bpo-40275: Avoid importing socket in test.support (GH-19603)

* Move socket related functions from test.support to socket_helper.
* Import socket, nntplib and urllib.error lazily in transient_internet().
* Remove importing multiprocess.

Author: serhiy-storchaka

Doc/library/test.rst

@@ -348,11 +348,6 @@ The :mod:`test.support` module defines the following constants:
    :data:`SHORT_TIMEOUT`.
 
 
-.. data:: IPV6_ENABLED
-
-    Set to ``True`` if IPV6 is enabled on this host, ``False`` otherwise.
-
-
 .. data:: SAVEDCWD
 
    Set to :func:`os.getcwd`.
@@ -901,12 +896,6 @@ The :mod:`test.support` module defines the following functions:
    A decorator for running tests that require support for xattr.
 
 
-.. decorator:: skip_unless_bind_unix_socket
-
-   A decorator for running tests that require a functional bind() for Unix
-   sockets.
-
-
 .. decorator:: anticipate_failure(condition)
 
    A decorator to conditionally mark tests with
@@ -1157,31 +1146,6 @@ The :mod:`test.support` module defines the following functions:
    is raised.
 
 
-.. function:: bind_port(sock, host=HOST)
-
-   Bind the socket to a free port and return the port number.  Relies on
-   ephemeral ports in order to ensure we are using an unbound port.  This is
-   important as many tests may be running simultaneously, especially in a
-   buildbot environment.  This method raises an exception if the
-   ``sock.family`` is :const:`~socket.AF_INET` and ``sock.type`` is
-   :const:`~socket.SOCK_STREAM`, and the socket has
-   :const:`~socket.SO_REUSEADDR` or :const:`~socket.SO_REUSEPORT` set on it.
-   Tests should never set these socket options for TCP/IP sockets.
-   The only case for setting these options is testing multicasting via
-   multiple UDP sockets.
-
-   Additionally, if the :const:`~socket.SO_EXCLUSIVEADDRUSE` socket option is
-   available (i.e. on Windows), it will be set on the socket.  This will
-   prevent anyone else from binding to our host/port for the duration of the
-   test.
-
-
-.. function:: bind_unix_socket(sock, addr)
-
-   Bind a unix socket, raising :exc:`unittest.SkipTest` if
-   :exc:`PermissionError` is raised.
-
-
 .. function:: catch_threading_exception()
 
    Context manager catching :class:`threading.Thread` exception using
@@ -1243,29 +1207,6 @@ The :mod:`test.support` module defines the following functions:
    .. versionadded:: 3.8
 
 
-.. function:: find_unused_port(family=socket.AF_INET, socktype=socket.SOCK_STREAM)
-
-   Returns an unused port that should be suitable for binding.  This is
-   achieved by creating a temporary socket with the same family and type as
-   the ``sock`` parameter (default is :const:`~socket.AF_INET`,
-   :const:`~socket.SOCK_STREAM`),
-   and binding it to the specified host address (defaults to ``0.0.0.0``)
-   with the port set to 0, eliciting an unused ephemeral port from the OS.
-   The temporary socket is then closed and deleted, and the ephemeral port is
-   returned.
-
-   Either this method or :func:`bind_port` should be used for any tests
-   where a server socket needs to be bound to a particular port for the
-   duration of the test.
-   Which one to use depends on whether the calling code is creating a Python
-   socket, or if an unused port needs to be provided in a constructor
-   or passed to an external program (i.e. the ``-accept`` argument to
-   openssl's s_server mode).  Always prefer :func:`bind_port` over
-   :func:`find_unused_port` where possible.  Using a hard coded port is
-   discouraged since it can make multiple instances of the test impossible to
-   run simultaneously, which is a problem for buildbots.
-
-
 .. function:: load_package_tests(pkg_dir, loader, standard_tests, pattern)
 
    Generic implementation of the :mod:`unittest` ``load_tests`` protocol for
@@ -1481,6 +1422,77 @@ The :mod:`test.support` module defines the following classes:
    it will be raised in :meth:`!__fspath__`.
 
