Rocket: Web-based Hello World! with tests

Part of the series about the Rocket web framework.

Create crate

In order to have a Rocket, we need to create a regular Rust crate.

cargo new hello-world
cd hello-world

Setup dependencies

Add

rocket = "0.5.0"

to the Cargo.toml file:

examples/rocket/hello-world/Cargo.toml

[package]
name = "hello-world"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
rocket = "0.5.0"

Setup the use of the macros

#[macro_use]
extern crate rocket;

Route

Define a route and what it should do and return.

#[get("/")]
fn index() -> &'static str {
    "Hello, world!"
}

This create a route that will handle any GET request arriving to the root of the site: /. The function will be executed and the return value of the function will be returned to the client.

Map the routes

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/", routes![index])
}

This maps the "/" request to the index function. At first it is strange that we need to define the mapping of urls twice, but later we'll see how this can be actually useful.

run the application

Just type in

cargo run

It will compile the code and start running the server listening on port 8000 by default.

Visit http://localhost:8000/ with your browser to see "Hello world!.

Content-type is text/plain

Using the curl command with the -i flag will show both the header and the content of the response. We can see that the content-type returned was text/plain.

$ curl -i http://localhost:8000
HTTP/1.1 200 OK
content-type: text/plain; charset=utf-8
server: Rocket
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
permissions-policy: interest-cohort=()
content-length: 13
date: Fri, 22 Dec 2023 10:13:03 GMT

Hello, world!

Testing the application

Before we end this example, let's see how can we test if it works properly. This is the testing code that goes into the src/main.rs file.

It sets up a fake client and uses that to GET a url (by calling the get method.

We then verify that the status code is 200 OK and we compare the received content to the expected content.

#[cfg(test)]
mod test {
    use rocket::http::Status;
    use rocket::local::blocking::Client;

    #[test]
    fn hello_world() {
        let client = Client::tracked(super::rocket()).unwrap();
        let response = client.get("/").dispatch();

        assert_eq!(response.status(), Status::Ok);
        assert_eq!(response.into_string(), Some("Hello, world!".into()));
    }
}

The full example

examples/rocket/hello-world/src/main.rs

#[macro_use]
extern crate rocket;

#[get("/")]
fn index() -> &'static str {
    "Hello, world!"
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/", routes![index])
}

#[cfg(test)]
mod test {
    use rocket::http::Status;
    use rocket::local::blocking::Client;

    #[test]
    fn hello_world() {
        let client = Client::tracked(super::rocket()).unwrap();
        let response = client.get("/").dispatch();

        assert_eq!(response.status(), Status::Ok);
        assert_eq!(response.into_string(), Some("Hello, world!".into()));
    }
}