Give back Writer on Encoder::finish()

[algesten]

If using a Cursor<Vec<u8>> to write to memory, or an auto-removing temp file (https://docs.rs/tempfile/3.5.0/tempfile/fn.tempfile.html#resource-leaking), there needs to be some way of getting the captured writer back.

I suggest adding the writer as output of the finish call, so we can get ownership of it back.

[AlexTMjugador]

Thank you for using this crate and submitting a PR! ❤️

Since finish does not currently return anything interesting on success, I think that it is a sensible idea to yield the sink back there.

However, the standard library provides a by_ref method for every Write, the purpose of which is to avoid transferring ownership of a writer to methods and data types that take a Write implementation, such as VorbisEncoder, by mutably borrowing it instead.

Does your PR solve any problem that by_ref does not? (Just asking, it could be merged even if it didn't 😄)

[algesten]

@AlexTMjugador thanks for the prompt reply!

My problem with using a borrowed writer is that the borrow lifetime parameter must leak upward into any wrapping struct.

In my case I have a struct Output which holds both the vorbis encoder as well as a mixer since they are used together.

struct Output {
  encoder: Encoder<File>,
  mixer: Mixer,
}

If this was Encoder<&'a mut File> it would force me to also have Output<'a>. It's possible, but "taints" my abstractions and breaks my encapsulation.

[AlexTMjugador]

Alright, that lifetime parameter propagation avoidance use case convinced me! I'd like to merge this after a little change 😉

[AlexTMjugador]

Nevermind the previous review, other VorbisEncoder fields have destructors that must be run when tearing down an encoder, and unwrapping the sink around is easier to reason about for correctness.

Merging this! 🎉

[algesten]

Thanks!

[AlexTMjugador]

This change has just been published in vorbis_rs v0.3.0! 🎉

I also took the opportunity to do some minor tidy-ups to the codebase and yanked v0.1.0, as it contains a known soundness issue.