Preserve alternate screen snapshots and speed builds

src/bin/dosh-server.rs

@@ -277,7 +277,7 @@ async fn handle_bootstrap_attach(
             session.parser.set_size(req.rows, req.cols);
         }
         let client_id = crypto::random_16();
-        let snapshot = session.parser.screen().state_formatted();
+        let snapshot = screen_snapshot(session.parser.screen());
         let screen = session.parser.screen().clone();
         let output_seq = session.output_seq;
         session.clients.insert(
@@ -385,7 +385,7 @@ async fn handle_ticket_attach(
             session.parser.set_size(req.rows, req.cols);
         }
         let client_id = crypto::random_16();
-        let snapshot = session.parser.screen().state_formatted();
+        let snapshot = screen_snapshot(session.parser.screen());
         let screen = session.parser.screen().clone();
         let output_seq = session.output_seq;
         session.clients.insert(
@@ -491,7 +491,7 @@ async fn handle_resume(
             session.pty.resize(req.cols, req.rows)?;
             session.parser.set_size(req.rows, req.cols);
         }
-        let snapshot = session.parser.screen().state_formatted();
+        let snapshot = screen_snapshot(session.parser.screen());
         client.last_screen = Some(session.parser.screen().clone());
         (client.send_seq, session.output_seq, snapshot)
     };
@@ -675,7 +675,7 @@ async fn broadcast_output(
             let current_screen = session.parser.screen().clone();
             let (bytes, snapshot) = if client.pending.len() >= retransmit_window {
                 client.pending.clear();
-                (current_screen.state_formatted(), true)
+                (screen_snapshot(&current_screen), true)
             } else {
                 (output.bytes.clone(), false)
             };
@@ -758,6 +758,17 @@ async fn broadcast_session_exit(
     Ok(())
 }
 
+fn screen_snapshot(screen: &vt100::Screen) -> Vec<u8> {
+    let mut bytes = Vec::new();
+    if screen.alternate_screen() {
+        bytes.extend_from_slice(b"\x1b[?1049h");
+    } else {
+        bytes.extend_from_slice(b"\x1b[?1049l");
+    }
+    bytes.extend(screen.state_formatted());
+    bytes
+}
+
 async fn retransmit_pending(
     state: &Arc<Mutex<ServerState>>,
     socket: &Arc<UdpSocket>,