ext/dyn-manifest.lv2/dyn-manifest.h

   1 /* Dynamic manifest specification for LV2
   2  * Revision 1
   3  *
   4  * Copyright (C) 2008, 2009 Stefano D'Angelo <zanga.mail@gmail.com>
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. The name of the author may not be used to endorse or promote products
  16  *    derived from this software without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  19  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  20  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  21  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  22  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  23  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  24  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  25  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  27  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  28  */
  29
  30 #ifndef LV2_DYN_MANIFEST_H_INCLUDED
  31 #define LV2_DYN_MANIFEST_H_INCLUDED
  32
  33 #include <stdio.h>
  34 #include "lv2.h"
  35
  36 #ifdef __cplusplus
  37 extern "C" {
  38 #endif
  39
  40
  41 /* ************************************************************************* */
  42
  43
  44 /** @file
  45  * C header for the LV2 Dynamic Manifest extension
  46  * <http://lv2plug.in/ns/ext/dyn-manifest>.
  47  * Revision: 1
  48  *
  49  * == Overview ==
  50  *
  51  * The LV2 API, on its own, cannot be used to write plugin libraries where
  52  * data is dynamically generated at runtime (e.g. API wrappers), since LV2
  53  * requires needed information to be provided in one or more static data (RDF)
  54  * files. This API addresses this limitation by extending the LV2 API.
  55  *
  56  * A host implementing support for this API should first detect that the plugin
  57  * library implements a dynamic manifest generator by examining its static
  58  * manifest file, then fetch data from the shared object file by accessing it as
  59  * usual (dlopen() and family) and using this API.
  60  *
  61  * The host is allowed to request regeneration of the dynamic manifest multiple
  62  * times, and the plugin library is expected to provide updated data if/when
  63  * possible. All data and references provided via this API before the last
  64  * regeneration of the dynamic manifest is to be considered invalid by the
  65  * host, including plugin descriptors whose URIs were discovered using this API.
  66  *
  67  * This API is extensible in a similar fashion as the LV2 plugin API.
  68  *
  69  * == Threading rules ==
  70  *
  71  * This specification defines threading rule classes, similarly to the LV2
  72  * specification.
  73  *
  74  * The functions defined by this API belong to:
  75  *
  76  *  - Dynamic manifest open class:  lv2_dyn_manifest_open()
  77  *  - Dynamic manifest close class: lv2_dyn_manifest_close()
  78  *  - Dynamic manifest file class:  lv2_dyn_manifest_get_subjects(),
  79  *                                  lv2_dyn_manifest_get_data()
  80  *
  81  * The rules that hosts must follow are these:
  82  *
  83  *  - When a function from the Dynamic manifest open or the Dynamic manifest
  84  *    close class is running, no other functions in the same shared object file
  85  *    may run.
  86  *  - When a function from the Dynamic manifest file class is called, no other
  87  *    functions from the same class may run if they are given at least one
  88  *    FILE * argument with the same value.
  89  *  - A function from the Dynamic manifest open class may not run after a
  90  *    successful call to a function from the same class, in case a function from
  91  *    the Dynamic manifest close class was not successfully called in the
  92  *    meanwhile.
  93  *  - A function from the Dynamic manifest close class may only run after a
  94  *    successful call to a function from the Dynamic manifest open class.
  95  *  - A function from the Dynamic manifest file class may only run beetween a
  96  *    successful call to a function from the Dynamic manifest open class and the
  97  *    following successful call to a function from the Dynamic manifest close
  98  *    class.
  99  *
 100  * Extensions to this specification which add new functions MUST declare in
 101  * which of these classes the functions belong, or define new classes for them;
 102  * furthermore, classes defined by such extensions MUST only allow calls after
 103  * a successful call to a function from the Dynamic manifest open class and
 104  * before the following successful call to a function from the Dynamic manifest
 105  * close class.
 106  *
 107  * Any simultaneous calls that are not explicitly forbidden by these rules are
 108  * allowed.
 109  */
 110
 111
 112 /* ************************************************************************* */
 113
 114
 115 /** Dynamic manifest generator handle.
 116  *
 117  * This handle indicates a particular status of a dynamic manifest generator.
 118  * The host MUST NOT attempt to interpret it and, unlikely LV2_Handle, it is NOT
 119  * even valid to compare this to NULL. The dynamic manifest generator may use it
 120  * to reference internal data. */
 121 typedef void * LV2_Dyn_Manifest_Handle;
 122
 123
 124 /* ************************************************************************* */
 125
 126
 127 /** Accessing data.
 128  *
 129  * Whenever a host wants to access data using this API, it could:
 130  *
 131  *  1. Call lv2_dyn_manifest_open();
 132  *  2. Create an empty resource identified by a FILE *;
 133  *  3. Get a "list" of exposed subject URIs using
 134  *     lv2_dyn_manifest_get_subjects();
 135  *  4. Call lv2_dyn_manifest_get_data() for each URI of interest, in order to
 136  *     get data related to that URI (either by calling the function subsequently
 137  *     with the same FILE * resource, or by creating more FILE * resources to
 138  *     perform parallel calls);
 139  *  5. Call lv2_dyn_manifest_close();
 140  *  6. Parse the content of the FILE * resource(s).
