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

src/libmtp.c

 /**
  * \file libmtp.c
  *
  * Copyright (C) 2005-2011 Linus Walleij <triad@df.lth.se>
  * Copyright (C) 2005-2008 Richard A. Low <richard@wentnet.com>
  * Copyright (C) 2007 Ted Bullock <tbullock@canada.com>
  * Copyright (C) 2007 Tero Saarni <tero.saarni@gmail.com>
  * Copyright (C) 2008 Florent Mertens <flomertens@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 4954 matching lines @@
       // This was not an OGG/FLAC file so discard it
       LIBMTP_destroy_track_t(track);
       return NULL;
     }
   }
   get_track_metadata(device, ob->oi.ObjectFormat, track);
   return track;
 }
 
 /**
+ * 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);

[Jorge Lucangeli Obes, 2012/11/15 01:46:10]

I'm not sure what the coding standard is for third_party, but we should be able
to keep it consistent inside one file. Did you write this code from scratch?

[Lei Zhang, 2012/11/15 01:50:11]

This is copied from line 5158. The code in this file is not 100% consistent with
itself. :)

+  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.
  */
 static uint16_t get_func_wrapper(PTPParams* params, void* priv, unsigned long wantlen, unsigned char *data, unsigned long *gotlen)
 {
   MTPDataHandler *handler = (MTPDataHandler *)priv;
   uint16_t ret;
   uint32_t local_gotlen = 0;
   ret = handler->getfunc(params, handler->priv, wantlen, data, &local_gotlen);
   *gotlen = local_gotlen;
@@ skipping 3909 matching lines @@
  * @param device the device which may have a cache to which the object should be updated.
  * @param object_id the object to update.
  */
 static void update_metadata_cache(LIBMTP_mtpdevice_t *device, uint32_t object_id)
 {
   PTPParams *params = (PTPParams *)device->params;
 
   ptp_remove_object_from_cache(params, object_id);
   add_object_to_cache(device, object_id);
 }