gh-122133: Rework pure Python socketpair tests to avoid use of importlib.reload. (#122493)

Co-authored-by: Gregory P. Smith <greg@krypto.org>

Lib/socket.py

@@ -592,16 +592,65 @@ if hasattr(_socket.socket, "share"):
         return socket(0, 0, 0, info)
     __all__.append("fromshare")
 
+# Origin: https://gist.github.com/4325783, by Geert Jansen.  Public domain.
+# This is used if _socket doesn't natively provide socketpair. It's
+# always defined so that it can be patched in for testing purposes.
+def _fallback_socketpair(family=AF_INET, type=SOCK_STREAM, proto=0):
+    if family == AF_INET:
+        host = _LOCALHOST
+    elif family == AF_INET6:
+        host = _LOCALHOST_V6
+    else:
+        raise ValueError("Only AF_INET and AF_INET6 socket address families "
+                         "are supported")
+    if type != SOCK_STREAM:
+        raise ValueError("Only SOCK_STREAM socket type is supported")
+    if proto != 0:
+        raise ValueError("Only protocol zero is supported")
+
+    # We create a connected TCP socket. Note the trick with
+    # setblocking(False) that prevents us from having to create a thread.
+    lsock = socket(family, type, proto)
+    try:
+        lsock.bind((host, 0))
+        lsock.listen()
+        # On IPv6, ignore flow_info and scope_id
+        addr, port = lsock.getsockname()[:2]
+        csock = socket(family, type, proto)
+        try:
+            csock.setblocking(False)
+            try:
+                csock.connect((addr, port))
+            except (BlockingIOError, InterruptedError):
+                pass
+            csock.setblocking(True)
+            ssock, _ = lsock.accept()
+        except:
+            csock.close()
+            raise
+    finally:
+        lsock.close()
+
+    # Authenticating avoids using a connection from something else
+    # able to connect to {host}:{port} instead of us.
+    # We expect only AF_INET and AF_INET6 families.
+    try:
+        if (
+            ssock.getsockname() != csock.getpeername()
+            or csock.getsockname() != ssock.getpeername()
+        ):
+            raise ConnectionError("Unexpected peer connection")
+    except:
+        # getsockname() and getpeername() can fail
+        # if either socket isn't connected.
+        ssock.close()
+        csock.close()
+        raise
+
+    return (ssock, csock)
+
 if hasattr(_socket, "socketpair"):
-
     def socketpair(family=None, type=SOCK_STREAM, proto=0):
-        """socketpair([family[, type[, proto]]]) -> (socket object, socket object)
-
-        Create a pair of socket objects from the sockets returned by the platform
-        socketpair() function.
-        The arguments are the same as for socket() except the default family is
-        AF_UNIX if defined on the platform; otherwise, the default is AF_INET.
-        """
         if family is None:
             try:
                 family = AF_UNIX
@@ -613,61 +662,7 @@ if hasattr(_socket, "socketpair"):
         return a, b
 
 else:
-
+    socketpair = _fallback_socketpair
-    # Origin: https://gist.github.com/4325783, by Geert Jansen.  Public domain.
-    def socketpair(family=AF_INET, type=SOCK_STREAM, proto=0):
-        if family == AF_INET:
-            host = _LOCALHOST
-        elif family == AF_INET6:
-            host = _LOCALHOST_V6
-        else:
-            raise ValueError("Only AF_INET and AF_INET6 socket address families "
-                             "are supported")
-        if type != SOCK_STREAM:
-            raise ValueError("Only SOCK_STREAM socket type is supported")
-        if proto != 0:
-            raise ValueError("Only protocol zero is supported")
-
-        # We create a connected TCP socket. Note the trick with
-        # setblocking(False) that prevents us from having to create a thread.
-        lsock = socket(family, type, proto)
-        try:
-            lsock.bind((host, 0))
-            lsock.listen()
-            # On IPv6, ignore flow_info and scope_id
-            addr, port = lsock.getsockname()[:2]
-            csock = socket(family, type, proto)
-            try:
-                csock.setblocking(False)
-                try:
-                    csock.connect((addr, port))
-                except (BlockingIOError, InterruptedError):
-                    pass
-                csock.setblocking(True)
-                ssock, _ = lsock.accept()
-            except:
-                csock.close()
-                raise
-        finally:
-            lsock.close()
-
-        # Authenticating avoids using a connection from something else
-        # able to connect to {host}:{port} instead of us.
-        # We expect only AF_INET and AF_INET6 families.
-        try:
-            if (
-                ssock.getsockname() != csock.getpeername()
-                or csock.getsockname() != ssock.getpeername()
-            ):
-                raise ConnectionError("Unexpected peer connection")
-        except:
-            # getsockname() and getpeername() can fail
-            # if either socket isn't connected.
-            ssock.close()
-            csock.close()
-            raise
-
-        return (ssock, csock)
     __all__.append("socketpair")
 
 socketpair.__doc__ = """socketpair([family[, type[, proto]]]) -> (socket object, socket object)

Lib/test/test_socket.py

@@ -4861,7 +4861,6 @@ class BasicSocketPairTest(SocketPairTest):
 
 
 class PurePythonSocketPairTest(SocketPairTest):
-
     # Explicitly use socketpair AF_INET or AF_INET6 to ensure that is the
     # code path we're using regardless platform is the pure python one where
     # `_socket.socketpair` does not exist.  (AF_INET does not work with
@@ -4876,28 +4875,21 @@ class PurePythonSocketPairTest(SocketPairTest):
     # Local imports in this class make for easy security fix backporting.
 
     def setUp(self):
-        import _socket
+        if hasattr(_socket, "socketpair"):
-        self._orig_sp = getattr(_socket, 'socketpair', None)
+            self._orig_sp = socket.socketpair
-        if self._orig_sp is not None:
             # This forces the version using the non-OS provided socketpair
             # emulation via an AF_INET socket in Lib/socket.py.
-            del _socket.socketpair
+            socket.socketpair = socket._fallback_socketpair
-            import importlib
-            global socket
-            socket = importlib.reload(socket)
         else:
-            pass  # This platform already uses the non-OS provided version.
+            # This platform already uses the non-OS provided version.
+            self._orig_sp = None
         super().setUp()
 
     def tearDown(self):
         super().tearDown()
-        import _socket
         if self._orig_sp is not None:
             # Restore the default socket.socketpair definition.
-            _socket.socketpair = self._orig_sp
+            socket.socketpair = self._orig_sp
-            import importlib
-            global socket
-            socket = importlib.reload(socket)
 
     def test_recv(self):
         msg = self.serv.recv(1024)