pub async fn get_filter_from_block(&self, filter: &Filter) -> Result<L2BlockNumber, Web3Error> {
        let mut connection = self.acquire_connection().await?;
        let pending_block = self
            .resolve_block_unchecked(
                &mut connection,
                api::BlockId::Number(api::BlockNumber::Pending),
            )
            .await?
            .context("Pending block number shouldn't be None")?;
        let block_number = match filter.from_block {
            Some(api::BlockNumber::Number(number)) => {
                let block_number = Self::u64_to_block_number(number);
                block_number.max(pending_block)
            }
            _ => pending_block,
        };
        Ok(block_number)
    }
Returns initial `from_block` for filter.
It is equal to max(filter.from_block, PENDING_BLOCK).
core/node/api_server/src/web3/state.rs