bpo-35347: Cleanup test_socket.NonBlockingTCPTests (GH-10818)

* Replace testInheritFlags() with two tests:
  testInheritFlagsBlocking() and testInheritFlagsTimeout()
  to test different default socket timeout. Moreover, the test now
  checks sock.gettimeout() rather than a functional test on recv().
* Replace time.time() with time.monotonic()
* Add socket_setdefaulttimeout() context manager to restore the
  default timeout when the test completes.
* Remove testConnect(): accept() wasn't blocking and testAccept()
  already tests non-blocking accept().
* Remove accept() functional test from testInitNonBlocking():
  already tested by testAccept()
* Rewrite testSetBlocking() with a new assert_sock_timeout() method
* Use addCleanup() and context manager to close sockets
* Replace assertTrue(x < y) with assertLess(x, y)

Lib/test/test_socket.py

@@ -34,7 +34,8 @@ except ImportError:
     fcntl = None
 
 HOST = support.HOST
-MSG = 'Michael Gilfix was here\u1234\r\n'.encode('utf-8') ## test unicode string and carriage return
+# test unicode string and carriage return
+MSG = 'Michael Gilfix was here\u1234\r\n'.encode('utf-8')
 MAIN_TIMEOUT = 60.0
 
 VSOCKPORT = 1234
@@ -111,9 +112,14 @@ def _have_socket_vsock():
     return ret
 
 
-def _is_fd_in_blocking_mode(sock):
-    return not bool(
-        fcntl.fcntl(sock, fcntl.F_GETFL, os.O_NONBLOCK) & os.O_NONBLOCK)
+@contextlib.contextmanager
+def socket_setdefaulttimeout(timeout):
+    old_timeout = socket.getdefaulttimeout()
+    try:
+        socket.setdefaulttimeout(timeout)
+        yield
+    finally:
+        socket.setdefaulttimeout(old_timeout)
 
 
 HAVE_SOCKET_CAN = _have_socket_can()
@@ -1069,18 +1075,16 @@ class GeneralModuleTests(unittest.TestCase):
         s.close()
 
         # Set the default timeout to 10, and see if it propagates
-        socket.setdefaulttimeout(10)
-        self.assertEqual(socket.getdefaulttimeout(), 10)
-        s = socket.socket()
-        self.assertEqual(s.gettimeout(), 10)
-        s.close()
+        with socket_setdefaulttimeout(10):
+            self.assertEqual(socket.getdefaulttimeout(), 10)
+            with socket.socket() as sock:
+                self.assertEqual(sock.gettimeout(), 10)
 
-        # Reset the default timeout to None, and see if it propagates
-        socket.setdefaulttimeout(None)
-        self.assertEqual(socket.getdefaulttimeout(), None)
-        s = socket.socket()
-        self.assertEqual(s.gettimeout(), None)
-        s.close()
+            # Reset the default timeout to None, and see if it propagates
+            socket.setdefaulttimeout(None)
+            self.assertEqual(socket.getdefaulttimeout(), None)
+            with socket.socket() as sock:
+                self.assertEqual(sock.gettimeout(), None)
 
         # Check that setting it to an invalid value raises ValueError
         self.assertRaises(ValueError, socket.setdefaulttimeout, -1)
@@ -4218,55 +4222,42 @@ class NonBlockingTCPTests(ThreadedTCPSocketTest):
         self.event = threading.Event()
         ThreadedTCPSocketTest.__init__(self, methodName=methodName)
 
+    def assert_sock_timeout(self, sock, timeout):
+        self.assertEqual(self.serv.gettimeout(), timeout)
+
+        blocking = (timeout != 0.0)
+        self.assertEqual(sock.getblocking(), blocking)
+
+        if fcntl is not None:
+            # When a Python socket has a non-zero timeout, it's switched
+            # internally to a non-blocking mode. Later, sock.sendall(),
+            # sock.recv(), and other socket operations use a select() call and
+            # handle EWOULDBLOCK/EGAIN on all socket operations. That's how
+            # timeouts are enforced.
+            fd_blocking = (timeout is None)
+
+            flag = fcntl.fcntl(sock, fcntl.F_GETFL, os.O_NONBLOCK)
+            self.assertEqual(not bool(flag & os.O_NONBLOCK), fd_blocking)
+
     def testSetBlocking(self):
-        # Testing whether set blocking works
+        # Test setblocking() and settimeout() methods
         self.serv.setblocking(True)
-        self.assertIsNone(self.serv.gettimeout())
-        self.assertTrue(self.serv.getblocking())
-        if fcntl:
-            self.assertTrue(_is_fd_in_blocking_mode(self.serv))
+        self.assert_sock_timeout(self.serv, None)
 
         self.serv.setblocking(False)
-        self.assertEqual(self.serv.gettimeout(), 0.0)
-        self.assertFalse(self.serv.getblocking())
-        if fcntl:
-            self.assertFalse(_is_fd_in_blocking_mode(self.serv))
+        self.assert_sock_timeout(self.serv, 0.0)
 
         self.serv.settimeout(None)
-        self.assertTrue(self.serv.getblocking())
-        if fcntl:
-            self.assertTrue(_is_fd_in_blocking_mode(self.serv))
+        self.assert_sock_timeout(self.serv, None)
 
         self.serv.settimeout(0)
-        self.assertFalse(self.serv.getblocking())
-        self.assertEqual(self.serv.gettimeout(), 0)
-        if fcntl:
-            self.assertFalse(_is_fd_in_blocking_mode(self.serv))
+        self.assert_sock_timeout(self.serv, 0)
 
