Rust SDK reference

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Last edited: Jul 22, 2024

Recent major versions

Version 2 of the Rust SDK makes the rustls dependency optional. There are no changes to the SDK API.

Version 1 of the Rust SDK replaces users with contexts. A context is a generalized way of referring to the people, services, machines, or other resources that encounter feature flags in your product. Contexts replace another data object in LaunchDarkly: "users."

If you have been using the beta version, you can learn more about implementing version 1 by reading Rust SDK v1 implementation guide and Best practices for upgrading users to contexts.

Overview

This topic documents how to get started with the server-side Rust SDK, and links to reference information on all of the supported features.

SDK quick links

LaunchDarkly's SDKs are open source. In addition to this reference guide, we provide source, API reference documentation, and a sample application:

Resource	Location
SDK API documentation	SDK API docs
GitHub repository	rust-server-sdk
Sample application	Rust
Published module	crates.io

Get started

After you complete the Get started process, follow these instructions to start using the LaunchDarkly SDK in your Rust application.

Install the SDK

First, install the LaunchDarkly SDK as a dependency in your application.

cargo add launchdarkly-server-sdk

Initialize the client

Next, import the LaunchDarkly client in your application code:

use launchdarkly_server_sdk::{Client, ConfigBuilder, ContextBuilder, ServiceEndpointsBuilder};

The Rust SDK uses an SDK key

The Rust SDK uses an SDK key. Keys are specific to each project and environment. They are available from the Environments list for each project. To learn more about key types, read Keys.

After you install and import the SDK, create a single, shared instance of the LaunchDarkly client. Specify your SDK key here so that your application is authorized to connect to LaunchDarkly, your application, and your environment.

Once you have created the client, start the client process and wait for the client to initialize. This SDK depends on the tokio crate to provide a default runtime and as such it is a required dependency.

Only create one instance of client.

Here's how:

#[tokio::main]
async fn main () {
    let config = ConfigBuilder::new(&sdk-key-123abc).build();
    let client = Client::build(config).unwrap();
    client.start_with_default_executor();
    if !client.initialized_async().await {
        panic!("Client failed to successfully initialize");
    }
}

To learn more about the specific configuration options available in this SDK, read Config.

client must be a singleton

It's important to make client a singleton for each LaunchDarkly project. The client instance maintains internal state that allows LaunchDarkly to serve feature flags without making any remote requests. Do not instantiate a new client with every request.

If you have multiple LaunchDarkly projects, you can create one LDClient for each. In this situation, the clients operate independently. For example, they do not share a single connection to LaunchDarkly.

Evaluate a context

You can use client to check which variation a particular context will receive for a given feature flag.

Here's how:

let context = ContextBuilder::new("context-key-123abc").build();
let show_feature = client.bool_variation(&context, "flag-key-123abc", false);
if show_feature {
  # application code to show the feature
} else {
  # the code to run if the feature is off
}

Shut down the client

Shut down the client when your application terminates. To learn more, read Shutting down.

Supported features

This SDK supports the following features: