engine

kona-engine

An extensible implementation of the OP Stack rollup node engine client.

Overview

The kona-engine crate provides a task-based engine client for interacting with Ethereum execution layers. It implements the Engine API specification and manages the execution layer state through a priority-driven task queue system.

Key Components

• Engine - Main task queue processor that executes engine operations atomically
• EngineClient - HTTP client for Engine API communication with JWT authentication
• EngineState - Tracks the current state of the execution layer
• Task Types - Specialized tasks for different engine operations:
  • InsertTask - Insert new payloads into the execution engine
  • BuildTask - Build new payloads with automatic forkchoice synchronization
  • ConsolidateTask - Consolidate unsafe payloads to advance the safe chain
  • FinalizeTask - Finalize safe payloads on L1 confirmation
  • SynchronizeTask - Internal task for execution layer forkchoice synchronization

Architecture

The engine implements a task-driven architecture where forkchoice synchronization is handled automatically:

• Automatic Forkchoice Handling: The BuildTask automatically performs forkchoice updates during block building, eliminating the need for explicit forkchoice management in user code.
• Internal Synchronization: SynchronizeTask handles internal execution layer synchronization and is primarily used by other tasks rather than directly by users.
• Priority-Based Execution: Tasks are executed in priority order to ensure optimal sequencer performance and block processing efficiency.

Usage

use kona_engine::{Engine, EngineClient, EngineState};
use kona_genesis::RollupConfig;
use alloy_rpc_types_engine::JwtSecret;
use url::Url;
use std::sync::Arc;

# async fn example() -> Result<(), Box<dyn std::error::Error>> {
// Create an engine client
let engine_url = Url::parse("http://localhost:8551")?;
let l1_url = Url::parse("http://localhost:8545")?;
let config = Arc::new(RollupConfig::default());
let jwt = JwtSecret::from_hex("0xabcd")?;

let client = EngineClient::new_http(engine_url, l1_url, config, jwt);

// Initialize engine state
let state = EngineState::default();

// Create task queue watchers
let (state_sender, _) = tokio::sync::watch::channel(state);
let (queue_sender, _) = tokio::sync::watch::channel(0);

// Create the engine
let engine = Engine::new(state, state_sender, queue_sender);
# Ok(())
# }

Engine API Compatibility

The crate supports multiple Engine API versions with automatic version selection based on the rollup configuration:

• Engine Forkchoice Updated: V2, V3
• Engine New Payload: V2, V3, V4
• Engine Get Payload: V2, V3, V4

Version selection follows Optimism hardfork activation times (Bedrock, Canyon, Delta, Ecotone, Isthmus).

Features

• metrics - Enable Prometheus metrics collection (optional)