gh-119461: Fix ThreadedVSOCKSocketStreamTest (#119465)

Add socket.VMADDR_CID_LOCAL constant.

Fix ThreadedVSOCKSocketStreamTest: if get_cid() returns the host
address or the "any" address, use the local communication address
(loopback): VMADDR_CID_LOCAL.

On Linux 6.9, apparently, the /dev/vsock device is now available but
get_cid() returns VMADDR_CID_ANY (-1).

Author: vstinner

Lib/test/test_socket.py

@@ -160,8 +160,8 @@ def _have_socket_qipcrtr():
 
 def _have_socket_vsock():
     """Check whether AF_VSOCK sockets are supported on this host."""
-    ret = get_cid() is not None
-    return ret
+    cid = get_cid()
+    return (cid is not None)
 
 
 def _have_socket_bluetooth():
@@ -520,8 +520,6 @@ 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,
-          "This test can only be run on a virtual guest.")
 class ThreadedVSOCKSocketStreamTest(unittest.TestCase, ThreadableTest):
 
     def __init__(self, methodName='runTest'):
@@ -543,6 +541,9 @@ def clientSetUp(self):
         self.cli = socket.socket(socket.AF_VSOCK, socket.SOCK_STREAM)
         self.addCleanup(self.cli.close)
         cid = get_cid()
+        if cid in (socket.VMADDR_CID_HOST, socket.VMADDR_CID_ANY):
+            # gh-119461: Use the local communication address (loopback)
+            cid = socket.VMADDR_CID_LOCAL
         self.cli.connect((cid, VSOCKPORT))
 
     def testStream(self):
@@ -2515,6 +2516,7 @@ def testVSOCKConstants(self):
         socket.SO_VM_SOCKETS_BUFFER_MAX_SIZE
         socket.VMADDR_CID_ANY
         socket.VMADDR_PORT_ANY
+        socket.VMADDR_CID_LOCAL
         socket.VMADDR_CID_HOST
         socket.VM_SOCKETS_INVALID_VERSION
         socket.IOCTL_VM_SOCKETS_GET_LOCAL_CID

Misc/NEWS.d/next/Library/2024-05-23-15-48-17.gh-issue-119461.82KqUW.rst

@@ -0,0 +1 @@
+Add ``socket.VMADDR_CID_LOCAL`` constant. Patch by Victor Stinner.

Modules/socketmodule.c

@@ -7596,6 +7596,7 @@ socket_exec(PyObject *m)
     ADD_INT_CONST(m, "SO_VM_SOCKETS_BUFFER_MAX_SIZE", 2);
     ADD_INT_CONST(m, "VMADDR_CID_ANY", 0xffffffff);
     ADD_INT_CONST(m, "VMADDR_PORT_ANY", 0xffffffff);
+    ADD_INT_CONST(m, "VMADDR_CID_LOCAL", 1);
     ADD_INT_CONST(m, "VMADDR_CID_HOST", 2);
     ADD_INT_CONST(m, "VM_SOCKETS_INVALID_VERSION", 0xffffffff);
     ADD_INT_CONST(m, "IOCTL_VM_SOCKETS_GET_LOCAL_CID",  _IO(7, 0xb9));