Trait rocket::data::FromData [] [src]

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

Trait implemented by data guards to derive a value from request body data.

Data Guards

A data guard is a request guard that operates on a request's body data. Data guards validate, parse, and optionally convert request body data. Validation and parsing/conversion is implemented through FromData. In other words, every type that implements FromData is a data guard.

Data guards are used as the target of the data route attribute parameter. A handler can have at most one data guard.


In the example below, var is used as the argument name for the data guard type T. When the submit route matches, Rocket will call the FromData implemention for the type T. The handler will only be called if the guard returns succesfully.

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


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

Provided Implementations

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


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) = 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::UnprocessableEntity, "':'".into()))

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

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

Associated Types

The associated error to be returned when the guard fails.

Required Methods

Validates, parses, and converts an instance of Self from the incoming request body data.

If validation and parsing succeeds, an outcome of Success is returned. If the data is not appropriate given the type of Self, Forward is returned. If parsing fails, Failure is returned.