plane 0.5.5

Session backend orchestrator for ambitious browser-based apps.
Documentation 
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use lru::LruCache;
use plane_common::{
    names::BackendName,
    protocol::{RouteInfo, RouteInfoRequest, RouteInfoResponse},
    types::BearerToken,
};
use std::{
    collections::HashMap,
    num::NonZeroUsize,
    sync::{Mutex, RwLock},
};
use tokio::sync::watch::Sender;
use valuable::Valuable;

const CACHE_SIZE: usize = 1_000;

type RequestSender = Box<dyn Fn(RouteInfoRequest) + Send + Sync + 'static>;

pub struct RouteMap {
    pub routes: Mutex<LruCache<BearerToken, Option<RouteInfo>>>,
    pub request_sender: RwLock<Option<RequestSender>>,
    pub listeners: Mutex<HashMap<BearerToken, Sender<()>>>,
}

impl Default for RouteMap {
    fn default() -> Self {
        Self::new()
    }
}

impl RouteMap {
    pub fn new() -> Self {
        Self {
            routes: Mutex::new(LruCache::new(
                NonZeroUsize::new(CACHE_SIZE).expect("Always valid conversion from constant."),
            )),
            request_sender: RwLock::new(None),
            listeners: Mutex::default(),
        }
    }

    pub fn set_sender<F>(&self, sender: F)
    where
        F: Fn(RouteInfoRequest) + Send + Sync + 'static,
    {
        *self
            .request_sender
            .write()
            .expect("Request sender was poisoned.") = Some(Box::new(sender));
    }

    pub async fn lookup(&self, token: &BearerToken) -> Option<RouteInfo> {
        {
            let mut lock = self.routes.lock().expect("Routes lock was poisoned.");
            if let Some(route_info) = lock.get(token) {
                return route_info.clone();
            }
        }

        let mut receiver = {
            let mut listener_lock = self.listeners.lock().expect("Listeners lock was poisoned.");
            let sender = listener_lock.entry(token.clone()).or_insert_with(|| {
                let (sender, _) = tokio::sync::watch::channel(());
                sender
            });
            sender.subscribe()
        };

        let message = RouteInfoRequest {
            token: token.clone(),
        };

        {
            let maybe_request_sender = self
                .request_sender
                .read()
                .expect("Request sender was poisoned.");

            let request_sender = match maybe_request_sender.as_ref() {
                Some(request_sender) => request_sender,
                None => return None,
            };

            (request_sender)(message);
        }

        receiver
            .changed()
            .await
            .expect("Sender was dropped unexpectedly.");
        self.routes
            .lock()
            .expect("Routes lock was poisoned.")
            .get(token)
            .and_then(|x| x.clone())
    }

    fn insert(&self, token: BearerToken, route_info: Option<RouteInfo>) {
        tracing::info!(
            token = token.as_value(),
            ?route_info,
            "Inserting route info"
        );
        self.routes
            .lock()
            .expect("Routes lock was poisoned.")
            .push(token.clone(), route_info);
        let mut listener_lock = self.listeners.lock().expect("Listeners lock was poisoned.");
        if let Some(channel) = listener_lock.get(&token) {
            // We are just using the watch channel as a signal; this will ensure that anyone listening on `.changed()` resolves.
            channel.send_modify(|()| ());
            listener_lock.remove(&token);
        };
    }

    pub fn receive(&self, response: RouteInfoResponse) {
        self.insert(response.token, response.route_info);
    }

    pub fn remove_backend(&self, backend: &BackendName) {
        // When a backend is terminated, we invalidate all routes that point to it.
        // We do this by looping over the connection tokens, but this is relatively inexpensive
        // because we have a maximum of <CACHE_SIZE> connection tokens in the LRU cache.
        let mut count = 0;
        let mut lock = self.routes.lock().expect("Routes lock was poisoned.");
        for (_, maybe_route_info) in lock.iter_mut() {
            if let Some(route_info) = maybe_route_info.as_mut() {
                if route_info.backend_id == *backend {
                    *maybe_route_info = None;
                    count += 1;
                }
            }
        }
        if count > 0 {
            tracing::info!(
                count,
                backend = backend.as_value(),
                "Removed routes for terminated backend."
            );
        }
    }
}