[Vala] Using a C library

[Justin Brown <justin brown fandingo org>]

Hello,

I'm just getting started with Vala, and I've run into a snag.
Unfortunately, even after crawling the internet for several hours trying to
find a solution, I can't seem to find any help. Sorry to ask such a basic
question.

I'm trying to wrap the proprietary libspotify C library. I've found this
guide (https://wiki.gnome.org/Projects/Vala/LegacyBindings), which is
really helping with wrapping types and methods. Combined with the Vala
tutorial, I've written a little bit of Vala code to start testing.

Unfortunately, I can't seem to find any information about how to compile my
program so far. I come from a Python background, so compiling and
including/importing other files is generally very simple, but I can't
figure out how to do it with Vala. I've even tried looking through C# and
Mono documentation, but that didn't seem useful.

My package manager has a libspotify package, so I installed it, which gives
me /usr/include/libspotify/api.h and /usr/lib64/libspotify.so. For my
program, I currently have two files fandingo.vala (main program) and
spotify.vala (classes for wrapping libspotify). They are both in the same
directory.

fandingo.vala is currently extremely simple and just has a class for DBus
communication (mostly cobbled together from a Vala DBus tutorial):

using Spotify;


[DBus (name = "org.fandingo.Fandingo")]

class Fandingo.fandingo : GLib.Object {

private int c;

 public int ping(string m) {

stdout.printf("%s\n", m);

return c++;

}


public int ping_with_signal(string m) {

stdout.printf("%s\n", m);

return c++;

}


public void ping_err() throws GLib.Error {

throw new FandingoError.SOME_ERROR("Error encountered");

}


public int sp_error_code() {

Spotify.Error err = Spotify.Error.OK;

stdout.printf("Error: %s, %d\n", err.to_string(), err);

return err;

}


public signal void pong(int count, string msg);

}


[DBus (name = "org.fandingo.FandingoError")]

public errordomain FandingoError {

SOME_ERROR

}


void on_bus_acquired(DBusConnection conn) {

try {

conn.register_object("/org/fandingo/fandingo", new Fandingo.fandingo());

} catch (IOError e) {

stderr.printf("No registration\n");

}

}


void main() {

Bus.own_name (BusType.SESSION, "org.fandingo.Fandingo",
BusNameOwnerFlags.NONE, on_bus_acquired, () => {}, () => stderr.printf("No
name\n"));

new MainLoop().run();

}



spotify.vala is very simple as well, and just wraps the error enum and
method to get an error string:

namespace Spotify {

[CCode (cname = "sp_error", cprefix = "SP_ERROR_", has_type_id= false)]

public enum Error {

OK,

BAD_API_VERSION,

API_INITIALIZATION_FAILED,

TRACK_NOT_PLAYABLE,

  // truncated


[CCode (cname = "sp_error_message")]

private static char* get_string(sp_error err);


public string to_string() {

return (string) Error.get_string(this);

}


}

}

I'm sure there are some programming errors, but I feel like I can work
through those if I can just figure out how to tell the compiler to use
libspotify/api.h.

When I just had fandingo.vala and was doing the DBus testing (without the
sp_error_code() method), compiling was easy:

valac --pkg gio-2.0 fandingo.vala

I've tried using

valac --pkg gio-2.0 fandingo.vala spotify.vala

But that gives me an error presumably because valac doesn't know how to
include api.h/libspotify.so.

spotify.vala:44.35-44.42: error: The type name `sp_error' could not be
found
                private static char* get_string(sp_error err);


                                                ^^^^^^^^


Compilation failed: 1 error(s), 0 warning(s)

I also tried adding a C-style include to spotify.vala: #include
<libspotify/api.h>, but that didn't work.

Again, sorry for the basic question, but I can't seem to figure this out.

Thanks,
Justin