NJB_Get_Track - Upload a copy of a song from the NJB to the host

libnjb

#include <sys/types.h> #include <libnjb.h>

extern int njb_error

int NJB_Get_Track (njb_t *njb, u_int32_t trackid, u_int32_t size, const char *path, XferCallback *callback, void *data)

This function uploads a song track from the NJB (without deleting it from the NJB) and saves it to the filename specified by *path.

The desired song's track ID is stored in trackid. Note that the calling program must also know the size of the file to be transferred, and sent in the size parameter. Both the track ID and the file size can be found in the song tag for the desired track, as returned by NJB_Get_Track_Tag (3). Generally, the calling program should fetch (and cache) the complete track list from the NJB, so that all of this information is readily available.

For reliability, the track is first downloaded to a temporary directory (see NJB_Get_TmpDir(3)) before being copied into place. By default, the temporary directory is /tmp, but it can be changed by the NJB_Set_TmpDir(3) function.

The callback parameter is actually a pointer to a function of type XferCallback, and is called after each file block is transferred. The definition for XferCallback is found in libnjb.h:

typedef int XferCallback(off_t sent, off_t total);

This callback function gives the calling program the ability to maintain a status bar, showing bytes transferred (the sent paramater), and the total size of the file being sent (in total). It also provides an "abort" capability, in case the end user wishes to cancel the file transfer: if the callback function returns -1, then the file transfer is aborted and the temporary copy of the file is removed.

The data parameter is a pointer to user data of any kind that the user of the library wants to associate with this transfer. This pointer is used for example when accessing several different jukeboxes from withing one program. The XferCallback will also be delivering this pointer to the target routine for dereferencing. If this parameter is not used (in for example single-device, single-threaded programs) it may be set to NULL.

If the transfer is successful, 0 is returned. Otherwise, -1 is returned and njb_error is set as follows:

EO_ABORTED

The transfer was aborted by the user (the callback function returned -1).

EO_BADSTATUS

A non-zero status was returned by the NJB during the file transfer.

EO_CANTMOVE

The transferred track could not be moved from the temporary directory to the specified location (see the *path parameter).

EO_NOMEM

There was not enough memory to allocate the file transfer buffer.

EO_NULLTMP

The temporary directory is undefined (a NULL pointer).

EO_RDSHORT

The NJB sent fewer bytes than expected on the bulk data pipe.

EO_TMPFILE

The temporary transfer file could not be created in the temporary directory.

EO_USBBLK

An I/O error occurred on the bulk data pipe.

EO_USBCTL

An I/O error occurred on the control pipe.

EO_WRFILE

An error occurred while writing to the temporary transfer file.

EO_XFERDENIED

The NJB returned a non-zero status when the file transfer was requested. The track may be write protected, or the given track ID may not exist.

EO_XFERERROR

The NJB returned a non-zero status when the host requested verification of the file transfer.

NJB_Get_TmpDir(3), NJB_Get_Track_Tag(3), NJB_Set_TmpDir(3), XferCallback(3)