A representation of the metadata provided by a substrate based node. This representation is optimized to be used by Subxt and related crates, and is independent of the different versions of metadata that can be provided from a node.

Typically, this will be constructed by either:

1. Calling Metadata::decode() given some metadata bytes obtained from a node (this uses codec::Decode).
2. Obtaining frame_metadata::RuntimeMetadataPrefixed, and then using .try_into() to convert it into Metadata.

subxt ·

Subxt is a library for interacting with Substrate based nodes in Rust and WebAssembly. It can:

• Submit Extrinsics (this is where the name comes from).
• Subscribe to blocks, reading the extrinsics and associated events from them.
• Read and iterate over storage values.
• Read constants and custom values from the metadata.
• Call runtime APIs, returning the results.
• Do all of the above via a safe, statically typed interface or via a dynamic one when you need the flexibility.
• Compile to WASM and run entirely in the browser.
• Do a bunch of things in a #[no_std] environment via the subxt-core crate.
• Use a built-in light client (smoldot) to interact with chains.

Usage

Take a look in the examples folder or the examples folder for various smaller or larger subxt usage examples, or read the guide to learn more.

Downloading metadata from a Substrate node

Use the subxt-cli tool to download the metadata for your target runtime from a node.

1. Install:

cargo install subxt-cli

2. Save the encoded metadata to a file:

subxt metadata -f bytes > metadata.scale

This defaults to querying the metadata of a locally running node on the default http://localhost:9933/. If querying a different node then the metadata command accepts a --url argument.

Subxt Documentation

For more details regarding utilizing subxt, please visit the documentation.

Integration Testing

Most tests require a running substrate node to communicate with. This is done by spawning an instance of the substrate node per test. It requires an up-to-date substrate executable on your path.

This can be installed from source via cargo:

cargo install --git https://github.com/paritytech/polkadot-sdk staging-node-cli --force

Real world usage

Please add your project to this list via a PR.

• cargo-contract CLI for interacting with Wasm smart contracts.
• xcm-cli CLI for submitting XCM messages.
• phala-pherry The relayer between Phala blockchain and the off-chain Secure workers.
• crunch CLI to claim staking rewards in batch every Era or X hours for substrate-based chains.
• interbtc-clients Client implementations for the interBTC parachain; notably the Vault / Relayer and Oracle.
• tidext Tidechain client with Stronghold signer.
• staking-miner-v2 Submit NPos election solutions and get rewards.
• polkadot-introspector Tools for monitoring Polkadot nodes.
• ink! Smart contract language that uses subxt for allowing developers to conduct End-to-End testing of their contracts.
• Chainflip A decentralised exchange for native cross-chain swaps.
• Hyperbridge A hyperscalable coprocessor for verifiable cross-chain interoperability.
• pop CLI The all-in-one tool for Polkadot development.

Alternatives

substrate-api-client provides similar functionality.

License

The entire code within this repository is dual licensed under the GPL-3.0 or Apache-2.0 licenses. See the LICENSE file for more details.

Please contact us if you have questions about the licensing of our products.