HTTP GET is a request for something at a URL. Viewing a webpage makes a GET request; the server can respond with HTML, JSON, or other content. A browser or phone may make many such requests in a day. section 19.1 section 24.1.1
In Rust, a reqwest `Client` can start a request with `.get("https://www.rust-lang.org")`. This returns a `RequestBuilder`, which can be configured before `.send()` sends the request. The ordinary client is asynchronous: calling `.send().unwrap()` immediately produces a compiler error because `.send()` returns a `Future`, not a completed response. For a few requests, `reqwest::blocking::Client` is presented as another option. section 19.1
A server needs somewhere to receive the request. With Axum, `.route("/", get(handler))` connects GET requests for `/` to a handler function. A route such as `/double/:number` can take a value from the URL and return a calculated string. If a requested path has no route, the browser can show a 404 error. section 24.1.1
use axum::{extract::Path, routing::get}; async fn double(Path(input): Path<String>) -> String { #1 match input.parse::<i32>() { #2 Ok(num) => format!("{} times 2 is {}!", num, num * 2), Err(e) => format!("Uh oh, weird input: {e}") } } #[tokio::main] async fn main() { let app = axum::Router::new() .route("/", get(|| async { "The server works!" })) #3 .route( #4 "/game/:guess", get(|Path(guess): Path<String>| async move { format!("The guess is {guess}") }), ) .route("/double/:number", get(double)); #5 axum::Server::bind(&"127.0.0.1:8080".parse().unwrap()) .serve(app.into_make_service()) .await .unwrap(); } #1 The signature here may look a bit odd, but it is just deconstructing the input inside the function signature. Axum uses this syntax a lot, so we’ll copy it. #2 Nothing else in this function is particularly surprising: it tries to parse a string into an <kbd>i32</kbd> and doubles it if it can. #3 This first route just lets us know that the server works, and we handle the response inside an async closure. #4 For the second route, we will also use an async function. The colon in <kbd>:guess</kbd> means to pass in whatever is after <kbd>/game/</kbd> to the function under the variable name <kbd>guess</kbd>. This time, we need <kbd>async move</kbd> because we want the function to take ownership of <kbd>guess</kbd>. Then we will return the guess to the user. #5 For the third route, we will use the previous doubling function. Here, as well, we pass in the path as the variable <kbd>number</kbd>, but inside the function itself, it will have a different name.
The Axum example connects three paths to GET handlers: one returns a greeting, one reads a guess from the path, and one doubles a number. section 24.1.1
