pub struct State<T>(_);
Expand description

A handler for sharing state across an application.

State is a handler that puts a clone of any Clone + Send + Sync + 'static type into every conn’s state map.

use std::sync::{atomic::{AtomicBool, Ordering}, Arc};
use trillium::{Conn, State};
use trillium_testing::prelude::*;

#[derive(Clone, Default)] // Clone is mandatory
struct MyFeatureFlag(Arc<AtomicBool>);

impl MyFeatureFlag {
    pub fn is_enabled(&self) -> bool {

    pub fn toggle(&self) {
       self.0.fetch_xor(true, Ordering::Relaxed);

let feature_flag = MyFeatureFlag::default();

let handler = (
    |conn: Conn| async move {
      if conn.state::<MyFeatureFlag>().unwrap().is_enabled() {
          conn.ok("feature enabled")
      } else {
          conn.ok("not enabled")

assert_ok!(get("/").on(&handler), "not enabled");
assert_ok!(get("/").on(&handler), "not enabled");
assert_ok!(get("/").on(&handler), "feature enabled");
assert_ok!(get("/").on(&handler), "feature enabled");

Please note that as with the above contrived example, if your state needs to be mutable, you need to choose your own interior mutability with whatever cross thread synchronization mechanisms are appropriate for your application. There will be one clones of the contained T type in memory for each http connection, and any locks should be held as briefly as possible so as to minimize impact on other conns.

Stability note: This is a common enough pattern that it currently exists in the public api, but may be removed at some point for simplicity.


Constructs a new State handler from any Clone + Send + Sync + 'static

Trait Implementations

Formats the value using the given formatter. Read more
Returns the “default value” for a type. Read more
Executes this handler, performing any modifications to the Conn that are desired. Read more
Performs one-time async set up on a mutable borrow of the Handler before the server starts accepting requests. This allows a Handler to be defined in synchronous code but perform async setup such as establishing a database connection or fetching some state from an external source. This is optional, and chances are high that you do not need this. Read more
Performs any final modifications to this conn after all handlers have been run. Although this is a slight deviation from the simple conn->conn->conn chain represented by most Handlers, it provides an easy way for libraries to effectively inject a second handler into a response chain. This is useful for loggers that need to record information both before and after other handlers have run, as well as database transaction handlers and similar library code. Read more
predicate function answering the question of whether this Handler would like to take ownership of the negotiated Upgrade. If this returns true, you must implement Handler::upgrade. The first handler that responds true to this will receive ownership of the trillium::Upgrade in a subsequent call to Handler::upgrade Read more
This will only be called if the handler reponds true to Handler::has_upgrade and will only be called once for this upgrade. There is no return value, and this function takes exclusive ownership of the underlying transport once this is called. You can downcast the transport to whatever the source transport type is and perform any non-http protocol communication that has been negotiated. You probably don’t want this unless you’re implementing something like websockets. Please note that for many transports such as TcpStreams, dropping the transport (and therefore the Upgrade) will hang up / disconnect. Read more
Customize the name of your handler. This is used in Debug implementations. The default is the type name of this handler. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.