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