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Revision 213 - (show annotations) (download)
Thu Jul 29 09:22:02 2004 UTC (14 years, 2 months ago) by capela
File size: 10224 byte(s)
* LSCP document draft (v.12); lscp_reset_sampler() added.

1 /**
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 (http://www.linuxsampler.org/api/draft-linuxsampler-protocol.html).
14
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 @ref lscp_event_t event, const char *buf, int buflen, void *client_data );
87
88 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
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 A client subscribes to receive event notifications by calling:<pre>
98
99 @ref lscp_client_subscribe (client, events);
100
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 @ref lscp_client_unsubscribe (client, events);
105
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 </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
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 @ref lscp_set_channel_audio_device (client, channel, audio_device);
120 @ref lscp_set_channel_audio_type (client, channel, audio_type);
121 @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 @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 @ref lscp_load_instrument_non_modal (client, file_name, instr_index, channel);
129 @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 @ref lscp_reset_sampler (client);
136
137 </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 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 */

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