/**

@mainpage liblscp


@section Intro

Hi all,

On the path to a GUI for linuxsampler, I've been taking some of my spare
time by writing an early implementation for the LSCP (the LinuxSampler
Control Protocol), as defined from the current available draft document
(http://www.linuxsampler.org/api/draft-linuxsampler-protocol-11.pdf).

My implementation, while still rather crude, is taking the form of a
programming library for plain conventional C, codenamed liblscp.

One of my objectives is that liblscp evolves as the implementation for a
linuxsampler API, while being a fair abstraction for the network and/or
IPC aspects of LSCP.

For the facts, liblscp is actually a wrapper for the LSCP specification,
taking all the TCP/UDP socket communication into it's main control, hiding
all or some of the protocol bureoucracy from the user and exposing a
simple and opaque C programming language interface, mainly by mapping
events to user function callback handlers.

The design of liblscp assumed that the programming interface provided is
useable and applicable either for server (linuxsampler itself) and/or
client (gui's) development.

Some design features (no rocket-sci here :)

- Multi-threaded or multiplexed server; clients block for synchronous
  request calls.
- Multi-client; one server instance serves many clients, local and/or
  remote.
- Server events broadcasted and delivered to client callbacks.
- Client requests processed on server supplied callback.

Please note that (as usual :) documentation is none at this stage but I'll
challenge you to look at the source code provided on the tarball below. A
barebones server and client test programs are included (lscp_server_test
and lscp_client_test).


@section Client

As a quick reference for the client programming, one links to liblscp to
create a client instance handle, just like this:<pre>

    #include <lscp/@ref:client.h>

    @ref lscp_client_t *client;

    client = @ref lscp_client_create (server_host, server_port,
        client_callback, client_data);

</pre>where server_host is the hostname of the server we wish to connect, and
server_port is the respective port number; client_callback is the client
supplied callback function that will handle every server notification
event; client_data is intended for client context and will be fed to
client_callback without intervention.

The client may issue a request to server by use of:<pre>

    @ref lscp_client_query (client, query);

</pre>where you'll submit a single command to the server and wait for it's response.
The query string must be null terminated. The server response result maybe
retrieved by:<pre>

    char *result;

    result = @ref lscp_client_get_result(client);

</pre>and the eventual error status code:<pre>

    int errno;

    errno = @ref lscp_client_get_errno(client);

</pre>The client callback function must have the following prototype (@ref lscp_client_proc_t):

- @ref lscp_status_t <i>client_callback</i> ( @ref lscp_client_t *client,
        @ref lscp_event_t event, const char *buf, int buflen, void *client_data );

where event is the specific event type notification, buf will be a pointer to
the event text which is buflen bytes in length; client_data is exactly the same
value given on @ref lscp_client_create call.

This callback function is the place to handle all server notifications and
will be only called if the client is currently subscribed. No response
from the client is expected while processing an event within
client_callback.

A client subscribes to receive event notifications by calling:<pre>

    @ref lscp_client_subscribe (client, events);

</pre>after which it will start receiving events by means of the supplied
client_callback function. To unsubscribe and stop this deliverance:<pre>

    @ref lscp_client_unsubscribe (client, events);

</pre>Finally, when a client is about to quit, the proper terminator is in order:<pre>

    @ref lscp_client_destroy (client);

</pre>As for the current protocol draft (04), the client interface already maps
the following functions defined in "@ref lscp_client.h", one for each corresponding
LSCP comand:<pre>

    @ref lscp_get_available_engines (client);
    @ref lscp_get_engine_info (client, engine_name);
    @ref lscp_get_channels (client);
    @ref lscp_add_channel (client);
    @ref lscp_load_engine (client, engine_name, channel);
    @ref lscp_set_channel_audio_device (client, channel, audio_device);
    @ref lscp_set_channel_audio_type (client, channel, audio_type);
    @ref lscp_set_channel_audio_channel (client, channel, audio_in, audio_out);
    @ref lscp_set_channel_midi_device (client, channel, midi_device);
    @ref lscp_set_channel_midi_type (client, channel, midi_type);
    @ref lscp_set_channel_midi_port (client, channel, midi_port);
    @ref lscp_set_channel_midi_channel (client, channel, midi_channel);
    @ref lscp_set_channel_volume (client, channel, volume);
    @ref lscp_load_instrument (client, file_name, instr_index, channel);
    @ref lscp_load_instrument_non_modal (client, file_name, instr_index, channel);
    @ref lscp_get_channel_info (client, channel);
    @ref lscp_get_channel_voice_count (client, channel);
    @ref lscp_get_channel_stream_count (client, channel);
    @ref lscp_get_channel_buffer_fill (client, usage_type, channel);
    @ref lscp_reset_channel (client, channel);
    @ref lscp_remove_channel (client, channel);

</pre>All these functions are wrappers to @ref lscp_client_query, and some will handle
and change the result string accordingly.


@section Server

Likewise, and least important yet as for server programming, you create a server
instance handle just like that:<pre>

    #include <lscp/@ref:server.h>

    @ref lscp_server_t *server;

    server = @ref lscp_server_create (server_port, server_callback, server_data);

</pre>where server_port is the port number where the server will be
listening for connections; server_callback is the server supplied
callback function that will handle every client request; server_data is
any reference to data that will be fed into server_callback without
modification.

The server callback function prototype is very similar to the client one
(@ref lscp_server_proc_t):

- @ref lscp_status_t <i>server_callback</i> ( @ref lscp_connect_t *conn,
        const char *request, int reqlen, void *server_data );

where conn is just a client connection handle, that shall be used for the
server responses; the request text which has a length of reqlen bytes;
server_data is the same value given on lscp_server_create.

There's two special server callback cases, flagged by a null request pointer
and described with reqlen as a boolean value: when zero it announces a new
client connection, otherwise it tells that a client connection has closed.

While handling each request the server must cook it's response and
eventually issue the following:<pre>

    @ref lscp_server_result (conn, result, reslen);

</pre>where conn is the client handle, and result is a pointer to the server
response literal text of reslen bytes. Of course the response shall obey
to the protocol specification.

The server issues a broadcast to its subscribers by simply issuing:<pre>

    @ref lscp_server_broadcast (server, buf, buflen);

</pre>which will trigger the client callback function, which will be fed with an
exact copy of buf/len; this is the intended way to deliver all
notifications to each subscribed client.

When its time to shutdown the server instance, just don't forget to call
the server destructor:<pre>

    @ref lscp_server_destroy (server);

</pre>and we're done with the server.


@section Outro

Nuff said. If you care or dare, track the revolving under:

- http://www.rncbc.org/ls/

Please note that the code is known to compile and run on Linux AND on
win32 (!). On Linux the main target is a shared library (liblscp.so) so
remember to set your LS_LIBRARY_PATH accordingly before running the test
programs.

A final disclaimer goes to the fact that I AM NOT a socket nor thread
programming guru, whatsoever. So fundamental mistakes may be lying around,
somewhere. Besides that ItJustWorks(tm:).

I'm eager to hear your feedback and comments. As usual, destructive
criticism will be sent to /dev/null ;)

Hope to be on the right track, and towards linuxsampler integration.

Otherwise sorry for the bandwidth waste.

Cheers.

rncbc aka Rui Nuno Capela
rncbc@rncbc.org

@see http://www.linuxsampler.org

*/