source/includes/lv2/state.h

   1 /*
   2   Copyright 2010-2016 David Robillard <http://drobilla.net>
   3   Copyright 2010 Leonard Ritter <paniq@paniq.org>
   4
   5   Permission to use, copy, modify, and/or distribute this software for any
   6   purpose with or without fee is hereby granted, provided that the above
   7   copyright notice and this permission notice appear in all copies.
   8
   9   THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10   WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11   MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12   ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14   ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16 */
  17
  18 /**
  19    @defgroup state State
  20    @ingroup lv2
  21
  22    An interface for LV2 plugins to save and restore state, see
  23    <http://lv2plug.in/ns/ext/state> for details.
  24
  25    @{
  26 */
  27
  28 #ifndef LV2_STATE_H
  29 #define LV2_STATE_H
  30
  31 #include "lv2.h"
  32
  33 #include <stdbool.h>
  34 #include <stddef.h>
  35 #include <stdint.h>
  36
  37 #define LV2_STATE_URI    "http://lv2plug.in/ns/ext/state"  ///< http://lv2plug.in/ns/ext/state
  38 #define LV2_STATE_PREFIX LV2_STATE_URI "#"                 ///< http://lv2plug.in/ns/ext/state#
  39
  40 #define LV2_STATE__State             LV2_STATE_PREFIX "State"              ///< http://lv2plug.in/ns/ext/state#State
  41 #define LV2_STATE__interface         LV2_STATE_PREFIX "interface"          ///< http://lv2plug.in/ns/ext/state#interface
  42 #define LV2_STATE__loadDefaultState  LV2_STATE_PREFIX "loadDefaultState"   ///< http://lv2plug.in/ns/ext/state#loadDefaultState
  43 #define LV2_STATE__freePath          LV2_STATE_PREFIX "freePath"           ///< http://lv2plug.in/ns/ext/state#freePath
  44 #define LV2_STATE__makePath          LV2_STATE_PREFIX "makePath"           ///< http://lv2plug.in/ns/ext/state#makePath
  45 #define LV2_STATE__mapPath           LV2_STATE_PREFIX "mapPath"            ///< http://lv2plug.in/ns/ext/state#mapPath
  46 #define LV2_STATE__state             LV2_STATE_PREFIX "state"              ///< http://lv2plug.in/ns/ext/state#state
  47 #define LV2_STATE__threadSafeRestore LV2_STATE_PREFIX "threadSafeRestore"  ///< http://lv2plug.in/ns/ext/state#threadSafeRestore
  48 #define LV2_STATE__StateChanged      LV2_STATE_PREFIX "StateChanged"       ///< http://lv2plug.in/ns/ext/state#StateChanged
  49
  50 #ifdef __cplusplus
  51 extern "C" {
  52 #endif
  53
  54 typedef void* LV2_State_Handle;            ///< Opaque handle for state save/restore
  55 typedef void* LV2_State_Free_Path_Handle;  ///< Opaque handle for state:freePath feature
  56 typedef void* LV2_State_Map_Path_Handle;   ///< Opaque handle for state:mapPath feature
  57 typedef void* LV2_State_Make_Path_Handle;  ///< Opaque handle for state:makePath feature
  58
  59 /**
  60    Flags describing value characteristics.
  61
  62    These flags are used along with the value's type URI to determine how to
  63    (de-)serialise the value data, or whether it is even possible to do so.
  64 */
  65 typedef enum {
  66         /**
  67            Plain Old Data.
  68
  69            Values with this flag contain no pointers or references to other areas
  70            of memory.  It is safe to copy POD values with a simple memcpy and store
  71            them for the duration of the process.  A POD value is not necessarily
  72            safe to trasmit between processes or machines (for example, filenames
  73            are POD), see LV2_STATE_IS_PORTABLE for details.
  74
  75            Implementations MUST NOT attempt to copy or serialise a non-POD value if
  76            they do not understand its type (and thus know how to correctly do so).
  77         */
  78         LV2_STATE_IS_POD = 1,
  79
  80         /**
  81            Portable (architecture independent) data.
  82
  83            Values with this flag are in a format that is usable on any
  84            architecture.  A portable value saved on one machine can be restored on
  85            another machine regardless of architecture.  The format of portable
  86            values MUST NOT depend on architecture-specific properties like
  87            endianness or alignment.  Portable values MUST NOT contain filenames.
