Splitting large payload into multiple messages

[delbonis]

I have a use-case where I need to split up a payload into a series of Noise messages, but it's not clear to me what the most efficient chunk size should be.

The TransportState type (and related types) doesn't provide a way to know the maximum size of a payload for a single message. It just says that if the final message would be larger than the 65535-byte maximum that it returns an Err.

Looking at the code I know the tag is 16 bytes (so it works out to be 65519 bytes I guess), but that's not exposed to me through the API in a convenient way.

I'm envisioning an interface where you can supply a large &[u8] and have the encryption call return the number of bytes consumed from the slice, so on subsequent calls we can move forwards the beginning of the slice and continue.

[mcginty]

Hey @delbonis! Yeah, the maximum payload size for transport messages should really be exposed in the API, good point.

True that it'd be nice to have a convenience method for large payloads. I was thinking snow might benefit from having some convenience APIs that return Vec<u8>s anyway, so a method that takes a large payload chunk and returns a Vec<Vec<u8>> could be on the table too.

In the mean time, if you haven't checked out slice::chunks(), it makes this type of thing a lot cleaner even without a convenience method :).