websocket-api: use IdPool to manage connection ids

src/api/websocket_v1.rs

@@ -1,4 +1,7 @@
-use std::net::SocketAddr;
+use std::{
+    net::SocketAddr,
+    sync::{Arc, Mutex},
+};
 
 use anyhow::Context;
 use futures::{stream::FuturesUnordered, StreamExt};
@@ -18,29 +21,45 @@ use mpvipc_async::{
     Switch,
 };
 use serde_json::{json, Value};
-use tokio::select;
+use tokio::{select, sync::watch};
 
-pub fn websocket_api(mpv: Mpv) -> Router {
+use crate::util::IdPool;
+
+#[derive(Debug, Clone)]
+struct WebsocketState {
+    mpv: Mpv,
+    id_pool: Arc<Mutex<IdPool>>,
+}
+
+pub fn websocket_api(mpv: Mpv, id_pool: Arc<Mutex<IdPool>>) -> Router {
+    let state = WebsocketState { mpv, id_pool };
     Router::new()
         .route("/", any(websocket_handler))
-        .with_state(mpv)
+        .with_state(state)
 }
 
 async fn websocket_handler(
     ws: WebSocketUpgrade,
     ConnectInfo(addr): ConnectInfo<SocketAddr>,
-    State(mpv): State<Mpv>,
+    State(WebsocketState { mpv, id_pool }): State<WebsocketState>,
 ) -> impl IntoResponse {
     let mpv = mpv.clone();
+    let id = match id_pool.lock().unwrap().request_id() {
+        Ok(id) => id,
+        Err(e) => {
+            log::error!("Failed to get id from id pool: {:?}", e);
+            return axum::http::StatusCode::INTERNAL_SERVER_ERROR.into_response();
+        }
+    };
 
-    // TODO: get an id provisioned by the id pool
-    ws.on_upgrade(move |socket| handle_connection(socket, addr, mpv, 1))
+    ws.on_upgrade(move |socket| handle_connection(socket, addr, mpv, id, id_pool))
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct InitialState {
     pub cached_timestamp: Option<f64>,
     pub chapters: Vec<Value>,
+    pub connections: u64,
     pub current_percent_pos: Option<f64>,
     pub current_track: String,
     pub duration: f64,
@@ -53,7 +72,7 @@ pub struct InitialState {
     pub volume: f64,
 }
 
-async fn get_initial_state(mpv: &Mpv) -> InitialState {
+async fn get_initial_state(mpv: &Mpv, id_pool: Arc<Mutex<IdPool>>) -> InitialState {
     let cached_timestamp = mpv
         .get_property_value("demuxer-cache-state")
         .await
@@ -69,6 +88,7 @@ async fn get_initial_state(mpv: &Mpv) -> InitialState {
         Ok(Some(Value::Array(chapters))) => chapters,
         _ => vec![],
     };
+    let connections = id_pool.lock().unwrap().id_count();
     let current_percent_pos = mpv.get_property("percent-pos").await.unwrap_or(None);
     let current_track = mpv.get_file_path().await.unwrap_or("".to_string());
     let duration = mpv.get_duration().await.unwrap_or(0.0);
@@ -104,6 +124,7 @@ async fn get_initial_state(mpv: &Mpv) -> InitialState {
     InitialState {
         cached_timestamp,
         chapters,
+        connections,
         current_percent_pos,
         current_track,
         duration,
@@ -147,12 +168,18 @@ async fn setup_default_subscribes(mpv: &Mpv) -> anyhow::Result<()> {
     Ok(())
 }
 