 
+:mod:`test.support.socket_helper` --- Utilities for socket tests
+================================================================
+
+.. module:: test.support.socket_helper
+   :synopsis: Support for socket tests.
+
+
+The :mod:`test.support.socket_helper` module provides support for socket tests.
+
+.. versionadded:: 3.9
+
+
+.. data:: IPV6_ENABLED
+
+    Set to ``True`` if IPv6 is enabled on this host, ``False`` otherwise.
+
+
+.. function:: find_unused_port(family=socket.AF_INET, socktype=socket.SOCK_STREAM)
+
+   Returns an unused port that should be suitable for binding.  This is
+   achieved by creating a temporary socket with the same family and type as
+   the ``sock`` parameter (default is :const:`~socket.AF_INET`,
+   :const:`~socket.SOCK_STREAM`),
+   and binding it to the specified host address (defaults to ``0.0.0.0``)
+   with the port set to 0, eliciting an unused ephemeral port from the OS.
+   The temporary socket is then closed and deleted, and the ephemeral port is
+   returned.
+
+   Either this method or :func:`bind_port` should be used for any tests
+   where a server socket needs to be bound to a particular port for the
+   duration of the test.
+   Which one to use depends on whether the calling code is creating a Python
+   socket, or if an unused port needs to be provided in a constructor
+   or passed to an external program (i.e. the ``-accept`` argument to
+   openssl's s_server mode).  Always prefer :func:`bind_port` over
+   :func:`find_unused_port` where possible.  Using a hard coded port is
+   discouraged since it can make multiple instances of the test impossible to
+   run simultaneously, which is a problem for buildbots.
+
+
+.. function:: bind_port(sock, host=HOST)
+
+   Bind the socket to a free port and return the port number.  Relies on
+   ephemeral ports in order to ensure we are using an unbound port.  This is
+   important as many tests may be running simultaneously, especially in a
+   buildbot environment.  This method raises an exception if the
+   ``sock.family`` is :const:`~socket.AF_INET` and ``sock.type`` is
+   :const:`~socket.SOCK_STREAM`, and the socket has
+   :const:`~socket.SO_REUSEADDR` or :const:`~socket.SO_REUSEPORT` set on it.
+   Tests should never set these socket options for TCP/IP sockets.
+   The only case for setting these options is testing multicasting via
+   multiple UDP sockets.
+
+   Additionally, if the :const:`~socket.SO_EXCLUSIVEADDRUSE` socket option is
+   available (i.e. on Windows), it will be set on the socket.  This will
+   prevent anyone else from binding to our host/port for the duration of the
+   test.
+
+
+.. function:: bind_unix_socket(sock, addr)
+
+   Bind a unix socket, raising :exc:`unittest.SkipTest` if
+   :exc:`PermissionError` is raised.
+
+
+.. decorator:: skip_unless_bind_unix_socket
+
+   A decorator for running tests that require a functional ``bind()`` for Unix
+   sockets.
+
+
 :mod:`test.support.script_helper` --- Utilities for the Python execution tests
 ==============================================================================
 

Lib/test/_test_multiprocessing.py

@@ -26,6 +26,7 @@
 import test.support
 import test.support.script_helper
 from test import support
+from test.support import socket_helper
 
 
 # Skip tests if _multiprocessing wasn't built.
@@ -2928,7 +2929,7 @@ def test_remote(self):
         authkey = os.urandom(32)
 
         manager = QueueManager(
-            address=(test.support.HOST, 0), authkey=authkey, serializer=SERIALIZER
+            address=(socket_helper.HOST, 0), authkey=authkey, serializer=SERIALIZER
             )
         manager.start()
         self.addCleanup(manager.shutdown)
@@ -2965,7 +2966,7 @@ def _putter(cls, address, authkey):
     def test_rapid_restart(self):
         authkey = os.urandom(32)
         manager = QueueManager(
-            address=(test.support.HOST, 0), authkey=authkey, serializer=SERIALIZER)
+            address=(socket_helper.HOST, 0), authkey=authkey, serializer=SERIALIZER)
         try:
             srvr = manager.get_server()
             addr = srvr.address
@@ -3455,7 +3456,7 @@ def _listener(cls, conn, families):
             new_conn.close()
             l.close()
 
-        l = socket.create_server((test.support.HOST, 0))
+        l = socket.create_server((socket_helper.HOST, 0))
         conn.send(l.getsockname())
         new_conn, addr = l.accept()
         conn.send(new_conn)
@@ -4593,7 +4594,7 @@ def _child_test_wait_socket(cls, address, slow):
 
     def test_wait_socket(self, slow=False):
         from multiprocessing.connection import wait
-        l = socket.create_server((test.support.HOST, 0))
+        l = socket.create_server((socket_helper.HOST, 0))
         addr = l.getsockname()
         readers = []
         procs = []

Lib/test/eintrdata/eintr_tester.py

@@ -22,6 +22,7 @@
 import unittest
 
 from test import support
+from test.support import socket_helper
 
 @contextlib.contextmanager
 def kill_on_error(proc):
@@ -283,14 +284,14 @@ def test_sendmsg(self):
         self._test_send(lambda sock, data: sock.sendmsg([data]))
 
     def test_accept(self):
-        sock = socket.create_server((support.HOST, 0))
+        sock = socket.create_server((socket_helper.HOST, 0))
         self.addCleanup(sock.close)
         port = sock.getsockname()[1]
 
         code = '\n'.join((
             'import socket, time',
             '',
-            'host = %r' % support.HOST,
+            'host = %r' % socket_helper.HOST,
             'port = %s' % port,
             'sleep_time = %r' % self.sleep_time,
             '',

Lib/test/ssl_servers.py

@@ -9,10 +9,11 @@
     SimpleHTTPRequestHandler, BaseHTTPRequestHandler)
 
 from test import support
+from test.support import socket_helper
 
 here = os.path.dirname(__file__)
 
-HOST = support.HOST
+HOST = socket_helper.HOST
 CERTFILE = os.path.join(here, 'keycert.pem')
 
 # This one's based on HTTPServer, which is based on socketserver