Implement incremental subscriptions on the client

crates/cli/src/subcommands/generate/rust.rs

@@ -1426,6 +1426,7 @@ impl __sdk::EventContext for EventContext {{
 
 /// A handle on a subscribed query.
 // TODO: Document this better after implementing the new subscription API.
+#[derive(Clone)]
 pub struct SubscriptionHandle {{
     imp: __sdk::SubscriptionHandleImpl<RemoteModule>,
 }}
@@ -1438,6 +1439,27 @@ impl __sdk::SubscriptionHandle for SubscriptionHandle {{
     fn new(imp: __sdk::SubscriptionHandleImpl<RemoteModule>) -> Self {{
         Self {{ imp }}
     }}
+
+    /// Returns true if this subscription has been terminated due to an unsubscribe call or an error.
+    fn is_ended(&self) -> bool {{
+        self.imp.is_ended()
+    }}
+
+    /// Returns true if this subscription has been applied and has not yet been unsubscribed.
+    fn is_active(&self) -> bool {{
+        self.imp.is_active()
+    }}
+
+    /// Unsubscribe from the query controlled by this `SubscriptionHandle`,
+    /// then run `on_end` when its rows are removed from the client cache.
+    fn unsubscribe_then(self, on_end: __sdk::OnEndedCallback<RemoteModule>) -> __anyhow::Result<()> {{
+        self.imp.unsubscribe_then(Some(on_end))
+    }}
+
+    fn unsubscribe(self) -> __anyhow::Result<()> {{
+        self.imp.unsubscribe_then(None)
+    }}
+
 }}
 
 /// Alias trait for a [`__sdk::DbContext`] connected to this module,

crates/cli/tests/snapshots/codegen__codegen_rust.snap

@@ -1544,6 +1544,7 @@ impl __sdk::EventContext for EventContext {
 
 /// A handle on a subscribed query.
 // TODO: Document this better after implementing the new subscription API.
+#[derive(Clone)]
 pub struct SubscriptionHandle {
     imp: __sdk::SubscriptionHandleImpl<RemoteModule>,
 }
@@ -1556,6 +1557,27 @@ impl __sdk::SubscriptionHandle for SubscriptionHandle {
     fn new(imp: __sdk::SubscriptionHandleImpl<RemoteModule>) -> Self {
         Self { imp }
     }
+
+    /// Returns true if this subscription has been terminated due to an unsubscribe call or an error.
+    fn is_ended(&self) -> bool {
+        self.imp.is_ended()
+    }
+
+    /// Returns true if this subscription has been applied and has not yet been unsubscribed.
+    fn is_active(&self) -> bool {
+        self.imp.is_active()
+    }
+
+    /// Unsubscribe from the query controlled by this `SubscriptionHandle`,
+    /// then run `on_end` when its rows are removed from the client cache.
+    fn unsubscribe_then(self, on_end: __sdk::OnEndedCallback<RemoteModule>) -> __anyhow::Result<()> {
+        self.imp.unsubscribe_then(Some(on_end))
+    }
+
+    fn unsubscribe(self) -> __anyhow::Result<()> {
+        self.imp.unsubscribe_then(None)
+    }
+
 }
 
 /// Alias trait for a [`__sdk::DbContext`] connected to this module,

crates/sdk/examples/quickstart-chat/main.rs

@@ -1,5 +1,7 @@
 #![allow(clippy::disallowed_macros)]
 mod module_bindings;
+use std::sync::{atomic::AtomicU8, Arc};
+
 use module_bindings::*;
 
 use spacetimedb_client_api_messages::websocket::Compression;
@@ -116,7 +118,6 @@ fn on_sub_applied(ctx: &EventContext) {
         print_message(ctx, &message);
     }
 }
-
 // ## Warn if set_name failed
 
 /// Our `on_set_name` callback: print a warning if the reducer failed.
@@ -178,12 +179,26 @@ fn connect_to_db() -> DbConnection {
 }
 
 // # Subscribe to queries
+fn subscribe_to_queries(ctx: &DbConnection, queries: &[&str], callback: fn(&EventContext)) {
+    if queries.is_empty() {
+        panic!("No queries to subscribe to.");
+    }
+    let remaining_queries = Arc::new(AtomicU8::new(queries.len() as u8));
+    for query in queries {
+        let remaining_queries = remaining_queries.clone();
+        ctx.subscription_builder()
+            .on_applied(move |ctx| {
+                if remaining_queries.fetch_sub(1, std::sync::atomic::Ordering::Relaxed) == 1 {
+                    callback(ctx);
+                }
+            })
+            .subscribe(query);
+    }
+}
 
 /// Register subscriptions for all rows of both tables.
 fn subscribe_to_tables(ctx: &DbConnection) {
-    ctx.subscription_builder()
-        .on_applied(on_sub_applied)
-        .subscribe(["SELECT * FROM user;", "SELECT * FROM message;"]);
+    subscribe_to_queries(ctx, &["SELECT * FROM user", "SELECT * FROM message"], on_sub_applied);
 }
 
 // # Handle user input