Fix a bad bounds check for downloads.

Previously, if we created a download with `auto_transfer=True` with the full
download smaller than the default `chunksize`, and then called
`StreamInChunks`, we'd end up downloading the full content twice. This was due
to a bad bounds check in setting a range header -- we'd end up with a header
like `Range: bytes=100-99`, and the server would ignore the start value,
giving us all the bytes again.

This adds a fix and a test.

apitools/base/py/transfer.py

@@ -350,7 +350,7 @@ def __NormalizeStartEnd(self, start, end=None):
     def __SetRangeHeader(self, request, start, end=None):
         if start < 0:
             request.headers['range'] = 'bytes=%d' % start
-        elif end is None:
+        elif end is None or end < start:
             request.headers['range'] = 'bytes=%d-' % start
         else:
             request.headers['range'] = 'bytes=%d-%d' % (start, end)

apitools/base/py/transfer_test.py

@@ -92,6 +92,46 @@ def testComputeEndByteSmallTotal(self):
                              download._Download__ComputeEndByte(start),
                              msg='Failed on start={0}'.format(start))
 
+    def testDownloadThenStream(self):
+        bytes_http = object()
+        http = object()
+        download_stream = six.StringIO()
+        download = transfer.Download.FromStream(download_stream,
+                                                total_size=26)
+        download.bytes_http = bytes_http
+        base_url = 'https://part.one/'
+        with mock.patch.object(http_wrapper, 'MakeRequest',
+                               autospec=True) as make_request:
+            make_request.return_value = http_wrapper.Response(
+                info={
+                    'content-range': 'bytes 0-25/26',
+                    'status': http_client.OK,
+                },
+                content=string.ascii_lowercase,
+                request_url=base_url,
+            )
+            request = http_wrapper.Request(url='https://part.one/')
+            download.InitializeDownload(request, http=http)
+            self.assertEqual(1, make_request.call_count)
+            received_request = make_request.call_args[0][1]
+            self.assertEqual(base_url, received_request.url)
+            self.assertRangeAndContentRangeCompatible(
+                received_request, make_request.return_value)
+
+        with mock.patch.object(http_wrapper, 'MakeRequest',
+                               autospec=True) as make_request:
+            make_request.return_value = http_wrapper.Response(
+                info={
+                    'status': http_client.REQUESTED_RANGE_NOT_SATISFIABLE,
+                },
+                content='error',
+                request_url=base_url,
+            )
+            download.StreamInChunks()
+            self.assertEqual(1, make_request.call_count)
+            received_request = make_request.call_args[0][1]
+            self.assertEqual('bytes=26-', received_request.headers['range'])
+
     def testGetRange(self):
         for (start_byte, end_byte) in [(0, 25), (5, 15), (0, 0), (25, 25)]:
             bytes_http = object()