How do I pass App data to service route handler function in actix-web when using function decorations?

Question

I found in the docs an example of how to create global state, protected by Mutex, shared among processing threads that is made available to all your route handlers. Perfect! However, I prefer to use attributes attached to my functions to wire up my route handlers. I do not know the syntax (if permitted) to use attributed functions and also pass in the global state.

Here is the example from the actix-web docs, from https://docs.rs/actix-web/1.0.2/actix_web/web/struct.Data.html

use std::sync::Mutex;
use actix_web::{web, App};

struct MyData {
    counter: usize,
}

/// Use `Data<T>` extractor to access data in handler.
fn index(data: web::Data<Mutex<MyData>>) {
    let mut data = data.lock().unwrap();
    data.counter += 1;
}

fn main() {
    let data = web::Data::new(Mutex::new(MyData{ counter: 0 }));

    let app = App::new()
        // Store `MyData` in application storage.
        .register_data(data.clone())
        .service(
            web::resource("/index.html").route(
                web::get().to(index)));
}

Notice how the route handler named index is being passed the web::Data.

Now here are some snippets of my code.

use actix_web::{get, App, HttpResponse, HttpServer, Responder};
pub mod request;
pub mod routes;

const SERVICE_NAME : &str = "Shy Rules Engine";
const SERVICE_VERSION : &str  = "0.1";

#[get("/")]
fn index() -> impl Responder {
    HttpResponse::Ok().body(format!("{} version {}", SERVICE_NAME, SERVICE_VERSION))
}

mod expression_execute {

  #[post("/expression/execute")]
  fn route(req: web::Json<ExpressionExecuteRequest>) -> HttpResponse {

    // ... lots of code omitted ...

    if response.has_error() {
        HttpResponse::Ok().json(response)
    }
    else {
        HttpResponse::BadRequest().json(response)
    }
  }

}

pub fn shy_service(ip : &str, port : &str) {
    HttpServer::new(|| {
        App::new()
            .service(index)
            .service(expression_execute::route)
    })
    .bind(format!("{}:{}", ip, port))
    .unwrap()
    .run()
    .unwrap();
}

Notice how I am calling method App::service to wire up my route handlers.

Also notice how my route handler does not receive global state (because I have not yet added it to my app). If I used a similar pattern as the docs using register_data to create global App data, what changes do I make to my method signature, the get and post attributes and anything else so that I can pass that global state to the handler?

Or is it not possible using get and post attributes to gain access to global state?

Answer 1

The two cases you listed really don't have much difference:

//# actix-web = "1.0.8"
use actix_web::{get, web, App, HttpResponse, HttpServer, Responder};
use std::sync::Mutex;

const SERVICE_NAME : &str = "Shy Rules Engine";
const SERVICE_VERSION : &str  = "0.1";

struct MyData {
    counter: usize,
}

#[get("/")]
fn index(data: web::Data<Mutex<MyData>>) -> impl Responder {
    let mut data = data.lock().unwrap();
    data.counter += 1;
    println!("Endpoint visited: {}", data.counter);
    HttpResponse::Ok().body(format!("{} version {}", SERVICE_NAME, SERVICE_VERSION))
}

pub fn shy_service(ip : &str, port : &str) {
    let data = web::Data::new(Mutex::new(MyData{ counter: 0 }));

    HttpServer::new(move || {
        App::new()
            .register_data(data.clone())
            .service(index)
    })
    .bind(format!("{}:{}", ip, port))
    .unwrap()
    .run()
    .unwrap();
}

fn main() {
    shy_service("127.0.0.1", "8080");
}

You can verify that it works by simply curl the http endpoint. For multiple extractors, you'll have to use tuple:

    #[post("/expression/execute")]
    fn route((req, data): (web::Json<ExpressionExecuteRequest>, web::Data<Mutex<MyData>>)) -> HttpResponse {
        unimplemented!()
    }