Allow empty files to be uploaded.

google/resumable_media/_upload.py

@@ -526,7 +526,7 @@ def _prepare_request(self):
                 u'This upload has not been initiated. Please call '
                 u'initiate() before beginning to transmit chunks.')
 
-        start_byte, end_byte, payload, content_range = get_next_chunk(
+        start_byte, payload, content_range = get_next_chunk(
             self._stream, self._chunk_size, self._total_bytes)
         if start_byte != self.bytes_uploaded:
             msg = _STREAM_ERROR_TEMPLATE.format(
@@ -784,14 +784,15 @@ def get_next_chunk(stream, chunk_size, total_bytes):
             in the ``stream``.
 
     Returns:
-        Tuple[int, int, bytes, str]: Quadruple of:
+        Tuple[int, bytes, str]: Triple of:
 
           * the start byte index
-          * the end byte index
           * the content in between the start and end bytes (inclusive)
           * content range header for the chunk (slice) that has been read
 
     Raises:
+        ValueError: If ``total_bytes == 0`` but ``stream.read()`` yields
+            non-empty content.
         ValueError: If there is no data left to consume. This corresponds
             exactly to the case ``end_byte < start_byte``, which can only
             occur if ``end_byte == start_byte - 1``.
@@ -807,6 +808,13 @@ def get_next_chunk(stream, chunk_size, total_bytes):
         if num_bytes_read < chunk_size:
             # We now **KNOW** the total number of bytes.
             total_bytes = end_byte + 1
+    elif total_bytes == 0:
+        # NOTE: We also expect ``start_byte == 0`` here but don't check
+        #       because ``_prepare_initiate_request()`` requires the
+        #       stream to be at the beginning.
+        if num_bytes_read != 0:
+            raise ValueError(
+                u'Stream specified as empty, but produced non-empty content.')
     else:
         if num_bytes_read == 0:
             raise ValueError(
@@ -817,7 +825,7 @@ def get_next_chunk(stream, chunk_size, total_bytes):
             raise ValueError(msg)
 
     content_range = get_content_range(start_byte, end_byte, total_bytes)
-    return start_byte, end_byte, payload, content_range
+    return start_byte, payload, content_range
 
 
 def get_content_range(start_byte, end_byte, total_bytes):

tests/unit/test__upload.py

@@ -860,6 +860,19 @@ def test_exhausted_known_size(self):
         exc_info.match(
             u'Stream is already exhausted. There is no content remaining.')
 
+    def test_exhausted_known_size_zero(self):
+        stream = io.BytesIO(b'')
+        answer = _upload.get_next_chunk(stream, 1, 0)
+        assert answer == (0, b'', 'bytes */0')
+
+    def test_exhausted_known_size_zero_nonempty(self):
+        stream = io.BytesIO(b'not empty WAT!')
+        with pytest.raises(ValueError) as exc_info:
+            _upload.get_next_chunk(stream, 1, 0)
+
+        exc_info.match(
+            u'Stream specified as empty, but produced non-empty content.')
+
     def test_read_past_known_size(self):
         data = b'more content than we expected'
         stream = io.BytesIO(data)
@@ -882,10 +895,10 @@ def test_success_known_size(self):
         result1 = _upload.get_next_chunk(stream, chunk_size, total_bytes)
         result2 = _upload.get_next_chunk(stream, chunk_size, total_bytes)
         result3 = _upload.get_next_chunk(stream, chunk_size, total_bytes)
-        assert result0 == (0, 2, b'012', u'bytes 0-2/10')
-        assert result1 == (3, 5, b'345', u'bytes 3-5/10')
-        assert result2 == (6, 8, b'678', u'bytes 6-8/10')
-        assert result3 == (9, 9, b'9', u'bytes 9-9/10')
+        assert result0 == (0, b'012', u'bytes 0-2/10')
+        assert result1 == (3, b'345', u'bytes 3-5/10')
+        assert result2 == (6, b'678', u'bytes 6-8/10')
+        assert result3 == (9, b'9', u'bytes 9-9/10')
         assert stream.tell() == total_bytes
 
     def test_success_unknown_size(self):
@@ -895,8 +908,8 @@ def test_success_unknown_size(self):
         # Splits into 4 chunks: abcdef, ghij
         result0 = _upload.get_next_chunk(stream, chunk_size, None)
         result1 = _upload.get_next_chunk(stream, chunk_size, None)
-        assert result0 == (0, chunk_size - 1, b'abcdef', u'bytes 0-5/*')
-        assert result1 == (chunk_size, len(data) - 1, b'ghij', u'bytes 6-9/10')
+        assert result0 == (0, b'abcdef', u'bytes 0-5/*')
+        assert result1 == (chunk_size, b'ghij', u'bytes 6-9/10')
         assert stream.tell() == len(data)
 
         # Do the same when the chunk size evenly divides len(data)
@@ -905,8 +918,8 @@ def test_success_unknown_size(self):
         # Splits into 2 chunks: `data` and empty string
         result0 = _upload.get_next_chunk(stream, chunk_size, None)
         result1 = _upload.get_next_chunk(stream, chunk_size, None)
-        assert result0 == (0, len(data) - 1, data, u'bytes 0-9/*')
-        assert result1 == (len(data), len(data) - 1, b'', u'bytes */10')
+        assert result0 == (0, data, u'bytes 0-9/*')
+        assert result1 == (len(data), b'', u'bytes */10')
         assert stream.tell() == len(data)