How to encrypt a large file without loading the whole file into memory?

I am new to Go so I am not sure if this is possible.

I found an example here for encrypting and decrypting a file, but as you can see, it requires the entire file to be loaded in memeory as a byte array.

It is possible to encrypt a file reader stream so that the result can be pipe into a writer stream using io.Copy()?

There's an example in the docs that does that!

https://golang.org/pkg/crypto/cipher/#example_StreamWriter

I really wouldn't recommend using it for anything serious because it hasn't been looked over by another set of eyes, but an interesting little package I wrote a while back was https://github.com/ericlagergren/boxer.

It uses secretbox (NaCl) to encrypt chunks and puts the chunk number in the nonce. The idea is from https://www.imperialviolet.org/2014/06/27/streamingencryption.html