XBridge

XBridge is a decentralized bridge between multiple blockchain networks, that leverages a custom cross-chain messaging protocol, the XBridge Protocol, and a decentralized network of nodes, the XBridge Network, to facilitate the transfer of messages and assets.

This repository contains the implementation of an XBridge Network Node in Rust, using the Substrate Framework.

Getting Started

Check the Install instructions for your platform.

Build

Use the following command to build the node without launching it:

cargo build --release

Single-Node Development Chain

The following command starts a single-node development chain that doesn't persist state:

./target/release/xbridge-node --dev

To purge the development chain's state, run the following command:

./target/release/xbridge-node purge-chain --dev

To start the development chain with detailed logging, run the following command:

RUST_BACKTRACE=1 ./target/release/xbridge-node -ldebug --dev

Development chains:

• Maintain state in a tmp folder while the node is running.
• Use the Alice and Bob accounts as default validator authorities.
• Use the Alice account as the default sudo account.
• Are preconfigured with a genesis state (/node/src/chain_spec.rs) that includes several prefunded development accounts.

To persist chain state between runs, specify a base path by running a command similar to the following:

// Create a folder to use as the db base path
$ mkdir my-chain-state

// Use of that folder to store the chain state
$ ./target/release/xbridge-node --dev --base-path ./my-chain-state/

// Check the folder structure created inside the base path after running the chain
$ ls ./my-chain-state
chains
$ ls ./my-chain-state/chains/
dev
$ ls ./my-chain-state/chains/dev
db keystore network

Connect with Polkadot-JS Apps Front-End

After you start the node locally, you can interact with it using the hosted version of the Polkadot/Substrate Portal front-end by connecting to the local node endpoint.

Multi-Node Local Testnet

If you want to see the multi-node consensus algorithm in action, see Simulate a network.

Repository Structure

Node

A blockchain node is an application that allows users to participate in a blockchain network. Substrate-based blockchain nodes expose a number of capabilities:

• Networking: Substrate nodes use the libp2p networking stack to allow the nodes in the network to communicate with one another.
• Consensus: Blockchains must have a way to come to consensus on the state of the network. Substrate makes it possible to supply custom consensus engines and also ships with several consensus mechanisms that have been built on top of Web3 Foundation research.
• RPC Server: A remote procedure call (RPC) server is used to interact with Substrate nodes.

There are several files in the node directory. Take special note of the following:

• chain_spec.rs: A chain specification is a source code file that defines a Substrate chain's initial (genesis) state. Chain specifications are useful for development and testing, and critical when architecting the launch of a production chain. Take note of the development_config and testnet_genesis functions,. These functions are used to define the genesis state for the local development chain configuration. These functions identify some well-known accounts and use them to configure the blockchain's initial state.
• service.rs: This file defines the node implementation. Take note of the libraries that this file imports and the names of the functions it invokes. In particular, there are references to consensus-related topics, such as the block finalization and forks and other consensus mechanisms such as Aura for block authoring and GRANDPA for finality.

Runtime

In Substrate, the terms "runtime" and "state transition function" are analogous. Both terms refer to the core logic of the blockchain that is responsible for validating blocks and executing the state changes they define. The Substrate project in this repository uses FRAME to construct a blockchain runtime. FRAME allows runtime developers to declare domain-specific logic in modules called "pallets". At the heart of FRAME is a helpful macro language that makes it easy to create pallets and flexibly compose them to create blockchains that can address a variety of needs.

The FRAME runtime implementation configures several pallets to include in the runtime. Each pallet configuration is defined by a code block that begins with impl $PALLET_NAME::Config for Runtime.

The pallets are composed into a single runtime by way of the construct_runtime! macro, which is part of the core FRAME pallet library.

Pallets

The runtime in this project is constructed using many FRAME pallets that ship with the Substrate repository.

A FRAME pallet is comprised of a number of blockchain primitives, including:

• Storage: FRAME defines a rich set of powerful storage abstractions that makes it easy to use Substrate's efficient key-value database to manage the evolving state of a blockchain.
• Dispatchables: FRAME pallets define special types of functions that can be invoked (dispatched) from outside of the runtime in order to update its state.
• Events: Substrate uses events to notify users of significant state changes.
• Errors: When a dispatchable fails, it returns an error.

Each pallet has its own Config trait which serves as a configuration interface to generically define the types and parameters it depends on.