Merge pull request #454 from reef-technologies/empty_stream_error

In case no data is provided from the stream, we still provide an empty WriteIntent

b2sdk/transfer/emerge/unbound_write_intent.py

@@ -174,6 +174,12 @@ def iterator(self) -> Iterator[WriteIntent]:
             offset += len(self.buffer)
             self._rotate_leftovers()
 
+        # If we didn't stream anything, we should still provide
+        # at least an empty WriteIntent, so that the file will be created.
+        if offset == 0:
+            source = UnboundSourceBytes(bytearray(), release_function=lambda: None)
+            yield WriteIntent(source, destination_offset=offset)
+
     def _trim_to_leftovers(self) -> None:
         if len(self.buffer) <= self.buffer_size_bytes:
             return

changelog.d/+can-stream-empty-stream.fixed.md

@@ -0,0 +1 @@
+Streaming from empty stream no longer ends with "Empty emerge parts iterator" error.

test/unit/bucket/test_bucket.py

@@ -2850,6 +2850,13 @@ def test_upload_unbound_stream(self):
             )
             test_case.assert_(file_version)
 
+    def test_upload_empty_unbound_stream(self):
+        for test_case in self.test_cases:
+            file_version = self.bucket.upload_unbound_stream(
+                io.BytesIO(b''), 'file1', **test_case.kwargs
+            )
+            test_case.assert_(file_version)
+
     def test_upload_local_file(self):
         for test_case in self.test_cases:
             with tempfile.TemporaryDirectory() as d: