Trait rocket::data::FromData

pub trait FromData: Sized {
    type Error;
    fn from_data(request: &Request, data: Data) -> Outcome<Self, Self::Error>;
}

Trait used to derive an object from incoming request data.

Types that implement this trait can be used as a target for the data = "<param>" route parmater, as illustrated below:

#[post("/submit", data = "<var>")]
fn submit(var: T) -> ... { ... }

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

Outcomes

The returned Outcome of a from_data 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 data parameter. As long as all other parsed types succeed, the request will be handled by the requesting handler.

• 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(Data)

  If the Outcome is Forward, the request will be forwarded to the next matching request. This requires that no data has been read from the Data parameter. Note that users can request an Option<S> to catch Forwards.

Example

Say that you have a custom type, Person:

struct Person {
    name: String,
    age: u16
}

Person has a custom serialization format, so the built-in JSON type doesn't suffice. The format is <name>:<age> with Content-Type: application/x-person. You'd like to use Person as a FromData type so that you can retrieve it directly from a client's request body:

#[post("/person", data = "<person>")]
fn person(person: Person) -> &'static str {
    "Saved the new person to the database!"
}

A FromData implementation allowing this looks like:

use std::io::Read;
use rocket::{Request, Data, Outcome};
use rocket::data::{self, FromData};
use rocket::http::{Status, ContentType};
use rocket::Outcome::*;

impl FromData for Person {
    type Error = String;

    fn from_data(req: &Request, data: Data) -> data::Outcome<Self, String> {
        // Ensure the content type is correct before opening the data.
        let person_ct = ContentType::new("application", "x-person");
        if req.content_type() != Some(person_ct) {
            return Outcome::Forward(data);
        }

        // Read the data into a String.
        let mut string = String::new();
        if let Err(e) = data.open().read_to_string(&mut string) {
            return Failure((Status::InternalServerError, format!("{:?}", e)));
        }

        // Split the string into two pieces at ':'.
        let (name, age) = match string.find(':') {
            Some(i) => (&string[..i], &string[(i + 1)..]),
            None => return Failure((Status::BadRequest, "Missing ':'.".into()))
        };

        // Parse the age.
        let age: u16 = match age.parse() {
            Ok(age) => age,
            Err(_) => return Failure((Status::BadRequest, "Bad age.".into()))
        };

        // Return successfully.
        Success(Person {
            name: name.into(),
            age: age
        })
    }
}

Associated Types

type Error

The associated error to be returned when parsing fails.

Required Methods

fn from_data(request: &Request, data: Data) -> Outcome<Self, Self::Error>

Parses an instance of Self from the incoming request body data.

If the parse is successful, an outcome of Success is returned. If the data does not correspond to the type of Self, Forward is returned. If parsing fails, Failure is returned.

Implementors

• impl<'f, T: FromForm<'f>> FromData for Form<'f, T> where
    T::Error: Debug, 
• impl FromData for Data
• impl<T: FromData> FromData for Result<T, T::Error>
• impl<T: FromData> FromData for Option<T>