src/calf/lv2_state.h

   1 /*
   2   Copyright 2010-2012 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    @file state.h
  20    C API for the LV2 State extension <http://lv2plug.in/ns/ext/state>.
  21 */
  22
  23 #ifndef LV2_STATE_H
  24 #define LV2_STATE_H
  25
  26 #include <stddef.h>
  27 #include <stdint.h>
  28
  29 #include "lv2/lv2plug.in/ns/lv2core/lv2.h"
  30
  31 #define LV2_STATE_URI    "http://lv2plug.in/ns/ext/state"
  32 #define LV2_STATE_PREFIX LV2_STATE_URI "#"
  33
  34 #define LV2_STATE__State            LV2_STATE_PREFIX "State"
  35 #define LV2_STATE__interface        LV2_STATE_PREFIX "interface"
  36 #define LV2_STATE__loadDefaultState LV2_STATE_PREFIX "loadDefaultState"
  37 #define LV2_STATE__makePath         LV2_STATE_PREFIX "makePath"
  38 #define LV2_STATE__mapPath          LV2_STATE_PREFIX "mapPath"
  39 #define LV2_STATE__state            LV2_STATE_PREFIX "state"
  40
  41 #ifdef __cplusplus
  42 extern "C" {
  43 #else
  44 #    include <stdbool.h>
  45 #endif
  46
  47 typedef void* LV2_State_Handle;
  48 typedef void* LV2_State_Map_Path_Handle;
  49 typedef void* LV2_State_Make_Path_Handle;
  50
  51 /**
  52    Flags describing value characteristics.
  53
  54    These flags are used along with the value's type URI to determine how to
  55    (de-)serialise the value data, or whether it is even possible to do so.
  56 */
  57 typedef enum {
  58         /**
  59            Plain Old Data.
  60
  61            Values with this flag contain no pointers or references to other areas
  62            of memory.  It is safe to copy POD values with a simple memcpy and store
  63            them for the duration of the process.  A POD value is not necessarily
  64            safe to trasmit between processes or machines (e.g. filenames are POD),
  65            see LV2_STATE_IS_PORTABLE for details.
  66
  67            Implementations MUST NOT attempt to copy or serialise a non-POD value if
  68            they do not understand its type (and thus know how to correctly do so).
  69         */
  70         LV2_STATE_IS_POD = 1,
  71
  72         /**
  73            Portable (architecture independent) data.
  74
  75            Values with this flag are in a format that is usable on any
  76            architecture.  A portable value saved on one machine can be restored on
  77            another machine regardless of architecture.  The format of portable
  78            values MUST NOT depend on architecture-specific properties like
  79            endianness or alignment.  Portable values MUST NOT contain filenames.
  80         */
  81         LV2_STATE_IS_PORTABLE = 1 << 1,
  82
  83         /**
  84            Native data.
  85
  86            This flag is used by the host to indicate that the saved data is only
  87            going to be used locally in the currently running process (e.g. for
  88            instance duplication or snapshots), so the plugin should use the most
  89            efficient representation possible and not worry about serialisation
  90            and portability.
  91         */
  92         LV2_STATE_IS_NATIVE = 1 << 2
  93 } LV2_State_Flags;
  94
  95 /** A status code for state functions. */
  96 typedef enum {
  97         LV2_STATE_SUCCESS         = 0,  /**< Completed successfully. */
  98         LV2_STATE_ERR_UNKNOWN     = 1,  /**< Unknown error. */
  99         LV2_STATE_ERR_BAD_TYPE    = 2,  /**< Failed due to unsupported type. */
 100         LV2_STATE_ERR_BAD_FLAGS   = 3,  /**< Failed due to unsupported flags. */
 101         LV2_STATE_ERR_NO_FEATURE  = 4,  /**< Failed due to missing features. */
 102         LV2_STATE_ERR_NO_PROPERTY = 5   /**< Failed due to missing property. */
 103 } LV2_State_Status;
 104
 105 /**
 106    A host-provided function to store a property.
 107    @param handle Must be the handle passed to LV2_State_Interface.save().
 108    @param key The key to store @p value under (URID).
 109    @param value Pointer to the value to be stored.
 110    @param size The size of @p value in bytes.
 111    @param type The type of @p value (URID).
 112    @param flags LV2_State_Flags for @p value.
 113    @return 0 on success, otherwise a non-zero error code.
 114
 115    The host passes a callback of this type to LV2_State_Interface.save(). This
 116    callback is called repeatedly by the plugin to store all the properties that
 117    describe its current state.
