1 files changed, 89 insertions, 0 deletions
diff --git a/src/server/headless/tests/surface_scroll.rs b/src/server/headless/tests/surface_scroll.rs
new file mode 100644
index 00000000..8975650b
--- /dev/null
+++ b/src/server/headless/tests/surface_scroll.rs
@@ -0,0 +1,89 @@
+use super::*;
+
+fn scrolling_lines(range: std::ops::Range<usize>) -> Vec<u8> {
+    range
+        .map(|n| {
+            format!(
+                "build step {n:>3}: compiled module_{n} in {}ms\r\n",
+                n * 7 % 97
+            )
+        })
+        .collect::<String>()
+        .into_bytes()
+}
+
+fn apply_rows(frame: &mut FrameData, rows: &[crate::protocol::PaneSurfacePatchRow]) {
+    for row in rows {
+        let start = usize::from(row.y) * usize::from(frame.width) + usize::from(row.x);
+        frame.cells[start..start + row.cells.len()].clone_from_slice(&row.cells);
+    }
+}
+
+#[tokio::test]
+async fn surface_scroll_sends_scrolling_output_as_a_shift_and_new_rows() {
+    let (mut server, _control_rx, render_rx, pane_id) =
+        retained_test_server_with_control(&scrolling_lines(0..40));
+    server
+        .clients
+        .get_mut(&1)
+        .expect("scroll client")
+        .render_state
+        .enable_surface_scroll(true);
+    server.render_and_stream();
+    let mut decoder = protocol::surface_reuse::Decoder::new(false, true);
+    let ServerMessage::PaneSurface(mut shell) = decoder
+        .decode(read_server_message(
+            render_rx.recv_timeout(Duration::from_secs(1)).unwrap(),
+        ))
+        .expect("initial surface")
+    else {
+        panic!("expected the initial pane surface");
+    };
+
+    write_shared_test_pane(&mut server, pane_id, &scrolling_lines(40..42));
+    assert!(server.render_retained_pane_surface_and_stream(&HashSet::from([pane_id])));
+    let bytes = render_rx.recv_timeout(Duration::from_secs(1)).unwrap();
+    let message = read_server_message(bytes.clone());
+    assert!(matches!(
+        &message,
+        ServerMessage::EndpointControl { kind, .. } if kind == protocol::surface_scroll::MESSAGE_KIND
+    ));
+
+    // The decoder hands the client shell an ordinary patch that reaches the
+    // server's committed surface exactly.
+    let ServerMessage::PaneSurfacePatch(patch) = decoder.decode(message).expect("scroll decode")
+    else {
+        panic!("expected an expanded pane patch");
+    };
+    apply_rows(&mut shell.frame, &patch.rows);
+    let committed = server.clients[&1]
+        .render_state
+        .last_pane_surface()
+        .expect("committed surface");
+    assert_eq!(shell.frame.cells, committed.frame.cells);
+    assert!(frame_text(&shell.frame).contains("module_41"));
+
+    let expanded = HeadlessServer::frame_server_message(&ServerMessage::PaneSurfacePatch(patch))
+        .expect("expanded frame");
+    assert!(
+        bytes.len() * 4 < expanded.len(),
+        "scroll frame {} should be far smaller than the rows it replaces {}",
+        bytes.len(),
+        expanded.len()
+    );
+    shutdown_test_runtimes(&mut server);
+}
+
+#[tokio::test]
+async fn surface_scroll_is_not_sent_to_a_peer_that_did_not_negotiate_it() {
+    let (mut server, _control_rx, render_rx, pane_id) =
+        retained_test_server_with_control(&scrolling_lines(0..40));
+    server.render_and_stream();
+    let _ = render_rx.recv_timeout(Duration::from_secs(1)).unwrap();
+
+    write_shared_test_pane(&mut server, pane_id, &scrolling_lines(40..42));
+    assert!(server.render_retained_pane_surface_and_stream(&HashSet::from([pane_id])));
+    let message = read_server_message(render_rx.recv_timeout(Duration::from_secs(1)).unwrap());
+    assert!(matches!(message, ServerMessage::PaneSurfacePatch(_)));
+    shutdown_test_runtimes(&mut server);
+}