IFACE()

#define GWY_SERIALIZABLE_GET_IFACE(obj) (G_TYPE_INSTANCE_GET_INTERFACE((obj), GWY_TYPE_SERIALIZABLE, GwySerializableIface))

Types and Values

GwySerializeSpec

typedef struct {
    guchar ctype;
    const guchar *name;
    gpointer value;
    guint32 *array_size;
} GwySerializeSpec;

A structure containing information for one object/struct component serialization or deserialization.

This component information is used in gwy_serialize_pack_object_struct() and gwy_serialize_unpack_object_struct() suitable for (de)serialization of struct-like objects.

Following atomic component types (ctype 's) exist: 'b' for a boolean, 'c' for a character, 'i' for a 32bit integer, 'q' for a 64bit integer, 'd' for a gdouble, 's' for a NUL-terminated string, 'o' for a serializable object.

And array component types: 'C' for a character array, 'I' for a 32bit integer array, 'Q' for a 64bit integer array, 'D' for a gdouble array, 'S' for an array of NUL-terminated strings, 'O' for an array of objects.

Members

GwySerializeValue

Helper serialization type that can hold any atomic value or pointer to non-atomic value.

Members

GwySerializeItem

typedef struct {
    guchar ctype;
    const guchar *name;
    GwySerializeValue value;
    guint32 array_size;
} GwySerializeItem;

A structure containing information for one object/struct component serialization or deserialization.

This component information is used in gwy_serialize_object_items() and gwy_deserialize_object_hash() suitable for (de)serialization of hash-like objects.

Members

GwySerializable

typedef struct _GwySerializable GwySerializable;

struct GwySerializableIface

struct GwySerializableIface {
    GwySerializeFunc serialize;
    GwyDeserializeFunc deserialize;
    void (*clone)(GObject *source, GObject *copy);
    GObject* (*duplicate)(GObject *object);
    gsize (*get_size)(GObject *object);
};

The methods a serializable objects has to implement.

Members