3 min read

Hosting quickly 2.5 - Discovering and calling a backend from Dioxus

We should make the backend serve some API that we can hit from the frontend.

We'll turn the root endpoint in the backend into a JSON-returning endpoint:

struct Response {
    name: String,

async fn home() -> Json<Response> {
    Json(Response {
        name: "Hello, World!".to_string(),

and then use that endpoint from the frontend:

struct Response {
    name: String,

pub async fn get_endpoint() -> Result<String, reqwest::Error> {
    let url = format!("/topstories.json");
    let res = reqwest::get(url).await?.json::<Response>().await?;


fn app(cx: Scope) -> Element {
    let response = use_future(cx, (), |_| get_endpoint());

    match response.value() {
        Some(Ok(name)) => cx.render(rsx! {
            h1 { "{name}" }
        Some(Err(_)) | None => cx.render(rsx! {
            h1 { "Error!" }

Let the frontend know

There's a very simple reason that this is a separate article: I need to figure out how to make the frontend discover the base URI of the backend API. There are a few options:

  1. Compile it in, either from an environment variable or as a hardcoded string.
  2. Serve it in configuration, like an /env.json file that can be loaded from the frontend or inserted into a script tag in the HTML.
  3. Ensure it's on the same domain, so that the frontend can just call /api.

I'm not a huge fan of compiling it into the code: I'd like to be able to use the same compiled code across different environments. Additional requests, like having an env.json or service discovery, will only slow down the page load. Routing is something I'd like to avoid depending on.

So instead, let's insert any environment variables into the index.html at startup! We'll start by loading it in Dioxus. I'll leave defining the EnvSettings as an exercise to the reader:

fn get_dioxus_env<'a>(cx: &Scope) -> EnvSettings {

For running the frontend locally and through Docker, we'll set it through the Justfile. For the docker-run command, we'll also make sure to forward the backend's port:

run $DIOXUS_ENV='BACKEND_API_URL="https://localhost:3000"': build
    dx serve --features ssr --hot-reload --platform desktop

docker-run: docker-build
    docker run -it -p 8081:8081 -p 8080:8080 -e BACKEND_API_URL=https://localhost:8081 cochrane-frontend:dev
I've hardcoded the environment for now. Ideally we'll want to load or parse it from some configuration file, so that we can make sure it's the same everywhere.

Call the API

To make this as simple as possible, let's create a special component that calls the API and returns either an error or the text response:

#[derive(PartialEq, Props)]
struct QueryingTextProps {
    backend_url: url::Url,

fn QueryingText(cx: Scope<QueryingTextProps>) -> Element {
    let result = use_future(cx, &cx.props.backend_url, |val| async move {
        let res = call_api(val).await;

    cx.render(match result.value() {
        Some(Ok(s)) => rsx! { p { "{s}" } },
        Some(Err(e)) => rsx! { p { "{e}" } },
        None => rsx! { p { "Loading..." } },

Note the call_api function that's undefined, we'll get there. There's some setup code here that's necessary for a Dioxus component: the QueryingTextProps struct to allow passing our API endpoint, the use_future call to actually call the async fn that we'll be defining. Otherwise it's fairly standard!

In fact, the call_api function is super simple. It's just a plain reqwest call. Of course, we could flesh this out by sprinkling in some serde_json and better error types, but this'll do for now:

async fn call_api(url: url::Url) -> Result<String, String> {
    let res = reqwest::get(url).await.map_err(|e| e.to_string())?;
    res.text().await.map_err(|e| e.to_string())

All that's left is actually using the component now:

let EnvSettings { backend_url } = get_dioxus_env(&cx);

And then add this to the returned rsx:

rsx! { QueryingText { backend_url: backend_url } },

Voila! It's all hooked up.


I've intentionally left certain elements for the reader to implement. Specifically, the exact definition of EnvSettings and the intricate details of error handling and JSON processing within the call_api function are not covered. Also, getting the environment info from a dotenv file or other configuration would probably improve this.

Anyway, I think it works out to be a nice way of configuring your frontend Docker image without having to rebuild your Rust code for each environment.