Subxt Starter Example

This project demonstrates how to interact with a Polkadot SDK-based blockchain (like Paseo) using Rust and the subxt library.

What does this code do?

• Connects to a blockchain node using a WebSocket endpoint.
• Fetches account information for a given address.
• Sends a "remark" transaction (a simple on-chain message).
• Watches for events to confirm that the transaction was successful.

SubXT: How it works

SubXT is a Rust client for Polkadot SDK-based chains that generates a type-safe API from a chain’s runtime metadata and then uses it to read storage, submit extrinsics, and decode events.

1. Fetch metadata with the subxt-cli:

   subxt metadata -f bytes --url <WS> -o metadata.scale

Installing the subxt-cli will greatly aid in fetching metadata from nodes - cargo install subxt-cli

2. Generate types dynamically using the macro:

   use #[subxt::subxt(runtime_metadata_path = "metadata.scale")]

   or, you can also generate the types for pallets/calls/events/storage/consts statically using subxt-cli:

   subxt codegen --url <WS> > src/chain.rs

3. Init client:

   let api = OnlineClient::<PolkadotConfig>::from_url(<WS>).await?;

4. Prepare a signer (you will need subxt-signer):

    let uri = SecretUri::from_str(mnemonic_str).expect("valid mnemonic");
    let signer = Keypair::from_uri(&uri).expect("valid keypair")

From here, you can query storage, send transactions, and watch events with ease.

Repository Structure

• main.rs: Example entry point showing how to fetch account info and send a remark.
• remark.rs: Utility functions for interacting with the blockchain.
• config.rs: Configuration and type definitions, including loading the types from the metadata located in artifacts/

Installation & Running

1. Ensure you have Rust installed.

2. Clone this repository and enter the directory.

3. Ensure you have the correct metadata:

   The metadata for the Paseo testnet (artifacts/paseo.scale) is already included, however if you wish to use a different network, you will need to use the subxt-cli.

4. Build and run:

   cargo run

   This will:

   • Fetch Alice's account info.
   • Send a remark transaction.
   • Print the result and any events.

Example Output

Account info for ALICE: Ok(AccountInfo { ... })
Remark success: Some(Remarked { ... })

Customizing

• To use a different account, change the address or mnemonic in the code.
• To send a different message, change the string passed to the remark function.

Moving Forward: Adding a UI

Because of subxt's native support for Wasm, there are a number of Rust-based UI/web frameworks you can use:

• Yew - A framework for creating reliable and efficient web applications.
• Iced - A cross-platform GUI library for Rust focused on simplicity and type-safety.

More Information

• Subxt documentation
• Subxt Examples
• Polkadot SDK documentation

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This project is for educational purposes and works with public test networks like Paseo.