Add LIBMTP_Get_Children() to read the list of raw IDs of a folder.

patches/19_raw_read_directory.patch

+diff --git src/libmtp.c src/libmtp.c
+index b91f246..bbe2642 100644
+--- src/libmtp.c
++++ src/libmtp.c
+@@ -4415,6 +4415,78 @@ LIBMTP_file_t * LIBMTP_Get_Files_And_Folders(LIBMTP_mtpdevice_t *device,
+   return retfiles;
+ }
+ 
++/**
++ * This function retrieves the list of ids of files and folders in a certain
++ * folder with id parent on a certain storage on a certain device.
++ * The device used with this operations must have been opened with
++ * LIBMTP_Open_Raw_Device_Uncached() or it will fail.
++ *
++ * NOTE: the request will always perform I/O with the device.
++ * @param device a pointer to the MTP device to report info from.
++ * @param storage a storage on the device to report info from. If
++ *        0 is passed in, the files for the given parent will be
++ *        searched across all available storages.
++ * @param parent the parent folder id.
++ * @param out the pointer where the array of ids is returned. It is
++ *        set only when the returned value > 0. The caller takes the
++ *        ownership of the array and has to free() it.
++ * @return the length of the returned array or -1 in case of failure.
++ */
++
++int LIBMTP_Get_Children(LIBMTP_mtpdevice_t *device,
++                        uint32_t const storage,
++                        uint32_t const parent,
++                        uint32_t **out)
++{
++  PTPParams *params = (PTPParams *) device->params;
++  PTP_USB *ptp_usb = (PTP_USB*) device->usbinfo;
++  LIBMTP_file_t *retfiles = NULL;
++  LIBMTP_file_t *curfile = NULL;
++  PTPObjectHandles currentHandles;
++  uint32_t storageid;
++  uint16_t ret;
++  int i = 0;
++
++  if (device->cached) {
++    // This function is only supposed to be used by devices
++    // opened as uncached!
++    LIBMTP_ERROR("tried to use %s on a cached device!\n", __func__);
++    return -1;
++  }
++
++  if (FLAG_BROKEN_GET_OBJECT_PROPVAL(ptp_usb)) {
++    // These devices cannot handle the commands needed for
++    // Uncached access!
++    LIBMTP_ERROR("tried to use %s on an unsupported device, "
++                 "this command does not work on all devices "
++                 "due to missing low-level support to read "
++                 "information on individual tracks\n",
++                 __func__);
++    return -1;
++  }
++
++  if (storage == 0)
++    storageid = PTP_GOH_ALL_STORAGE;
++  else
++    storageid = storage;
++
++  ret = ptp_getobjecthandles(params,
++                             storageid,
++                             PTP_GOH_ALL_FORMATS,
++                             parent,
++                             &currentHandles);
++
++  if (ret != PTP_RC_OK) {
++    add_ptp_error_to_errorstack(device, ret,
++        "LIBMTP_Get_Children(): could not get object handles.");
++    return -1;
++  }
++
++  if (currentHandles.Handler == NULL || currentHandles.n == 0)
++    return 0;
++  *out = currentHandles.Handler;
++  return currentHandles.n;
++}
+ 
+ /**
+  * This creates a new track metadata structure and allocates memory
+diff --git src/libmtp.h src/libmtp.h
+index 33fac41..f923cc1 100644
+--- src/libmtp.h
++++ src/libmtp.h
+@@ -875,6 +875,10 @@ LIBMTP_file_t *LIBMTP_Get_Filelisting_With_Callback(LIBMTP_mtpdevice_t *,
+ LIBMTP_file_t * LIBMTP_Get_Files_And_Folders(LIBMTP_mtpdevice_t *,
+                                             uint32_t const,
+                                             uint32_t const);
++int LIBMTP_Get_Children(LIBMTP_mtpdevice_t *,
++                        uint32_t const,
++                        uint32_t const,
++                        uint32_t **);
+ LIBMTP_file_t *LIBMTP_Get_Filemetadata(LIBMTP_mtpdevice_t *, uint32_t const);
+ int LIBMTP_Get_File_Chunk(LIBMTP_mtpdevice_t*, uint32_t, uint32_t, uint32_t,
+                           unsigned char**, uint32_t*);
+diff --git src/libmtp.h.in src/libmtp.h.in
+index b49d449..2b2f0bb 100644
+--- src/libmtp.h.in
++++ src/libmtp.h.in
+@@ -875,6 +875,10 @@ LIBMTP_file_t *LIBMTP_Get_Filelisting_With_Callback(LIBMTP_mtpdevice_t *,
+ LIBMTP_file_t * LIBMTP_Get_Files_And_Folders(LIBMTP_mtpdevice_t *,
+                                             uint32_t const,
+                                             uint32_t const);
++int LIBMTP_Get_Children(LIBMTP_mtpdevice_t *,
++                        uint32_t const,
++                        uint32_t const,
++                        uint32_t**);
+ LIBMTP_file_t *LIBMTP_Get_Filemetadata(LIBMTP_mtpdevice_t *, uint32_t const);
+ int LIBMTP_Get_File_Chunk(LIBMTP_mtpdevice_t*, uint32_t, uint32_t, uint32_t,
+                           unsigned char**, uint32_t*);
+diff --git src/libmtp.sym src/libmtp.sym
+index b6951b2..4130fe8 100644
+--- src/libmtp.sym
++++ src/libmtp.sym
+@@ -48,6 +48,7 @@ LIBMTP_Get_Filetype_Description
+ LIBMTP_Get_Filelisting
+ LIBMTP_Get_Filelisting_With_Callback
+ LIBMTP_Get_Files_And_Folders
++LIBMTP_Get_Children
+ LIBMTP_Get_Filemetadata
+ LIBMTP_Get_File_Chunk
+ LIBMTP_Get_File_To_File