Trait rocket::catcher::Handler[][src]

pub trait Handler: Cloneable + Send + Sync + 'static {
    fn handle<'r, 'life0, 'life1, 'async_trait>(
        &'life0 self,
        status: Status,
        req: &'r Request<'life1>
    ) -> Pin<Box<dyn Future<Output = Result<'r>> + Send + 'async_trait>>
        'r: 'async_trait,
        'life0: 'async_trait,
        'life1: 'async_trait,
        Self: 'async_trait
; }
Expand description

Trait implemented by Catcher error handlers.

This trait is exactly like a Route’s Handler except it handles errors instead of requests. Thus, the documentation for route::Handler applies to this trait as well. We defer to it for full details.

Async Trait

This is an async trait. Implementations must be decorated #[rocket::async_trait].


Say you’d like to write a handler that changes its functionality based on a Kind enum value that the user provides. Such a handler might be written and used as follows:

use rocket::{Request, Catcher, catcher};
use rocket::response::{Response, Responder};
use rocket::http::Status;

#[derive(Copy, Clone)]
enum Kind {

struct CustomHandler(Kind);

impl catcher::Handler for CustomHandler {
    async fn handle<'r>(&self, status: Status, req: &'r Request<'_>) -> catcher::Result<'r> {
        let inner = match self.0 {
            Kind::Simple => "simple".respond_to(req)?,
            Kind::Intermediate => "intermediate".respond_to(req)?,
            Kind::Complex => "complex".respond_to(req)?,


impl CustomHandler {
    /// Returns a `default` catcher that uses `CustomHandler`.
    fn default(kind: Kind) -> Vec<Catcher> {
        vec![Catcher::new(None, CustomHandler(kind))]

    /// Returns a catcher for code `status` that uses `CustomHandler`.
    fn catch(status: Status, kind: Kind) -> Vec<Catcher> {
        vec![Catcher::new(status.code, CustomHandler(kind))]

fn rocket() -> _ {
        // to handle only `404`
        .register("/", CustomHandler::catch(Status::NotFound, Kind::Simple))
        // or to register as the default
        .register("/", CustomHandler::default(Kind::Simple))

Note the following:

  1. CustomHandler implements Clone. This is required so that CustomHandler implements Cloneable automatically. The Cloneable trait serves no other purpose but to ensure that every Handler can be cloned, allowing Catchers to be cloned.
  2. CustomHandler’s methods return Vec<Route>, allowing for use directly as the parameter to rocket.register("/", ).
  3. Unlike static-function-based handlers, this custom handler can make use of internal state.

Required methods

Called by Rocket when an error with status for a given Request should be handled by this handler.

Error handlers should not fail and thus should always return Ok. Nevertheless, failure is allowed, both for convenience and necessity. If an error handler fails, Rocket’s default 500 catcher is invoked. If it succeeds, the returned Response is used to respond to the client.