Chain Adjacent Service

Espresso's Chain Adjacent Service (CAS) is a data availability service integrated with the Espresso network. It implements Rollup's DA API to handle requests from the batch poster.

Unlike a standard DA service, CAS does not only store data with Espresso - it also verifies that the data ordering is consistent with the ordering agreed upon by the Espresso network. Once verified, CAS returns a certificate to the batch poster, which is then posted on-chain and validated by the SequencerInbox contract.

This certificate contains a TEE signature and associated metadata, providing proof that the batch poster's data matches the data CAS has certified as correct.

Currently supported: Arbitrum Nitro (v3.9.9 and v3.10).

Architecture

Key modules under src/:

Module	Purpose
da_api/	JSON-RPC DA provider server (axum). Handles Store/GetByHash and supports calldata + AnyTrust providers.
streamer/	Polls Espresso blocks, extracts namespace transactions, manages verification queue.
submitter/	Batches feed messages and submits Espresso transactions.
espresso_client/	HTTP/WS client for the Espresso sequencer API.
key_manager/	TEE key management (AWS Nitro Enclaves), attestation verification, on-chain signer registration.
rollups/	Rollup trait definition + Nitro implementation (batch parsing, L1 monitor, feed relay).
secrets.rs	AWS Secrets Manager integration for runtime secret overrides.
config.rs	JSON configuration deserialization.

Feature Flags

Nitro protocol versions are mutually exclusive features:

Feature	Description
nitro-v3_9_9 (default)	Arbitrum Nitro v3.9.9 protocol
nitro-v3_10	Arbitrum Nitro v3.10 protocol

Build for a specific version:

cargo build --release --no-default-features --features nitro-v3_10

Development

Prerequisites

• Rust 1.93.1 (pinned in rust-toolchain.toml)
• Docker (for E2E tests)

Getting Started

# Ensure rustup picks up rust-toolchain.toml automatically.

# Verify prerequisites
just check

# Build
just build

# Check formatting
just fmt

# Clippy (pick one — features are mutually exclusive)
just clippy-v3_9_9
just clippy-v3_10

Configuration

CAS reads a JSON config file specified via CLI or environment variable:

chain-adjacent-service --config /path/to/config.json

Secrets can be injected at runtime via AWS Secrets Manager — see .env.example for the required environment variables.

Running

Binary

just build
./target/release/chain-adjacent-service --config config.json

Docker

# Default build (Nitro v3.9.9)
just docker-build

# Nitro v3.10
docker build --build-arg CARGO_FEATURES=nitro-v3_10 -t cas:v3.10 .

# Run
docker run -v /path/to/config.json:/etc/cas/config.json cas:v3.10

The image runs as a non-root user and expects the config at /etc/cas/config.json by default.

Testing

Unit Tests

just test

Runs cargo test --all-features (sequential).

E2E Tests

E2E tests spin up a full Nitro stack via Docker Compose.

# Nitro v3.10 (default)
just test-e2e

# Nitro v3.9.9 (requires generated L1 state)
just generate-l1-state-v3_9_9
just test-e2e-v3_9_9

# Optional: filter to a specific test
just test-e2e test_e2e_anytrust

Docker Compose Helpers

just e2e-up              # Start Nitro v3.10 stack
just e2e-down            # Stop Nitro v3.10 stack
just e2e-up-v3_9_9       # Start Nitro v3.9.9 stack
just e2e-down-v3_9_9     # Stop Nitro v3.9.9 stack
just clean               # Tear down all leftover E2E containers

CI

GitHub Actions runs on every push to main and on pull requests:

Job	What it does
Formatting	cargo fmt --all --check
Tests	cargo test --all-targets
Clippy	Runs separately per Nitro version (mutually exclusive features)
Audit	cargo audit via rustsec

License

Copyright (c) 2022 Espresso Systems espresso-network was developed by Espresso Systems. While we plan to adopt an open source license, we have not yet selected one. As such, all rights are reserved for the time being. Please reach out to us if you have thoughts on licensing.

Disclaimer

DISCLAIMER: This software is provided "as is" and its security has not been externally audited. Use at your own risk.

DISCLAIMER: The Rust library crates provided in this repository are intended primarily for use by the binary targets in this repository. We make no guarantees of public API stability. If you are building on these crates, reach out by opening an issue to discuss the APIs you need.