/* Dynamic manifest specification for LV2 * Revision 1 * * Copyright (C) 2008, 2009 Stefano D'Angelo * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote products * derived from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #ifndef LV2_DYN_MANIFEST_H_INCLUDED #define LV2_DYN_MANIFEST_H_INCLUDED #include #include "lv2.h" #ifdef __cplusplus extern "C" { #endif /* ************************************************************************* */ /** @file * C header for the LV2 Dynamic Manifest extension * . * Revision: 1 * * == Overview == * * The LV2 API, on its own, cannot be used to write plugin libraries where * data is dynamically generated at runtime (e.g. API wrappers), since LV2 * requires needed information to be provided in one or more static data (RDF) * files. This API addresses this limitation by extending the LV2 API. * * A host implementing support for this API should first detect that the plugin * library implements a dynamic manifest generator by examining its static * manifest file, then fetch data from the shared object file by accessing it as * usual (dlopen() and family) and using this API. * * The host is allowed to request regeneration of the dynamic manifest multiple * times, and the plugin library is expected to provide updated data if/when * possible. All data and references provided via this API before the last * regeneration of the dynamic manifest is to be considered invalid by the * host, including plugin descriptors whose URIs were discovered using this API. * * This API is extensible in a similar fashion as the LV2 plugin API. * * == Threading rules == * * This specification defines threading rule classes, similarly to the LV2 * specification. * * The functions defined by this API belong to: * * - Dynamic manifest open class: lv2_dyn_manifest_open() * - Dynamic manifest close class: lv2_dyn_manifest_close() * - Dynamic manifest file class: lv2_dyn_manifest_get_subjects(), * lv2_dyn_manifest_get_data() * * The rules that hosts must follow are these: * * - When a function from the Dynamic manifest open or the Dynamic manifest * close class is running, no other functions in the same shared object file * may run. * - When a function from the Dynamic manifest file class is called, no other * functions from the same class may run if they are given at least one * FILE * argument with the same value. * - A function from the Dynamic manifest open class may not run after a * successful call to a function from the same class, in case a function from * the Dynamic manifest close class was not successfully called in the * meanwhile. * - A function from the Dynamic manifest close class may only run after a * successful call to a function from the Dynamic manifest open class. * - A function from the Dynamic manifest file class may only run beetween a * successful call to a function from the Dynamic manifest open class and the * following successful call to a function from the Dynamic manifest close * class. * * Extensions to this specification which add new functions MUST declare in * which of these classes the functions belong, or define new classes for them; * furthermore, classes defined by such extensions MUST only allow calls after * a successful call to a function from the Dynamic manifest open class and * before the following successful call to a function from the Dynamic manifest * close class. * * Any simultaneous calls that are not explicitly forbidden by these rules are * allowed. */ /* ************************************************************************* */ /** Dynamic manifest generator handle. * * This handle indicates a particular status of a dynamic manifest generator. * The host MUST NOT attempt to interpret it and, unlikely LV2_Handle, it is NOT * even valid to compare this to NULL. The dynamic manifest generator may use it * to reference internal data. */ typedef void * LV2_Dyn_Manifest_Handle; /* ************************************************************************* */ /** Accessing data. * * Whenever a host wants to access data using this API, it could: * * 1. Call lv2_dyn_manifest_open(); * 2. Create an empty resource identified by a FILE *; * 3. Get a "list" of exposed subject URIs using * lv2_dyn_manifest_get_subjects(); * 4. Call lv2_dyn_manifest_get_data() for each URI of interest, in order to * get data related to that URI (either by calling the function subsequently * with the same FILE * resource, or by creating more FILE * resources to * perform parallel calls); * 5. Call lv2_dyn_manifest_close(); * 6. Parse the content of the FILE * resource(s). * 7. Free/delete/unlink the FILE * resource(s). * * The content of the FILE * resources has to be interpreted by the host as a * regular file in Turtle syntax. This also means that each FILE * resource * should also contain needed prefix definitions, in case any are used. * * Each call to lv2_dyn_manifest_open() automatically implies the (re)generation * of the dynamic manifest on the library side. * * When such calls are made, data fetched from the involved library using this * API before such call is to be considered no more valid. * * In case the library uses this same API to access other dynamic manifests, it * MUST implement some mechanism to avoid potentially endless loops (such as A * loads B, B loads A, etc.) in functions from the Dynamic manifest open class * (the open-like operation MUST fail). For this purpose, use of a static * boolean flag is suggested. */ /** Function that (re)generates the dynamic manifest. * * handle is a pointer to an uninitialized dynamic manifest generator handle. * * features is a NULL terminated array of LV2_Feature structs which * represent the features the host supports. The dynamic manifest geenrator may * refuse to (re)generate the dynamic manifest if required features are not * found here (however hosts SHOULD NOT use this as a discovery mechanism, * instead of reading the static manifest file). This array must always exist; * if a host has no features, it MUST pass a single element array containing * NULL. * * This function MUST return 0 on success, otherwise a non-zero error code, and * the host SHOULD evaluate the result of the operation by examining the * returned value, rather than try to interpret the value of handle. */ int lv2_dyn_manifest_open(LV2_Dyn_Manifest_Handle * handle, const LV2_Feature *const * features); /** Function that fetches a "list" of subject URIs exposed by the dynamic * manifest generator. * * handle is the dynamic manifest generator handle. * * fp is the FILE * identifying the resource the host has to set up for the * dynamic manifest generator. The host MUST pass a writable, empty resource to * this function, and the dynamic manifest generator MUST ONLY perform write * operations on it at the end of the stream (e.g. use only fprintf(), fwrite() * and similar). * * The dynamic manifest generator has to fill the resource only with the needed * triples to make the host aware of the "objects" it wants to expose. For * example, if the library exposes a regular LV2 plugin, it should output only a * triple like the following: * * a lv2:Plugin . * * This function MUST return 0 on success, otherwise a non-zero error code. */ int lv2_dyn_manifest_get_subjects(LV2_Dyn_Manifest_Handle handle, FILE * fp); /** Function that fetches data related to a specific URI. * * handle is the dynamic manifest generator handle. * * fp is the FILE * identifying the resource the host has to set up for the * dynamic manifest generator. The host MUST pass a writable resource to this * function, and the dynamic manifest generator MUST ONLY perform write * operations on it at the current position of the stream (e.g. use only * fprintf(), fwrite() and similar). * * uri is the URI to get data about (in the "plain" form, a.k.a. without RDF * prefixes). * * The dynamic manifest generator has to fill the resource with data related to * the URI. For example, if the library exposes a regular LV2 plugin whose URI, * as retrieved by the host using lv2_dyn_manifest_get_subjects() is * http://www.example.com/plugin/uri, it should output something like: * * a lv2:Plugin; * lv2:binary ; * doap:name "My Plugin"; * ... etc... * * This function MUST return 0 on success, otherwise a non-zero error code. */ int lv2_dyn_manifest_get_data(LV2_Dyn_Manifest_Handle handle, FILE * fp, const char * uri); /** Function that ends the operations on the dynamic manifest generator. * * handle is the dynamic manifest generator handle. * * This function should be used by the dynamic manifest generator to perform * cleanup operations, etc. */ void lv2_dyn_manifest_close(LV2_Dyn_Manifest_Handle handle); #ifdef __cplusplus } #endif #endif /* LV2_DYN_MANIFEST_H_INCLUDED */