commit 9a132872dd12e68edc0c6153213da06e20163c32
Author: Dmitry Nezhevenko <dion@dion.org.ua>
Date:   Mon May 30 10:14:36 2016 +0300

    dpbx: upload last chunk with files_upload_session_finish to avoid extra request

diff --git a/duplicity/backends/dpbxbackend.py b/duplicity/backends/dpbxbackend.py
index a5c53ef..46666a5 100644
--- a/duplicity/backends/dpbxbackend.py
+++ b/duplicity/backends/dpbxbackend.py
@@ -190,10 +190,11 @@ class DPBXBackend(duplicity.backend.Backend):
             requested_offset = None
             current_chunk_size = DPBX_UPLOAD_CHUNK_SIZE
             retry_number = globals.num_retries
+            is_eof = False
 
             # We're doing our own error handling and retrying logic because
             # we can benefit from Dpbx chunked upload and retry only failed chunk
-            while (f.tell() < file_size) or not res_metadata:
+            while not is_eof or not res_metadata:
                 try:
                     if requested_offset is not None:
                         upload_cursor.offset = requested_offset
@@ -202,12 +203,17 @@ class DPBXBackend(duplicity.backend.Backend):
                         f.seek(upload_cursor.offset)
                     buf = f.read(current_chunk_size)
 
+                    is_eof = f.tell() >= file_size
+                    if not is_eof and len(buf) == 0:
+                        continue
+
                     # reset temporary status variables
                     requested_offset = None
                     current_chunk_size = DPBX_UPLOAD_CHUNK_SIZE
                     retry_number = globals.num_retries
 
-                    if len(buf) != 0:
+                    if not is_eof:
+                        assert len(buf) != 0
                         log.Debug('dpbx,files_upload_sesssion_append([%d bytes], offset=%d)' % (len(buf), upload_cursor.offset))
                         self.api_client.files_upload_session_append(buf, upload_cursor.session_id, upload_cursor.offset)
                     else: