JNA: The specified procedure could not be found

[Nathan Barraille]

Hello,

I was trying to learn how JNA works, so I decided to use the spotify API (libspotify 0.0.7). I managed to load my dll correctly, but then it looks like my code is not finding any of the method defined in the API:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'sp_session_create': The specified procedure could not be found.

	at com.sun.jna.Function.<init>(Function.java:129)
	at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:250)
	at com.sun.jna.Library$Handler.invoke(Library.java:191)
	at $Proxy0.sp_session_create(Unknown Source)
	at com.nbarraille.jspotify.main.Test.main(Test.java:50)

I'm running Windows 7 x86 and I'm running my code in Eclipse.


Here is my code:

Main class

public class Test{
	private static final int SPOTIFY_API_VERSION = 7;
	private static final char[] APP_KEY = { 0x01, 0xF8, ... /* The rest of my key here */ };
	
	static{
		System.loadLibrary("libspotify");
	}
	
	public static void main(String[] args){
		JLibspotify libs = JLibspotify.INSTANCE;
		
		sp_session mySession = new sp_session();
		sp_session_config cfg = new sp_session_config();
		cfg.api_version = SPOTIFY_API_VERSION;
		cfg.cache_location = "tmp";
		cfg.settings_location = "tmp";
		cfg.application_key = APP_KEY;
		cfg.application_key_size = APP_KEY.length;
		cfg.user_agent = "spshell";
		cfg.callbacks = null;
		
		libs.sp_session_create(cfg, mySession.getPointer());
	}
}

My Library wrapping interface:

public interface JLibspotify extends StdCallLibrary {	
	JLibspotify INSTANCE = (JLibspotify)Native.loadLibrary("libspotify", JLibspotify.class);
	
	// Methods definitions
	sp_error sp_session_create(sp_session_config config, Pointer sess);
}

Here is the declaration of the method I'm trying to call

/** * Initialize a session. The session returned will be initialized, but you will need * to log in before you can perform any other operation * * Here is a snippet from \c spshell.c: * @dontinclude spshell.c * @skip config.api_version * @until } * * @param[in] config The configuration to use for the session * @param[out] sess If successful, a new session - otherwise NULL * * @return One of the following errors, from ::sp_error * SP_ERROR_OK * SP_ERROR_BAD_API_VERSION * SP_ERROR_BAD_USER_AGENT * SP_ERROR_BAD_APPLICATION_KEY * SP_ERROR_API_INITIALIZATION_FAILED */ SP_LIBEXPORT(sp_error) sp_session_create(const sp_session_config *config, sp_session **sess);


The domain classes:

public class sp_session_config extends Structure{
	public int api_version; // The version of the Spotify API your application is compiled with.
	public String cache_location;
	public String settings_location;
	public char[] application_key; // Your application key.
	public int application_key_size; // The size of the application key in bytes
	public String user_agent;
	public sp_session_callbacks callbacks; // Delivery callbacks for session events. NULL if not interested in any callbacks
	public Pointer userdata; // User supplied data for your application
	public boolean compress_playlists;
	public boolean dont_save_metadata_for_playlists;
	public boolean initially_unload_playlists;
}

// sp_session is an opaque C++ class, so I create it as a PointerType
public class sp_session extends PointerType{
	public sp_session(Pointer address) {
		super(address);
	}
	public sp_session() {
		super();
	}
}

public enum sp_error {
	SP_ERROR_OK, 
	SP_ERROR_BAD_API_VERSION, 
	SP_ERROR_API_INITIALIZATION_FAILED, 
	SP_ERROR_TRACK_NOT_PLAYABLE, 
	SP_ERROR_RESOURCE_NOT_LOADED, 
	SP_ERROR_BAD_APPLICATION_KEY, 
	SP_ERROR_BAD_USERNAME_OR_PASSWORD, 
	SP_ERROR_USER_BANNED, 
	SP_ERROR_UNABLE_TO_CONTACT_SERVER, 
	SP_ERROR_CLIENT_TOO_OLD, 
	SP_ERROR_OTHER_PERMANENT, 
	SP_ERROR_BAD_USER_AGENT, 
	SP_ERROR_MISSING_CALLBACK, 
	SP_ERROR_INVALID_INDATA, 
	SP_ERROR_INDEX_OUT_OF_RANGE, 
	SP_ERROR_USER_NEEDS_PREMIUM, 
	SP_ERROR_OTHER_TRANSIENT, 
	SP_ERROR_IS_LOADING, 
	SP_ERROR_NO_STREAM_AVAILABLE, 
	SP_ERROR_PERMISSION_DENIED, 
	SP_ERROR_INBOX_IS_FULL, 
	SP_ERROR_NO_CACHE, 
	SP_ERROR_NO_SUCH_USER
}

Do you have any idea of what's happening? Do you see any problem with my code?

Thank you!!!

nbarraille

[Nathan Barraille]

I finally found the solution by opening the libspotify.dll with Dependency Walker: The compiler added some extra information to the method name (a underscore prefix and a @4 or @8 suffix).

I had to:

- Create an implementation of FunctionMapper that renamed all my methods according to the real names (available in Dependency Walker)
- Instantiate my Library with an instance of this mapper in the options map.