add frontier/ethereum example (#1557)

* add ethereum example

The ethereum config doesn't work with the default PolkadotConfig which
this shows how to do.

Tested with a frontier node

* address grumbles

* Update subxt/examples/tx_basic_frontier.rs

* Update subxt/examples/tx_basic_frontier.rs

signer/src/eth.rs

@@ -298,7 +298,7 @@ mod test {
     use proptest::prelude::*;
     use secp256k1::Secp256k1;
 
-    use subxt_core::{config::*, tx::Signer as SignerT, utils::H256};
+    use subxt_core::{config::*, tx::signer::Signer as SignerT, utils::H256};
 
     use super::*;
 

subxt/Cargo.toml

@@ -119,7 +119,7 @@ sp-core = { workspace = true }
 sp-keyring = { workspace = true }
 sp-runtime = { workspace = true }
 assert_matches = { workspace = true }
-subxt-signer = { path = "../signer" }
+subxt-signer = { path = "../signer", features = ["unstable-eth"] }
 # Tracing subscriber is useful for light-client examples to ensure that
 # the `bootNodes` and chain spec are configured correctly. If all is fine, then
 # the light-client wlll emit INFO logs with
@@ -146,4 +146,4 @@ features = ["default", "substrate-compat", "unstable-light-client"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [package.metadata.playground]
-features = ["default", "substrate-compat", "unstable-light-client"]
+features = ["default", "substrate-compat", "unstable-light-client"]

subxt/examples/tx_basic_frontier.rs

@@ -0,0 +1,64 @@
+//! Example to use subxt to talk to substrate-based nodes with ethereum accounts
+//! which is not the default for subxt which is why we need to provide a custom config.
+//!
+//! This example requires to run a local frontier/moonbeam node to work.
+
+#![allow(missing_docs)]
+
+use subxt::OnlineClient;
+use subxt_signer::eth::{dev, AccountId20, Signature};
+
+#[subxt::subxt(runtime_metadata_path = "../artifacts/frontier_metadata_small.scale")]
+mod eth_runtime {}
+
+enum EthRuntimeConfig {}
+
+impl subxt::Config for EthRuntimeConfig {
+    type Hash = subxt::utils::H256;
+    type AccountId = AccountId20;
+    type Address = AccountId20;
+    type Signature = Signature;
+    type Hasher = subxt::config::substrate::BlakeTwo256;
+    type Header =
+        subxt::config::substrate::SubstrateHeader<u32, subxt::config::substrate::BlakeTwo256>;
+    type ExtrinsicParams = subxt::config::SubstrateExtrinsicParams<Self>;
+    type AssetId = u32;
+}
+
+// This helper makes it easy to use our `AccountId20`'s with generated
+// code that expects a generated `eth_runtime::runtime_types::fp_account:AccountId20` type.
+impl From<AccountId20> for eth_runtime::runtime_types::fp_account::AccountId20 {
+    fn from(a: AccountId20) -> Self {
+        eth_runtime::runtime_types::fp_account::AccountId20(a.0)
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let api = OnlineClient::<EthRuntimeConfig>::from_insecure_url("ws://127.0.0.1:9944").await?;
+
+    let alith = dev::alith();
+    let baltathar = dev::baltathar();
+    let dest = baltathar.account_id();
+
+    println!("baltathar pub:  {}", hex::encode(baltathar.public_key().0));
+    println!("baltathar addr: {}", hex::encode(dest));
+
+    let balance_transfer_tx = eth_runtime::tx()
+        .balances()
+        .transfer_allow_death(dest.into(), 10_001);
+
+    let events = api
+        .tx()
+        .sign_and_submit_then_watch_default(&balance_transfer_tx, &alith)
+        .await?
+        .wait_for_finalized_success()
+        .await?;
+
+    let transfer_event = events.find_first::<eth_runtime::balances::events::Transfer>()?;
+    if let Some(event) = transfer_event {
+        println!("Balance transfer success: {event:?}");
+    }
+
+    Ok(())
+}