Reuse existing BytesIO object

ia-upload-stream

@@ -101,8 +101,13 @@ def readinto_size_limit(fin, fout, size, blockSize = 1048576):
 		size -= len(d)
 
 
-def get_part(f, partSize, progress):
-	data = io.BytesIO()
+def get_part(f, partSize, progress, _data = None):
+	if _data is not None:
+		data = _data
+		data.seek(0)
+		data.truncate()
+	else:
+		data = io.BytesIO()
 	with maybe_file_progress_bar(progress, data, 'write', 'reading input') as w:
 		readinto_size_limit(f, w, partSize)
 	data.seek(0)
@@ -198,7 +203,7 @@ def upload_one(url, uploadId, partNumber, data, contentMd5, size, headers, progr
 			raise UploadError(f'Got {err} from IA S3 on uploading part {partNumber}', r = r, uploadId = uploadId) # parts is added in wait_first
 		time.sleep(sleepTime)
 		data.seek(0)
-	return partNumber, r.headers['ETag']
+	return partNumber, r.headers['ETag'], data
 
 
 def wait_first(tasks, parts):
@@ -206,13 +211,14 @@ def wait_first(tasks, parts):
 	done, _ = concurrent.futures.wait({task})
 	assert task in done
 	try:
-		partNumber, eTag = task.result()
+		partNumber, eTag, data = task.result()
 	except UploadError as e:
 		# The upload task can't add an accurate parts list, so add that here and reraise
 		e.parts = parts
 		raise
 	parts.append((partNumber, eTag))
 	logger.info(f'Upload of part {partNumber} OK, ETag: {eTag}')
+	return data
 
 
 def upload(item, filename, metadata, *, iaConfigFile = None, partSize = 100*1024*1024, tries = 3, partTimeout = None, concurrency = 1, queueDerive = True, keepOldVersion = True, complete = True, uploadId = None, parts = None, progress = True, sizeHint = None):
@@ -277,9 +283,10 @@ def upload(item, filename, metadata, *, iaConfigFile = None, partSize = 100*1024
 		tasks.append(task)
 
 		for partNumber in itertools.count(start = len(parts) + 2):
+			data = None
 			while len(tasks) >= concurrency:
-				wait_first(tasks, parts)
-			data, size, contentMd5 = get_part(f, partSize, progress)
+				data = wait_first(tasks, parts)
+			data, size, contentMd5 = get_part(f, partSize, progress, _data = data)
 			if not size:
 				# We're done!
 				break