/[svn]/liblscp/trunk/doc/reference.dox
ViewVC logotype

Annotation of /liblscp/trunk/doc/reference.dox

Parent Directory Parent Directory | Revision Log Revision Log


Revision 213 - (hide annotations) (download)
Thu Jul 29 09:22:02 2004 UTC (19 years, 8 months ago) by capela
File size: 10224 byte(s)
* LSCP document draft (v.12); lscp_reset_sampler() added.

1 capela 103 /**
2    
3     @mainpage liblscp
4    
5    
6     @section Intro
7    
8     Hi all,
9    
10     On the path to a GUI for linuxsampler, I've been taking some of my spare
11     time by writing an early implementation for the LSCP (the LinuxSampler
12     Control Protocol), as defined from the current available draft document
13 capela 213 (http://www.linuxsampler.org/api/draft-linuxsampler-protocol.html).
14 capela 103
15     My implementation, while still rather crude, is taking the form of a
16     programming library for plain conventional C, codenamed liblscp.
17    
18     One of my objectives is that liblscp evolves as the implementation for a
19     linuxsampler API, while being a fair abstraction for the network and/or
20     IPC aspects of LSCP.
21    
22     For the facts, liblscp is actually a wrapper for the LSCP specification,
23     taking all the TCP/UDP socket communication into it's main control, hiding
24     all or some of the protocol bureoucracy from the user and exposing a
25     simple and opaque C programming language interface, mainly by mapping
26     events to user function callback handlers.
27    
28     The design of liblscp assumed that the programming interface provided is
29     useable and applicable either for server (linuxsampler itself) and/or
30     client (gui's) development.
31    
32     Some design features (no rocket-sci here :)
33    
34     - Multi-threaded or multiplexed server; clients block for synchronous
35     request calls.
36     - Multi-client; one server instance serves many clients, local and/or
37     remote.
38     - Server events broadcasted and delivered to client callbacks.
39     - Client requests processed on server supplied callback.
40    
41     Please note that (as usual :) documentation is none at this stage but I'll
42     challenge you to look at the source code provided on the tarball below. A
43     barebones server and client test programs are included (lscp_server_test
44     and lscp_client_test).
45    
46    
47     @section Client
48    
49     As a quick reference for the client programming, one links to liblscp to
50     create a client instance handle, just like this:<pre>
51    
52     #include <lscp/@ref:client.h>
53    
54     @ref lscp_client_t *client;
55    
56     client = @ref lscp_client_create (server_host, server_port,
57     client_callback, client_data);
58    
59     </pre>where server_host is the hostname of the server we wish to connect, and
60     server_port is the respective port number; client_callback is the client
61     supplied callback function that will handle every server notification
62     event; client_data is intended for client context and will be fed to
63     client_callback without intervention.
64    
65     The client may issue a request to server by use of:<pre>
66    
67     @ref lscp_client_query (client, query);
68    
69     </pre>where you'll submit a single command to the server and wait for it's response.
70     The query string must be null terminated. The server response result maybe
71     retrieved by:<pre>
72    
73     char *result;
74    
75     result = @ref lscp_client_get_result(client);
76    
77     </pre>and the eventual error status code:<pre>
78    
79     int errno;
80    
81     errno = @ref lscp_client_get_errno(client);
82    
83     </pre>The client callback function must have the following prototype (@ref lscp_client_proc_t):
84    
85     - @ref lscp_status_t <i>client_callback</i> ( @ref lscp_client_t *client,
86 capela 156 @ref lscp_event_t event, const char *buf, int buflen, void *client_data );
87 capela 103
88 capela 156 where event is the specific event type notification, buf will be a pointer to
89     the event text which is buflen bytes in length; client_data is exactly the same
90     value given on @ref lscp_client_create call.
91 capela 103
92     This callback function is the place to handle all server notifications and
93     will be only called if the client is currently subscribed. No response
94     from the client is expected while processing an event within
95     client_callback.
96    
97 capela 156 A client subscribes to receive event notifications by calling:<pre>
98 capela 103
99 capela 156 @ref lscp_client_subscribe (client, events);
100 capela 103
101     </pre>after which it will start receiving events by means of the supplied
102     client_callback function. To unsubscribe and stop this deliverance:<pre>
103    
104 capela 156 @ref lscp_client_unsubscribe (client, events);
105 capela 103
106     </pre>Finally, when a client is about to quit, the proper terminator is in order:<pre>
107    
108     @ref lscp_client_destroy (client);
109    
110 capela 188 </pre>As for the current protocol draft (11), the client interface already maps
111     the following functions defined in <lscp/@ref:client.h>, one for each corresponding
112     LSCP comand, and regarding the sampler channel space:<pre>
113 capela 103
114     @ref lscp_get_available_engines (client);
115     @ref lscp_get_engine_info (client, engine_name);
116     @ref lscp_get_channels (client);
117     @ref lscp_add_channel (client);
118     @ref lscp_load_engine (client, engine_name, channel);
119 capela 156 @ref lscp_set_channel_audio_device (client, channel, audio_device);
120 capela 103 @ref lscp_set_channel_audio_type (client, channel, audio_type);
121 capela 156 @ref lscp_set_channel_audio_channel (client, channel, audio_in, audio_out);
122     @ref lscp_set_channel_midi_device (client, channel, midi_device);
123     @ref lscp_set_channel_midi_type (client, channel, midi_type);
124     @ref lscp_set_channel_midi_port (client, channel, midi_port);
125 capela 103 @ref lscp_set_channel_midi_channel (client, channel, midi_channel);
126     @ref lscp_set_channel_volume (client, channel, volume);
127     @ref lscp_load_instrument (client, file_name, instr_index, channel);
128 capela 156 @ref lscp_load_instrument_non_modal (client, file_name, instr_index, channel);
129 capela 103 @ref lscp_get_channel_info (client, channel);
130     @ref lscp_get_channel_voice_count (client, channel);
131     @ref lscp_get_channel_stream_count (client, channel);
132     @ref lscp_get_channel_buffer_fill (client, usage_type, channel);
133     @ref lscp_reset_channel (client, channel);
134     @ref lscp_remove_channel (client, channel);
135 capela 213 @ref lscp_reset_sampler (client);
136 capela 103
137 capela 188 </pre>For the audio output and MIDI input device configuration interface,
138     the following functions are respectively defined in <lscp/@ref:device.h>:<pre>
139    
140     @ref lscp_get_available_audio_drivers (client);
141     @ref lscp_get_audio_driver_info (client, audio_driver);
142     @ref lscp_get_audio_driver_param_info (client, audio_driver, param_key, deplist);
143     @ref lscp_create_audio_device (client, audio_driver, params);
144     @ref lscp_destroy_audio_device (client, audio_device);
145     @ref lscp_get_audio_devices (client);
146     @ref lscp_list_audio_devices (client);
147     @ref lscp_get_audio_device_info (client, audio_device);
148     @ref lscp_set_audio_device_param (client, audio_device, param);
149     @ref lscp_get_audio_channel_info (client, audio_device, audio_channel);
150     @ref lscp_get_audio_channel_param_info (client, audio_device, audio_channel, param);
151     @ref lscp_set_audio_channel_param (client, audio_device, audio_channel, param);
152    
153     @ref lscp_get_available_midi_drivers (client);
154     @ref lscp_get_midi_driver_info (client, midi_driver);
155     @ref lscp_get_midi_driver_param_info (client, midi_driver, param_key, deplist);
156     @ref lscp_create_midi_device (client, midi_driver, params);
157     @ref lscp_destroy_midi_device (client, midi_device);
158     @ref lscp_get_midi_devices (client);
159     @ref lscp_list_midi_devices (client);
160     @ref lscp_get_midi_device_info (client, midi_device);
161     @ref lscp_set_midi_device_param (client, midi_device, param);
162     @ref lscp_get_midi_port_info (client, midi_device, midi_port);
163     @ref lscp_get_midi_port_param_info (client, midi_device, midi_port, param);
164     @ref lscp_set_midi_port_param (client, midi_device, midi_port, param);
165    
166     </pre>Most of these functions are wrappers to @ref lscp_client_query, and some will handle
167 capela 103 and change the result string accordingly.
168    
169    
170     @section Server
171    
172     Likewise, and least important yet as for server programming, you create a server
173     instance handle just like that:<pre>
174    
175     #include <lscp/@ref:server.h>
176    
177     @ref lscp_server_t *server;
178    
179     server = @ref lscp_server_create (server_port, server_callback, server_data);
180    
181     </pre>where server_port is the port number where the server will be
182     listening for connections; server_callback is the server supplied
183     callback function that will handle every client request; server_data is
184     any reference to data that will be fed into server_callback without
185     modification.
186    
187     The server callback function prototype is very similar to the client one
188     (@ref lscp_server_proc_t):
189    
190     - @ref lscp_status_t <i>server_callback</i> ( @ref lscp_connect_t *conn,
191     const char *request, int reqlen, void *server_data );
192    
193     where conn is just a client connection handle, that shall be used for the
194     server responses; the request text which has a length of reqlen bytes;
195     server_data is the same value given on lscp_server_create.
196    
197     There's two special server callback cases, flagged by a null request pointer
198     and described with reqlen as a boolean value: when zero it announces a new
199     client connection, otherwise it tells that a client connection has closed.
200    
201     While handling each request the server must cook it's response and
202     eventually issue the following:<pre>
203    
204     @ref lscp_server_result (conn, result, reslen);
205    
206     </pre>where conn is the client handle, and result is a pointer to the server
207     response literal text of reslen bytes. Of course the response shall obey
208     to the protocol specification.
209    
210     The server issues a broadcast to its subscribers by simply issuing:<pre>
211    
212     @ref lscp_server_broadcast (server, buf, buflen);
213    
214     </pre>which will trigger the client callback function, which will be fed with an
215     exact copy of buf/len; this is the intended way to deliver all
216     notifications to each subscribed client.
217    
218     When its time to shutdown the server instance, just don't forget to call
219     the server destructor:<pre>
220    
221     @ref lscp_server_destroy (server);
222    
223     </pre>and we're done with the server.
224    
225    
226     @section Outro
227    
228     Nuff said. If you care or dare, track the revolving under:
229    
230     - http://www.rncbc.org/ls/
231    
232     Please note that the code is known to compile and run on Linux AND on
233     win32 (!). On Linux the main target is a shared library (liblscp.so) so
234     remember to set your LS_LIBRARY_PATH accordingly before running the test
235     programs.
236    
237     A final disclaimer goes to the fact that I AM NOT a socket nor thread
238     programming guru, whatsoever. So fundamental mistakes may be lying around,
239     somewhere. Besides that ItJustWorks(tm:).
240    
241     I'm eager to hear your feedback and comments. As usual, destructive
242     criticism will be sent to /dev/null ;)
243    
244     Hope to be on the right track, and towards linuxsampler integration.
245    
246     Otherwise sorry for the bandwidth waste.
247    
248     Cheers.
249    
250     rncbc aka Rui Nuno Capela
251     rncbc@rncbc.org
252    
253     @see http://www.linuxsampler.org
254    
255     */

  ViewVC Help
Powered by ViewVC