Turbocharger

Autogenerated async RPC bindings that instantly connect a JS frontend to a Rust backend service via WebSockets and WASM.

See https://github.com/trevyn/turbocharger-template for a full turnkey template repository.

Makes a Rust backend function, e.g.:

#[turbocharger::backend]
async fn get_person(id: i64) -> Person {
 // ... write any async backend code here; ...
 // ... query a remote database, API, etc. ...
 Person { name: "Bob", age: 21 }
}

instantly available, with no additional boilerplate, to a frontend as

• an async JavaScript function
• with full TypeScript type definitions
• that calls the backend over the network:

// export function get_person(id: number): Promise<Person>;

let person = await backend.get_person(1);

Works with any types that are supported by wasm-bindgen, which includes most basic types and custom structs with fields of supported types, but not yet enum variants with values (which would come out the other end as TypeScript discriminated unions).

How It Works

A proc macro auto-generates a frontend wasm-bindgen module, which serializes the JS function call parameters with bincode. These requests are sent over a shared WebSocket connection to a provided warp endpoint on the backend server, which calls your Rust function and serializes the response. This is sent back over the WebSocket and resolves the Promise returned by the original function call.

Multiple async requests can be simultaneously in-flight over a single multiplexed connection; it all just works.

Complete Example: A full SQLite-powered backend with frontend bindings

See https://github.com/trevyn/turbocharger-template for a full turnkey template repository.

main.rs

use turbocharger::{backend, server_only};
use wasm_bindgen::prelude::*;

#[cfg(not(target_arch = "wasm32"))]
use turbosql::{select, Turbosql};

#[backend]
#[cfg_attr(not(target_arch = "wasm32"), derive(Turbosql))]
pub struct Person {
 pub rowid: Option<i64>,
 pub name: Option<String>,
}

#[backend]
async fn insert_person(p: Person) -> Result<i64, turbosql::Error> {
 p.insert() // returns rowid
}

#[backend]
async fn get_person(rowid: i64) -> Result<Person, turbosql::Error> {
 select!(Person "WHERE rowid = ?", rowid)
}

#[server_only]
#[tokio::main]
async fn main() {
 #[derive(rust_embed::RustEmbed)]
 #[folder = "build"]
 struct Frontend;

 eprintln!("Serving on http://127.0.0.1:8080");
 warp::serve(turbocharger::warp_routes(Frontend)).run(([127, 0, 0, 1], 8080)).await;
}

index.js

import turbocharger_init, * as backend from "./turbocharger_generated";

(async () => {
 await turbocharger_init();
 let person = Object.assign(new backend.Person(), { name: "Bob" });
 let rowid = await backend.insert_person(person);
 console.log((await backend.get_person(rowid)).toJSON());
})();

Usage

Your main.rs file is the entry point for both the server bin target and a wasm-bindgen lib target. The #[backend] macro outputs three functions:

• Your function, unchanged, for the server bin target; you can call it directly from other server code if you wish.
• An internal function for the server bin target providing the RPC dispatch glue.
• A #[wasm_bindgen] function for the frontend lib target that makes the RPC call and delivers the response.

Because the project is compiled to both wasm32-unknown-unknown and the host triple, all functions and structs in main.rs should be annotated with one of #[backend], #[server_only], or #[wasm_only].

Error Handling

#[backend] functions that need to return an error can return a Result<T, E> where T is a wasm-bindgen-compatible type and E is a type that implements std::error::Error, including Box<dyn std::error::Error>> and anyhow::Error. Errors crossing the network boundary are converted to a String representation on the server via their to_string() method and delivered as a Promise rejection on the JS side.

Server

Currently, the server side is batteries-included with warp, but this could be decoupled in the future. If this decoupling would be useful to you, please open a GitHub issue describing a use case.

WASM-only functions

You can also easily add standard #[wasm-bindgen]-style Rust functions to the WASM module, accessible from the frontend only:

#[turbocharger::wasm_only]
async fn get_wasm_greeting() -> String {
 "Hello from WASM".to_string()
}

To Do / Future Directions

• Better WebSocket status management / reconnect
• Streaming responses with futures::stream
• Many things tarpc does, particularly around timeouts and cancellation.

License: MIT OR Apache-2.0 OR CC0-1.0 (public domain)