Chunk terminal output below MTU

src/pty.rs

@@ -7,6 +7,12 @@ use std::sync::{Arc, Mutex};
 use std::thread;
 use tokio::sync::mpsc;
 
+// Keep live terminal output comfortably below common path MTUs after Dosh's
+// protocol header, AEAD tag, UDP/IP headers, and bincode framing. Full-screen
+// TUIs often write several KiB on the first draw; sending that as one UDP
+// datagram can fragment and vanish, leaving only a blank alternate screen.
+const PTY_OUTPUT_CHUNK_BYTES: usize = 1024;
+
 /// Backing for a PTY master held by the server.
 ///
 /// `Owned` means this process spawned the shell as a child and is responsible
@@ -264,11 +270,13 @@ fn spawn_reader_thread(
                         break;
                     }
                     Ok(n) => {
-                        let _ = tx.send(PtyOutput {
-                            session: reader_session.clone(),
-                            bytes: buf[..n].to_vec(),
-                            exited: false,
-                        });
+                        for chunk in buf[..n].chunks(PTY_OUTPUT_CHUNK_BYTES) {
+                            let _ = tx.send(PtyOutput {
+                                session: reader_session.clone(),
+                                bytes: chunk.to_vec(),
+                                exited: false,
+                            });
+                        }
                     }
                     Err(_) => {
                         let _ = tx.send(PtyOutput {
@@ -297,4 +305,9 @@ mod tests {
         assert!(!terminfo_available("definitely-not-a-real-terminal-xyz"));
         assert!(!terminfo_available(""));
     }
+
+    #[test]
+    fn pty_output_chunk_size_stays_mtu_safe() {
+        assert!(PTY_OUTPUT_CHUNK_BYTES <= 1200);
+    }
 }