VLN Node

A Substrate based blockchain node for the Valiu Liquidity Network, a blockchain where liquidity providers of fiat and crypto assets like Valiu come together to enable regular non crypto-savy users convert their local currency easily to Valiu Dollars(USDv), a stable-coin backed by other USD pegged assets to protect them from their home country's volatile economy. To close the cycle, liquidity providers in different countries allow for an easy and decentralized way to cash-out USDv remittances without the final receipient being exposed to the complexities of the cryptocurrency world.

Local Development

Follow these steps to prepare a local Substrate development environment 🛠️

Simple Setup

Install all the required dependencies with a single command (be patient, this can take up to 30 minutes).

curl https://getsubstrate.io -sSf | bash -s -- --fast

Manual Setup

Find manual setup instructions at the Substrate Developer Hub.

Build

Once the development environment is set up, build the node. This command will build the Wasm and native code:

Please note that we have two different runtimes

• vln-node - The standalone "validator" node runtime
• vln-parachain - The parachain-compliant "collator" node runtime which runs on Rococo

For development, we recommend to run the vln-node.

# build in debug mode
cargo build -p $RUNTIME

# build in release mode 
cargo build --release -p $RUNTIME

# build the standalone vln node
cargo build --release -p vln-node

# build the vln-parachain collator node 
cargo build --release -p vln-parachain

Run

Refer this doc on how to run VLN parachain

Single Node Development Chain

Purge any existing dev chain state:

./target/release/vln_node purge-chain --dev

Start a dev chain:

./target/release/vln_node --dev

Or, start a dev chain with detailed logging:

RUST_LOG=debug RUST_BACKTRACE=1 ./target/release/vln_node -lruntime=debug --dev

Multi-Node Local Testnet

To see the multi-node consensus algorithm in action, run a local testnet with two validator nodes, Alice and Bob, that have been configured as the initial authorities of the local testnet chain and endowed with testnet units.

Note: this will require two terminal sessions (one for each node).

Start Alice's node first. The command below uses the default TCP port (30333) and specifies /tmp/alice as the chain database location. Alice's node ID will be 12D3KooWEyoppNCUx8Yx66oV9fJnriXwCcXwDDUA2kj6vnc6iDEp (legacy representation: QmRpheLN4JWdAnY7HGJfWFNbfkQCb6tFf4vvA6hgjMZKrR); this is determined by the node-key.

cargo run -- \
  --base-path /tmp/alice \
  --chain=local \
  --alice \
  --node-key 0000000000000000000000000000000000000000000000000000000000000001 \
  --telemetry-url 'ws://telemetry.polkadot.io:1024 0' \
  --validator

In another terminal, use the following command to start Bob's node on a different TCP port (30334) and with a chain database location of /tmp/bob. The --bootnodes option will connect his node to Alice's on TCP port 30333:

cargo run -- \
  --base-path /tmp/bob \
  --bootnodes /ip4/127.0.0.1/tcp/30333/p2p/12D3KooWEyoppNCUx8Yx66oV9fJnriXwCcXwDDUA2kj6vnc6iDEp \
  --chain=local \
  --bob \
  --port 30334 \
  --ws-port 9945 \
  --telemetry-url 'ws://telemetry.polkadot.io:1024 0' \
  --validator

Execute cargo run -- --help to learn more about the node's CLI options.

Project Structure

A Substrate project such as this consists of a number of components that are spread across a few directories.

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, which 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 longest chain rule, the Aura block authoring mechanism and the GRANDPA finality gadget.

After the node has been built, refer to the embedded documentation to learn more about the capabilities and configuration parameters that it exposes:

./target/release/vln_node --help

Runtime

In Substrate, the terms "runtime" and "state transition function" are analogous - they 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 the FRAME framework 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.

Review the FRAME runtime implementation included and note the following:

• This file configures several pallets to include in the runtime. Each pallet configuration is defined by a code block that begins with impl $PALLET_NAME::Trait for Runtime.
• The pallets are composed into a single runtime by way of the construct_runtime! macro, which is part of the core FRAME Support library.

Pallets

The runtime in this project is constructed using many FRAME pallets that ship with the core Substrate repository and custom ones defined in the pallets directory.

A FRAME pallet is compromised of a number of blockchain primitives:

• 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 important changes in the runtime.
• Errors: When a dispatchable fails, it returns an error.
• Trait: The Trait configuration interface is used to define the types and parameters upon which a FRAME pallet depends.

Polkadot-js UI

The polkadot-js UI UI can be used to interact with the vln-node. Some custom types will need to be specified in the Settings > Developer section of the UI. The definitions for these types can currently be found in the types.json file.