Struct Flash

pub struct Flash<R> { /* private fields */ }

Sets a “flash” cookie that will be removed when it is accessed. The analogous request type is FlashMessage.

This type makes it easy to send messages across requests. It is typically used for “status” messages after redirects. For instance, if a user attempts to visit a page he/she does not have access to, you may want to redirect the user to a safe place and show a message indicating what happened on the redirected page. The message should only persist for a single request. This can be accomplished with this type.

Usage

Each Flash message consists of a name and some msg contents. A generic constructor (new) can be used to construct a message with any name, while the warning, success, and error constructors create messages with the corresponding names.

Messages can be retrieved on the request side via the FlashMessage type and the name and msg methods.

Response

The Responder implementation for Flash sets the message cookie and then uses the passed in responder res to complete the response. In other words, it simply sets a cookie and delegates the rest of the response handling to the wrapped responder.

Example

The following complete Rocket application illustrates the use of a Flash message on both the request and response sides.

use rocket::response::{Flash, Redirect};
use rocket::request::FlashMessage;
use rocket::http::RawStr;

#[post("/login/<name>")]
fn login(name: &RawStr) -> Result<&'static str, Flash<Redirect>> {
    if name == "special_user" {
        Ok("Hello, special user!")
    } else {
        Err(Flash::error(Redirect::to("/"), "Invalid username."))
    }
}

#[get("/")]
fn index(flash: Option<FlashMessage>) -> String {
    flash.map(|msg| format!("{}: {}", msg.name(), msg.msg()))
         .unwrap_or_else(|| "Welcome!".to_string())
}

fn main() {
    rocket::ignite().mount("/", routes![login, index]).launch();
}

On the response side (in login), a Flash error message is set if some fictional authentication failed, and the user is redirected to "/". On the request side (in index), the handler emits the flash message if there is one and otherwise emits a standard welcome message. Note that if the user were to refresh the index page after viewing a flash message, the user would receive the standard welcome message.

Implementations

impl<'r, R: Responder<'r>> Flash<R>

pub fn new<N: AsRef<str>, M: AsRef<str>>(res: R, name: N, msg: M) -> Flash<R>

Constructs a new Flash message with the given name, msg, and underlying responder.

Examples

Construct a “suggestion” message with contents “Try this out!” that redirects to “/”.

use rocket::response::{Redirect, Flash};

let msg = Flash::new(Redirect::to("/"), "suggestion", "Try this out!");

pub fn success<S: AsRef<str>>(responder: R, msg: S) -> Flash<R>

Constructs a “success” Flash message with the given responder and msg.

Examples

Construct a “success” message with contents “It worked!” that redirects to “/”.

use rocket::response::{Redirect, Flash};

let msg = Flash::success(Redirect::to("/"), "It worked!");

pub fn warning<S: AsRef<str>>(responder: R, msg: S) -> Flash<R>

Constructs a “warning” Flash message with the given responder and msg.

Examples

Construct a “warning” message with contents “Watch out!” that redirects to “/”.

use rocket::response::{Redirect, Flash};

let msg = Flash::warning(Redirect::to("/"), "Watch out!");

pub fn error<S: AsRef<str>>(responder: R, msg: S) -> Flash<R>

Constructs an “error” Flash message with the given responder and msg.

Examples

Construct an “error” message with contents “Whoops!” that redirects to “/”.

use rocket::response::{Redirect, Flash};

let msg = Flash::error(Redirect::to("/"), "Whoops!");

impl<'a, 'r> Flash<&'a Request<'r>>

pub fn name(&self) -> &str

Returns the name of this message.

pub fn msg(&self) -> &str

Returns the msg contents of this message.

Trait Implementations

impl<R: Debug> Debug for Flash<R>

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

Formats the value using the given formatter.

impl<'a, 'r> FromRequest<'a, 'r> for Flash<&'a Request<'r>>

Retrieves a flash message from a flash cookie. If there is no flash cookie, or if the flash cookie is malformed, an empty Err is returned.

The suggested use is through an Option and the FlashMessage type alias in request: Option<FlashMessage>.

type Error = ()

The associated error to be returned if derivation fails.

fn from_request(req: &'a Request<'r>) -> Outcome<Self, Self::Error>

Derives an instance of Self from the incoming request metadata.

impl<'r, R: Responder<'r>> Responder<'r> for Flash<R>

Sets the message cookie and then uses the wrapped responder to complete the response. In other words, simply sets a cookie and delegates the rest of the response handling to the wrapped responder. As a result, the Outcome of the response is the Outcome of the wrapped Responder.

fn respond_to(self, req: &Request<'_>) -> Result<Response<'r>, Status>

Returns Ok if a Response could be generated successfully. Otherwise, returns an Err with a failing Status.