-async fn handle_connection(mut socket: WebSocket, addr: SocketAddr, mpv: Mpv, channel_id: u64) {
+async fn handle_connection(
+    mut socket: WebSocket,
+    addr: SocketAddr,
+    mpv: Mpv,
+    channel_id: u64,
+    id_pool: Arc<Mutex<IdPool>>,
+) {
     // TODO: There is an asynchronous gap between gathering the initial state and subscribing to the properties
     //       This could lead to missing events if they happen in that gap. Send initial state, but also ensure
     //       that there is an additional "initial state" sent upon subscription to all properties to ensure that
     //       the state is correct.
-    let initial_state = get_initial_state(&mpv).await;
+    let initial_state = get_initial_state(&mpv, id_pool.clone()).await;
 
     let message = Message::Text(
         json!({
@@ -166,11 +193,73 @@ async fn handle_connection(mut socket: WebSocket, addr: SocketAddr, mpv: Mpv, ch
 
     setup_default_subscribes(&mpv).await.unwrap();
 
-    let connection_loop_mpv = mpv.clone();
-    let connection_loop = tokio::spawn(async move {
-        let mut event_stream = connection_loop_mpv.get_event_stream().await;
+    let id_count_watch_receiver = id_pool.lock().unwrap().get_id_count_watch_receiver();
+
+    let connection_loop_result = tokio::spawn(connection_loop(
+        socket,
+        addr,
+        mpv.clone(),
+        channel_id,
+        id_count_watch_receiver,
+    ));
+
+    match connection_loop_result.await {
+        Ok(Ok(())) => {
+            log::trace!("Connection loop ended for {:?}", addr);
+        }
+        Ok(Err(e)) => {
+            log::error!("Error in connection loop for {:?}: {:?}", addr, e);
+        }
+        Err(e) => {
+            log::error!("Error in connection loop for {:?}: {:?}", addr, e);
+        }
+    }
+
+    match mpv.unobserve_property(channel_id).await {
+        Ok(()) => {
+            log::trace!("Unsubscribed from properties for {:?}", addr);
+        }
+        Err(e) => {
+            log::error!(
+                "Error unsubscribing from properties for {:?}: {:?}",
+                addr,
+                e
+            );
+        }
+    }
+
+    match id_pool.lock().unwrap().release_id(channel_id) {
+        Ok(()) => {
+            log::trace!("Released id {} for {:?}", channel_id, addr);
+        }
+        Err(e) => {
+            log::error!("Error releasing id {} for {:?}: {:?}", channel_id, addr, e);
+        }
+    }
+}
+
+async fn connection_loop(
+    mut socket: WebSocket,
+    addr: SocketAddr,
+    mpv: Mpv,
+    channel_id: u64,
+    mut id_count_watch_receiver: watch::Receiver<u64>,
+) -> Result<(), anyhow::Error> {
+    let mut event_stream = mpv.get_event_stream().await;
     loop {
         select! {
+          id_count = id_count_watch_receiver.changed() => {
+            if let Err(e) = id_count {
+              anyhow::bail!("Error reading id count watch receiver for {:?}: {:?}", addr, e);
+            }
+
+            let message = Message::Text(json!({
+              "type": "connection_count",
+              "value": id_count_watch_receiver.borrow().clone(),
+            }).to_string());
+
+            socket.send(message).await?;
+          }
           message = socket.recv() => {
               log::trace!("Received command from {:?}: {:?}", addr, message);
 
@@ -207,7 +296,7 @@ async fn handle_connection(mut socket: WebSocket, addr: SocketAddr, mpv: Mpv, ch
               log::trace!("Handling command from {:?}: {:?}", addr, message_json);
 
               // TODO: handle errors
-                  match handle_message(message_json, connection_loop_mpv.clone(), channel_id).await {
+              match handle_message(message_json, mpv.clone(), channel_id).await {
                 Ok(Some(response)) => {
                   log::trace!("Handled command from {:?} successfully, sending response", addr);
                   let message = Message::Text(json!({
@@ -246,32 +335,6 @@ async fn handle_connection(mut socket: WebSocket, addr: SocketAddr, mpv: Mpv, ch
           }
         }
     }
-    });
-
-    match connection_loop.await {
-        Ok(Ok(())) => {
-            log::trace!("Connection loop ended for {:?}", addr);
-        }
-        Ok(Err(e)) => {
-            log::error!("Error in connection loop for {:?}: {:?}", addr, e);
-        }
-        Err(e) => {
-            log::error!("Error in connection loop for {:?}: {:?}", addr, e);
-        }
-    }
-
-    match mpv.unobserve_property(channel_id).await {
-        Ok(()) => {
-            log::trace!("Unsubscribed from properties for {:?}", addr);
-        }
-        Err(e) => {
-            log::error!(
-                "Error unsubscribing from properties for {:?}: {:?}",
-                addr,
-                e
-            );
-        }
-    }
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -279,7 +342,6 @@ async fn handle_connection(mut socket: WebSocket, addr: SocketAddr, mpv: Mpv, ch
 pub enum WSCommand {
     // Subscribe { property: String },
     // UnsubscribeAll,
-
     Load { urls: Vec<String> },
     TogglePlayback,
     Volume { volume: f64 },

