Don't write entire tar file in to memory

[sts10]

To speed up performance and lower memory consumption, Bottle should archive, compress and encrypt the contents of a file (tar or otherwise) in chunks when encrypting/decrypting.

Currently, when encrypting a directory, Bottle writes the entire directory's contents to tar file on the file system, then read that tar file back into memory in order to compress it.

https://github.com/sts10/bottle-rs/blob/main/src/lib.rs#L187-L200

Not great! I think attacking this part of the pipeline would be best.

Thankfully, the Builder of the tar crate we're using takes a Writer, so we should be able to make our own Writer impl that directs the tar stream into compression.[1] I'm not sure how to do that yet, so any comments or PRs welcome!

If done right, this will also eliminate the need to write the (unencrypted) tar file to the file system, removing a potential security issue.

After that, we'll have to figure out how to "chunk" the compress-to-encryption pipeline.

(1) Relevant Rust book pages: 178 and in O'Reilly: 428?

[sts10]

c1f0fcb at least makes it so Bottle doesn't write the tar file to the file system when encrypting a directory. It still reads the entire file into memory -- we still need to chunk it.

[sts10]

More potentially useful links for me to consult when I'm ready to make another go at this:

• https://docs.rs/tar/latest/tar/struct.Archive.html
• https://doc.rust-lang.org/std/io/trait.Write.html