Carla/source/includes/lv2/state.h

/*
  Copyright 2010-2012 David Robillard <http://drobilla.net>
  Copyright 2010 Leonard Ritter <paniq@paniq.org>

  Permission to use, copy, modify, and/or distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.

  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

/**
   @defgroup state State

   An interface for LV2 plugins to save and restore state, see
   <http://lv2plug.in/ns/ext/state> for details.

   @{
*/

#ifndef LV2_STATE_H
#define LV2_STATE_H

#include <stddef.h>
#include <stdint.h>

#include "lv2.h"

#define LV2_STATE_URI    "http://lv2plug.in/ns/ext/state"
#define LV2_STATE_PREFIX LV2_STATE_URI "#"

#define LV2_STATE__State            LV2_STATE_PREFIX "State"
#define LV2_STATE__interface        LV2_STATE_PREFIX "interface"
#define LV2_STATE__loadDefaultState LV2_STATE_PREFIX "loadDefaultState"
#define LV2_STATE__makePath         LV2_STATE_PREFIX "makePath"
#define LV2_STATE__mapPath          LV2_STATE_PREFIX "mapPath"
#define LV2_STATE__state            LV2_STATE_PREFIX "state"

#ifdef __cplusplus
extern "C" {
#else
#    include <stdbool.h>
#endif

typedef void* LV2_State_Handle;
typedef void* LV2_State_Map_Path_Handle;
typedef void* LV2_State_Make_Path_Handle;

/**
   Flags describing value characteristics.

   These flags are used along with the value's type URI to determine how to
   (de-)serialise the value data, or whether it is even possible to do so.
*/
typedef enum {
	/**
	   Plain Old Data.

	   Values with this flag contain no pointers or references to other areas
	   of memory.  It is safe to copy POD values with a simple memcpy and store
	   them for the duration of the process.  A POD value is not necessarily
	   safe to trasmit between processes or machines (e.g. filenames are POD),
	   see LV2_STATE_IS_PORTABLE for details.

	   Implementations MUST NOT attempt to copy or serialise a non-POD value if
	   they do not understand its type (and thus know how to correctly do so).
	*/
	LV2_STATE_IS_POD = 1,

	/**
	   Portable (architecture independent) data.

	   Values with this flag are in a format that is usable on any
	   architecture.  A portable value saved on one machine can be restored on
	   another machine regardless of architecture.  The format of portable
	   values MUST NOT depend on architecture-specific properties like
	   endianness or alignment.  Portable values MUST NOT contain filenames.
	*/
	LV2_STATE_IS_PORTABLE = 1 << 1,

	/**
	   Native data.

	   This flag is used by the host to indicate that the saved data is only
	   going to be used locally in the currently running process (e.g. for
	   instance duplication or snapshots), so the plugin should use the most
	   efficient representation possible and not worry about serialisation
	   and portability.
	*/
	LV2_STATE_IS_NATIVE = 1 << 2
} LV2_State_Flags;

/** A status code for state functions. */
typedef enum {
	LV2_STATE_SUCCESS         = 0,  /**< Completed successfully. */
	LV2_STATE_ERR_UNKNOWN     = 1,  /**< Unknown error. */
	LV2_STATE_ERR_BAD_TYPE    = 2,  /**< Failed due to unsupported type. */
	LV2_STATE_ERR_BAD_FLAGS   = 3,  /**< Failed due to unsupported flags. */
	LV2_STATE_ERR_NO_FEATURE  = 4,  /**< Failed due to missing features. */
	LV2_STATE_ERR_NO_PROPERTY = 5   /**< Failed due to missing property. */
} LV2_State_Status;

/**
   A host-provided function to store a property.
   @param handle Must be the handle passed to LV2_State_Interface.save().
   @param key The key to store `value` under (URID).
   @param value Pointer to the value to be stored.
   @param size The size of `value` in bytes.
   @param type The type of `value` (URID).
   @param flags LV2_State_Flags for `value`.
   @return 0 on success, otherwise a non-zero error code.

   The host passes a callback of this type to LV2_State_Interface.save(). This
   callback is called repeatedly by the plugin to store all the properties that
   describe its current state.

   DO NOT INVENT NONSENSE URI SCHEMES FOR THE KEY.  Best is to use keys from
   existing vocabularies.  If nothing appropriate is available, use http URIs
   that point to somewhere you can host documents so documentation can be made
   resolvable (e.g. a child of the plugin or project URI).  If this is not
   possible, invent a URN scheme, e.g. urn:myproj:whatever.  The plugin MUST
   NOT pass an invalid URI key.