src/main.rs

@@ -5,13 +5,18 @@ use clap_verbosity_flag::Verbosity;
 use futures::StreamExt;
 use mpv_setup::{connect_to_mpv, create_mpv_config_file, show_grzegorz_image};
 use mpvipc_async::{Event, Mpv, MpvDataType, MpvExt};
-use std::net::{IpAddr, SocketAddr};
+use std::{
+    net::{IpAddr, SocketAddr},
+    sync::{Arc, Mutex},
+};
 use systemd_journal_logger::JournalLog;
 use tempfile::NamedTempFile;
 use tokio::task::JoinHandle;
+use util::IdPool;
 
 mod api;
 mod mpv_setup;
+mod util;
 
 #[derive(Parser)]
 struct Args {
@@ -119,8 +124,7 @@ async fn setup_systemd_notifier(mpv: Mpv) -> anyhow::Result<JoinHandle<()>> {
         systemd_update_play_status(playing, &current_song);
 
         loop {
-            match event_stream.next().await {
-                Some(Ok(Event::PropertyChange { name, data, .. })) => {
+            if let Some(Ok(Event::PropertyChange { name, data, .. })) = event_stream.next().await {
                 match (name.as_str(), data) {
                     ("media-title", Some(MpvDataType::String(s))) => {
                         current_song = Some(s);
@@ -141,8 +145,6 @@ async fn setup_systemd_notifier(mpv: Mpv) -> anyhow::Result<JoinHandle<()>> {
 
                 systemd_update_play_status(playing, &current_song)
             }
-                _ => {}
-            }
         }
     });
 
@@ -226,9 +228,11 @@ async fn main() -> anyhow::Result<()> {
     let socket_addr = SocketAddr::new(addr, args.port);
     log::info!("Starting API on {}", socket_addr);
 
+    let id_pool = Arc::new(Mutex::new(IdPool::new_with_max_limit(1024)));
+
     let app = Router::new()
         .nest("/api", api::rest_api_routes(mpv.clone()))
-        .nest("/ws", api::websocket_api(mpv.clone()))
+        .nest("/ws", api::websocket_api(mpv.clone(), id_pool.clone()))
         .merge(api::rest_api_docs(mpv.clone()))
         .into_make_service_with_connect_info::<SocketAddr>();
 

src/util.rs

@@ -0,0 +1,3 @@
+mod id_pool;
+
+pub use id_pool::IdPool;

