Add ability to cache / reuse scan results by SHA1

[volodymyrsmirnov]

Think about the way to cache SHA1 hash-sum of scanned files in order not to scan same files from multiple sources more than a single time.

[P3GLEG]

How do you feel about using the Redis backend to hold this info?

[TristanWasTaken]

It would be a good idea to save the hash directly with Redis or in the MongoDB database with Redis caching.
I would generate the hash when uploading files from the browser/client and send it to the api. If the hash is already in the database, I would reject the upload and use the data saved for the hash. This saves time and computing power. In addition, if the hash that was sent to the api is not in the database and the file was uploaded, I would let the server check the hash again. Someone could alter the hash and use it as an attack and fill the server's hard drive.