 118
 119    DO NOT INVENT NONSENSE URI SCHEMES FOR THE KEY.  Best is to use keys from
 120    existing vocabularies.  If nothing appropriate is available, use http URIs
 121    that point to somewhere you can host documents so documentation can be made
 122    resolvable (e.g. a child of the plugin or project URI).  If this is not
 123    possible, invent a URN scheme, e.g. urn:myproj:whatever.  The plugin MUST
 124    NOT pass an invalid URI key.
 125
 126    The host MAY fail to store a property for whatever reason, but SHOULD
 127    store any property that is LV2_STATE_IS_POD and LV2_STATE_IS_PORTABLE.
 128    Implementations SHOULD use the types from the LV2 Atom extension
 129    (http://lv2plug.in/ns/ext/atom) wherever possible.  The plugin SHOULD
 130    attempt to fall-back and avoid the error if possible.
 131
 132    Note that @p size MUST be > 0, and @p value MUST point to a valid region of
 133    memory @p size bytes long (this is required to make restore unambiguous).
 134
 135    The plugin MUST NOT attempt to use this function outside of the
 136    LV2_State_Interface.restore() context.
 137 */
 138 typedef LV2_State_Status (*LV2_State_Store_Function)(
 139         LV2_State_Handle handle,
 140         uint32_t         key,
 141         const void*      value,
 142         size_t           size,
 143         uint32_t         type,
 144         uint32_t         flags);
 145
 146 /**
 147    A host-provided function to retrieve a property.
 148    @param handle Must be the handle passed to LV2_State_Interface.restore().
 149    @param key The key of the property to retrieve (URID).
 150    @param size (Output) If non-NULL, set to the size of the restored value.
 151    @param type (Output) If non-NULL, set to the type of the restored value.
 152    @param flags (Output) If non-NULL, set to the flags for the restored value.
 153    @return A pointer to the restored value (object), or NULL if no value
 154    has been stored under @p key.
 155
 156    A callback of this type is passed by the host to
 157    LV2_State_Interface.restore().  This callback is called repeatedly by the
 158    plugin to retrieve any properties it requires to restore its state.
 159
 160    The returned value MUST remain valid until LV2_State_Interface.restore()
 161    returns.  The plugin MUST NOT attempt to use this function, or any value
 162    returned from it, outside of the LV2_State_Interface.restore() context.
 163 */
 164 typedef const void* (*LV2_State_Retrieve_Function)(
 165         LV2_State_Handle handle,
 166         uint32_t         key,
 167         size_t*          size,
 168         uint32_t*        type,
 169         uint32_t*        flags);
 170
 171 /**
 172    LV2 Plugin State Interface.
 173
 174    When the plugin's extension_data is called with argument
 175    LV2_STATE__interface, the plugin MUST return an LV2_State_Interface
 176    structure, which remains valid for the lifetime of the plugin.
 177
 178    The host can use the contained function pointers to save and restore the
 179    state of a plugin instance at any time, provided the threading restrictions
 180    of the functions are met.
 181
 182    Stored data is only guaranteed to be compatible between instances of plugins
 183    with the same URI (i.e. if a change to a plugin would cause a fatal error
 184    when restoring state saved by a previous version of that plugin, the plugin
 185    URI MUST change just as it must when ports change incompatibly).  Plugin
 186    authors should consider this possibility, and always store sensible data
 187    with meaningful types to avoid such problems in the future.
 188 */
 189 typedef struct _LV2_State_Interface {
 190         /**
 191            Save plugin state using a host-provided @p store callback.
 192
 193            @param instance The instance handle of the plugin.
 194            @param store The host-provided store callback.
 195            @param handle An opaque pointer to host data which MUST be passed as the
 196            handle parameter to @p store if it is called.
 197            @param flags Flags describing desired properties of this save.  These
 198            flags may be used to determine the most appropriate values to store.
 199            @param features Extensible parameter for passing any additional
 200            features to be used for this save.
 201
 202            The plugin is expected to store everything necessary to completely
 203            restore its state later.  Plugins SHOULD store simple POD data whenever
 204            possible, and consider the possibility of state being restored much
 205            later on a different machine.
 206
 207            The @p handle pointer and @p store function MUST NOT be used
 208            beyond the scope of save().
 209
 210            This function has its own special threading class: it may not be called
 211            concurrently with any "Instantiation" function, but it may be called
 212            concurrently with functions in any other class, unless the definition of
 213            that class prohibits it (e.g. it may not be called concurrently with a
 214            "Discovery" function, but it may be called concurrently with an "Audio"
 215            function.  The plugin is responsible for any locking or lock-free
 216            techniques necessary to make this possible.
 217
 218            Note that in the simple case where state is only modified by restore(),
 219            there are no synchronization issues since save() is never called
 220            concurrently with restore() (though run() may read it during a save).
 221
 222            Plugins that dynamically modify state while running, however, must take
 223            care to do so in such a way that a concurrent call to save() will save a
 224            consistent representation of plugin state for a single instant in time.
