From 896c459d444f78a167acdf565b56271eb5e5d240 Mon Sep 17 00:00:00 2001
From: Peter Corke <peter.i.corke@gmail.com>
Date: Fri, 21 Aug 2026 15:48:19 +1000
Subject: [PATCH] fix: run() lets a disconnect-during-step() crash out as a raw
 traceback

A disconnect noticed *during* step() (SwiftRoute.py's expect_message()/
producer racing wait_closed(), jhavl/swift#130) raises TimeoutError
directly out of step() -- run()'s own loop only ever expected a
disconnect to surface via _check_disconnected()'s poll *between*
steps, so this propagated straight out of run() as an uncaught
exception instead of the same graceful "Swift browser tab closed."
message/return every other disconnect path already gets.

Not a hypothetical: closing the browser tab mid-session (e.g. an
interactive robot.teach(backend="swift") built on run()) reliably hits
this, every time, now that #130 made disconnect detection fast enough
to land mid-step almost always rather than rarely.
---
 src/swift/Swift.py     | 14 +++++++++++++-
 tests/test_protocol.py | 23 +++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/swift/Swift.py b/src/swift/Swift.py
index d259425..ff23a94 100644
--- a/src/swift/Swift.py
+++ b/src/swift/Swift.py
@@ -1108,7 +1108,19 @@ def run(self, duration: float | None = None, dt: float = 0.05, timeout: float |
 
         try:
             while duration is None or (self.sim_time - start_time) < duration:
-                self.step(dt)
+                try:
+                    self.step(dt)
+                except TimeoutError:
+                    # A disconnect noticed *during* step() (SwiftRoute.py's
+                    # expect_message()/producer racing wait_closed()) raises
+                    # here directly, rather than only ever surfacing via
+                    # the _check_disconnected() poll below -- without this,
+                    # it would propagate straight out of run() as a raw
+                    # traceback instead of the same graceful message/return
+                    # every other disconnect path already gets.
+                    print("\nSwift browser tab closed.")
+                    self.close()
+                    return
                 time.sleep(dt)
                 disconnected_since, expired = self._check_disconnected(disconnected_since, timeout)
                 if expired:
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
index 629ca06..1d5480d 100644
--- a/tests/test_protocol.py
+++ b/tests/test_protocol.py
@@ -725,6 +725,29 @@ def sleep_raises(s):
     assert closed == [True]
 
 
+def test_run_exits_quietly_on_disconnect_during_step(capsys):
+    # A disconnect noticed *during* step() (SwiftRoute.py's
+    # expect_message()/producer racing wait_closed()) raises TimeoutError
+    # directly out of step(), rather than only ever surfacing via
+    # _check_disconnected()'s poll between steps -- run() must catch this
+    # the same way it already handles that poll-detected case (print,
+    # close(), return), not let it propagate as a raw traceback.
+    env = make_env()
+    env.headless = True
+
+    def step_raises(dt=0.05, render=True):
+        raise TimeoutError("Swift browser tab stopped responding")
+
+    env.step = step_raises
+    closed = []
+    env.close = lambda *a, **kw: closed.append(True)
+
+    env.run()  # must return normally, not raise
+
+    assert closed == [True]
+    assert "Swift browser tab closed." in capsys.readouterr().out
+
+
 def test_hold_exits_quietly_on_keyboard_interrupt(monkeypatch):
     env = make_env()
     env.headless = True