itemserializerplugin.h

/*
    SPDX-FileCopyrightText: 2007 Till Adam <adam@kde.org>
    SPDX-FileCopyrightText: 2007 Volker Krause <vkrause@kde.org>
 
    SPDX-License-Identifier: LGPL-2.0-or-later
*/
 
#pragma once
 
#include <QByteArray>
#include <QSet>
 
#include "akonadicore_export.h"
#include "item.h"
 
class QIODevice;
 
namespace Akonadi
{
/**
 * @short The base class for item type serializer plugins.
 *
 * Serializer plugins convert between the payload of Akonadi::Item objects and
 * a textual or binary representation of the actual content data.
 * This allows to easily add support for new types to Akonadi.
 *
 * The following example shows how to implement a serializer plugin for
 * a new data type PimNote.
 *
 * The PimNote data structure:
 * @code
 * typedef struct {
 *   QString author;
 *   QDateTime dateTime;
 *   QString text;
 * } PimNote;
 * @endcode
 *
 * The serializer plugin code:
 * @code
 * #include <qplugin.h>
 *
 * class SerializerPluginPimNote : public QObject, public Akonadi::ItemSerializerPlugin
 * {
 *   Q_OBJECT
 *   Q_INTERFACES( Akonadi::ItemSerializerPlugin )
 *
 *   public:
 *     bool deserialize( Akonadi::Item& item, const QByteArray& label, QIODevice& data, int version )
 *     {
 *       // we don't handle versions in this example
 *       Q_UNUSED(version)
 *
 *       // we work only on full payload
 *       if ( label != Akonadi::Item::FullPayload )
 *         return false;
 *
 *       QDataStream stream( &data );
 *
 *       PimNote note;
 *       stream >> note.author;
 *       stream >> note.dateTime;
 *       stream >> note.text;
 *
 *       item.setPayload<PimNote>( note );
 *
 *       return true;
 *     }
 *
 *     void serialize( const Akonadi::Item& item, const QByteArray& label, QIODevice& data, int &version )
 *     {
 *       // we don't handle versions in this example
 *       Q_UNUSED(version)
 *
 *       if ( label != Akonadi::Item::FullPayload || !item.hasPayload<PimNote>() )
 *         return;
 *
 *       QDataStream stream( &data );
 *
 *       PimNote note = item.payload<PimNote>();
 *
 *       stream << note.author;
 *       stream << note.dateTime;
 *       stream << note.text;
 *     }
 * };
 *
 * Q_EXPORT_PLUGIN2( akonadi_serializer_pimnote, SerializerPluginPimNote )
 *
 * @endcode
 *
 * The desktop file:
 * @code
 * [Misc]
 * Name=Pim Note Serializer
 * Comment=An Akonadi serializer plugin for note objects
 *
 * [Plugin]
 * Type=application/x-pimnote
 * X-KDE-Library=akonadi_serializer_pimnote
 * @endcode
 *
 * @author Till Adam <adam@kde.org>, Volker Krause <vkrause@kde.org>
 */
class AKONADICORE_EXPORT ItemSerializerPlugin
{
public:
    /**
     * Destroys the item serializer plugin.
     */
    virtual ~ItemSerializerPlugin();
 
    /**
     * Converts serialized item data provided in @p data into payload for @p item.
     *
     * @param item The item to which the payload should be added.
     *             It is guaranteed to have a mime type matching one of the supported
     *             mime types of this plugin.
     *             However it might contain a unsuited payload added manually
     *             by the application developer.
     *             Verifying the payload type in case a payload is already available
     *             is recommended therefore.
     * @param label The part identifier of the part to deserialize.
     *              @p label might be an unsupported item part, return @c false if this is the case.
     * @param data A QIODevice providing access to the serialized data.
     *             The QIODevice is opened in read-only mode and positioned at the beginning.
     *             The QIODevice is guaranteed to be valid.
     * @param version The version of the data format as set by the user in serialize() or @c 0 (default).
     * @return @c false if the specified part is not supported by this plugin, @c true if the part
     *            could be de-serialized successfully.
     */
    virtual bool deserialize(Item &item, const QByteArray &label, QIODevice &data, int version) = 0;
 
    /**
     * Convert the payload object provided in @p item into its serialzed form into @p data.
     *
     * @param item The item which contains the payload.
     *             It is guaranteed to have a mimetype matching one of the supported
     *             mimetypes of this plugin as well as the existence of a payload object.
     *             However it might contain an unsupported payload added manually by
     *             the application developer.
     *             Verifying the payload type is recommended therefore.
     * @param label The part identifier of the part to serialize.
     *              @p label will be one of the item parts returned by parts().
     * @param data The QIODevice where the serialized data should be written to.
     *             The QIODevice is opened in write-only mode and positioned at the beginning.
     *             The QIODevice is guaranteed to be valid.
     * @param version The version of the data format. Can be set by the user to handle different
     *                versions.
     */
    virtual void serialize(const Item &item, const QByteArray &label, QIODevice &data, int &version) = 0;
 
    /**
     * Returns a list of available parts for the given item payload.
     * The default implementation returns Item::FullPayload if a payload is set.
     *
     * @param item The item.
     */
    virtual QSet<QByteArray> parts(const Item &item) const;
 
    /**
     * Override the plugin-lookup with @p plugin.
     *
     * After calling this each lookup will always return @p plugin.
     * This is useful to inject a special plugin for testing purposes.
     * To reset the plugin, set to 0.
     *
     * @since 4.12
     */
    static void overridePluginLookup(QObject *plugin);
 
    /**
     * Merges the payload parts in @p other into @p item.
     *
     * The default implementation is slow as it requires serializing @p other, and deserializing @p item multiple times.
     * Reimplementing this is recommended if your type uses payload parts.
     * @param item receives merged parts from @p other
     * @param other the paylod parts to merge into @p item
     * @since 4.4
     */
    virtual void apply(Item &item, const Item &other);
 
    /**
     * Returns the parts available in the item @p item.
     *
     * This should be reimplemented to return available parts.
     *
     * The default implementation returns an empty set if the item has a payload,
     * and a set containing Item::FullPayload if the item has no payload.
     * @param item the item for which to list payload parts
     * @since 4.4
     */
    virtual QSet<QByteArray> availableParts(const Item &item) const;
 
    /**
     * Returns the parts available in the item @p item that can be stored using
     * foreign payload mechanism. Is only called for items whose payload has been
     * set via Item::setPayloadPath().
     *
     * By default returns "RFC822", which can always be stored as foreign payload.
     * Some implementations can also allow "HEAD" to be stored as foreign payload,
     * if HEAD is only a subset of RFC822 part.
     *
     * @since 5.7
     */
    virtual QSet<QByteArray> allowedForeignParts(const Item &item) const;
 
protected:
    explicit ItemSerializerPlugin() = default;
 
private:
    Q_DISABLE_COPY_MOVE(ItemSerializerPlugin)
};
 
}
 
Q_DECLARE_INTERFACE(Akonadi::ItemSerializerPlugin, "org.freedesktop.Akonadi.ItemSerializerPlugin/2.0")