Distributed Transaction Sequencer

Read the full Litepaper

Warning

The design of this sequencer has not been finalized! This is a research project and hasn't been audited. Use at your own risk.

Recommended: Run a local network of 4 Nodes with Docker

I began taking this passion project quite seriously, so I added an SQLite DB to store Blocks and Transactions. Transactions are still read as a single chunk so the txpool for each Block must fit in memory, I do intend to change this.

To run the docker image with 2 nodes that will each have a db e.g. node-1.sqlite, node-2.sqlite where the temporary txpool and all finalized Blocks are stored, run:

docker compose up

Port forwarding should make the nodes available a 8080 and 8081. I plan to simulate larger networks in the future but for now it is designed to spawn 2 instances that synchronize blocks and commit to proposals / contribute to consensus. The default consensus threshold is 1 - see config directory.

API Routes

Internal

        .route("/schedule", post(schedule))
        .route("/commit", post(commit))
        .route("/propose", post(propose))
        .route("/merkle_proof", post(merkle_proof))

External

        .route("/get/pool", get(get_pool))
        .route("/get/commitments", get(get_commitments))
        .route("/get/block/:height", get(get_block))
        .route("/get/state_root_hash", get(state_root_hash))

To view a Block when running the example setup, request 127.0.0.1:8080/get/block/<id>, or 127.0.0.1:8081/get/block/<id>.

Merkle Proofs

Whenever a Block is stored, all transactions in that block are inserted into the custom Merkle Patricia Trie.

My Trie library supports merkle proofs which will be exposed by the sequencer API - inclusion can be proven for individual transactions.

I will likely add support for the eth-trie crate soon, but for this project I chose to be extra fancy and write a custom Trie from scratch.

Each Transaction has a Key that is unique. The Key is generated like this:

        let mut leaf = Leaf::new(Vec::new(), Some(transaction.data.clone()));
        leaf.hash();
        leaf.key = leaf
            .hash
            .clone()
            .unwrap()
            .iter()
            .flat_map(|&byte| (0..8).rev().map(move |i| (byte >> i) & 1))
            .collect();
        leaf.hash();
        let transaction_key_json = serde_json::to_string(&leaf.key).unwrap();
        let merkle_proof_response = client
            .post("http://127.0.0.1:8080/merkle_proof")
            .header("Content-Type", "application/json")
            .body(transaction_key_json)
            .send()
            .await
            .unwrap();

The example above includes a request that will obtain a merkle proof for the Transaction that belongs to this Key.

The merkle proof can be verified against the Root Hash of the Trie that it was requested for:

        ...
        let transaction_key_json = serde_json::to_string(&leaf.key).unwrap();
        let merkle_proof_response = client
            .post("http://127.0.0.1:8080/merkle_proof")
            .header("Content-Type", "application/json")
            .body(transaction_key_json)
            .send()
            .await
            .unwrap();
        let merkle_proof_json = merkle_proof_response.text().await.unwrap();
        let merkle_proof: MerkleProof = serde_json::from_str(&merkle_proof_json).unwrap();
        let state_root_hash_response = client
            .get("http://127.0.0.1:8080/get/state_root_hash")
            .send()
            .await
            .unwrap();
        let state_root_hash: Root =
            serde_json::from_str(&state_root_hash_response.text().await.unwrap()).unwrap();
        let mut inner_proof = merkle_proof.nodes;
        inner_proof.reverse();
        println!("Inner Proof: {:?}", &inner_proof);
        verify_merkle_proof(inner_proof, state_root_hash.hash.unwrap());
        ...

Note that verify_merkle_proof will revert if the merkle proof is invalid / doesn't sum up to the provided Trie Root.