  88         */
  89         LV2_STATE_IS_PORTABLE = 1 << 1,
  90
  91         /**
  92            Native data.
  93
  94            This flag is used by the host to indicate that the saved data is only
  95            going to be used locally in the currently running process (for things
  96            like instance duplication or snapshots), so the plugin should use the
  97            most efficient representation possible and not worry about serialisation
  98            and portability.
  99         */
 100         LV2_STATE_IS_NATIVE = 1 << 2
 101 } LV2_State_Flags;
 102
 103 /** A status code for state functions. */
 104 typedef enum {
 105         LV2_STATE_SUCCESS         = 0,  /**< Completed successfully. */
 106         LV2_STATE_ERR_UNKNOWN     = 1,  /**< Unknown error. */
 107         LV2_STATE_ERR_BAD_TYPE    = 2,  /**< Failed due to unsupported type. */
 108         LV2_STATE_ERR_BAD_FLAGS   = 3,  /**< Failed due to unsupported flags. */
 109         LV2_STATE_ERR_NO_FEATURE  = 4,  /**< Failed due to missing features. */
 110         LV2_STATE_ERR_NO_PROPERTY = 5,  /**< Failed due to missing property. */
 111         LV2_STATE_ERR_NO_SPACE    = 6   /**< Failed due to insufficient space. */
 112 } LV2_State_Status;
 113
 114 /**
 115    A host-provided function to store a property.
 116    @param handle Must be the handle passed to LV2_State_Interface.save().
 117    @param key The key to store `value` under (URID).
 118    @param value Pointer to the value to be stored.
 119    @param size The size of `value` in bytes.
 120    @param type The type of `value` (URID).
 121    @param flags LV2_State_Flags for `value`.
 122    @return 0 on success, otherwise a non-zero error code.
 123
 124    The host passes a callback of this type to LV2_State_Interface.save(). This
 125    callback is called repeatedly by the plugin to store all the properties that
 126    describe its current state.
 127
 128    DO NOT INVENT NONSENSE URI SCHEMES FOR THE KEY.  Best is to use keys from
 129    existing vocabularies.  If nothing appropriate is available, use http URIs
 130    that point to somewhere you can host documents so documentation can be made
 131    resolvable (typically a child of the plugin or project URI).  If this is not
 132    possible, invent a URN scheme, e.g. urn:myproj:whatever.  The plugin MUST
 133    NOT pass an invalid URI key.
 134
 135    The host MAY fail to store a property for whatever reason, but SHOULD
 136    store any property that is LV2_STATE_IS_POD and LV2_STATE_IS_PORTABLE.
 137    Implementations SHOULD use the types from the LV2 Atom extension
 138    (http://lv2plug.in/ns/ext/atom) wherever possible.  The plugin SHOULD
 139    attempt to fall-back and avoid the error if possible.
 140
 141    Note that `size` MUST be > 0, and `value` MUST point to a valid region of
 142    memory `size` bytes long (this is required to make restore unambiguous).
 143
 144    The plugin MUST NOT attempt to use this function outside of the
 145    LV2_State_Interface.restore() context.
 146 */
 147 typedef LV2_State_Status (*LV2_State_Store_Function)(
 148         LV2_State_Handle handle,
 149         uint32_t         key,
 150         const void*      value,
 151         size_t           size,
 152         uint32_t         type,
 153         uint32_t         flags);
 154
 155 /**
 156    A host-provided function to retrieve a property.
 157    @param handle Must be the handle passed to LV2_State_Interface.restore().
 158    @param key The key of the property to retrieve (URID).
 159    @param size (Output) If non-NULL, set to the size of the restored value.
 160    @param type (Output) If non-NULL, set to the type of the restored value.
 161    @param flags (Output) If non-NULL, set to the flags for the restored value.
 162    @return A pointer to the restored value (object), or NULL if no value
 163    has been stored under `key`.
 164
 165    A callback of this type is passed by the host to
 166    LV2_State_Interface.restore().  This callback is called repeatedly by the
 167    plugin to retrieve any properties it requires to restore its state.
 168
 169    The returned value MUST remain valid until LV2_State_Interface.restore()
 170    returns.  The plugin MUST NOT attempt to use this function, or any value
 171    returned from it, outside of the LV2_State_Interface.restore() context.
