axum-server 0.8.0

High level server designed to be used with axum framework.
Documentation 
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use crate::{notify_once::NotifyOnce, server::Address};
use std::{
    sync::{
        atomic::{AtomicUsize, Ordering},
        Arc, Mutex,
    },
    time::Duration,
};
use tokio::{sync::Notify, time::sleep};

/// A handle for [`Server`](crate::server::Server).
#[derive(Clone, Debug)]
pub struct Handle<A: Address> {
    inner: Arc<HandleInner<A>>,
}

impl<A: Address> Default for Handle<A> {
    fn default() -> Self {
        Self {
            inner: Default::default(),
        }
    }
}

#[derive(Debug)]
struct HandleInner<A: Address> {
    addr: Mutex<Option<A>>,
    addr_notify: Notify,
    conn_count: AtomicUsize,
    shutdown: NotifyOnce,
    graceful: NotifyOnce,
    graceful_dur: Mutex<Option<Duration>>,
    conn_end: NotifyOnce,
}

// Manually implemented as the derive macro will want A to be Default.
impl<A: Address> Default for HandleInner<A> {
    fn default() -> Self {
        Self {
            addr: Default::default(),
            addr_notify: Default::default(),
            conn_count: Default::default(),
            shutdown: Default::default(),
            graceful: Default::default(),
            graceful_dur: Default::default(),
            conn_end: Default::default(),
        }
    }
}

impl<A: Address> Handle<A> {
    /// Create a new handle.
    pub fn new() -> Self {
        Self::default()
    }

    /// Get the number of connections.
    pub fn connection_count(&self) -> usize {
        self.inner.conn_count.load(Ordering::SeqCst)
    }

    /// Shutdown the server.
    pub fn shutdown(&self) {
        self.inner.shutdown.notify_waiters();
    }

    /// Gracefully shutdown the server.
    ///
    /// `None` means indefinite grace period.
    pub fn graceful_shutdown(&self, duration: Option<Duration>) {
        *self.inner.graceful_dur.lock().unwrap() = duration;

        self.inner.graceful.notify_waiters();
    }

    /// Returns local address and port when server starts listening.
    ///
    /// Returns `None` if server fails to bind.
    pub async fn listening(&self) -> Option<A> {
        let notified = self.inner.addr_notify.notified();

        if let Some(addr) = self.inner.addr.lock().unwrap().clone() {
            return Some(addr);
        }

        notified.await;

        self.inner.addr.lock().unwrap().clone()
    }

    pub(crate) fn notify_listening(&self, addr: Option<A>) {
        *self.inner.addr.lock().unwrap() = addr;

        self.inner.addr_notify.notify_waiters();
    }

    pub(crate) fn watcher(&self) -> Watcher<A> {
        Watcher::new(self.clone())
    }

    pub(crate) async fn wait_shutdown(&self) {
        self.inner.shutdown.notified().await;
    }

    pub(crate) async fn wait_graceful_shutdown(&self) {
        self.inner.graceful.notified().await;
    }

    pub(crate) async fn wait_connections_end(&self) {
        if self.inner.conn_count.load(Ordering::SeqCst) == 0 {
            return;
        }

        let deadline = *self.inner.graceful_dur.lock().unwrap();

        match deadline {
            Some(duration) => tokio::select! {
                biased;
                _ = sleep(duration) => self.shutdown(),
                _ = self.inner.conn_end.notified() => (),
            },
            None => self.inner.conn_end.notified().await,
        }
    }
}

pub(crate) struct Watcher<A: Address> {
    handle: Handle<A>,
}

impl<A: Address> Watcher<A> {
    fn new(handle: Handle<A>) -> Self {
        handle.inner.conn_count.fetch_add(1, Ordering::SeqCst);

        Self { handle }
    }

    pub(crate) async fn wait_graceful_shutdown(&self) {
        self.handle.wait_graceful_shutdown().await
    }

    pub(crate) async fn wait_shutdown(&self) {
        self.handle.wait_shutdown().await
    }
}

impl<A: Address> Drop for Watcher<A> {
    fn drop(&mut self) {
        let count = self.handle.inner.conn_count.fetch_sub(1, Ordering::SeqCst) - 1;

        if count == 0 && self.handle.inner.graceful.is_notified() {
            self.handle.inner.conn_end.notify_waiters();
        }
    }
}