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      • Affix State Shared Data in Requests

      The Affix State middleware is used to add shared data to the Depot. To use the Affix State feature, you need to enable the affix-state feature in Cargo.toml.

      Feature Analysis

      Affix State provides a simple way to share data during request processing. It allows you to:

      • Inject global configurations or shared data during route configuration
      • Access this data via the Depot in any handler
      • Support any cloneable type as state data

      Comparison with Other Frameworks for Quick Concept Understanding

      FrameworkLanguageState Management Approach
      Salvo (Affix State)RustStores and accesses via Depot, supports multiple types
      AxumRustStores state via Extension, similar but with different usage
      Actix-webRustUses App Data and Web::Data to share state
      GinGoUses context.Set and context.Get to store and retrieve data
      EchoGoUses context.Set and context.Get to manage shared state
      SpringJavaUses ApplicationContext or @Bean annotations for dependency management
      QuarkusJavaUses CDI and dependency injection mechanisms
      Express.jsJavaScriptUses app.locals or req.app.locals to store global state
      Nest.jsJavaScriptUses a dependency injection system to manage shared services
      Koa.jsJavaScriptUses ctx.state to store request-level state

      Common Use Cases

      • Database connection pool sharing
      • Application configuration sharing
      • Cache instance sharing
      • API client sharing
      • Global counters or state tracking

      The advantage of Affix State lies in its simplicity and flexibility, allowing easy sharing of any type of data across different routes and handlers without extensive boilerplate code. Example Code

      main.rs
      Cargo.toml
      use std::sync::Arc;
use std::sync::Mutex;

use salvo::prelude::*;

// Configuration structure with username and password
#[allow(dead_code)]
#[derive(Default, Clone, Debug)]
struct Config {
    username: String,
    password: String,
}

// State structure to hold a list of fail messages
#[derive(Default, Debug)]
struct State {
    fails: Mutex<Vec<String>>,
}

#[handler]
async fn hello(depot: &mut Depot) -> String {
    // Obtain the Config instance from the depot
    let config = depot.obtain::<Config>().unwrap();
    // Get custom data from the depot
    let custom_data = depot.get::<&str>("custom_data").unwrap();
    // Obtain the shared State instance from the depot
    let state = depot.obtain::<Arc<State>>().unwrap();
    // Lock the fails vector and add a new fail message
    let mut fails_ref = state.fails.lock().unwrap();
    fails_ref.push("fail message".into());
    // Format and return the response string
    format!("Hello World\nConfig: {config:#?}\nFails: {fails_ref:#?}\nCustom Data: {custom_data}")
}

#[tokio::main]
async fn main() {
    // Initialize the tracing subscriber for logging
    tracing_subscriber::fmt().init();

    // Create a Config instance with default username and password
    let config = Config {
        username: "root".to_string(),
        password: "pwd".to_string(),
    };

    // Set up the router with state injection and custom data
    let router = Router::new()
        // Use hoop to inject middleware and data into the request context
        .hoop(
            affix_state::inject(config)
                // Inject a shared State instance into the request context
                .inject(Arc::new(State {
                    fails: Mutex::new(Vec::new()),
                }))
                // Insert custom data into the request context
                .insert("custom_data", "I love this world!"),
        )
        // Register the hello handler for the root path
        .get(hello)
        // Add an additional route for the path "/hello" with the same handler
        .push(Router::with_path("hello").get(hello));

    // Bind the server to port 8698 and start serving
    let acceptor = TcpListener::new("0.0.0.0:8698").bind().await;
    Server::new(acceptor).serve(router).await;
}