socket.connect - support custom family value

[jborean93]

Feature or enhancement

Currently socket.connect() accepts a wide range of values when connecting to a socket with the code in socketmodule.c transforming it based on the family the socket was created with. Unfortunately there is a check that fails the connection if the family is unrecognized

cpython/Modules/socketmodule.c

Lines 2530 to 2534 in 9d85aba

	default:
	PyErr_SetString(PyExc_OSError, "getsockaddrlen: bad family");
	return 0;
	}

.

My proposal is to allow a caller to bypass this check if passing in a raw byte value to be used as the addr info on the native call.

Pitch

The reason why I am hoping for this feature is to support clients connecting to a Hyper-V socket. This uses the AF_HYPERV family which isn't known to Python so any attempts to connect to it won't work.

Currently I am using the following to work around this restriction by using ctypes to call the C API directly and using the fileno:

import ctypes
import socket
import uuid

HV_GUID_VM_SESSION_SERVICE_ID = uuid.UUID("999e53d4-3d5c-4c3e-8779-bed06ec056e1")
HV_GUID_VM_SESSION_SERVICE_ID_2 = uuid.UUID("a5201c21-2770-4c11-a68e-f182edb29220")
AF_HYPERV = 34
HV_PROTOCOL_RAW = 1

# This is the GUID of the Win VM to connect to
vm_id = uuid.UUID("...")

win32sock = ctypes.WinDLL("Ws2_32.dll")

raw_sock = win32sock.socket(AF_HYPERV, socket.SOCK_STREAM, HV_PROTOCOL_RAW)
if raw_sock == -1:
    err = win32sock.WSAGetLastError()
    raise ctypes.WinError(code=err)

try:
    sock_addr = b"\x22\x00\x00\x00" + vm_id.bytes_le + HV_GUID_VM_SESSION_SERVICE_ID.bytes_le
    res = win32sock.connect(raw_sock, sock_addr, len(sock_addr))
    if res:
        err = win32sock.WSAGetLastError()
        raise ctypes.WinError(code=err)

    sock = socket.socket(fileno=raw_sock)
except:
    win32sock.closesocket(raw_sock)
    raise

...

sock.close()

It would be good to be able to do this instead

import socket

sock = socket.socket(AF_HYPERV, socket.SOCK_STREAM, HV_PROTOCOL_RAW)
sock_addr = b"\x22\x00\x00\x00" + vm_id.bytes_le + HV_GUID_VM_SESSION_SERVICE_ID.bytes_le
sock.connect(sock_addr)

...

sock.close()

Currently that fails due to the hardcoded check against unknown families

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: connect(): bad family

Another option is to add support for AF_HYPERV on Windows and support a tuple of (vm_id, service_id) and have Python create the struct. This could be done as a separate feature request potentially.

Linked PRs

• gh-92658: Fix typo in docs and tests for HV_GUID_PARENT #105267
• [3.12] gh-92658: Fix typo in docs and tests for HV_GUID_PARENT (GH-105267) #105398

[ronaldoussoren]

It would IMHO be better to add explicit support for this new address family.

[jborean93]

I agree, especially from a UX perspective but would it also be nice if it supported arbitrary bytes in the cases when Python does not support the family for other protocols, now and in the future?

[jborean93]

I've added a PR that adds explicit support for the new address family. I'm not too experienced on the C side so any pointers or comments would be greatly appreciated #92755.

[vstinner]

I agree, especially from a UX perspective but would it also be nice if it supported arbitrary bytes in the cases when Python does not support the family for other protocols, now and in the future?

I don't think that it's a good idea. Each protocol is different and requires special code.

[jborean93]

Fair enough, I mostly only desired it for the Hyper V stuff and was mindful if I came across another family I would have the same problem but that makes sense.