Implement getBlobs endpoint

[jimmygchen]

Description

This spec was recently merged:
ethereum/beacon-APIs#546

We should get this into our testnet releases so potential L2 users could consume this on testnets.

[Thegaram]

Hi @jimmygchen @chong-he, I understand this did not make it into the testnet release. With PeerDAS going live, will /eth/v1/beacon/blob_sidecars stop working once Fusaka goes live on Sepolia?

[pawanjay176]

/eth/v1/beacon/blob_sidecars should still work post fusaka. We however do not compute the correct blob kzg proof and instead stub it out with all zeroes. Would that work for your requirements since the getBlobs endpoint also doesn't actually return the kzg proof?

[Thegaram]

Great, thank you! For us (Scroll), only the blob and the kzg commitment are needed, we do not use the kzg proof.

[jimmygchen]

Hi @Thegaram could you describe how you use the kzg commitments please? Trying to figure out whether we should add it to the new endpoint

[Thegaram]

We just use it to compute the blobVersionedHash here.

[jimmygchen]

Oh right, so with the new /eth/v1/beacon/ blobs endpoint, you can now query the blob by version hashes - would you still require the commitments?

There's a thread on Eth R&D discord discussing about the requirement, if you're interested in participating:
https://discord.com/channels/595666850260713488/1423741917769891891/1424977894077366313

[Thegaram]

Thank you! Actually I found this issue via that discussion, but here I was told that the new endpoint would still require the block_id.

In any case, if /eth/v1/beacon/blob_sidecars will continue to work for our use case, we'll continue to use it, otherwise it should be easy to switch to /eth/v1/beacon/blobs, assuming Lighthouse can still serve all recent blobs via this API.