A data guard for parsing FromForm types leniently.

This type implements the FromData trait, and like Form, provides a generic means to parse arbitrary structures from incoming form data. Unlike Form, this type uses a lenient parsing strategy: forms that contains a superset of the expected fields (i.e, extra fields) will parse successfully.

Leniency

A LenientForm<T> will parse successfully from an incoming form if the form contains a superset of the fields in T. Said another way, a LenientForm<T> automatically discards extra fields without error. For instance, if an incoming form contains the fields “a”, “b”, and “c” while T only contains “a” and “c”, the form will parse as LenientForm<T>.

Usage

The usage of a LenientForm type is equivalent to that of Form, so we defer details to its documentation.

LenientForm implements FromData, so it can be used directly as a target of the data = "<param>" route parameter. For instance, if some structure of type T implements the FromForm trait, an incoming form can be automatically parsed into the T structure with the following route and handler:

use rocket::request::LenientForm;

#[derive(FromForm)]
struct UserInput {
    value: String
}

#[post("/submit", data = "<user_input>")]
fn submit_task(user_input: LenientForm<UserInput>) -> String {
    format!("Your value: {}", user_input.value)
}

Incoming Data Limits

A LenientForm obeys the same data limits as a Form and defaults to 32KiB. The limit can be increased by setting the limits.forms configuration parameter. For instance, to increase the forms limit to 512KiB for all environments, you may add the following to your Rocket.toml:

[global.limits]
forms = 524288