gh-145548: Use VMADDR_CID_LOCAL in VSOCK socket tests

Prefer VMADDR_CID_LOCAL instead of VMADDR_CID_ANY for bind() in the
server. Skip the test if bind() fails with EADDRNOTAVAIL.

Author: vstinner

Lib/test/test_socket.py

@@ -563,8 +563,8 @@ def clientTearDown(self):
 @unittest.skipIf(WSL, 'VSOCK does not work on Microsoft WSL')
 @unittest.skipUnless(HAVE_SOCKET_VSOCK,
           'VSOCK sockets required for this test.')
-@unittest.skipUnless(get_cid() != 2,  # VMADDR_CID_HOST
-                     "This test can only be run on a virtual guest.")
+@unittest.skipIf(get_cid() == getattr(socket, 'VMADDR_CID_HOST', 2),
+                 "This test can only be run on a virtual guest.")
 class ThreadedVSOCKSocketStreamTest(unittest.TestCase, ThreadableTest):
 
     def __init__(self, methodName='runTest'):
@@ -574,7 +574,16 @@ def __init__(self, methodName='runTest'):
     def setUp(self):
         self.serv = socket.socket(socket.AF_VSOCK, socket.SOCK_STREAM)
         self.addCleanup(self.serv.close)
-        self.serv.bind((socket.VMADDR_CID_ANY, VSOCKPORT))
+        cid = get_cid()
+        if cid in (socket.VMADDR_CID_HOST, socket.VMADDR_CID_ANY):
+            cid = socket.VMADDR_CID_LOCAL
+        try:
+            self.serv.bind((cid, VSOCKPORT))
+        except OSError as exc:
+            if exc.errno == errno.EADDRNOTAVAIL:
+                self.skipTest(f"bind() failed with {exc!r}")
+            else:
+                raise
         self.serv.listen()
         self.serverExplicitReady()
         self.serv.settimeout(support.LOOPBACK_TIMEOUT)