github twitter linkedin
Tonic: gRPC has come to async/await!
Oct 2, 2019
3 minutes read

Tonic: gRPC has come to async/await!

I am pleased to finally announce a crate that I have been working very hard on for the past few months. tonic has finally hit the initial 0.1.0-alpha.1 release! Stable releases will follow in the coming months.

What is Tonic?

Tonic is a gRPC-over-HTTP/2 implementation focused on high performance, interoperability, and flexibility. This library was created to have first class support of async/await and to act as a core building block for production systems written in Rust.

Tonic began its life as tower-grpc, which was built to satisfy linkerd’s need for a production-ready gRPC implementation. tower-grpc was based upon futures 0.1 and built ontop of the tower library, which has production uses in systems such as the linkerd-proxy, vector, and the noria database at MIT. The tower library has also seen usage in additional libraries such as warp, tower-web, and actix-net.

With async/await’s forthcoming stabilization, we created Tonic to support the new syntax natively. This means clients will support async/await out of the box and server implementations can be defined via async_traits. This provides an unparalleled experience for writing async services quickly and efficiently. Not only does Tonic provide a fully featured gRPC implementation but it also comes with a fully featured, batteries-included, HTTP/2 client and server built around hyper, tokio and tower. Both the client and server implementation provide TLS backed by either openssl or rustls. The client provides load balancing, interceptors (middleware), timeouts, rate limiting, concurrency control and more!

Tonic also boasts strong interoperability and correctness. Every commit is checked that it passes the gRPC interop test cases against the grpc-go implementation. Hopefully, more languages can be added in the future.


Tonic’s goal is to provide a good batteries-included experience. It already supports many features, with many more planned! Here is a list of features:

  • Implemented in pure Rust (minus openssl which is optional)
  • Interoperability tested via tonic-interop
  • Bi-directional streaming
  • Custom metadata
  • Trailing metadata
  • Codegen via prost
  • Exposes tracing diagnostics
  • Fully featured HTTP/2 client and server based on hyper
  • TLS backed by either openssl or rustls
  • Load balancing powered by tower
  • Reliability features such as timeouts, rate limiting, concurrency control, and more
  • gRPC interceptors
  • And much more to come


helloworld client example:

let mut client = GreeterClient::connect("http://[::1]:50051")?;
let request = Request::new(HelloRequest {
    name: "hello".into(),
let response = client.say_hello(request).await?;
println!("RESPONSE={:?}", response);

This shows how easy it is to build a simple gRPC client using code generated by the tonic-build crate. Internally, connect will create the most basic “channel/client” but it is possible to configure this to support TLS, load balancing, timeouts and more.

helloworld server example:

impl Greeter for MyGreeter {
    async fn say_hello(&self, req: Request<HelloRequest>)
        -> Result<Response<HelloReply>, Status>
        println!("Got a request: {:?}", req);
        let reply = HelloReply {
            message: "Zomg, it works!".into(),

Servers are simple to implement using dtolnay’s amazing async_trait crate, which allow server implementations to use async fn for their implementation. The tonic-examples crate demonstrates more advanced cases with TLS, authentication, load balancing, streaming and more.

Moving forward

Today marks Tonic’s first alpha release, and over the next few months we will be working hard to ensure that Tonic is ready for production usage. A lot of the implementation has already been proven in production environments via tower-grpc. Over the next few months as tokio 0.2 comes closer to a full stable release, Tonic will follow with its own stable releases.


tonic is now available! There is documentation, examples and an issue tracker! Please provide any feedback, as we would love to improve this library any way we can!

Thank you to all the super awesome contributors that have helped over the past few months! Your feedback has been immensely important and valuable!

Back to posts