test_uuid: test_getnode and test_windll_getnode fail if connected to the Internet via an Android phone

[native-api]

BPO	31643
Nosy	@warsaw, @xdegaye, @serhiy-storchaka, @native-api
PRs	bpo-31643: test_uuid: allow zero MAC address #4448 bpo-31643: test_uuid: allow zero MAC address #4804

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-09-29.21:37:18.944>
labels = ['type-bug', 'tests', '3.9', '3.10', '3.11']
title = 'test_uuid: test_getnode and test_windll_getnode fail if connected to the Internet via an Android phone'
updated_at = <Date 2021-06-14.21:55:20.385>
user = 'https://github.com/native-api'

bugs.python.org fields:

activity = <Date 2021-06-14.21:55:20.385>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2017-09-29.21:37:18.944>
creator = 'Ivan.Pozdeev'
dependencies = []
files = []
hgrepos = []
issue_num = 31643
keywords = []
message_count = 7.0
messages = ['303360', '303373', '308097', '308100', '308104', '308152', '308194']
nosy_count = 5.0
nosy_names = ['barry', '__Vano', 'xdegaye', 'serhiy.storchaka', 'Ivan.Pozdeev']
pr_nums = ['4448', '4804']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31643'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[native-api]

Ethernet emulation for some devices like Android phones' tethering use all-zero MAC addresses (which is okay since they don't actually pass Ethernet frames to other NICs). This results in a node ID of 0 if I'm currently connected to the Net via such a device. Which fails range checks in the corresponding tests.

RFC 4122 doesn't actually have any prohibitions of using a node ID of 0. Neither does IEEE 802.3 (or rather, whatever info I gathered on it since the standard's text is not freely available) assign any special meaning to an all-zero MAC address.

The patch also corrects the check call in test_windll_getnode since the tested function always generates UUID from a MAC address.

[native-api]

Example failure:

======================================================================
FAIL: test_windll_getnode (test.test_uuid.TestInternals)
----------------------------------------------------------------------

Traceback (most recent call last):
 File "C:\Ivan\cpython\lib\test\test_uuid.py", line 501, in test_windll_getnode

 self.check_node(node)
 File "C:\Ivan\cpython\lib\test\test_uuid.py", line 449, in check_node
 "%s is not an RFC 4122 node ID" % hex)
AssertionError: False is not true : 000000000000 is not an RFC 4122 node ID

======================================================================
FAIL: test_getnode (test.test_uuid.TestUUID)
----------------------------------------------------------------------

Traceback (most recent call last):
 File "C:\Ivan\cpython\lib\test\test_uuid.py", line 296, in test_getnode
 self.assertTrue(0 < node1 < (1 << 48), '%012x' % node1)
AssertionError: False is not true : 000000000000

[xdegaye]

On a Samsung device with Android 5.1 and tethering enabled, only one network device has a MAC address and it is not an all-zero MAC address.

Ivan can you please provide more information about this problem: which device, what Android version, what is the output of 'ip link' ?

[serhiy-storchaka]

I'm not sure that 000000000000 is better than a random address. Even if an all-zero MAC address is not explicitly prohibited it is used in a multiple independent devices. A random address looks more appropriate fore the purpose of generating a UUID.

[xdegaye]

I'm not sure that 000000000000 is better than a random address.

I agree, getnode() when obtained from a MAC address should not return 0.

RFC 4122 states (emphasis on 'uniqueness' is mine):

This document specifies three algorithms to generate UUIDs: the
first leverages the unique values of 802 MAC addresses to
guarantee *uniqueness*, ...

[Vano]

Xavier de Gaye <xdegaye@gmail.com> added the comment:

On a Samsung device with Android 5.1 and tethering enabled, only one network device has a MAC address and it is not an all-zero MAC address.

Ivan can you please provide more information about this problem: which device, what Android version, what is the output of 'ip link' ?

C:\> ipconfig -all
<...>
Samsung Galaxy S7 - Ethernet адаптер:

DNS-суффикс этого подключения . . :
Описание . . . . . . . . . . . . : Android USB Ethernet/RNDIS
Физический адрес. . . . . . . . . : 00-00-00-00-00-00
Dhcp включен. . . . . . . . . . . : да
Автонастройка включена . . . . . : да
IP-адрес . . . . . . . . . . . . : 192.168.42.2
Маска подсети . . . . . . . . . . : 255.255.255.0
Основной шлюз . . . . . . . . . . : 192.168.42.129
DHCP-сервер . . . . . . . . . . . : 192.168.42.129
DNS-серверы . . . . . . . . . . . : 192.168.42.129

Device name: Samsung Galaxy S7
Model number: SM-G930F
Android version: 6.0.1
Firmware version: G930FXXU1APGJ
Baseband version: G930VVRS4APH1
Build number: MMB29M.G930VVRU2APG5

Serhiy Storchaka<storchaka+cpython@gmail.com> added the comment:

I'm not sure that 000000000000 is better than a random address. Even if an all-zero MAC address is not explicitly prohibited it is used in a multiple independent devices. A random address looks more appropriate fore the purpose of generating a UUID.
The question is not whether it's good UUID source material. The
question, for the purpose of the test, is whether it's valid getnode()
output -- which it is for the current logic.

[xdegaye]

C:\> ipconfig -all

So the all-zero MAC address occurs on a Windows box and that explains the test_windll_getnode failure (this test is skipped on Android). I missed that point in your initial post and knowing what Android device you are using is irrelevant.