Add LIBMTP_Get_File_Chunk() to read an arbitrary amount of data into memory. The existing APIs only…

patches/15_read_chunks.diff

Index: patches/15_read_chunks.diff
===================================================================
--- patches/15_read_chunks.diff	(revision 0)
+++ patches/15_read_chunks.diff	(revision 0)
@@ -0,0 +1,99 @@
+Index: src/libmtp.c
+===================================================================
+--- src/libmtp.c	(revision 167447)
++++ src/libmtp.c	(working copy)
+@@ -4972,6 +4972,56 @@
+ }
+ 
+ /**
++ * This copies a chunk of a file off the device to memory.
++ * @param device a pointer to the device to get the track from.
++ * @param id the file ID of the file to retrieve.
++ * @param offset the offset of the file to read from.
++ * @param count the amount of data to read.
++ * @param data a pointer to the data from the device. Must be
++ *             <coded>free()</code>:ed by the caller after use.
++ * @param datalen the amount of data written to <code>data</code>.
++ * @return 0 if the transfer was successful, any other value means
++ *           failure.
++ */
++int LIBMTP_Get_File_Chunk(LIBMTP_mtpdevice_t* device, uint32_t id,
++                          uint32_t offset, uint32_t count,
++                          unsigned char** data, uint32_t* datalen)
++{
++  uint16_t ret;
++  PTPParams *params = (PTPParams *) device->params;
++  PTP_USB *ptp_usb = (PTP_USB*) device->usbinfo;
++  PTPObject *ob;
++
++  if (!data || !datalen) {
++    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL, "LIBMTP_Get_File_Chunk(): Invalid parameter.");
++    return -1;
++  }
++
++  ret = ptp_object_want (params, id, PTPOBJECT_OBJECTINFO_LOADED, &ob);
++  if (ret != PTP_RC_OK) {
++    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL, "LIBMTP_Get_File_Chunk(): Could not get object info.");
++    return -1;
++  }
++  if (ob->oi.ObjectFormat == PTP_OFC_Association) {
++    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL, "LIBMTP_Get_File_Chunk(): Bad object format.");
++    return -1;
++  }
++
++  ret = ptp_getpartialobject(params, id, offset, count, data, datalen);
++
++  if (ret == PTP_ERROR_CANCEL) {
++    add_error_to_errorstack(device, LIBMTP_ERROR_CANCELLED, "LIBMTP_Get_File_Chunk(): Cancelled transfer.");
++    return -1;
++  }
++  if (ret != PTP_RC_OK) {
++    add_ptp_error_to_errorstack(device, ret, "LIBMTP_Get_File_Chunk(): Could not get file from device.");
++    return -1;
++  }
++
++  return 0;
++}
++
++/**
+  * This is a manual conversion from MTPDataGetFunc to PTPDataGetFunc
+  * to isolate the internal type.
+  */
+Index: src/libmtp.h
+===================================================================
+--- src/libmtp.h	(revision 167447)
++++ src/libmtp.h	(working copy)
+@@ -876,6 +876,8 @@
+ 					     uint32_t const,
+ 					     uint32_t const);
+ 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*);
+ int LIBMTP_Get_File_To_File(LIBMTP_mtpdevice_t*, uint32_t, char const * const,
+ 			LIBMTP_progressfunc_t const, void const * const);
+ int LIBMTP_Get_File_To_File_Descriptor(LIBMTP_mtpdevice_t*,
+Index: src/libmtp.h.in
+===================================================================
+--- src/libmtp.h.in	(revision 167447)
++++ src/libmtp.h.in	(working copy)
+@@ -876,6 +876,8 @@
+ 					     uint32_t const,
+ 					     uint32_t const);
+ 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*);
+ int LIBMTP_Get_File_To_File(LIBMTP_mtpdevice_t*, uint32_t, char const * const,
+ 			LIBMTP_progressfunc_t const, void const * const);
+ int LIBMTP_Get_File_To_File_Descriptor(LIBMTP_mtpdevice_t*,
+Index: src/libmtp.sym
+===================================================================
+--- src/libmtp.sym	(revision 167447)
++++ src/libmtp.sym	(working copy)
+@@ -49,6 +49,7 @@
+ LIBMTP_Get_Filelisting_With_Callback
+ LIBMTP_Get_Files_And_Folders
+ LIBMTP_Get_Filemetadata
++LIBMTP_Get_File_Chunk
+ LIBMTP_Get_File_To_File
+ LIBMTP_Get_File_To_File_Descriptor
+ LIBMTP_Get_File_To_Handler