feat(zero-rust): wait JS's 5 minutes before a hidden client disconnects

.changeset/zero-rust-hidden-delay.md

@@ -0,0 +1,5 @@
+---
+'zero-rust': minor
+---
+
+`ZeroOptions::hidden_disconnect_delay_ms` now defaults to 5 minutes, as JS's `hiddenTabDisconnectDelay` does, instead of 0: after `Zero::set_visible(false)`, the client stays connected for 5 minutes before it disconnects. An app that wants the old behavior, such as a mobile app the system suspends in the background, sets `hidden_disconnect_delay_ms: 0.0`.

rust/PARITY.md

@@ -78,12 +78,14 @@ factory.
 | `slowMaterializeThreshold`                                                         | `slow_materialize_threshold_ms` (5,000, as in JS)                     |
 | `maxRecentQueries` (deprecated)                                                    | not ported: JS keeps no recent queries by default either              |
 
-Two defaults differ from JS. `storage` is `ZeroStorage::Memory`, since
-SQLite is an opt-in feature, where JS keeps its data in IndexedDB.
-`hidden_disconnect_delay_ms` is 0 where JS waits 5 minutes, as in Swift:
-a native app is suspended soon after it goes to the background, so the
-client disconnects as soon as the app says it is hidden. A desktop app
-whose window can stay hidden for long can set JS's 300,000.
+One default differs from JS, on purpose: `storage` is
+`ZeroStorage::Memory`, where JS keeps its data in IndexedDB. SQLite
+storage is the opt-in `sqlite` feature, so the default build has no
+third-party dependencies, and an app chooses where its replica lives
+(`ZeroStorage::Sqlite { directory }`); an app that wants its data across
+restarts sets it. `hidden_disconnect_delay_ms` is JS's 5 minutes; a mobile
+app, which the system suspends soon after it goes to the background, can
+set 0 to disconnect as soon as it says it is hidden, as Swift does.
 
 ### The client
 

rust/zero-client/src/client/engine.rs

@@ -207,7 +207,10 @@ pub struct ZeroOptions {
     /// Where messages are logged. Defaults to [`StderrLogSink`].
     pub log_sink: Option<Rc<dyn LogSink>>,
     /// How long the app is hidden before the client disconnects
-    /// (`hiddenTabDisconnectDelay`); see [`Zero::set_visible`].
+    /// (`hiddenTabDisconnectDelay`); see [`Zero::set_visible`]. 5 minutes
+    /// by default, as in JS. A mobile app, which the system suspends soon
+    /// after it goes to the background, can set 0 to disconnect as soon as
+    /// it is hidden.
     ///
     /// [`Zero::set_visible`]: crate::client::Zero::set_visible
     pub hidden_disconnect_delay_ms: f64,
@@ -249,7 +252,7 @@ impl Default for ZeroOptions {
             on_storage_failure: None,
             log_level: LogLevel::Warn,
             log_sink: None,
-            hidden_disconnect_delay_ms: 0.0,
+            hidden_disconnect_delay_ms: 300_000.0,
             get_traceparent: None,
             batch_view_updates: None,
             slow_materialize_threshold_ms: 5_000.0,

rust/zero-client/tests/visibility.rs

@@ -0,0 +1,71 @@
+//! `ZeroOptions::default()` waits JS's 5 minutes (`hiddenTabDisconnectDelay`)
+//! after `set_visible(false)` before it disconnects. The conformance vectors
+//! set the delay themselves, so they don't check the default.
+
+use std::rc::Rc;
+use std::sync::Arc;
+use zero_client::client::{ConnectionState, Zero, ZeroOptions};
+use zero_client::json;
+use zero_client::schema::Schema;
+use zero_client::testing::{ManualScheduler, MockSocketFactory, RecordingLogSink};
+
+#[test]
+fn a_hidden_client_disconnects_after_five_minutes_by_default() {
+    let schema = Schema::from_json(
+        &json::parse(
+            r#"{"tables": {"issue": {"name": "issue", "primaryKey": ["id"],
+                "columns": {"id": {"type": "string"}}}}}"#,
+        )
+        .unwrap(),
+    )
+    .unwrap();
+    let scheduler = ManualScheduler::new(1_700_000_000_000.0);
+    let factory = MockSocketFactory::new();
+    let options = ZeroOptions {
+        cache_url: Some("http://zero.test".into()),
+        user_id: Some("u1".into()),
+        log_sink: Some(Rc::new(RecordingLogSink::default())),
+        ..ZeroOptions::default()
+    };
+    let zero: Zero = Zero::new(
+        Arc::new(schema),
+        (),
+        vec![],
+        options,
+        scheduler.clone(),
+        Some(factory.clone()),
+    )
+    .unwrap();
+    let settle = || {
+        zero.dispatch(|| {});
+        scheduler.run_due_timers();
+    };
+    settle();
+    let socket = factory.sockets().last().cloned().expect("a socket");
+    socket.receive_text(r#"["connected",{"wsid":"w1"}]"#);
+    settle();
+    assert_eq!(zero.connection().state(), ConnectionState::Connected);
+
+    zero.set_visible(false);
+    settle();
+    // Answer pings, so the connection stays up while the app is hidden.
+    let mut waited = 0.0;
+    while waited < 299_000.0 {
+        scheduler.advance(1_000.0);
+        waited += 1_000.0;
+        socket.receive_text(r#"["pong",{}]"#);
+        settle();
+    }
+    assert_eq!(zero.connection().state(), ConnectionState::Connected);
+
+    scheduler.advance(1_000.0);
+    settle();
+    assert!(
+        matches!(
+            zero.connection().state(),
+            ConnectionState::Disconnected { .. }
+        ),
+        "{:?}",
+        zero.connection().state()
+    );
+}