Module flash 

modo::flash

Cookie-based flash messages for one-time cross-request notifications.

This module is always available; no feature flag is required.

Provides:

• FlashLayer — Tower Layer that enables flash cookie support on a router.
• FlashMiddleware — Tower Service produced by FlashLayer.
• Flash — axum extractor for writing and reading flash messages in handlers.
• FlashEntry — a single message carrying a severity level and message text.

Flash messages are stored in a signed cookie and cleared after being read. They survive exactly one redirect: the current request writes a message and the next request reads it. Once read, the cookie is removed from the response.

Requires FlashLayer to be applied to the router before using the Flash extractor.

When the templates feature is enabled, TemplateContextLayer automatically injects a flash_messages() callable into every MiniJinja template context. Calling it from a template is equivalent to calling Flash::messages from a handler — it marks the messages as consumed and clears the cookie on the response.

Quick start

use modo::cookie::{CookieConfig, key_from_config};
use modo::flash::FlashLayer;
use modo::Flash;
use axum::{Router, routing::{get, post}, response::Redirect};

// Build the layer from your cookie config
let config: CookieConfig = app_config.cookie.clone();
let key = key_from_config(&config).unwrap();

let app = Router::new()
    .route("/form", post(submit_handler))
    .route("/result", get(result_handler))
    .layer(FlashLayer::new(&config, &key));

// Write a flash message and redirect
async fn submit_handler(flash: Flash) -> Redirect {
    flash.success("Record saved.");
    Redirect::to("/result")
}

// Read flash messages on the next request
async fn result_handler(flash: Flash) -> String {
    let msgs = flash.messages();
    msgs.iter()
        .map(|m| format!("[{}] {}", m.level, m.message))
        .collect::<Vec<_>>()
        .join("\n")
}

Structs

Flash

Axum extractor for reading and writing flash messages within a request.

FlashEntry

A single flash message carrying a severity level and a text body.

FlashLayer

Tower Layer that enables cookie-based flash messages for a router.

FlashMiddleware

Tower Service produced by FlashLayer.