 172 */
 173 typedef const void* (*LV2_State_Retrieve_Function)(
 174         LV2_State_Handle handle,
 175         uint32_t         key,
 176         size_t*          size,
 177         uint32_t*        type,
 178         uint32_t*        flags);
 179
 180 /**
 181    LV2 Plugin State Interface.
 182
 183    When the plugin's extension_data is called with argument
 184    LV2_STATE__interface, the plugin MUST return an LV2_State_Interface
 185    structure, which remains valid for the lifetime of the plugin.
 186
 187    The host can use the contained function pointers to save and restore the
 188    state of a plugin instance at any time, provided the threading restrictions
 189    of the functions are met.
 190
 191    Stored data is only guaranteed to be compatible between instances of plugins
 192    with the same URI (i.e. if a change to a plugin would cause a fatal error
 193    when restoring state saved by a previous version of that plugin, the plugin
 194    URI MUST change just as it must when ports change incompatibly).  Plugin
 195    authors should consider this possibility, and always store sensible data
 196    with meaningful types to avoid such problems in the future.
 197 */
 198 typedef struct {
 199         /**
 200            Save plugin state using a host-provided `store` callback.
 201
 202            @param instance The instance handle of the plugin.
 203            @param store The host-provided store callback.
 204            @param handle An opaque pointer to host data which MUST be passed as the
 205            handle parameter to `store` if it is called.
 206            @param flags Flags describing desired properties of this save.  These
 207            flags may be used to determine the most appropriate values to store.
 208            @param features Extensible parameter for passing any additional
 209            features to be used for this save.
 210
 211            The plugin is expected to store everything necessary to completely
 212            restore its state later.  Plugins SHOULD store simple POD data whenever
 213            possible, and consider the possibility of state being restored much
 214            later on a different machine.
 215
 216            The `handle` pointer and `store` function MUST NOT be used
 217            beyond the scope of save().
 218
 219            This function has its own special threading class: it may not be called
 220            concurrently with any "Instantiation" function, but it may be called
 221            concurrently with functions in any other class, unless the definition of
 222            that class prohibits it (for example, it may not be called concurrently
 223            with a "Discovery" function, but it may be called concurrently with an
 224            "Audio" function.  The plugin is responsible for any locking or
 225            lock-free techniques necessary to make this possible.
 226
 227            Note that in the simple case where state is only modified by restore(),
 228            there are no synchronization issues since save() is never called
 229            concurrently with restore() (though run() may read it during a save).
 230
 231            Plugins that dynamically modify state while running, however, must take
 232            care to do so in such a way that a concurrent call to save() will save a
 233            consistent representation of plugin state for a single instant in time.
 234         */
 235         LV2_State_Status (*save)(LV2_Handle                 instance,
 236                                  LV2_State_Store_Function   store,
 237                                  LV2_State_Handle           handle,
 238                                  uint32_t                   flags,
 239                                  const LV2_Feature *const * features);
 240
 241         /**
 242            Restore plugin state using a host-provided `retrieve` callback.
 243
 244            @param instance The instance handle of the plugin.
 245            @param retrieve The host-provided retrieve callback.
 246            @param handle An opaque pointer to host data which MUST be passed as the
 247            handle parameter to `retrieve` if it is called.
 248            @param flags Currently unused.
 249            @param features Extensible parameter for passing any additional
 250            features to be used for this restore.
 251
 252            The plugin MAY assume a restored value was set by a previous call to
 253            LV2_State_Interface.save() by a plugin with the same URI.
 254
 255            The plugin MUST gracefully fall back to a default value when a value can
 256            not be retrieved.  This allows the host to reset the plugin state with
 257            an empty map.
 258
 259            The `handle` pointer and `store` function MUST NOT be used
 260            beyond the scope of restore().
 261
 262            This function is in the "Instantiation" threading class as defined by
 263            LV2. This means it MUST NOT be called concurrently with any other
 264            function on the same plugin instance.