         self.serv.settimeout(10)
-        self.assertTrue(self.serv.getblocking())
-        self.assertEqual(self.serv.gettimeout(), 10)
-        if fcntl:
-            # When a Python socket has a non-zero timeout, it's
-            # switched internally to a non-blocking mode.
-            # Later, sock.sendall(), sock.recv(), and other socket
-            # operations use a `select()` call and handle EWOULDBLOCK/EGAIN
-            # on all socket operations.  That's how timeouts are
-            # enforced.
-            self.assertFalse(_is_fd_in_blocking_mode(self.serv))
+        self.assert_sock_timeout(self.serv, 10)
 
         self.serv.settimeout(0)
-        self.assertFalse(self.serv.getblocking())
-        if fcntl:
-            self.assertFalse(_is_fd_in_blocking_mode(self.serv))
-
-        start = time.time()
-        try:
-            self.serv.accept()
-        except OSError:
-            pass
-        end = time.time()
-        self.assertTrue((end - start) < 1.0, "Error setting non-blocking mode.")
+        self.assert_sock_timeout(self.serv, 0)
 
     def _testSetBlocking(self):
         pass
@@ -4277,8 +4268,10 @@ class NonBlockingTCPTests(ThreadedTCPSocketTest):
         import _testcapi
         if _testcapi.UINT_MAX >= _testcapi.ULONG_MAX:
             self.skipTest('needs UINT_MAX < ULONG_MAX')
+
         self.serv.setblocking(False)
         self.assertEqual(self.serv.gettimeout(), 0.0)
+
         self.serv.setblocking(_testcapi.UINT_MAX + 1)
         self.assertIsNone(self.serv.gettimeout())
 
@@ -4288,50 +4281,51 @@ class NonBlockingTCPTests(ThreadedTCPSocketTest):
                          'test needs socket.SOCK_NONBLOCK')
     @support.requires_linux_version(2, 6, 28)
     def testInitNonBlocking(self):
-        # reinit server socket
+        # create a socket with SOCK_NONBLOCK
         self.serv.close()
-        self.serv = socket.socket(socket.AF_INET, socket.SOCK_STREAM |
-                                                  socket.SOCK_NONBLOCK)
-        self.assertFalse(self.serv.getblocking())
-        self.assertEqual(self.serv.gettimeout(), 0)
-        self.port = support.bind_port(self.serv)
-        self.serv.listen()
-        # actual testing
-        start = time.time()
-        try:
-            self.serv.accept()
-        except OSError:
-            pass
-        end = time.time()
-        self.assertTrue((end - start) < 1.0, "Error creating with non-blocking mode.")
+        self.serv = socket.socket(socket.AF_INET,
+                                  socket.SOCK_STREAM | socket.SOCK_NONBLOCK)
+        self.assert_sock_timeout(self.serv, 0)
 
     def _testInitNonBlocking(self):
         pass
 
-    def testInheritFlags(self):
-        # Issue #7995: when calling accept() on a listening socket with a
-        # timeout, the resulting socket should not be non-blocking.
-        self.serv.settimeout(10)
-        try:
+    def testInheritFlagsBlocking(self):
+        # bpo-7995: accept() on a listening socket with a timeout and the
+        # default timeout is None, the resulting socket must be blocking.
+        with socket_setdefaulttimeout(None):
+            self.serv.settimeout(10)
             conn, addr = self.serv.accept()
-            message = conn.recv(len(MSG))
-        finally:
-            conn.close()
-            self.serv.settimeout(None)
+            self.addCleanup(conn.close)
+            self.assertIsNone(conn.gettimeout())
 
-    def _testInheritFlags(self):
-        time.sleep(0.1)
+    def _testInheritFlagsBlocking(self):
+        self.cli.connect((HOST, self.port))
+
+    def testInheritFlagsTimeout(self):
+        # bpo-7995: accept() on a listening socket with a timeout and the
+        # default timeout is None, the resulting socket must inherit
+        # the default timeout.
+        default_timeout = 20.0
+        with socket_setdefaulttimeout(default_timeout):
+            self.serv.settimeout(10)
+            conn, addr = self.serv.accept()
+            self.addCleanup(conn.close)
+            self.assertEqual(conn.gettimeout(), default_timeout)
+
+    def _testInheritFlagsTimeout(self):
         self.cli.connect((HOST, self.port))
-        time.sleep(0.5)
-        self.cli.send(MSG)
 
     def testAccept(self):
         # Testing non-blocking accept
         self.serv.setblocking(0)
 
         # connect() didn't start: non-blocking accept() fails
+        start_time = time.monotonic()
         with self.assertRaises(BlockingIOError):
             conn, addr = self.serv.accept()
+        dt = time.monotonic() - start_time
+        self.assertLess(dt, 1.0)
 
         self.event.set()
 
@@ -4351,15 +4345,6 @@ class NonBlockingTCPTests(ThreadedTCPSocketTest):
 
         self.cli.connect((HOST, self.port))
 
-    def testConnect(self):
-        # Testing non-blocking connect
-        conn, addr = self.serv.accept()
-        conn.close()
-
-    def _testConnect(self):
-        self.cli.settimeout(10)
-        self.cli.connect((HOST, self.port))
-
     def testRecv(self):
         # Testing non-blocking recv
         conn, addr = self.serv.accept()