P2P: async buffer

[Boog900]

This adds an async buffer that works as a queue which supports arbitrary weights for values.

This is used between the block downloader and Cuprate.

[Boog900]

ready @hinto-janai @SyntheticBird45

[SyntheticBird45]

I may be a bad reviewer on this one since I'm not comfortable with async implementations, but I didn't found anything strange.

[hinto-janai]

Will review tomorrow but some questions:

• Could this be in cuprate_helper::asynch?
• What does weight mean in this context? What does it do?
• Is there no other data structure like this? Do we have to make/maintain one?

[Boog900]

Could this be in cuprate_helper::asynch

I don't think so, this is more than just a helper function/ type

What does weight mean in this context? What does it do?

It's used to bound the channel, you specify a max weight and a weight for each item. For the block downloader the weight will be the size, in bytes, of the downloaded batch of blocks.

Is there no other data structure like this? Do we have to make/maintain one?

I couldn't find one, I don't think this is too much to maintain.