Estimate Gas Not Working With Geth

[nlordell]

Eth::estimate_gas does not seem to work when connected to a geth node. From what I can gather this is because ethereum/go-ethereum#2586 where geth does not implement the documented Web3 specification for eth_estimateGas.

According to the specification, eth_estimateGas expects the same parameters as eth_call, that is (in rust-web3 terms) a CallRequest and a BlockNumber. However, geth seems to only accept a CallRequest and with fail when a BlockNumber is specified.

This is a problem when using any geth node (such as when using Infura). The following code illustrates this problem:

use futures::future::Future;
use serde_json::json;
use std::env;
use web3::api::Web3;
use web3::transports::Http;
use web3::types::CallRequest;
use web3::Transport;

fn main() {
    let (eloop, http) = {
        let project_id = env::var("INFURA_PROJECT_ID").unwrap();
        Http::new(&format!("https://rinkeby.infura.io/v3/{}", project_id)).unwrap()
    };
    eloop.into_remote();
    let web3 = Web3::new(http.clone());

    println!(
        "Client version: {:?}",
        web3.web3().client_version().wait().unwrap()
    ); // Client version: "Geth/v1.9.7-omnibus-cc8122b7-20191122/linux-amd64/go1.13.4"

    let gas = web3
        .eth()
        .estimate_gas(
            CallRequest {
                from: None,
                to: "000102030405060708090a0b0c0d0e0f10111213".parse().unwrap(),
                gas: None,
                gas_price: None,
                value: None,
                data: None,
            },
            None,
        )
        .wait();
    println!("{:?}", gas); // Err("too many arguments, want at most 1")

    let gas = http
        .execute(
            "eth_estimateGas",
            vec![json!({
                "to": "0x000102030405060708090a0b0c0d0e0f10111213",
            })],
        )
        .wait();
    println!("{:?}", gas); // Ok("0x5208") == 21000 == BASE_GAS_PRICE (as expected)
}

I suggest doing as web3.py does (ethereum/web3.py#1046) and only send the CallRequest parameter on a eth_estimateGas request when the specified BlockNumber is None. This works with other nodes such as parity and development nodes such as Ganache so it shouldn't impact rust-web3 users while allowing them to successfully call eth_estimateGas when connected to geth nodes.

This feels icky as it requires rust-web3 to work around an issue that is arguably a geth bug, but seeing as ethereum/go-ethereum#2586 has been open since 2016 I think it is a worthwhile workaround (especially since geth is widely used, and used with Infura).

[tomusdrw]

Yeah, not sending the second parameter in case BlockNumber is None seems like a good solution to me. We already have some node-specific workarounds in the codebase afair, so I'm happy to accept a PR fixing this.