I have react front-end and flask backend web application. In this web app, I upload large CSV files from client to server via HTTP multipart/form-data. To achieve this, I take file information in <form encType='multipart/form-data'> element, with <input type='file'>. Then I use axios.post to make a POST request to the server.
On the flask server side, I access the file using request.files['file'] and save the file using file.save. This works as expected. The file is transferred successfully.
I'm thinking to compute MD5 checksum on both client and server side in order to make sure that both sides have files with same MD5 hash. However, this requires reading the file in chunks from the disk and compute the MD5. (since I'm dealing with large files, it is not possible to load the entire file in memory). So, I think this is little inefficient. I want to know whether this transfer via 'HTTP multipart/form-data' provide reliability guarantee? If so, I can ignore the MD5 verification right?
If reliability is not guaranteed, is there any good approach to make sure that both sides have exact same file copy? Thanks in advance.
HTTP integrity is as reliable as the underlying transport protocol, be it TCP (HTTP/1 and 2) or UDP (HTTP/3). Bits can fall over and still yield a valid checksum. This does happen.
If you want to make absolutely sure that you've received the same file as the uploader intended, you need to add a checksum yourself, using for example SHA or MD5.