Trait rocket::request::FromRequest [−] [src]

pub trait FromRequest<'a, 'r>: Sized {
    type Error: Debug;
    fn from_request(request: &'a Request<'r>) -> Outcome<Self, Self::Error>;
}

Trait used to derive an object from incoming request metadata.

An arbitrary number of types that implement this trait can appear as parameters in a route handler, as illustrated below:

#[get("/")]
fn index(a: A, b: B, c: C) -> ... { ... }

In this example, A, B, and C can be any types that implements FromRequest. There can be any number of FromRequest types in the function signature. Note that unlike every other derived object in Rocket, FromRequest parameter names do not need to be declared in the route attribute.

Derivation of FromRequest arguments is always attemped in left-to-right declaration order. In the example above, for instance, the order will be a followed by b followed by c. If a deriviation fails, the following aren't attempted.

Outcomes

The returned Outcome of a from_request call determines how the incoming request will be processed.

  • Success(S)

    If the Outcome is Success, then the Success value will be used as the value for the corresponding parameter. As long as all other parsed types succeed, the request will be handled.

  • Failure(Status, E)

    If the Outcome is Failure, the request will fail with the given status code and error. The designated error Catcher will be used to respond to the request. Note that users can request types of Result<S, E> and Option<S> to catch Failures and retrieve the error value.

  • Forward

    If the Outcome is Forward, the request will be forwarded to the next matching request. Note that users can request an Option<S> to catch Forwards.

Provided Implementations

Rocket implements FromRequest for several built-in types. Their behavior is documented here.

  • &URI

    Extracts the URI from the incoming request.

    This implementation always returns successfully.

  • Method

    Extracts the Method from the incoming request.

    This implementation always returns successfully.

  • &Cookies

    Returns a borrow to the Cookies in the incoming request. Note that Cookies implements internal mutability, so a handle to &Cookies allows you to get and set cookies in the request.

    This implementation always returns successfully.

  • ContentType

    Extracts the ContentType from the incoming request. If the request didn't specify a Content-Type, the request is forwarded.

  • SocketAddr

    Extracts the remote address of the incoming request as a SocketAddr. If the remote address is not known, the request is forwarded.

    This implementation always returns successfully.

  • Option<T> where T: FromRequest

    The type T is derived from the incoming request using T's FromRequest implementation. If the derivation is a Success, the dervived value is returned in Some. Otherwise, a None is returned.

    This implementation always returns successfully.

  • Result<T, T::Error> where T: FromRequest

    The type T is derived from the incoming request using T's FromRequest implementation. If derivation is a Success, the value is returned in Ok. If the derivation is a Failure, the error value is returned in Err. If the derivation is a Forward, the request is forwarded.

Example

Imagine you're running an authenticated API service that requires that some requests be sent along with a valid API key in a header field. You want to ensure that the handlers corresponding to these requests don't get called unless there is an API key in the request and the key is valid. The following example implements this using an APIKey type and a FromRequest implementation for that type. The APIKey type is then used in the senstive handler.

use rocket::Outcome;
use rocket::http::Status;
use rocket::request::{self, Request, FromRequest};

struct APIKey(String);

/// Returns true if `key` is a valid API key string.
fn is_valid(key: &str) -> bool {
    key == "valid_api_key"
}

impl<'a, 'r> FromRequest<'a, 'r> for APIKey {
    type Error = ();

    fn from_request(request: &'a Request<'r>) -> request::Outcome<APIKey, ()> {
        let keys: Vec<_> = request.headers().get("x-api-key").collect();
        if keys.len() != 1 {
            return Outcome::Failure((Status::BadRequest, ()));
        }

        let key = keys[0];
        if !is_valid(keys[0]) {
            return Outcome::Forward(());
        }

        return Outcome::Success(APIKey(key.to_string()));
    }
}

#[get("/sensitive")]
fn sensitive(key: APIKey) -> &'static str {
    "Sensitive data."
}

Associated Types

The associated error to be returned if derivation fails.

Required Methods

Derives an instance of Self from the incoming request metadata.

If the derivation is successful, an outcome of Success is returned. If the derivation fails in an unrecoverable fashion, Failure is returned. Forward is returned to indicate that the request should be forwarded to other matching routes, if any.

Implementors