reth_engine_tree/engine.rs
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//! An engine API handler for the chain.
use crate::{
backfill::BackfillAction,
chain::{ChainHandler, FromOrchestrator, HandlerEvent},
download::{BlockDownloader, DownloadAction, DownloadOutcome},
};
use alloy_primitives::B256;
use futures::{Stream, StreamExt};
use reth_beacon_consensus::{BeaconConsensusEngineEvent, BeaconEngineMessage};
use reth_chain_state::ExecutedBlock;
use reth_engine_primitives::EngineTypes;
use reth_primitives::SealedBlockWithSenders;
use std::{
collections::HashSet,
fmt::Display,
sync::mpsc::Sender,
task::{ready, Context, Poll},
};
use tokio::sync::mpsc::UnboundedReceiver;
/// A [`ChainHandler`] that advances the chain based on incoming requests (CL engine API).
///
/// This is a general purpose request handler with network access.
/// This type listens for incoming messages and processes them via the configured request handler.
///
/// ## Overview
///
/// This type is an orchestrator for incoming messages and responsible for delegating requests
/// received from the CL to the handler.
///
/// It is responsible for handling the following:
/// - Delegating incoming requests to the [`EngineRequestHandler`].
/// - Advancing the [`EngineRequestHandler`] by polling it and emitting events.
/// - Downloading blocks on demand from the network if requested by the [`EngineApiRequestHandler`].
///
/// The core logic is part of the [`EngineRequestHandler`], which is responsible for processing the
/// incoming requests.
#[derive(Debug)]
pub struct EngineHandler<T, S, D> {
/// Processes requests.
///
/// This type is responsible for processing incoming requests.
handler: T,
/// Receiver for incoming requests (from the engine API endpoint) that need to be processed.
incoming_requests: S,
/// A downloader to download blocks on demand.
downloader: D,
}
impl<T, S, D> EngineHandler<T, S, D> {
/// Creates a new [`EngineHandler`] with the given handler and downloader and incoming stream of
/// requests.
pub const fn new(handler: T, downloader: D, incoming_requests: S) -> Self
where
T: EngineRequestHandler,
{
Self { handler, incoming_requests, downloader }
}
/// Returns a mutable reference to the request handler.
pub fn handler_mut(&mut self) -> &mut T {
&mut self.handler
}
}
impl<T, S, D> ChainHandler for EngineHandler<T, S, D>
where
T: EngineRequestHandler,
S: Stream + Send + Sync + Unpin + 'static,
<S as Stream>::Item: Into<T::Request>,
D: BlockDownloader,
{
type Event = T::Event;
fn on_event(&mut self, event: FromOrchestrator) {
// delegate event to the handler
self.handler.on_event(event.into());
}
fn poll(&mut self, cx: &mut Context<'_>) -> Poll<HandlerEvent<Self::Event>> {
loop {
// drain the handler first
while let Poll::Ready(ev) = self.handler.poll(cx) {
match ev {
RequestHandlerEvent::HandlerEvent(ev) => {
return match ev {
HandlerEvent::BackfillAction(target) => {
// bubble up backfill sync request request
self.downloader.on_action(DownloadAction::Clear);
Poll::Ready(HandlerEvent::BackfillAction(target))
}
HandlerEvent::Event(ev) => {
// bubble up the event
Poll::Ready(HandlerEvent::Event(ev))
}
HandlerEvent::FatalError => Poll::Ready(HandlerEvent::FatalError),
}
}
RequestHandlerEvent::Download(req) => {
// delegate download request to the downloader
self.downloader.on_action(DownloadAction::Download(req));
}
}
}
// pop the next incoming request
if let Poll::Ready(Some(req)) = self.incoming_requests.poll_next_unpin(cx) {
// and delegate the request to the handler
self.handler.on_event(FromEngine::Request(req.into()));
// skip downloading in this iteration to allow the handler to process the request
continue
}
// advance the downloader
if let Poll::Ready(outcome) = self.downloader.poll(cx) {
if let DownloadOutcome::Blocks(blocks) = outcome {
// delegate the downloaded blocks to the handler
self.handler.on_event(FromEngine::DownloadedBlocks(blocks));
}
continue
}
return Poll::Pending
}
}
}
/// A type that processes incoming requests (e.g. requests from the consensus layer, engine API,
/// such as newPayload).
///
/// ## Control flow
///
/// Requests and certain updates, such as a change in backfill sync status, are delegated to this
/// type via [`EngineRequestHandler::on_event`]. This type is responsible for processing the
/// incoming requests and advancing the chain and emit events when it is polled.
pub trait EngineRequestHandler: Send + Sync {
/// Event type this handler can emit
type Event: Send;
/// The request type this handler can process.
type Request;
/// Informs the handler about an event from the [`EngineHandler`].
fn on_event(&mut self, event: FromEngine<Self::Request>);
/// Advances the handler.
fn poll(&mut self, cx: &mut Context<'_>) -> Poll<RequestHandlerEvent<Self::Event>>;
}
/// An [`EngineRequestHandler`] that processes engine API requests by delegating to an execution
/// task.
///
/// This type is responsible for advancing the chain during live sync (following the tip of the
/// chain).
///
/// It advances the chain based on received engine API requests by delegating them to the tree
/// executor.
///
/// There are two types of requests that can be processed:
///
/// - `on_new_payload`: Executes the payload and inserts it into the tree. These are allowed to be
/// processed concurrently.
/// - `on_forkchoice_updated`: Updates the fork choice based on the new head. These require write
/// access to the database and are skipped if the handler can't acquire exclusive access to the
/// database.
