Writer

Writer is used to write content to 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);
}

Their differences are:

Different uses, Writer represents writing specific content to Response, which is implemented by specific content, such as strings, error messages, etc. Handler is used to process the entire request .
Writer is created in Handler, it will consume itself when the write function is called, it is a one-time call. And Handler is common to all requests;
Writer can be used as the content of Result returned by Handler;
The FlowCtrl parameter does not exist in Writer, and cannot control the execution flow of the entire request.

Scribe implements Writer, but with less functionality than Writer:

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

Scribe's rendering function just writes data to Response, this process cannot get information from Request or Depot.

# Writer

Writer