Trait rocket::response::Responder [−] [src]

pub trait Responder<'r> {
    fn respond(self) -> Result<Response<'r>, Status>;
}

Trait implemented by types that generate responses for clients.

Types that implement this trait can be used as the return type of a handler, as illustrated below:

#[get("/")]
fn index() -> T { ... }

In this example, T can be any type that implements Responder.

Return Value

A Responder returns an Ok(Response) or an Err(Status):

  • An Ok variant means that the Responder was successful in generating a Response. The Response will be written out to the client.

  • An Err variant means that the Responder could not or did not generate a Response. The contained Status will be used to find the relevant error catcher which then generates an error response.

Provided Implementations

Rocket implements Responder for several standard library types. Their behavior is documented here. Note that the Result implementation is overloaded, allowing for two Responders to be used at once, depending on the variant.

  • &str

    Sets the Content-Type to text/plain. The string is used as the body of the response, which is fixed size and not streamed. To stream a raw string, use Stream::from(Cursor::new(string)).

  • String

    Sets the Content-Typet to text/plain. The string is used as the body of the response, which is fixed size and not streamed. To stream a string, use Stream::from(Cursor::new(string)).

  • File

    Streams the File to the client. This is essentially an alias to Stream::from(file).

  • ()

    Responds with an empty body. No Content-Type is set.

  • Option<T>

    If the Option is Some, the wrapped responder is used to respond to the client. Otherwise, an Err with status 404 Not Found is returned and a warning is printed to the console.

  • Result<T, E> where E: Debug

    If the Result is Ok, the wrapped responder is used to respond to the client. Otherwise, an Err with status 500 Internal Server Error is returned and the error is printed to the console using the Debug implementation.

  • Result<T, E> where E: Debug + Responder

    If the Result is Ok, the wrapped Ok responder is used to respond to the client. If the Result is Err, the wrapped Err responder is used to respond to the client.

Implementation Tips

This section describes a few best practices to take into account when implementing Responder.

Debug

A type implementing Responder should implement the Debug trait when possible. This is because the Responder implementation for Result requires its Err type to implement Debug. Therefore, a type implementing Debug can more easily be composed.

Joining and Merging

When chaining/wrapping other Responders, use the merge or join methods on the Response or ResponseBuilder struct. Ensure that you document the merging or joining behavior appropriately.

Example

Say that you have a custom type, Person:

struct Person {
    name: String,
    age: u16
}

You'd like to use Person as a Responder so that you can return a Person directly from a handler:

#[get("/person/<id>")]
fn person(id: usize) -> Option<Person> {
    Person::from_id(id)
}

You want the Person responder to set two header fields: X-Person-Name and X-Person-Age as well as supply a custom representation of the object (Content-Type: application/x-person) in the body of the response. The following Responder implementation accomplishes this:

use std::io::Cursor;

use rocket::response::{self, Response, Responder};
use rocket::http::ContentType;

impl<'r> Responder<'r> for Person {
    fn respond(self) -> response::Result<'r> {
        Response::build()
            .sized_body(Cursor::new(format!("{}:{}", self.name, self.age)))
            .raw_header("X-Person-Name", self.name)
            .raw_header("X-Person-Age", self.age.to_string())
            .header(ContentType::new("application", "x-person"))
            .ok()
    }
}

Required Methods

Returns Ok if a Response could be generated successfully. Otherwise, returns an Err with a failing Status.

When using Rocket's code generation, if an Ok(Response) is returned, the response will be written out to the client. If an Err(Status) is returned, the error catcher for the given status is retrieved and called to generate a final error response, which is then written out to the client.

Implementors