From 1c22c68e4b4469370ff78166f2f005545cdfdc50 Mon Sep 17 00:00:00 2001
From: Andrew Bulat <andrii.bulat@gmail.com>
Date: Thu, 9 Jan 2025 14:22:57 +0000
Subject: [PATCH] Fix race condition error in `http.get_rest_hosts` when
 `fallback_realtime_host` is set

---
 ably/http/http.py      |  3 ++-
 test/unit/http_test.py | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 test/unit/http_test.py

diff --git a/ably/http/http.py b/ably/http/http.py
index e47ffb8f..6a5a4f71 100644
--- a/ably/http/http.py
+++ b/ably/http/http.py
@@ -146,7 +146,8 @@ def get_rest_hosts(self):
         if host is None:
             return hosts
 
-        if time.time() > self.__host_expires:
+        # unstore saved fallback host after fallbackRetryTimeout (RSC15f)
+        if self.__host_expires is not None and time.time() > self.__host_expires:
             self.__host = None
             self.__host_expires = None
             return hosts
diff --git a/test/unit/http_test.py b/test/unit/http_test.py
new file mode 100644
index 00000000..45f362ed
--- /dev/null
+++ b/test/unit/http_test.py
@@ -0,0 +1,19 @@
+from ably import AblyRest
+
+
+def test_http_get_rest_hosts_works_when_fallback_realtime_host_is_set():
+    ably = AblyRest(token="foo")
+    ably.options.fallback_realtime_host = ably.options.get_rest_hosts()[0]
+    # Should not raise TypeError
+    hosts = ably.http.get_rest_hosts()
+    assert isinstance(hosts, list)
+    assert all(isinstance(host, str) for host in hosts)
+
+
+def test_http_get_rest_hosts_works_when_fallback_realtime_host_is_not_set():
+    ably = AblyRest(token="foo")
+    ably.options.fallback_realtime_host = None
+    # Should not raise TypeError
+    hosts = ably.http.get_rest_hosts()
+    assert isinstance(hosts, list)
+    assert all(isinstance(host, str) for host in hosts)