I’m encountering a MalformedXML error when calling the CompleteMultipartUpload operation with AWS S3. Here’s a summary of the situation:

I am trying to upload a large file to S3 using multipart upload. The file is larger than 1GB, so I am splitting it into parts and uploading each part separately. After uploading all parts, I call complete_multipart_upload to finalize the upload. However, I’m receiving the following error:
“An error occurred (MalformedXML) when calling the CompleteMultipartUpload operation: The XML you provided was not well-formed or did not validate against our published schema”

I try this,

def save_uploaded_file_data(self, data): # data - file object
    try:
        file_extension = Path(data.filename).suffix[1:]
        content = data.read()
        file_size = len(content)
        file_data = FileData(name=data.filename, size=file_size, extension=file_extension)

        s3_client = boto3.client(
            service_name='s3',
            region_name=Config.AWS_REGION,
            aws_access_key_id=Config.AWS_ACCESS_KEY_ID,
            aws_secret_access_key=Config.AWS_SECRET_ACCESS_KEY
        )

        bucket_name = 'uploaderbuck'
        key = data.filename

        if file_size >= 1 * 1024 * 1024 * 1024:
            part_size = 500 * 1024 * 1024

            response = s3_client.create_multipart_upload(Bucket=bucket_name, Key=key, StorageClass='DEEP_ARCHIVE')
            upload_id = response['UploadId']
            parts = []
            part_number = 1
            with data.stream as f:
                while True:
                    part_data = f.read(part_size)
                    if not part_data:
                        break

                    part_response = s3_client.upload_part(
                        Bucket=bucket_name,
                        Key=key,
                        PartNumber=part_number,
                        UploadId=upload_id,
                        Body=part_data
                    )

                    parts.append({'PartNumber': part_number, 'ETag': part_response['ETag']})
                    print(f"Uploaded part {part_number}")
                    part_number += 1


            s3_client.complete_multipart_upload(
                Bucket=bucket_name,
                Key=key,
                UploadId=upload_id,
                MultipartUpload={'Parts': parts}
            )

        else:
            s3_client.upload_fileobj(data, bucket_name, key, ExtraArgs={'StorageClass': 'DEEP_ARCHIVE'})

        file_data.save()
        return {}, 200
    except Exception as e:
        return jsonify(str(e)), 500