Add API for propagating cursor locations (#61)

backend/sync_server/src/app_state/websocket/broadcasts.rs

@@ -0,0 +1,63 @@
+use std::{collections::HashMap, sync::Arc};
+
+use anyhow::Context;
+use tokio::sync::{Mutex, broadcast};
+
+use super::models::WebSocketServerMessageWithOrigin;
+use crate::{
+    app_state::database::models::VaultId, config::server_config::ServerConfig, errors::server_error,
+};
+
+#[derive(Debug, Clone)]
+pub struct Broadcasts {
+    max_clients_per_vault: usize,
+    tx: Arc<Mutex<HashMap<VaultId, broadcast::Sender<WebSocketServerMessageWithOrigin>>>>,
+}
+
+impl Broadcasts {
+    pub fn new(server_config: &ServerConfig) -> Self {
+        Self {
+            max_clients_per_vault: server_config.max_clients_per_vault,
+            tx: Arc::new(Mutex::new(HashMap::new())),
+        }
+    }
+
+    pub async fn get_receiver(
+        &self,
+        vault: VaultId,
+    ) -> broadcast::Receiver<WebSocketServerMessageWithOrigin> {
+        let tx = self.get_or_create(vault).await;
+
+        tx.subscribe()
+    }
+
+    /// Notify all clients (who are subscribed to the vault) about an update.
+    /// We only log failures.
+    pub async fn send_document_update(
+        &self,
+        vault: VaultId,
+        document: WebSocketServerMessageWithOrigin,
+    ) {
+        let tx = self.get_or_create(vault).await;
+
+        let result = tx
+            .send(document)
+            .context("Cannot broadcast server message to websocket listeners")
+            .map_err(server_error);
+
+        if result.is_err() {
+            log::debug!("Failed to send message: {result:?}");
+        }
+    }
+
+    async fn get_or_create(
+        &self,
+        vault: VaultId,
+    ) -> broadcast::Sender<WebSocketServerMessageWithOrigin> {
+        let mut tx = self.tx.lock().await;
+
+        tx.entry(vault)
+            .or_insert_with(|| broadcast::channel(self.max_clients_per_vault).0.clone())
+            .clone()
+    }
+}