src/util/id_pool.rs

@@ -0,0 +1,145 @@
+use std::{collections::BTreeSet, fmt::Debug};
+
+use tokio::sync::watch;
+
+/// A relatively naive ID pool implementation.
+pub struct IdPool {
+    max_id: u64,
+    free_ids: BTreeSet<u64>,
+    id_count: u64,
+    id_count_watch_sender: watch::Sender<u64>,
+    id_count_watch_receiver: watch::Receiver<u64>,
+}
+
+impl Debug for IdPool {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("IdPool")
+            .field("max_id", &self.max_id)
+            .field("free_ids", &self.free_ids)
+            .field("id_count", &self.id_count)
+            .finish()
+    }
+}
+
+impl Default for IdPool {
+    fn default() -> Self {
+        let (id_count_watch_sender, id_count_watch_receiver) = watch::channel(0);
+        Self {
+            max_id: u64::MAX,
+            free_ids: BTreeSet::new(),
+            id_count: 0,
+            id_count_watch_sender,
+            id_count_watch_receiver,
+        }
+    }
+}
+
+//TODO: thiserror
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum IdPoolError {
+    NoFreeIds,
+    IdNotInUse(u64),
+    IdOutOfBound(u64),
+}
+
+impl IdPool {
+    pub fn new_with_max_limit(max_id: u64) -> Self {
+        let (id_count_watch_sender, id_count_watch_receiver) = watch::channel(0);
+        Self {
+            max_id,
+            free_ids: BTreeSet::new(),
+            id_count: 0,
+            id_count_watch_sender,
+            id_count_watch_receiver,
+        }
+    }
+
+    pub fn id_count(&self) -> u64 {
+        self.id_count - self.free_ids.len() as u64
+    }
+
+    pub fn id_is_used(&self, id: u64) -> Result<bool, IdPoolError> {
+        if id > self.max_id {
+            Err(IdPoolError::IdOutOfBound(id))
+        } else if self.free_ids.contains(&id) {
+            return Ok(false);
+        } else {
+            return Ok(id <= self.id_count);
+        }
+    }
+
+    pub fn request_id(&mut self) -> Result<u64, IdPoolError> {
+        if !self.free_ids.is_empty() {
+            let id = self.free_ids.pop_first().unwrap();
+            self.update_watch();
+            Ok(id)
+        } else if self.id_count < self.max_id {
+            self.id_count += 1;
+            self.update_watch();
+            Ok(self.id_count)
+        } else {
+            Err(IdPoolError::NoFreeIds)
+        }
+    }
+
+    pub fn release_id(&mut self, id: u64) -> Result<(), IdPoolError> {
+        if !self.id_is_used(id)? {
+            Err(IdPoolError::IdNotInUse(id))
+        } else {
+            self.free_ids.insert(id);
+            self.update_watch();
+            Ok(())
+        }
+    }
+
+    fn update_watch(&self) {
+        self.id_count_watch_sender.send(self.id_count()).unwrap();
+    }
+
+    pub fn get_id_count_watch_receiver(&self) -> watch::Receiver<u64> {
+        self.id_count_watch_receiver.clone()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_id_pool() {
+        let mut pool = IdPool::new_with_max_limit(10);
+        assert_eq!(pool.request_id(), Ok(1));
+        assert_eq!(pool.request_id(), Ok(2));
+        assert_eq!(pool.request_id(), Ok(3));
+        assert_eq!(pool.request_id(), Ok(4));
+        assert_eq!(pool.id_count(), 4);
+        assert_eq!(pool.request_id(), Ok(5));
+        assert_eq!(pool.request_id(), Ok(6));
+        assert_eq!(pool.request_id(), Ok(7));
+        assert_eq!(pool.request_id(), Ok(8));
+        assert_eq!(pool.request_id(), Ok(9));
+        assert_eq!(pool.request_id(), Ok(10));
+        assert_eq!(pool.id_count(), 10);
+        assert_eq!(pool.request_id(), Err(IdPoolError::NoFreeIds));
+        assert_eq!(pool.release_id(5), Ok(()));
+        assert_eq!(pool.release_id(5), Err(IdPoolError::IdNotInUse(5)));
+        assert_eq!(pool.id_count(), 9);
+        assert_eq!(pool.request_id(), Ok(5));
+        assert_eq!(pool.release_id(11), Err(IdPoolError::IdOutOfBound(11)));
+    }
+
+    #[test]
+    fn test_id_pool_watch() {
+        let mut pool = IdPool::new_with_max_limit(10);
+        let receiver = pool.get_id_count_watch_receiver();
+
+        assert_eq!(receiver.borrow().clone(), 0);
+        pool.request_id().unwrap();
+        assert_eq!(receiver.borrow().clone(), 1);
+        pool.request_id().unwrap();
+        assert_eq!(receiver.borrow().clone(), 2);
+        pool.release_id(1).unwrap();
+        assert_eq!(receiver.borrow().clone(), 1);
+    }
+}