Progress tracker for index creation

[aschmahmann]

Index creation can be very expensive for large CARs and it'd be nice to be able to track (and in the CLI emit) progress as it's being generated.

If

go-car/v2/index_gen.go

Line 43 in e48b3f1

func LoadIndex(idx index.Index, r io.Reader, opts ...Option) error {

took a context I'd probably recommend attaching the tracker there (and probably also allowing the caller to bail via context cancellation). We could potentially put it into the Options struct, but I don't know if that fits the model of what that struct is aiming for.

Any suggestions on acceptable API modifications (or new function introductions) here?

[willscott]

I think somewhere else we tracked progress by knowing the total length of the reader and tracking how much had been read so far.

Can you do it that way?

[BigLep]

During IPLD triage: do you need more input here @aschmahmann ? Do you think you'll proceed with this change?