 225         */
 226         LV2_State_Status (*save)(LV2_Handle                 instance,
 227                                  LV2_State_Store_Function   store,
 228                                  LV2_State_Handle           handle,
 229                                  uint32_t                   flags,
 230                                  const LV2_Feature *const * features);
 231
 232         /**
 233            Restore plugin state using a host-provided @p retrieve callback.
 234
 235            @param instance The instance handle of the plugin.
 236            @param retrieve The host-provided retrieve callback.
 237            @param handle An opaque pointer to host data which MUST be passed as the
 238            handle parameter to @p retrieve if it is called.
 239            @param flags Currently unused.
 240            @param features Extensible parameter for passing any additional
 241            features to be used for this restore.
 242
 243            The plugin MAY assume a restored value was set by a previous call to
 244            LV2_State_Interface.save() by a plugin with the same URI.
 245
 246            The plugin MUST gracefully fall back to a default value when a value can
 247            not be retrieved.  This allows the host to reset the plugin state with
 248            an empty map.
 249
 250            The @p handle pointer and @p store function MUST NOT be used
 251            beyond the scope of restore().
 252
 253            This function is in the "Instantiation" threading class as defined by
 254            LV2. This means it MUST NOT be called concurrently with any other
 255            function on the same plugin instance.
 256         */
 257         LV2_State_Status (*restore)(LV2_Handle                  instance,
 258                                     LV2_State_Retrieve_Function retrieve,
 259                                     LV2_State_Handle            handle,
 260                                     uint32_t                    flags,
 261                                     const LV2_Feature *const *  features);
 262 } LV2_State_Interface;
 263
 264 /**
 265    Feature data for state:mapPath (LV2_STATE__mapPath).
 266 */
 267 typedef struct {
 268         /**
 269            Opaque host data.
 270         */
 271         LV2_State_Map_Path_Handle handle;
 272
 273         /**
 274            Map an absolute path to an abstract path for use in plugin state.
 275            @param handle MUST be the @p handle member of this struct.
 276            @param absolute_path The absolute path of a file.
 277            @return An abstract path suitable for use in plugin state.
 278
 279            The plugin MUST use this function to map any paths that will be stored
 280            in plugin state.  The returned value is an abstract path which MAY not
 281            be an actual file system path; @ref absolute_path() MUST be used to map
 282            it to an actual path in order to use the file.
 283
 284            Plugins MUST NOT make any assumptions about abstract paths except that
 285            they can be mapped back to the absolute path of the "same" file (though
 286            not necessarily the same original path) using @ref absolute_path().
 287
 288            This function may only be called within the context of
 289            LV2_State_Interface methods.  The caller is responsible for freeing the
 290            returned value with free().
 291         */
 292         char* (*abstract_path)(LV2_State_Map_Path_Handle handle,
 293                                const char*               absolute_path);
 294
 295         /**
 296            Map an abstract path from plugin state to an absolute path.
 297            @param handle MUST be the @p handle member of this struct.
 298            @param abstract_path An abstract path (e.g. a path from plugin state).
 299            @return An absolute file system path.
 300
 301            The plugin MUST use this function in order to actually open or otherwise
 302            use any paths loaded from plugin state.
 303
 304            This function may only be called within the context of
 305            LV2_State_Interface methods.  The caller is responsible for freeing the
 306            returned value with free().
 307         */
 308         char* (*absolute_path)(LV2_State_Map_Path_Handle handle,
 309                                const char*               abstract_path);
 310 } LV2_State_Map_Path;
 311
 312 /**
 313    Feature data for state:makePath (@ref LV2_STATE__makePath).
 314 */
 315 typedef struct {
 316         /**
 317            Opaque host data.
 318         */
 319         LV2_State_Make_Path_Handle handle;
 320
 321         /**
 322            Return a path the plugin may use to create a new file.
 323            @param handle MUST be the @p handle member of this struct.
 324            @param path The path of the new file within a namespace unique to this
 325            plugin instance.
 326            @return The absolute path to use for the new file.
 327
 328            This function can be used by plugins to create files and directories,
 329            either at state saving time (if this feature is passed to
 330            LV2_State_Interface.save()) or any time (if this feature is passed to
 331            LV2_Descriptor.instantiate()).
 332
 333            The host MUST do whatever is necessary for the plugin to be able to
 334            create a file at the returned path (e.g. using fopen), including
 335            creating any leading directories.
 336
 337            If this function is passed to LV2_Descriptor.instantiate(), it may be
 338            called from any non-realtime context.  If it is passed to
 339            LV2_State_Interface.save(), it may only be called within the dynamic
 340            scope of that function call.
 341
 342            The caller is responsible for freeing the returned value with free().
 343         */
 344         char* (*path)(LV2_State_Make_Path_Handle handle,
 345                       const char*                path);
 346 } LV2_State_Make_Path;
 347
 348 #ifdef __cplusplus
 349 } /* extern "C" */
 350 #endif
 351
 352 #endif /* LV2_STATE_H */