feat(examples): minimal viable ExEx (#7565)

Co-authored-by: Oliver Nordbjerg <hi@notbjerg.me>
Co-authored-by: Oliver Nordbjerg <onbjerg@users.noreply.github.com>

examples/exex/minimal/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "minimal"
+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-core.workspace = true
+reth-node-ethereum.workspace = true
+reth-primitives.workspace = true
+reth-provider.workspace = true
+
+eyre.workspace = true
+tokio.workspace = true
+futures.workspace = true

examples/exex/minimal/src/main.rs

@@ -0,0 +1,58 @@
+use std::{
+    pin::Pin,
+    task::{ready, Context, Poll},
+};
+
+use futures::Future;
+use reth::builder::FullNodeTypes;
+use reth_exex::{ExExContext, ExExEvent};
+use reth_node_ethereum::EthereumNode;
+use reth_provider::CanonStateNotification;
+
+/// A minimal example of an ExEx that simply prints out commit and reorg notifications.
+struct MinimalExEx<Node: FullNodeTypes> {
+    ctx: ExExContext<Node>,
+}
+
+impl<Node: FullNodeTypes> Future for MinimalExEx<Node> {
+    type Output = eyre::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+
+        // Process all new chain state notifications until there are no more
+        while let Some(notification) = ready!(this.ctx.notifications.poll_recv(cx)) {
+            // Process one notification
+            match &notification {
+                CanonStateNotification::Commit { new } => {
+                    println!("Received commit: {:?}", new.first().number..=new.tip().number);
+                }
+                CanonStateNotification::Reorg { old, new } => {
+                    println!(
+                        "Received reorg: {:?} -> {:?}",
+                        old.first().number..=old.tip().number,
+                        new.first().number..=new.tip().number
+                    );
+                }
+            };
+
+            // Send a finished height event, signaling the node that we don't need any blocks below
+            // this height anymore
+            this.ctx.events.send(ExExEvent::FinishedHeight(notification.tip().number))?;
+        }
+
+        Poll::Pending
+    }
+}
+
+fn main() -> eyre::Result<()> {
+    reth::cli::Cli::parse_args().run(|builder, _| async move {
+        let handle = builder
+            .node(EthereumNode::default())
+            .install_exex("Minimal", move |ctx| async { Ok(MinimalExEx { ctx }) })
+            .launch()
+            .await?;
+
+        handle.wait_for_node_exit().await
+    })
+}