Hello World

#![deny(warnings)]
use warp::Filter;

#[tokio::main]
async fn main() {
    // Match any request and return hello world!
    let routes = warp::any().map(|| "Hello, World!");

    warp::serve(routes).run(([127, 0, 0, 1], 3030)).await;
}

Run the example:

cargo run --example hello

Using your browser visit http://localhost:3030/

You will see the browser displaying Hello, World!.

In another terminal you can check the site using curl sending a GET request to the URL:

$ curl http://localhost:3030
Hello, World!

This is a very simple example that has many issues. We'll see some of them and step-by-step we'll improve.

Problems

This example will respond to any request with the same content.

A GET request to any other path:

curl http://localhost:3030/hi

A POST request to any path:

curl -X POST http://localhost:3030/oups

We cannot test this code without launching a server.

I don't have much to say about it. It is what it is. We'll soon have a way to test the code easily.

This code sets the Content-type to text/plain.

In order to see this change the content of the string to <b>Hello</b>, World!, that is we would like to return some HTML as well.

Using Ctrl-C stop the server process and run it again.

If you reload the web page at http://localhost:3030/ you will see it display the HTML tag instead of making the work bold.

This happens when the server returns the content with the Content-type set to text/plain.

Using the -i flag of curl we can see the header that shows the content-type being text/plain.

$ curl -i http://localhost:3030
HTTP/1.1 200 OK
content-type: text/plain; charset=utf-8
content-length: 20
date: Sat, 12 Apr 2025 07:11:14 GMT

<b>Hello</b>, World!