   The host MAY fail to store a property for whatever reason, but SHOULD
   store any property that is LV2_STATE_IS_POD and LV2_STATE_IS_PORTABLE.
   Implementations SHOULD use the types from the LV2 Atom extension
   (http://lv2plug.in/ns/ext/atom) wherever possible.  The plugin SHOULD
   attempt to fall-back and avoid the error if possible.

   Note that `size` MUST be > 0, and `value` MUST point to a valid region of
   memory `size` bytes long (this is required to make restore unambiguous).

   The plugin MUST NOT attempt to use this function outside of the
   LV2_State_Interface.restore() context.
*/
typedef LV2_State_Status (*LV2_State_Store_Function)(
	LV2_State_Handle handle,
	uint32_t         key,
	const void*      value,
	size_t           size,
	uint32_t         type,
	uint32_t         flags);

/**
   A host-provided function to retrieve a property.
   @param handle Must be the handle passed to LV2_State_Interface.restore().
   @param key The key of the property to retrieve (URID).
   @param size (Output) If non-NULL, set to the size of the restored value.
   @param type (Output) If non-NULL, set to the type of the restored value.
   @param flags (Output) If non-NULL, set to the flags for the restored value.
   @return A pointer to the restored value (object), or NULL if no value
   has been stored under `key`.

   A callback of this type is passed by the host to
   LV2_State_Interface.restore().  This callback is called repeatedly by the
   plugin to retrieve any properties it requires to restore its state.

   The returned value MUST remain valid until LV2_State_Interface.restore()
   returns.  The plugin MUST NOT attempt to use this function, or any value
   returned from it, outside of the LV2_State_Interface.restore() context.
*/
typedef const void* (*LV2_State_Retrieve_Function)(
	LV2_State_Handle handle,
	uint32_t         key,
	size_t*          size,
	uint32_t*        type,
	uint32_t*        flags);

/**
   LV2 Plugin State Interface.

   When the plugin's extension_data is called with argument
   LV2_STATE__interface, the plugin MUST return an LV2_State_Interface
   structure, which remains valid for the lifetime of the plugin.

   The host can use the contained function pointers to save and restore the
   state of a plugin instance at any time, provided the threading restrictions
   of the functions are met.

   Stored data is only guaranteed to be compatible between instances of plugins
   with the same URI (i.e. if a change to a plugin would cause a fatal error
   when restoring state saved by a previous version of that plugin, the plugin
   URI MUST change just as it must when ports change incompatibly).  Plugin
   authors should consider this possibility, and always store sensible data
   with meaningful types to avoid such problems in the future.
*/
typedef struct _LV2_State_Interface {
	/**
	   Save plugin state using a host-provided `store` callback.

	   @param instance The instance handle of the plugin.
	   @param store The host-provided store callback.
	   @param handle An opaque pointer to host data which MUST be passed as the
	   handle parameter to `store` if it is called.
	   @param flags Flags describing desired properties of this save.  These
	   flags may be used to determine the most appropriate values to store.
	   @param features Extensible parameter for passing any additional
	   features to be used for this save.

	   The plugin is expected to store everything necessary to completely
	   restore its state later.  Plugins SHOULD store simple POD data whenever
	   possible, and consider the possibility of state being restored much
	   later on a different machine.

	   The `handle` pointer and `store` function MUST NOT be used
	   beyond the scope of save().

	   This function has its own special threading class: it may not be called
	   concurrently with any "Instantiation" function, but it may be called
	   concurrently with functions in any other class, unless the definition of
	   that class prohibits it (e.g. it may not be called concurrently with a
	   "Discovery" function, but it may be called concurrently with an "Audio"
	   function.  The plugin is responsible for any locking or lock-free
	   techniques necessary to make this possible.

	   Note that in the simple case where state is only modified by restore(),
	   there are no synchronization issues since save() is never called
	   concurrently with restore() (though run() may read it during a save).

	   Plugins that dynamically modify state while running, however, must take
	   care to do so in such a way that a concurrent call to save() will save a
	   consistent representation of plugin state for a single instant in time.
	*/
	LV2_State_Status (*save)(LV2_Handle                 instance,
	                         LV2_State_Store_Function   store,
	                         LV2_State_Handle           handle,
	                         uint32_t                   flags,
	                         const LV2_Feature *const * features);

	/**
	   Restore plugin state using a host-provided `retrieve` callback.