///
/// In case required blocks are missing, the handler will request them from the network, by emitting
/// a download request upstream.
#[derive(Debug)]
pub struct EngineApiRequestHandler<Request> {
/// channel to send messages to the tree to execute the payload.
to_tree: Sender<FromEngine<Request>>,
/// channel to receive messages from the tree.
from_tree: UnboundedReceiver<EngineApiEvent>,
}
impl<Request> EngineApiRequestHandler<Request> {
/// Creates a new `EngineApiRequestHandler`.
pub const fn new(
to_tree: Sender<FromEngine<Request>>,
from_tree: UnboundedReceiver<EngineApiEvent>,
) -> Self {
Self { to_tree, from_tree }
}
}
impl<Request> EngineRequestHandler for EngineApiRequestHandler<Request>
where
Request: Send,
{
type Event = BeaconConsensusEngineEvent;
type Request = Request;
fn on_event(&mut self, event: FromEngine<Self::Request>) {
// delegate to the tree
let _ = self.to_tree.send(event);
}
fn poll(&mut self, cx: &mut Context<'_>) -> Poll<RequestHandlerEvent<Self::Event>> {
let Some(ev) = ready!(self.from_tree.poll_recv(cx)) else {
return Poll::Ready(RequestHandlerEvent::HandlerEvent(HandlerEvent::FatalError))
};
let ev = match ev {
EngineApiEvent::BeaconConsensus(ev) => {
RequestHandlerEvent::HandlerEvent(HandlerEvent::Event(ev))
}
EngineApiEvent::BackfillAction(action) => {
RequestHandlerEvent::HandlerEvent(HandlerEvent::BackfillAction(action))
}
EngineApiEvent::Download(action) => RequestHandlerEvent::Download(action),
};
Poll::Ready(ev)
}
}
/// The type for specifying the kind of engine api.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum EngineApiKind {
/// The chain contains Ethereum configuration.
#[default]
Ethereum,
/// The chain contains Optimism configuration.
OpStack,
}
impl EngineApiKind {
/// Returns true if this is the ethereum variant
pub const fn is_ethereum(&self) -> bool {
matches!(self, Self::Ethereum)
}
/// Returns true if this is the ethereum variant
pub const fn is_opstack(&self) -> bool {
matches!(self, Self::OpStack)
}
}
/// The request variants that the engine API handler can receive.
#[derive(Debug)]
pub enum EngineApiRequest<T: EngineTypes> {
/// A request received from the consensus engine.
Beacon(BeaconEngineMessage<T>),
/// Request to insert an already executed block, e.g. via payload building.
InsertExecutedBlock(ExecutedBlock),
}
impl<T: EngineTypes> Display for EngineApiRequest<T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Beacon(msg) => msg.fmt(f),
Self::InsertExecutedBlock(block) => {
write!(f, "InsertExecutedBlock({:?})", block.block().num_hash())
}
}
}
}
impl<T: EngineTypes> From<BeaconEngineMessage<T>> for EngineApiRequest<T> {
fn from(msg: BeaconEngineMessage<T>) -> Self {
Self::Beacon(msg)
}
}
impl<T: EngineTypes> From<EngineApiRequest<T>> for FromEngine<EngineApiRequest<T>> {
fn from(req: EngineApiRequest<T>) -> Self {
Self::Request(req)
}
}
/// Events emitted by the engine API handler.
#[derive(Debug)]
pub enum EngineApiEvent {
/// Event from the consensus engine.
// TODO(mattsse): find a more appropriate name for this variant, consider phasing it out.
BeaconConsensus(BeaconConsensusEngineEvent),
/// Backfill action is needed.
BackfillAction(BackfillAction),
/// Block download is needed.
Download(DownloadRequest),
}
impl EngineApiEvent {
/// Returns `true` if the event is a backfill action.
pub const fn is_backfill_action(&self) -> bool {
matches!(self, Self::BackfillAction(_))
}
}
impl From<BeaconConsensusEngineEvent> for EngineApiEvent {
fn from(event: BeaconConsensusEngineEvent) -> Self {
Self::BeaconConsensus(event)
}
}
/// Events received from the engine.
#[derive(Debug)]
pub enum FromEngine<Req> {
/// Event from the top level orchestrator.
Event(FromOrchestrator),
/// Request from the engine.
Request(Req),
/// Downloaded blocks from the network.
DownloadedBlocks(Vec<SealedBlockWithSenders>),
}
impl<Req: Display> Display for FromEngine<Req> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Event(ev) => write!(f, "Event({ev:?})"),
Self::Request(req) => write!(f, "Request({req})"),
Self::DownloadedBlocks(blocks) => {
write!(f, "DownloadedBlocks({} blocks)", blocks.len())
}
}
}
}
impl<Req> From<FromOrchestrator> for FromEngine<Req> {
fn from(event: FromOrchestrator) -> Self {
Self::Event(event)
}
}
/// Requests produced by a [`EngineRequestHandler`].
#[derive(Debug)]
pub enum RequestHandlerEvent<T> {
/// An event emitted by the handler.
HandlerEvent(HandlerEvent<T>),
/// Request to download blocks.
Download(DownloadRequest),
}
/// A request to download blocks from the network.
#[derive(Debug)]
pub enum DownloadRequest {
/// Download the given set of blocks.
BlockSet(HashSet<B256>),
/// Download the given range of blocks.
BlockRange(B256, u64),
}
impl DownloadRequest {
/// Returns a [`DownloadRequest`] for a single block.
pub fn single_block(hash: B256) -> Self {
Self::BlockSet(HashSet::from([hash]))
}
}