feat: add exex for in memory state (#8108)

examples/exex/in-memory-state/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "exex-in-memory-state"
+version = "0.0.0"
+publish = false
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+reth.workspace = true
+reth-exex.workspace = true
+reth-node-api.workspace = true
+reth-node-ethereum.workspace = true
+reth-tracing.workspace = true
+
+eyre.workspace = true

examples/exex/in-memory-state/src/main.rs

@@ -0,0 +1,49 @@
+#![warn(unused_crate_dependencies)]
+
+use reth::providers::BundleStateWithReceipts;
+use reth_exex::{ExExContext, ExExEvent, ExExNotification};
+use reth_node_api::FullNodeComponents;
+use reth_node_ethereum::EthereumNode;
+use reth_tracing::tracing::info;
+
+/// An ExEx that keeps track of the entire state in memory
+async fn track_state<Node: FullNodeComponents>(mut ctx: ExExContext<Node>) -> eyre::Result<()> {
+    // keeps the entire plain state of the chain in memory
+    let mut state = BundleStateWithReceipts::default();
+
+    while let Some(notification) = ctx.notifications.recv().await {
+        match &notification {
+            ExExNotification::ChainCommitted { new } => {
+                info!(committed_chain = ?new.range(), "Received commit");
+            }
+            ExExNotification::ChainReorged { old, new } => {
+                // revert to block before the reorg
+                state.revert_to(new.first().number - 1);
+                info!(from_chain = ?old.range(), to_chain = ?new.range(), "Received reorg");
+            }
+            ExExNotification::ChainReverted { old } => {
+                state.revert_to(old.first().number - 1);
+                info!(reverted_chain = ?old.range(), "Received revert");
+            }
+        };
+
+        if let Some(committed_chain) = notification.committed_chain() {
+            // extend the state with the new chain
+            state.extend(committed_chain.state().clone());
+            ctx.events.send(ExExEvent::FinishedHeight(committed_chain.tip().number))?;
+        }
+    }
+    Ok(())
+}
+
+fn main() -> eyre::Result<()> {
+    reth::cli::Cli::parse_args().run(|builder, _| async move {
+        let handle = builder
+            .node(EthereumNode::default())
+            .install_exex("in-memory-state", |ctx| async move { Ok(track_state(ctx)) })
+            .launch()
+            .await?;
+
+        handle.wait_for_node_exit().await
+    })
+}