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SDK Architecture

Bitwarden provides a public Software Development Kit (SDK) for Secrets Manager and an internal SDK for the Bitwarden Password Manager. The SDK is written in Rust and provides bindings for multiple languages. The general end goal of the SDK is to own everything up to the presentational layers. This includes but is not limited to: API calls, data models, encryption, and business logic.

Architecture​

The Bitwarden SDK is structured as a single Git repository with multiple internal crates. Review the repository README for more information about the different crates.

We generally strive towards extracting features into separate crates to keep the core bitwarden crate as lean as possible. This has multiple benefits such as faster compile-time and clear ownership of features.

bitwarden crate​

The bitwarden crate is the main entry point for the SDK and is responsible for wiring up the sub crates. It contains a Client struct which represents a single account instance in the SDK. The Client struct implements multiple callable methods that may manipulate the state of the SDK.

Language bindings​

The SDK is currently exposed with multiple language bindings. Currently we utilize a mix of hand written bindings for a C API, and programmatically generated bindings.

C bindings​

Many language bindings utilize the bitwarden-c crate that exposes a C API. This is then combined with hand written bindings for the specific language. Since manually writing FFI bindings is time consuming and difficult we generally provide a JSON based API through the bitwarden-json crate which allows the language bindings to just contain three FFI functions, init, run_command and free_memory.

Mobile bindings​

We use UniFFI to generate bindings for the mobile platforms, more specifically we publish Android and iOS libraries with Kotlin and Swift bindings, respectively. While UniFFI supports additional languages they typically lag a few releases behind the UniFFI core library.

The Android bindings are currently published on GitHub Packages in the SDK repository. The swift package is published in the sdk-swift repository.

Web bindings​

For the web bindings we use wasm-bindgen to generate a WebAssembly module that can be used in JavaScript / TypeScript. To ensure compatibility with browsers that do not support WebAssembly, we also generate a JavaScript module from the WebAssembly that can be used as a fallback.

The WebAssembly module is published on npm and prerelease builds are published on GitHub Packages.