feat: beacon API support for blob fetching

[sam-iamm]

Component

Anvil

Describe the feature you would like

Anvil supports anvil_getBlobsByTransactionHash and anvil_getBlobByHash to fetch blobs, but it does not support the beacon API method to fetch blobs: /eth/v1/beacon/blob_sidecars/{block_id}

By supporting this beacon API method, we can test with anvil using code that expects access to a beacon API endpoint to fetch blobs.

Additional context

This is useful for testing an L2 that sends blob transactions to Anvil and then needs a beacon API endpoint to fetch blobs and perform derivation. Our CL binary, for example, is unaware of the anvil methods and currently expects to use the beacon api to fetch blobs.

[mattsse]

this endpoint is returning https://github.com/alloy-rs/alloy/blob/249310a0b503fb7db9f4e90ab44f2b3096bb2e9d/crates/rpc-types-beacon/src/sidecar.rs#L87-L87

what we can do is simply returning either returning

https://github.com/alloy-rs/alloy/blob/249310a0b503fb7db9f4e90ab44f2b3096bb2e9d/crates/eips/src/eip4844/sidecar.rs#L38-L38

for the entire block, or a flattened version of that

similar to

foundry/crates/anvil/src/eth/api.rs

Lines 1349 to 1353 in f3625e0

	/// Handler for RPC call: `anvil_getBlobsByTransactionHash`
	pub fn anvil_get_blob_by_tx_hash(&self, hash: B256) -> Result<Option<Vec<Blob>>> {
	node_info!("anvil_getBlobsByTransactionHash");
	Ok(self.backend.get_blob_by_tx_hash(hash)?)
	}

TODO

• add endpoint like

  foundry/crates/anvil/core/src/eth/mod.rs

  Lines 185 to 187 in f3625e0

  	/// Returns the blobs for a given transaction hash.
  	#[serde(rename = "anvil_getBlobsByTransactionHash", with = "sequence")]
  	GetBlobByTransactionHash(TxHash),

• impl endpoint like anvil_getBlobsByTransactionHash

we can also add another endpoint that exactly mirrors the beacon api and use fake data when where we dont have access to

https://github.com/alloy-rs/alloy/blob/249310a0b503fb7db9f4e90ab44f2b3096bb2e9d/crates/rpc-types-beacon/src/sidecar.rs#L11-L11

[mablr]

May I do it 👍

[sam-iamm]

Is it possible to make this accessible through a REST interface, like the beacon apis? This getBlobSidecars would be called by a GET at path /eth/v1/beacon/blob_sidecars/{block_id} as described in https://ethereum.github.io/beacon-APIs/#/Beacon/getBlobSidecars rather than via JSON-RPC under the anvil namespace.

That would be the ideal case, but we can workaround this if not.