Module salvo_core::handler

Handler module for handle Request.

Middleware is actually also a Handler. They can do some processing before or after the request reaches the Handler that officially handles the request, such as: login verification, data compression, etc.

Middleware is added through the hoop function of Router. The added middleware will affect the current Router and all its internal descendants Router.

Macro #[handler]

#[handler] can greatly simplify the writing of the code, and improve the flexibility of the code.

It can be added to a function to make it implement Handler:

use salvo_core::prelude::*;

#[handler]
async fn hello() -> &'static str {
    "hello world!"
}

This is equivalent to:

use salvo_core::prelude::*;

#[allow(non_camel_case_types)]
struct hello;

#[async_trait]
impl Handler for hello {
    async fn handle(&self, _req: &mut Request, _depot: &mut Depot, res: &mut Response, _ctrl: &mut FlowCtrl) {
        res.render(Text::Plain("hello world!"));
    }
}

As you can see, in the case of using #[handler], the code becomes much simpler:

• No need to manually add #[async_trait].
• The parameters that are not needed in the function have been omitted, and the required parameters can be arranged in any order.
• For objects that implement Writer or Scribe abstraction, it can be directly used as the return value of the function. Here &'static str implements Scribe, so it can be returned directly as the return value of the function.

#[handler] can not only be added to the function, but also can be added to the impl of struct to let struct implement Handler. At this time, the handle function in the impl code block will be Identified as the specific implementation of handle in Handler:

use salvo_core::prelude::*;

struct Hello;

#[handler]
impl Hello {
    async fn handle(&self, res: &mut Response) {
        res.render(Text::Plain("hello world!"));
    }
}

Handle errors

Handler in Salvo can return Result, only the types of Ok and Err in Result are implemented Writer trait.

Taking into account the widespread use of anyhow, the Writer implementation of anyhow::Error is provided by default if anyhow feature is enabled, and anyhow::Error is Mapped to InternalServerError.

For custom error types, you can output different error pages according to your needs.

use anyhow::anyhow;
use salvo_core::prelude::*;

struct CustomError;
#[async_trait]
impl Writer for CustomError {
    async fn write(self, _req: &mut Request, _depot: &mut Depot, res: &mut Response) {
        res.status_code(StatusCode::INTERNAL_SERVER_ERROR);
        res.render("custom error");
    }
}

#[handler]
async fn handle_anyhow() -> Result<(), anyhow::Error> {
    Err(anyhow::anyhow!("anyhow error"))
}
#[handler]
async fn handle_custom() -> Result<(), CustomError> {
    Err(CustomError)
}

#[tokio::main]
async fn main() {
    let router = Router::new()
        .push(Router::new().path("anyhow").get(handle_anyhow))
        .push(Router::new().path("custom").get(handle_custom));
    let acceptor = TcpListener::new("127.0.0.1:5800").bind().await;
    Server::new(acceptor).serve(router).await;
}

Implement Handler trait directly

Under certain circumstances, We need to implment Handler direclty.

use salvo_core::prelude::*;
 use crate::salvo_core::http::Body;

pub struct MaxSizeHandler(u64);
#[async_trait]
impl Handler for MaxSizeHandler {
    async fn handle(&self, req: &mut Request, _depot: &mut Depot, res: &mut Response, ctrl: &mut FlowCtrl) {
        if let Some(upper) = req.body().size_hint().upper() {
            if upper > self.0 {
                res.render(StatusError::payload_too_large());
                ctrl.skip_rest();
            }
        }
    }
}

Traits

• Handler
  Handler is used for handle Request.
• Skipper
  Skipper is used to check if the request should be skipped.

Functions

• empty
  This is a empty implement for Handler.
• none_skipper
  none_skipper will skipper nothing.