Rust SDK

The Rust SDK is the reference implementation for all EvidentSource language SDKs.

Status: Reference Implementation

SDK Components

Component	Description
core	Core library: events, selectors, constraints, identifiers
client	Client library: gRPC connectivity to EvidentSource servers
functions	Server Functions library: WASM components for state changes and state views

Requirements

• Rust 1.84 or later
• For WASM components: rustup target add wasm32-wasip2
• Protocol Buffers compiler (protoc)

Installation

Add to your Cargo.toml:

[dependencies]
evidentsource-client = { git = "https://github.com/evidentsystems/evidentsource-sdks", branch = "main" }

# For building WASM components
evidentsource-functions = { git = "https://github.com/evidentsystems/evidentsource-sdks", branch = "main" }

Quick Start

Client Usage

use evidentsource_client::EvidentSourceClient;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut client = EvidentSourceClient::new("https://localhost:50051").await?;
    let db = client.create_database("my-database".to_string()).await?;

    println!("Created database at revision {}", db.revision());
    Ok(())
}

Server Functions Usage

State changes and state views are built as WASM components using proc macros:

use evidentsource_functions::prelude::*;

#[derive(Deserialize)]
struct CreateAccountCommand {
    account_id: String,
    name: String,
}

#[state_change]
fn create_account(
    db: &impl Database,
    cmd: CreateAccountCommand,
    _meta: StateChangeMetadata,
) -> StateChangeResult {
    // Validate
    if cmd.name.is_empty() {
        return Err(StateChangeError::validation("Name is required"));
    }

    // Create event
    let event = CloudEventBuilder::new()
        .event_type("com.example.account.opened")
        .subject(&cmd.account_id)
        .stream("accounts")
        .json_data(&AccountOpened {
            account_id: cmd.account_id.clone(),
            name: cmd.name,
        })?
        .build();

    // Return events with DCB constraint
    Ok(DecideResult::new()
        .event(event)
        .condition(fail_if_events_match(
            Subject::equals(&cmd.account_id)
                .and(EventType::equals("com.example.account.opened"))
        )))
}

Building WASM Components

# Add the WASM target
rustup target add wasm32-wasip2

# Build a component
cd state-changes/create-account
cargo build --release --target wasm32-wasip2

Examples

Example	Description
TodoMVC	Classic todo list with CRUD operations
Savings Account	Banking example with deposits, withdrawals, interest calculations

Project Structure

rust/
├── core/                   # Core library (foundation types)
├── client/                 # Client library (gRPC connectivity)
├── functions/
│   ├── evidentsource-functions/          # Server Functions library
│   └── evidentsource-functions-macros/   # Proc macros for WASM components
├── interface/              # Proto files for gRPC API
└── examples/
    ├── todomvc/            # Todo list example
    └── savings-account/    # Banking example

API Reference

API documentation will be available on docs.rs when packages are published to crates.io.

Next Steps

• Getting Started - Build your first EvidentSource application
• State Changes - Learn about command handling
• State Views - Learn about view materialization