CarWriter.fromIterable(roots, blockIterator)

[rvagg]

@alanshaw had an API suggestion over @ storacha/ipfs-car#74

const out = await CarWriter.fromIterable([root], blockstore.blocks())

Some things to be resolved:

1. Should it be named fromBlockIterable() to make absolutely clear that this is a {cid,bytes} iterator it wants, because every other fromIterable() in the API currently is a Uint8Array iterator? This API would be able to take as input a CarBlockIterator, so we have prior-art for that name. (fs.createWriteStream('out.car', CarWriter.fromIterable([], await CarBlockIterator.fromIterable(fs.createReadStream('in.car')) [transferring roots is possible but it would take more than one line!]).
2. Does it need an await and if so what is it waiting on? Looking at the code, I think CarWriter.create() now is sync and doesn't need the await even though I see I've used it on the README! I don't think there's any good reason why a CarWriter.fromIterable() couldn't return out straight away, so maybe the await is entirely unnecessary here. The AsyncIterable protocol gives us everything we need to set up async constructions and should also allow proper error propagation regardless of where it happens in this chain.

[alanshaw]

❤️ I think both of these suggestions make sense.