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

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

Parent Directory Parent Directory | Revision Log Revision Log


Revision 144 - (show annotations) (download)
Thu Jun 24 18:25:11 2004 UTC (15 years, 9 months ago) by capela
File size: 8134 byte(s)
* Major change to client event protocol interface on attempt
  to comply with draft-protocol v.11.

* New function entries added: lscp_load_instrument_non_modal(),
  lscp_set_channel_audio_device() and lscp_set_channel_midi_device().

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-11.pdf).
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 const char *buf, int buflen, void *client_data );
87
88 where buf will be a pointer to the event text which is buflen bytes in
89 length; client_data is exactly the same value given on @ref lscp_client_create
90 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 notifications by calling:<pre>
98
99 @ref lscp_client_subscribe (client);
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);
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 (04), the client interface already maps
111 the following functions defined in "@ref lscp_client.h", one for each corresponding
112 LSCP comand:<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_channel (client, channel, audio_channel);
120 @ref lscp_set_channel_audio_type (client, channel, audio_type);
121 @ref lscp_set_channel_midi_channel (client, channel, midi_channel);
122 @ref lscp_set_channel_midi_port (client, channel, midi_port);
123 @ref lscp_set_channel_midi_type (client, channel, midi_type);
124 @ref lscp_set_channel_volume (client, channel, volume);
125 @ref lscp_load_instrument (client, file_name, instr_index, channel);
126 @ref lscp_get_channel_info (client, channel);
127 @ref lscp_get_channel_voice_count (client, channel);
128 @ref lscp_get_channel_stream_count (client, channel);
129 @ref lscp_get_channel_buffer_fill (client, usage_type, channel);
130 @ref lscp_reset_channel (client, channel);
131 @ref lscp_remove_channel (client, channel);
132
133 </pre>All these functions are wrappers to @ref lscp_client_query, and some will handle
134 and change the result string accordingly.
135
136
137 @section Server
138
139 Likewise, and least important yet as for server programming, you create a server
140 instance handle just like that:<pre>
141
142 #include <lscp/@ref:server.h>
143
144 @ref lscp_server_t *server;
145
146 server = @ref lscp_server_create (server_port, server_callback, server_data);
147
148 </pre>where server_port is the port number where the server will be
149 listening for connections; server_callback is the server supplied
150 callback function that will handle every client request; server_data is
151 any reference to data that will be fed into server_callback without
152 modification.
153
154 The server callback function prototype is very similar to the client one
155 (@ref lscp_server_proc_t):
156
157 - @ref lscp_status_t <i>server_callback</i> ( @ref lscp_connect_t *conn,
158 const char *request, int reqlen, void *server_data );
159
160 where conn is just a client connection handle, that shall be used for the
161 server responses; the request text which has a length of reqlen bytes;
162 server_data is the same value given on lscp_server_create.
163
164 There's two special server callback cases, flagged by a null request pointer
165 and described with reqlen as a boolean value: when zero it announces a new
166 client connection, otherwise it tells that a client connection has closed.
167
168 While handling each request the server must cook it's response and
169 eventually issue the following:<pre>
170
171 @ref lscp_server_result (conn, result, reslen);
172
173 </pre>where conn is the client handle, and result is a pointer to the server
174 response literal text of reslen bytes. Of course the response shall obey
175 to the protocol specification.
176
177 The server issues a broadcast to its subscribers by simply issuing:<pre>
178
179 @ref lscp_server_broadcast (server, buf, buflen);
180
181 </pre>which will trigger the client callback function, which will be fed with an
182 exact copy of buf/len; this is the intended way to deliver all
183 notifications to each subscribed client.
184
185 When its time to shutdown the server instance, just don't forget to call
186 the server destructor:<pre>
187
188 @ref lscp_server_destroy (server);
189
190 </pre>and we're done with the server.
191
192
193 @section Outro
194
195 Nuff said. If you care or dare, track the revolving under:
196
197 - http://www.rncbc.org/ls/
198
199 Please note that the code is known to compile and run on Linux AND on
200 win32 (!). On Linux the main target is a shared library (liblscp.so) so
201 remember to set your LS_LIBRARY_PATH accordingly before running the test
202 programs.
203
204 A final disclaimer goes to the fact that I AM NOT a socket nor thread
205 programming guru, whatsoever. So fundamental mistakes may be lying around,
206 somewhere. Besides that ItJustWorks(tm:).
207
208 I'm eager to hear your feedback and comments. As usual, destructive
209 criticism will be sent to /dev/null ;)
210
211 Hope to be on the right track, and towards linuxsampler integration.
212
213 Otherwise sorry for the bandwidth waste.
214
215 Cheers.
216
217 rncbc aka Rui Nuno Capela
218 rncbc@rncbc.org
219
220 @see http://www.linuxsampler.org
221
222 */

  ViewVC Help
Powered by ViewVC