cannot get earlier transactions and blocks

[yuvalelmo]

I am using helios as library (0.5.2) for some reason, it seems like i cannot get the data of blocks that are not the latest block. i use the get_block_by_number function and it returns None, unless it is the latest block in the chain(using BlockTag::Number with the block number).

the same goes with transactions - cannot fetch information about transactions using transaction hash. the RPC provider is alchemy.

for example, this code would work and return the block:

let block_number = client.get_block_number().await?;
    let block = client
        .get_block_by_number(BlockTag::Number(block_number.as_u64()), true)
        .await?;
    info!("block: {:?}", block);

but this code would return None, even though there is a block with this block number:

let block_number: u64 = 19075597;

    let block = client
        .get_block_by_number(BlockTag::Number(block_number), true)
        .await?;
    info!("block: {:?}", block);

am i using it wrong?

[ncitron]

Can you please provide the full code example so I can help you debug?

[yuvalelmo]

sure, there's the whole function:

#[tokio::main]
async fn main() -> Result<()> {
    dotenv().ok();
    set_logger();

    let network = Network::GOERLI;
    let cf = checkpoints::CheckpointFallback::new()
        .build()
        .await
        .unwrap();
    info!("Checkpoint fallback services built");

    let checkpoint = cf.fetch_latest_checkpoint(&network).await.unwrap();
    let checkpoint = format!("{:?}", checkpoint);

    let execution_rpc_url = get_env_variable("EXECUTION_RPC")?;
    let consensus_rpc_url = get_env_variable("CONSENSUS_RPC")?;

    let mut client: Client<FileDB> = ClientBuilder::new()
        .network(network)
        .execution_rpc(&execution_rpc_url)
        .consensus_rpc(&consensus_rpc_url)
        .load_external_fallback()
        .checkpoint(&checkpoint)
        .data_dir("/tmp/helios".parse()?)
        .build()?;
    info!("client created");

    client.start().await?;
    client.wait_synced().await;

    let block_number: u64 = 19075597;

    let block = client
        .get_block_by_number(BlockTag::Number(block_number), true)
        .await?;
    info!("block: {:?}", block);
    Ok(())
}

[ncitron]

Oh I see what is happening here. Helios only stores block data for blocks that start either after helios starts or within 64 blocks of the current block number (whichever is higher).

This is mostly a limitation due to efficiency as well as how the light client protocol works.

[yuvalelmo]

@ncitron first, thanks for your help!

I have a similar problem now but with transactions. I use the get_transaction_receipt function in order to get the receipt of a transaction that is created after the start of the client, but I keep getting a None result for some reason.

I inject the hash of the transaction to the tx_hash_str variable using a breakpoint, and i am taking a transaction hash from etherscan explorer. I tried both pending transactions and approved transactions, but both gives the same result of None, when the transaction is clearly created after the client. I use the same code as above, but with changing the block fetching part with the following:

	let tx_hash_str = "";
	//here i use a breakpoint and put the hash string into tx_hash_str
    let tx_hash = H256::from_str(tx_hash_str).unwrap();
    let tx = client
        .get_transaction_receipt(&tx_hash)
        .await?;

[ncitron]

Can you confirm that you can fetch a block for the block number of the transaction?

[yuvalelmo]

Yes, I can do this.

[ncitron]

Hmm it seems I am able to fetch a receipt using this simple example:

client.start().await?;
client.wait_synced().await;

let head_block_num = client.get_block_number().await?;
let head_block = client.get_block_by_number(BlockTag::Number(head_block_num.as_u64()), false).await;
let tx_hash = head_block.unwrap().unwrap().transactions.hashes()[0];
let receipt = client.get_transaction_receipt(&tx_hash).await.unwrap().unwrap();
println!("{:?}", receipt);

I wonder if the breakpoints are causing it to act up. If helios can fetch the block it should always be able to get a receipt from within that block.

[yuvalelmo]

Thanks for all the help! It seems I did not understand the light client's logics just right. I now understand that I would be able to fetch only transactions from already fetched blocks.