 265         */
 266         LV2_State_Status (*restore)(LV2_Handle                  instance,
 267                                     LV2_State_Retrieve_Function retrieve,
 268                                     LV2_State_Handle            handle,
 269                                     uint32_t                    flags,
 270                                     const LV2_Feature *const *  features);
 271 } LV2_State_Interface;
 272
 273 /**
 274    Feature data for state:mapPath (@ref LV2_STATE__mapPath).
 275 */
 276 typedef struct {
 277         /**
 278            Opaque host data.
 279         */
 280         LV2_State_Map_Path_Handle handle;
 281
 282         /**
 283            Map an absolute path to an abstract path for use in plugin state.
 284            @param handle MUST be the `handle` member of this struct.
 285            @param absolute_path The absolute path of a file.
 286            @return An abstract path suitable for use in plugin state.
 287
 288            The plugin MUST use this function to map any paths that will be stored
 289            in plugin state.  The returned value is an abstract path which MAY not
 290            be an actual file system path; absolute_path() MUST be used to map
 291            it to an actual path in order to use the file.
 292
 293            Plugins MUST NOT make any assumptions about abstract paths except that
 294            they can be mapped back to the absolute path of the "same" file (though
 295            not necessarily the same original path) using absolute_path().
 296
 297            This function may only be called within the context of
 298            LV2_State_Interface methods.  The caller must free the returned value
 299            with LV2_State_Free_Path.free_path().
 300         */
 301         char* (*abstract_path)(LV2_State_Map_Path_Handle handle,
 302                                const char*               absolute_path);
 303
 304         /**
 305            Map an abstract path from plugin state to an absolute path.
 306            @param handle MUST be the `handle` member of this struct.
 307            @param abstract_path An abstract path (typically from plugin state).
 308            @return An absolute file system path.
 309
 310            The plugin MUST use this function in order to actually open or otherwise
 311            use any paths loaded from plugin state.
 312
 313            This function may only be called within the context of
 314            LV2_State_Interface methods.  The caller must free the returned value
 315            with LV2_State_Free_Path.free_path().
 316         */
 317         char* (*absolute_path)(LV2_State_Map_Path_Handle handle,
 318                                const char*               abstract_path);
 319 } LV2_State_Map_Path;
 320
 321 /**
 322    Feature data for state:makePath (@ref LV2_STATE__makePath).
 323 */
 324 typedef struct {
 325         /**
 326            Opaque host data.
 327         */
 328         LV2_State_Make_Path_Handle handle;
 329
 330         /**
 331            Return a path the plugin may use to create a new file.
 332            @param handle MUST be the `handle` member of this struct.
 333            @param path The path of the new file within a namespace unique to this
 334            plugin instance.
 335            @return The absolute path to use for the new file.
 336
 337            This function can be used by plugins to create files and directories,
 338            either at state saving time (if this feature is passed to
 339            LV2_State_Interface.save()) or any time (if this feature is passed to
 340            LV2_Descriptor.instantiate()).
 341
 342            The host MUST do whatever is necessary for the plugin to be able to
 343            create a file at the returned path (for example, using fopen()),
 344            including creating any leading directories.
 345
 346            If this function is passed to LV2_Descriptor.instantiate(), it may be
 347            called from any non-realtime context.  If it is passed to
 348            LV2_State_Interface.save(), it may only be called within the dynamic
 349            scope of that function call.
 350
 351            The caller must free the returned value with
 352            LV2_State_Free_Path.free_path().
 353         */
 354         char* (*path)(LV2_State_Make_Path_Handle handle,
 355                       const char*                path);
 356 } LV2_State_Make_Path;
 357
 358 /**
 359    Feature data for state:freePath (@ref LV2_STATE__freePath).
 360 */
 361 typedef struct {
 362         /**
 363            Opaque host data.
 364         */
 365         LV2_State_Free_Path_Handle handle;
 366
 367         /**
 368            Free a path returned by a state feature.
 369
 370            @param handle MUST be the `handle` member of this struct.
 371            @param path The path previously returned by a state feature.
 372
 373            This function can be used by plugins to free paths allocated by the host
 374            and returned by state features (LV2_State_Map_Path.abstract_path(),
 375            LV2_State_Map_Path.absolute_path(), and LV2_State_Make_Path.path()).
 376         */
 377         void (*free_path)(LV2_State_Free_Path_Handle handle,
 378                           char*                      path);
 379 } LV2_State_Free_Path;
 380
 381 #ifdef __cplusplus
 382 } /* extern "C" */
 383 #endif
 384
 385 #endif /* LV2_STATE_H */
 386
 387 /**
 388    @}
 389 */