Fix race condition in InThreadIMDServer by auto-binding to free port (#94)

* fix #81
* Implement fix for race condition in InThreadIMDServer


---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ljwoods2 <145226270+ljwoods2@users.noreply.github.com>

Author: Copilot

imdclient/tests/server.py

@@ -29,14 +29,25 @@ def __init__(self, traj):
         self.listen_socket = None
         self.conn = None
         self.accept_thread = None
+        self._bound_port = None
 
     def set_imdsessioninfo(self, imdsinfo):
         self.imdsinfo = imdsinfo
 
-    def handshake_sequence(self, host, port, first_frame=True):
+    @property
+    def port(self):
+        """Get the port the server is bound to.
+        
+        Returns:
+            int: The port number, or None if not bound yet.
+        """
+        return self._bound_port
+
+    def handshake_sequence(self, host, first_frame=True):
         s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-        s.bind((host, port))
-        logger.debug(f"InThreadIMDServer: Listening on {host}:{port}")
+        s.bind((host, 0))  # Bind to port 0 to get a free port
+        self._bound_port = s.getsockname()[1]  # Store the actual bound port
+        logger.debug(f"InThreadIMDServer: Listening on {host}:{self._bound_port}")
         s.listen(60)
         self.listen_socket = s
 

imdclient/tests/test_imdclient.py

@@ -15,7 +15,6 @@
 from imdclient.IMDClient import imdframe_memsize, IMDClient
 from imdclient.IMDProtocol import IMDHeaderType
 from .utils import (
-    get_free_port,
     create_default_imdsinfo_v3,
 )
 from .server import InThreadIMDServer
@@ -46,10 +45,6 @@
 
 class TestIMDClientV3:
 
-    @pytest.fixture
-    def port(self):
-        return get_free_port()
-
     @pytest.fixture
     def universe(self):
         return mda.Universe(COORDINATES_TOPOLOGY, COORDINATES_H5MD)
@@ -59,13 +54,13 @@ def imdsinfo(self):
         return create_default_imdsinfo_v3()
 
     @pytest.fixture
-    def server_client_two_frame_buf(self, universe, imdsinfo, port):
+    def server_client_two_frame_buf(self, universe, imdsinfo):
         server = InThreadIMDServer(universe.trajectory)
         server.set_imdsessioninfo(imdsinfo)
-        server.handshake_sequence("localhost", port, first_frame=False)
+        server.handshake_sequence("localhost", first_frame=False)
         client = IMDClient(
             f"localhost",
-            port,
+            server.port,
             universe.trajectory.n_atoms,
             buffer_size=imdframe_memsize(universe.trajectory.n_atoms, imdsinfo)
             * 2,
@@ -76,14 +71,14 @@ def server_client_two_frame_buf(self, universe, imdsinfo, port):
         server.cleanup()
 
     @pytest.fixture(params=[">", "<"])
-    def server_client(self, universe, imdsinfo, port, request):
+    def server_client(self, universe, imdsinfo, request):
         server = InThreadIMDServer(universe.trajectory)
         imdsinfo.endianness = request.param
         server.set_imdsessioninfo(imdsinfo)
-        server.handshake_sequence("localhost", port, first_frame=False)
+        server.handshake_sequence("localhost", first_frame=False)
         client = IMDClient(
             f"localhost",
-            port,
+            server.port,
             universe.trajectory.n_atoms,
         )
         server.join_accept_thread()
@@ -153,13 +148,13 @@ def test_pause_resume_no_disconnect(self, server_client_two_frame_buf):
         server.expect_packet(IMDHeaderType.IMD_DISCONNECT)
 
     @pytest.mark.parametrize("cont", [True, False])
-    def test_continue_after_disconnect(self, universe, imdsinfo, port, cont):
+    def test_continue_after_disconnect(self, universe, imdsinfo, cont):
         server = InThreadIMDServer(universe.trajectory)
         server.set_imdsessioninfo(imdsinfo)
-        server.handshake_sequence("localhost", port, first_frame=False)
+        server.handshake_sequence("localhost", first_frame=False)
         client = IMDClient(
             f"localhost",
-            port,
+            server.port,
             universe.trajectory.n_atoms,
             continue_after_disconnect=cont,
         )
@@ -170,10 +165,6 @@ def test_continue_after_disconnect(self, universe, imdsinfo, port, cont):
 
 
 class TestIMDClientV3ContextManager:
-    @pytest.fixture
-    def port(self):
-        return get_free_port()
-
     @pytest.fixture
     def universe(self):
         return mda.Universe(COORDINATES_TOPOLOGY, COORDINATES_H5MD)
@@ -183,19 +174,19 @@ def imdsinfo(self):
         return create_default_imdsinfo_v3()
 
     @pytest.fixture
-    def server(self, universe, imdsinfo, port):
+    def server(self, universe, imdsinfo):
         server = InThreadIMDServer(universe.trajectory)
         server.set_imdsessioninfo(imdsinfo)
         yield server
         server.cleanup()
 
-    def test_context_manager_traj_unchanged(self, server, port, universe):
-        server.handshake_sequence("localhost", port, first_frame=False)
+    def test_context_manager_traj_unchanged(self, server, universe):
+        server.handshake_sequence("localhost", first_frame=False)
 
         i = 0
         with IMDClient(
             "localhost",
-            port,
+            server.port,
             universe.trajectory.n_atoms,
         ) as client:
             server.send_frames(0, 5)