check port with bind over connect_ex

reflex/utils/processes.py

@@ -53,7 +53,7 @@ def get_num_workers() -> int:
     return (os.cpu_count() or 1) * 2 + 1
 
 
-def _is_address_responsive(
+def _can_bind_at_port(
     address_family: socket.AddressFamily | int, address: str, port: int
 ) -> bool:
     """Check if a given address and port are responsive.
@@ -68,9 +68,14 @@ def _is_address_responsive(
     """
     try:
         with closing(socket.socket(address_family, socket.SOCK_STREAM)) as sock:
-            return sock.connect_ex((address, port)) == 0
+            sock.bind((address, port))
+    except OverflowError:
+        return False
+    except PermissionError:
+        return False
     except OSError:
         return False
+    return True
 
 
 def is_process_on_port(port: int) -> bool:
@@ -82,9 +87,9 @@ def is_process_on_port(port: int) -> bool:
     Returns:
         Whether a process is running on the given port.
     """
-    return _is_address_responsive(  # Test IPv4 localhost (127.0.0.1)
+    return not _can_bind_at_port(  # Test IPv4 localhost (127.0.0.1)
         socket.AF_INET, "127.0.0.1", port
-    ) or _is_address_responsive(
+    ) or not _can_bind_at_port(
         socket.AF_INET6, "::1", port
     )  # Test IPv6 localhost (::1)
 
@@ -99,8 +104,15 @@ def change_port(port: int, _type: str) -> int:
     Returns:
         The new port.
 
+    Raises:
+        Exit: If the port is invalid or if the new port is occupied.
     """
     new_port = port + 1
+    if new_port < 0 or new_port > 65535:
+        console.error(
+            f"The {_type} port: {port} is invalid. It must be between 0 and 65535."
+        )
+        raise click.exceptions.Exit(1)
     if is_process_on_port(new_port):
         return change_port(new_port, _type)
     console.info(

tests/units/utils/test_processes.py

@@ -0,0 +1,161 @@
+"""Test process utilities."""
+
+import socket
+import threading
+import time
+from contextlib import closing
+from unittest import mock
+
+import pytest
+
+from reflex.utils.processes import is_process_on_port
+
+
+def test_is_process_on_port_free_port():
+    """Test is_process_on_port returns False when port is free."""
+    # Find a free port
+    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as sock:
+        sock.bind(("127.0.0.1", 0))
+        free_port = sock.getsockname()[1]
+
+    # Port should be free after socket is closed
+    assert not is_process_on_port(free_port)
+
+
+def test_is_process_on_port_occupied_port():
+    """Test is_process_on_port returns True when port is occupied."""
+    # Create a server socket to occupy a port
+    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    server_socket.bind(("127.0.0.1", 0))
+    server_socket.listen(1)
+
+    occupied_port = server_socket.getsockname()[1]
+
+    try:
+        # Port should be occupied
+        assert is_process_on_port(occupied_port)
+    finally:
+        server_socket.close()
+
+
+def test_is_process_on_port_ipv6():
+    """Test is_process_on_port works with IPv6."""
+    # Test with IPv6 socket
+    try:
+        server_socket = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
+        server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        server_socket.bind(("::1", 0))
+        server_socket.listen(1)
+
+        occupied_port = server_socket.getsockname()[1]
+
+        try:
+            # Port should be occupied on IPv6
+            assert is_process_on_port(occupied_port)
+        finally:
+            server_socket.close()
+    except OSError:
+        # IPv6 might not be available on some systems
+        pytest.skip("IPv6 not available on this system")
+
+
+def test_is_process_on_port_both_protocols():
+    """Test is_process_on_port detects occupation on either IPv4 or IPv6."""
+    # Create IPv4 server
+    ipv4_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    ipv4_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    ipv4_socket.bind(("127.0.0.1", 0))
+    ipv4_socket.listen(1)
+
+    port = ipv4_socket.getsockname()[1]
+
+    try:
+        # Should detect IPv4 occupation
+        assert is_process_on_port(port)
+    finally:
+        ipv4_socket.close()
+
+
+@pytest.mark.parametrize("port", [0, 1, 80, 443, 8000, 3000, 65535])
+def test_is_process_on_port_various_ports(port):
+    """Test is_process_on_port with various port numbers.
+
+    Args:
+        port: The port number to test.
+    """
+    # This test just ensures the function doesn't crash with different port numbers
+    # The actual result depends on what's running on the system
+    result = is_process_on_port(port)
+    assert isinstance(result, bool)
+
+
+def test_is_process_on_port_mock_socket_error():
+    """Test is_process_on_port handles socket errors gracefully."""
+    with mock.patch("socket.socket") as mock_socket:
+        mock_socket_instance = mock.MagicMock()
+        mock_socket.return_value = mock_socket_instance
+        mock_socket_instance.__enter__.return_value = mock_socket_instance
+        mock_socket_instance.bind.side_effect = OSError("Mock socket error")
+
+        # Should return True when socket operations fail
+        result = is_process_on_port(8080)
+        assert result is True
+
+
+def test_is_process_on_port_permission_error():
+    """Test is_process_on_port handles permission errors."""
+    with mock.patch("socket.socket") as mock_socket:
+        mock_socket_instance = mock.MagicMock()
+        mock_socket.return_value = mock_socket_instance
+        mock_socket_instance.__enter__.return_value = mock_socket_instance
+        mock_socket_instance.bind.side_effect = PermissionError("Permission denied")
+
+        # Should return True when permission is denied (can't bind = port is "occupied")
+        result = is_process_on_port(80)
+        assert result is True
+
+
+@pytest.mark.parametrize("should_listen", [True, False])
+def test_is_process_on_port_concurrent_access(should_listen):
+    """Test is_process_on_port works correctly with concurrent access.
+
+    Args:
+        should_listen: Whether the server socket should call listen() or just bind().
+    """
+
+    def create_server_and_test(port_holder, listen):
+        server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        server.bind(("127.0.0.1", 0))
+
+        if listen:
+            server.listen(1)
+
+        port = server.getsockname()[1]
+        port_holder[0] = port
+
+        # Small delay to ensure the test runs while server is active
+        time.sleep(0.1)
+        server.close()
+
+    port_holder = [None]
+    thread = threading.Thread(
+        target=create_server_and_test, args=(port_holder, should_listen)
+    )
+    thread.start()
+
+    # Wait a bit for the server to start
+    time.sleep(0.05)
+
+    if port_holder[0] is not None:
+        # Port should be occupied while server is running (both bound-only and listening)
+        assert is_process_on_port(port_holder[0])
+
+    thread.join()
+
+    # After thread ends and server closes, port should be free
+    if port_holder[0] is not None:
+        # Give it a moment for the socket to be fully released
+        time.sleep(0.1)
+        assert not is_process_on_port(port_holder[0])