Struct rocket4::request::State

pub struct State<'r, T>(_)
where
    T: 'static + Send + Sync;

Request guard to retrieve managed state.

This type can be used as a request guard to retrieve the state Rocket is managing for some type T. This allows for the sharing of state across any number of handlers. A value for the given type must previously have been registered to be managed by Rocket via Rocket::manage(). The type being managed must be thread safe and sendable across thread boundaries. In other words, it must implement Send + Sync + 'static.

Example

Imagine you have some configuration struct of the type MyConfig that you’d like to initialize at start-up and later access it in several handlers. The following example does just this:

use rocket::State;

// In a real application, this would likely be more complex.
struct MyConfig {
    user_val: String
}

#[get("/")]
fn index(state: State<MyConfig>) -> String {
    format!("The config value is: {}", state.user_val)
}

#[get("/raw")]
fn raw_config_value<'r>(state: State<'r, MyConfig>) -> &'r str {
    // use `inner()` to get a lifetime longer than `deref` gives us
    state.inner().user_val.as_str()
}

fn main() {
    let config = MyConfig {
        user_val: "user input".to_string()
    };

    rocket::ignite()
        .mount("/", routes![index, raw_config_value])
        .manage(config)
        .launch();
}

Within Request Guards

Because State is itself a request guard, managed state can be retrieved from another request guard’s implementation. In the following code example, Item retrieves the MyConfig managed state in its FromRequest implementation using the Request::guard() method.

use rocket::State;
use rocket::request::{self, Request, FromRequest};

struct Item(String);

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

    fn from_request(request: &'a Request<'r>) -> request::Outcome<Item, ()> {
        request.guard::<State<MyConfig>>()
            .map(|my_config| Item(my_config.user_val.clone()))
    }
}

Testing with State

When unit testing your application, you may find it necessary to manually construct a type of State to pass to your functions. To do so, use the State::from() static method:

use rocket::State;

struct MyManagedState(usize);

#[get("/")]
fn handler(state: State<MyManagedState>) -> String {
    state.0.to_string()
}

let rocket = rocket::ignite().manage(MyManagedState(127));
let state = State::from(&rocket).expect("managing `MyManagedState`");
assert_eq!(handler(state), "127");

Implementations

impl<'r, T> State<'r, T>where
    T: 'static + Send + Sync,

pub fn inner(&self) -> &'r T

Retrieve a borrow to the underlying value with a lifetime of 'r.

Using this method is typically unnecessary as State implements Deref with a Deref::Target of T. This means Rocket will automatically coerce a State<T> to an &T as required. This method should only be used when a longer lifetime is required.

Example

use rocket::State;

struct MyConfig {
    user_val: String
}

// Use `inner()` to get a lifetime of `'r`
fn handler1<'r>(config: State<'r, MyConfig>) -> &'r str {
    &config.inner().user_val
}

// Use the `Deref` implementation which coerces implicitly
fn handler2(config: State<MyConfig>) -> String {
    config.user_val.clone()
}

pub fn from(rocket: &'r Rocket) -> Option<State<'r, T>>

Returns the managed state value in rocket for the type T if it is being managed by rocket. Otherwise, returns None.

Example

use rocket::State;

#[derive(Debug, PartialEq)]
struct Managed(usize);

#[derive(Debug, PartialEq)]
struct Unmanaged(usize);

let rocket = rocket::ignite().manage(Managed(7));

let state: Option<State<Managed>> = State::from(&rocket);
assert_eq!(state.map(|s| s.inner()), Some(&Managed(7)));

let state: Option<State<Unmanaged>> = State::from(&rocket);
assert_eq!(state, None);

Trait Implementations

impl<'r, T> Debug for State<'r, T>where
    T: 'static + Debug + Send + Sync,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'r, T> Deref for State<'r, T>where
    T: 'static + Send + Sync,

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<'a, 'r, T> FromRequest<'a, 'r> for State<'r, T>where
    T: 'static + Send + Sync,

type Error = ()

The associated error to be returned if derivation fails.

fn from_request(req: &'a Request<'r>) -> Outcome<State<'r, T>, (Status, ()), ()>

Derives an instance of Self from the incoming request metadata.

impl<'r, T> Hash for State<'r, T>where
    T: 'static + Hash + Send + Sync,

fn hash<__H>(&self, state: &mut __H)where
    __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)where
    H: Hasher,
    Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<'r, T> Ord for State<'r, T>where
    T: 'static + Ord + Send + Sync,

fn cmp(&self, other: &State<'r, T>) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere
    Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval.

impl<'r, T> PartialEq<State<'r, T>> for State<'r, T>where
    T: 'static + PartialEq<T> + Send + Sync,

fn eq(&self, other: &State<'r, T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<'r, T> PartialOrd<State<'r, T>> for State<'r, T>where
    T: 'static + PartialOrd<T> + Send + Sync,

fn partial_cmp(&self, other: &State<'r, T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<'r, T> Eq for State<'r, T>where
    T: 'static + Eq + Send + Sync,

impl<'r, T> StructuralEq for State<'r, T>where
    T: 'static + Send + Sync,

impl<'r, T> StructuralPartialEq for State<'r, T>where
    T: 'static + Send + Sync,