The Spin Rust SDK

The Spin Rust SDK makes it easy to build Spin components in Rust.

Writing Spin HTTP components in Rust

This library simplifies writing Spin HTTP components. Below is an example of such a component:

// lib.rs
use anyhow::Result;
use spin_sdk::{
    http::{Request, Response},
    http_component,
};

/// A simple Spin HTTP component.
#[http_component]
fn hello_world(req: Request) -> Result<Response> {
    println!("{:?}", req.headers);
    Ok(Response::new_with_headers(200, &[] "Hello, Fermyon!"))
}

The important things to note in the function above:

• the spin_sdk::http_component macro — this marks the function as the entrypoint for the Spin component
• the function signature — fn hello_world(req: Request) -> Result<Response> — req can be any number of types including the built in Request type or the http::Request from the popular http crate. Likewise, the response type can be many things including the built in Response type or the http::Response type from the http crate.

Making outbound HTTP requests

Let's see an example where the component makes an outbound HTTP request to a server, modifies the result, then returns it:

#[http_component]
async fn hello_world(_req: Request) -> Result<Response> {
    let mut res: http::Response<String> = spin_sdk::http::send(
        http::Request::builder()
            .method("GET")
            .uri("https://fermyon.com")
            .body(())?,
    ).await?;

    res.headers_mut()
        .insert(http::header::SERVER, "spin/0.1.0".try_into()?);

    Ok(res)
}

In order for the component above to be allowed to make the outbound HTTP request, the destination host must be declared in the Spin application configuration:

[[component]]
id = "hello"
source = "target/wasm32-wasi/release/spinhelloworld.wasm"
allowed_outbound_hosts = [ "https://fermyon.com" ]
[component.trigger]
route = "/hello"

Making a request to this component, we can see the appended header, and that the response contains the expected body:

$ curl -I localhost:3000/hello
HTTP/1.1 200 OK
content-length: 29350
content-type: text/html; charset=utf-8
server: spin/0.1.0