CARv2 implementation

[jmg-duarte]

Description

Add a CARv2 reader and writer along with a basic block store as an higher-level interface to the writer.

Further development is required to make the interfaces more usable but that can, and should, be informed by usage needs.

Important points for reviewers

Specifications

• https://ipld.io/specs/transport/car/carv1/
• https://ipld.io/specs/transport/car/carv2/
• https://github.com/ipfs/specs/blob/main/UNIXFS.md

Design based on

• https://github.com/n0-computer/beetle/tree/main/iroh-car
• https://github.com/n0-computer/beetle/tree/main/iroh-unixfs

Couldn't simply take it into our system as not only the libraries are no longer maintained, they're also dependent on other components that we don't care about.

Checklist

• Are there important points that reviewers should know?
  • If yes, which ones?
• Make sure that you described what this change does.
• If there are follow-ups, have you created issues for them?
  • If yes, which ones? / List them here
• Have you tested this solution?
• Were there any alternative implementations considered?
• Did you document new (or modified) APIs?

fixes #25

[serg-temchenko]

After a high-level overview, I have some questions about the layer at which this implementation should be. Right now, it is under the binary crate file-storage, but I thought that the car implementation is abstract enough to be in a more low-level implementation, such as a library, rather than a binary, so we could at some point publish it on the crates.io. Additionally, the public API is not clear to me; it only exposes the generate_multihash function and the MultihashCode trait in mod.rs.

Overall, the layers are mixed and the scope is a bit broken here, as we have a separate task for the polka-storage crate implementation here.

Perhaps it's my fault that we didn't discuss this properly before implementation. Sorry about that.

[jmg-duarte]

After a high-level overview, I have some questions about the layer at which this implementation should be. Right now, it is under the binary crate file-storage, but I thought that the car implementation is abstract enough to be in a more low-level implementation, such as a library, rather than a binary, so we could at some point publish it on the crates.io.

Agreed, I just moved it under file-storage because there was no guide under the parachain implementations on division and I err'd on keeping it under one roof. I'll move it out.

About the public API, it's still not finished, hence looking a bit quirky.

[cernicc]

Nice 💪 I imagine this took a lot of work. I left some comments and questions :D

[serg-temchenko]

Huge 🔥 Thanks @jmg-duarte!

[th7nder]

I didn't go through it all, but it's a piece of great work mate! All I have are questions/minor comments.

[th7nder]

🚀 🚀

[serg-temchenko]

@jmg-duarte please check the CI.