Fix DifferentChainID error (#722)

PR #699 attempted to remove the startup-time dependency on the API
by moving the point at which we get the chain ID to transaction
creation time.

However, this wasn't valid because the signer needs to be
configured with the correct chain ID. Instead, we wrap our
provider in a `tokio::sync::OnceCell` and lazily initialise it.

This means the signer is initialised with the result of the call
from `eth_chainId`, but we don't need to make this call until
someone uses the faucet.

products/eth-spout/src/main.rs

@@ -14,11 +14,11 @@ use ethers::{
     middleware::{signer::SignerMiddlewareError, SignerMiddleware},
     providers::{Http, Middleware, Provider},
     signers::LocalWallet,
-    types::{Address, TransactionRequest, H256},
+    types::{Address, TransactionRequest, H160, H256},
     utils::{parse_checksummed, parse_ether, to_checksum, ConversionError, WEI_IN_ETHER},
 };
 use serde::Deserialize;
-use tokio::sync::Mutex;
+use tokio::sync::{Mutex, OnceCell};
 
 #[derive(Template)]
 #[template(path = "home.html")]
@@ -36,11 +36,20 @@ enum RequestStatus {
     AddrErr(anyhow::Error),
     SendErr(SignerMiddlewareError<Provider<Http>, LocalWallet>),
     RateLimitErr(Duration),
+    ConfigErr(anyhow::Error),
 }
 
-async fn home_inner(State(state): State<Arc<AppState>>, status: Option<RequestStatus>) -> Home {
+async fn home_inner(State(state): State<Arc<AppState>>, mut status: Option<RequestStatus>) -> Home {
+    let addr = match state.provider().await {
+        Ok(p) => p.address(),
+        Err(e) => {
+            eprintln!("{e:?}");
+            status = Some(RequestStatus::ConfigErr(e));
+            H160::zero()
+        }
+    };
     Home {
-        from_addr: to_checksum(&state.provider.address(), None),
+        from_addr: to_checksum(&addr, None),
         native_token_symbol: state.config.native_token_symbol.clone(),
         amount: state.config.eth_amount.clone(),
         explorer_url: state.config.explorer_url.clone(),
@@ -55,6 +64,7 @@ async fn home_inner(State(state): State<Arc<AppState>>, status: Option<RequestSt
                 "Request made too recently, please wait {} seconds before trying again",
                 d.as_secs()
             )),
+            Some(RequestStatus::ConfigErr(e)) => Some(format!("Spout is misconfigured: {e:?}")),
             _ => None,
         },
     }
@@ -150,16 +160,17 @@ async fn request(State(state): State<Arc<AppState>>, Form(request): Form<Request
         }
     }
 
-    let value = parse_ether(&state.config.eth_amount).unwrap_or(WEI_IN_ETHER);
-    let chain_id = match state.provider.get_chainid().await {
-        Ok(c) => c,
+    let provider = match state.provider().await {
+        Ok(p) => p,
         Err(e) => {
             eprintln!("{e:?}");
-            return home_inner(State(state.clone()), Some(RequestStatus::SendErr(e))).await;
+            return home_inner(State(state.clone()), Some(RequestStatus::ConfigErr(e))).await;
         }
     };
-    let tx = TransactionRequest::pay(address, value).chain_id(chain_id.low_u64());
-    let status = match state.provider.send_transaction(tx, None).await {
+
+    let value = parse_ether(&state.config.eth_amount).unwrap_or(WEI_IN_ETHER);
+    let tx = TransactionRequest::pay(address, value);
+    let status = match provider.send_transaction(tx, None).await {
         Ok(t) => RequestStatus::Sent(t.tx_hash()),
         Err(e) => {
             eprintln!("{e:?}");
@@ -217,22 +228,29 @@ impl Config {
 }
 
 struct AppState {
-    provider: SignerMiddleware<Provider<Http>, LocalWallet>,
+    provider: OnceCell<SignerMiddleware<Provider<Http>, LocalWallet>>,
     config: Config,
     last_request: Mutex<HashMap<Address, Instant>>,
 }
 
+impl AppState {
+    async fn provider(&self) -> Result<&SignerMiddleware<Provider<Http>, LocalWallet>> {
+        let provider = Provider::try_from(&self.config.rpc_url)?;
+        let wallet: LocalWallet = self.config.private_key.parse()?;
+        Ok(self
+            .provider
+            .get_or_try_init(|| SignerMiddleware::new_with_provider_chain(provider, wallet))
+            .await?)
+    }
+}
+
 #[tokio::main]
 async fn main() -> Result<()> {
     let config = Config::from_env()?;
 
-    let provider = Provider::try_from(&config.rpc_url)?;
-    let wallet: LocalWallet = config.private_key.parse()?;
-    let provider = SignerMiddleware::new(provider, wallet);
-
     let addr = ("0.0.0.0".parse::<IpAddr>()?, config.http_port);
     let state = Arc::new(AppState {
-        provider,
+        provider: OnceCell::new(),
         config,
         last_request: Default::default(),
     });