Writer

Writer is used to write content to the Response:

#[async_trait]
pub trait Writer {
    async fn write(mut self, req: &mut Request, depot: &mut Depot, res: &mut Response);
}

Compared to Handler:

#[async_trait]
pub trait Handler: Send + Sync + 'static {
    async fn handle(&self, req: &mut Request, depot: &mut Depot, res: &mut Response, ctrl: &mut FlowCtrl);
}

The direct differences between them are:

Different purposes: Writer represents writing specific content to the Response and is implemented by the specific content (e.g., strings, error messages, etc.). In contrast, Handler is used to process the entire request.
Writer is created within a Handler and consumes itself when its write function is called, making it a one-time use. In contrast, Handler is shared across all requests.
A Writer can be the content within the Result returned by a Handler.
Writer does not have a FlowCtrl parameter and cannot control the execution flow of the entire request.

Scribe implements Writer, but it offers fewer functionalities than Writer:

pub trait Scribe {
    fn render(self, res: &mut Response);
}

The rendering function of Scribe only writes data to the Response; this process cannot access information from the Request or Depot.

#Writer

Writer