 141  *  7. Free/delete/unlink the FILE * resource(s).
 142  *
 143  * The content of the FILE * resources has to be interpreted by the host as a
 144  * regular file in Turtle syntax. This also means that each FILE * resource
 145  * should also contain needed prefix definitions, in case any are used.
 146  *
 147  * Each call to lv2_dyn_manifest_open() automatically implies the (re)generation
 148  * of the dynamic manifest on the library side.
 149  *
 150  * When such calls are made, data fetched from the involved library using this
 151  * API before such call is to be considered no more valid.
 152  *
 153  * In case the library uses this same API to access other dynamic manifests, it
 154  * MUST implement some mechanism to avoid potentially endless loops (such as A
 155  * loads B, B loads A, etc.) in functions from the Dynamic manifest open class
 156  * (the open-like operation MUST fail). For this purpose, use of a static
 157  * boolean flag is suggested.
 158  */
 159
 160 /** Function that (re)generates the dynamic manifest.
 161  *
 162  * handle is a pointer to an uninitialized dynamic manifest generator handle.
 163  *
 164  * features is a NULL terminated array of LV2_Feature structs which
 165  * represent the features the host supports. The dynamic manifest geenrator may
 166  * refuse to (re)generate the dynamic manifest if required features are not
 167  * found here (however hosts SHOULD NOT use this as a discovery mechanism,
 168  * instead of reading the static manifest file). This array must always exist;
 169  * if a host has no features, it MUST pass a single element array containing
 170  * NULL.
 171  *
 172  * This function MUST return 0 on success, otherwise a non-zero error code, and
 173  * the host SHOULD evaluate the result of the operation by examining the
 174  * returned value, rather than try to interpret the value of handle.
 175  */
 176 int lv2_dyn_manifest_open(LV2_Dyn_Manifest_Handle *  handle,
 177                           const LV2_Feature *const * features);
 178
 179 /** Function that fetches a "list" of subject URIs exposed by the dynamic
 180  *  manifest generator.
 181  *
 182  * handle is the dynamic manifest generator handle.
 183  *
 184  * fp is the FILE * identifying the resource the host has to set up for the
 185  * dynamic manifest generator. The host MUST pass a writable, empty resource to
 186  * this function, and the dynamic manifest generator MUST ONLY perform write
 187  * operations on it at the end of the stream (e.g. use only fprintf(), fwrite()
 188  * and similar).
 189  *
 190  * The dynamic manifest generator has to fill the resource only with the needed
 191  * triples to make the host aware of the "objects" it wants to expose. For
 192  * example, if the library exposes a regular LV2 plugin, it should output only a
 193  * triple like the following:
 194  *
 195  *   <http://www.example.com/plugin/uri> a lv2:Plugin;
 196  *
 197  * This function MUST return 0 on success, otherwise a non-zero error code.
 198  */
 199 int lv2_dyn_manifest_get_subjects(LV2_Dyn_Manifest_Handle handle,
 200                                   FILE *                  fp);
 201
 202 /** Function that fetches data related to a specific URI.
 203  *
 204  * handle is the dynamic manifest generator handle.
 205  *
 206  * fp is the FILE * identifying the resource the host has to set up for the
 207  * dynamic manifest generator. The host MUST pass a writable resource to this
 208  * function, and the dynamic manifest generator MUST ONLY perform write
 209  * operations on it at the current position of the stream (e.g. use only
 210  * fprintf(), fwrite() and similar).
 211  *
 212  * uri is the URI to get data about (in the "plain" form, a.k.a. without RDF
 213  * prefixes).
 214  *
 215  * The dynamic manifest generator has to fill the resource with data related to
 216  * the URI. For example, if the library exposes a regular LV2 plugin whose URI,
 217  * as retrieved by the host using lv2_dyn_manifest_get_subjects() is
 218  * http://www.example.com/plugin/uri, it should output something like:
 219  *
 220  *   <http://www.example.com/plugin/uri> a lv2:Plugin;
 221  *       lv2:binary <mylib.so>;
 222  *       doap:name "My Plugin";
 223  *       ... etc...
 224  *
 225  * This function MUST return 0 on success, otherwise a non-zero error code.
 226  */
 227 int lv2_dyn_manifest_get_data(LV2_Dyn_Manifest_Handle handle,
 228                               FILE *                  fp,
 229                               const char *            uri);
 230
 231 /** Function that ends the operations on the dynamic manifest generator.
 232  *
 233  * handle is the dynamic manifest generator handle.
 234  *
 235  * This function should be used by the dynamic manifest generator to perform
 236  * cleanup operations, etc.
 237  */
 238 void lv2_dyn_manifest_close(LV2_Dyn_Manifest_Handle handle);
 239
 240 #ifdef __cplusplus
 241 }
 242 #endif
 243
 244 #endif /* LV2_DYN_MANIFEST_H_INCLUDED */
 245