How do I implement a custom RPC client for no_std with substrate-api-client?

You need to disable default features in Cargo.toml and implement the Request and Subscribe traits based on your hardware's WebSocket library, as shown in the tungstenite example for std environments. This requires understanding low-level WebSocket handling.

substrate-api-client vs subxt: which is better for my project?

Choose substrate-api-client if you need no_std support or a lightweight option for embedded/TEE projects; subxt is better for feature-rich applications in standard environments with more documentation and community support.

Why does my transaction fail with 'Bad input data' using substrate-api-client?

This usually indicates a runtime config mismatch. You must manually configure parameters like tips, as the library doesn't auto-fetch all node data. Check if your node uses the Asset pallet and select the appropriate config.

How stable is substrate-api-client for production use?

It's used by projects like Integritee and Ajuna, but the README notes breaking changes can occur in minor releases, and backports aren't guaranteed. Test thoroughly and monitor release notes for updates.

Can I use substrate-api-client with Polkadot.js for debugging?

Yes, the README recommends cross-checking state queries with Polkadot.js to verify return types and decoding, as substrate-api-client requires explicit type definitions for storage queries.

How to upgrade from an older version of substrate-api-client?

Refer to the example upgrades in the Integritee worker repository, as breaking changes are common. Always check release notes and be prepared for manual code adjustments.

Open-Awesome

Rust API Client

Apache-2.0Rustv1.21.0

A Rust library for connecting to Substrate-based blockchains via RPC, with a focus on no_std and embedded environments.

GitHub

264 stars125 forks0 contributors

What is Rust API Client?

Substrate-api-client is a Rust library that provides an RPC client for connecting to and interacting with Substrate-based blockchain nodes. It allows developers to submit transactions, query on-chain state, and subscribe to events, specifically designed to work in resource-constrained no_std environments like trusted execution environments and embedded systems.

Target Audience

Rust developers building applications or services that need to interact with Substrate, Polkadot, or Kusama blockchains, particularly those working in embedded systems, TEEs, or other no_std environments.

Value Proposition

It offers a simpler, more focused alternative to subxt with strong no_std support, making it the preferred choice for developers who need lightweight blockchain interaction in constrained environments without the overhead of a full-featured client.

Overview

Library for connecting to substrate API over WebSockets

Use Cases

Best For

Building blockchain clients for embedded devices or IoT
Developing applications within trusted execution environments (TEEs)
Creating lightweight tools for Substrate chain interaction
Implementing custom RPC clients for specialized hardware
Projects requiring no_std compatibility with Substrate
Educational or experimental Substrate RPC implementations

Not Ideal For

Projects requiring a full-featured RPC client with extensive built-in abstractions and minimal custom code
Teams prioritizing long-term API stability and frequent bugfix backports over no_std compatibility
Applications that rely on seamless, out-of-the-box WebSocket integration without implementing custom RPC clients

Pros & Cons

Pros

No_std First Design

Most of the library is no_std compatible, explicitly targeting trusted execution environments and embedded devices, which is rare among Substrate clients.

Multiple Backend Support

Supports three WebSocket crates (jsonrpsee, tungstenite, ws) for flexibility, allowing developers to choose based on environment constraints.

Sync and Async APIs

Provides both synchronous and asynchronous implementations, catering to different application needs without forcing a paradigm.

Lightweight Simplicity

Prioritizes a simpler, less extensive codebase compared to subxt, reducing overhead for specialized use cases.

Cons

Incomplete Runtime Configs

The README admits extrinsic submission can fail due to manual runtime configuration, with only two pre-defined configs, forcing custom work for non-standard nodes.

Custom RPC Client Required

For no_std builds, developers must implement their own RPC client by hand, as the library only provides std-compatible clients, adding significant setup complexity.

Frequent Breaking Changes

Versioning allows breaking changes in minor releases, and the README warns about API shifts, requiring careful upgrades and potential code rewrites.

Frequently Asked Questions

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