	   @param instance The instance handle of the plugin.
	   @param retrieve The host-provided retrieve callback.
	   @param handle An opaque pointer to host data which MUST be passed as the
	   handle parameter to `retrieve` if it is called.
	   @param flags Currently unused.
	   @param features Extensible parameter for passing any additional
	   features to be used for this restore.

	   The plugin MAY assume a restored value was set by a previous call to
	   LV2_State_Interface.save() by a plugin with the same URI.

	   The plugin MUST gracefully fall back to a default value when a value can
	   not be retrieved.  This allows the host to reset the plugin state with
	   an empty map.

	   The `handle` pointer and `store` function MUST NOT be used
	   beyond the scope of restore().

	   This function is in the "Instantiation" threading class as defined by
	   LV2. This means it MUST NOT be called concurrently with any other
	   function on the same plugin instance.
	*/
	LV2_State_Status (*restore)(LV2_Handle                  instance,
	                            LV2_State_Retrieve_Function retrieve,
	                            LV2_State_Handle            handle,
	                            uint32_t                    flags,
	                            const LV2_Feature *const *  features);
} LV2_State_Interface;

/**
   Feature data for state:mapPath (@ref LV2_STATE__mapPath).
*/
typedef struct {
	/**
	   Opaque host data.
	*/
	LV2_State_Map_Path_Handle handle;

	/**
	   Map an absolute path to an abstract path for use in plugin state.
	   @param handle MUST be the `handle` member of this struct.
	   @param absolute_path The absolute path of a file.
	   @return An abstract path suitable for use in plugin state.

	   The plugin MUST use this function to map any paths that will be stored
	   in plugin state.  The returned value is an abstract path which MAY not
	   be an actual file system path; absolute_path() MUST be used to map
	   it to an actual path in order to use the file.

	   Plugins MUST NOT make any assumptions about abstract paths except that
	   they can be mapped back to the absolute path of the "same" file (though
	   not necessarily the same original path) using absolute_path().

	   This function may only be called within the context of
	   LV2_State_Interface methods.  The caller is responsible for freeing the
	   returned value with free().
	*/
	char* (*abstract_path)(LV2_State_Map_Path_Handle handle,
	                       const char*               absolute_path);

	/**
	   Map an abstract path from plugin state to an absolute path.
	   @param handle MUST be the `handle` member of this struct.
	   @param abstract_path An abstract path (e.g. a path from plugin state).
	   @return An absolute file system path.

	   The plugin MUST use this function in order to actually open or otherwise
	   use any paths loaded from plugin state.

	   This function may only be called within the context of
	   LV2_State_Interface methods.  The caller is responsible for freeing the
	   returned value with free().
	*/
	char* (*absolute_path)(LV2_State_Map_Path_Handle handle,
	                       const char*               abstract_path);
} LV2_State_Map_Path;

/**
   Feature data for state:makePath (@ref LV2_STATE__makePath).
*/
typedef struct {
	/**
	   Opaque host data.
	*/
	LV2_State_Make_Path_Handle handle;

	/**
	   Return a path the plugin may use to create a new file.
	   @param handle MUST be the `handle` member of this struct.
	   @param path The path of the new file within a namespace unique to this
	   plugin instance.
	   @return The absolute path to use for the new file.

	   This function can be used by plugins to create files and directories,
	   either at state saving time (if this feature is passed to
	   LV2_State_Interface.save()) or any time (if this feature is passed to
	   LV2_Descriptor.instantiate()).

	   The host MUST do whatever is necessary for the plugin to be able to
	   create a file at the returned path (e.g. using fopen), including
	   creating any leading directories.

	   If this function is passed to LV2_Descriptor.instantiate(), it may be
	   called from any non-realtime context.  If it is passed to
	   LV2_State_Interface.save(), it may only be called within the dynamic
	   scope of that function call.

	   The caller is responsible for freeing the returned value with free().
	*/
	char* (*path)(LV2_State_Make_Path_Handle handle,
	              const char*                path);
} LV2_State_Make_Path;

#ifdef __cplusplus
} /* extern "C" */
#endif

#endif /* LV2_STATE_H */

/**
   @}
*/