networking: refactor is_physical from cloudinit.net (#457)

As the first refactor PR, this also includes the initial structure for tests.

LP: #1884619

2 files changed, 56 insertions, 2 deletions

diff --git a/cloudinit/distros/networking.py b/cloudinit/distros/networking.py
index eecdccc6..e421a2ce 100644
--- a/cloudinit/distros/networking.py
+++ b/cloudinit/distros/networking.py
@@ -1,4 +1,5 @@
 import abc
+import os
 
 from cloudinit import net
 
@@ -79,8 +80,15 @@ class Networking(metaclass=abc.ABCMeta):
     def is_bridge(self, devname: DeviceName) -> bool:
         return net.is_bridge(devname)
 
+    @abc.abstractmethod
     def is_physical(self, devname: DeviceName) -> bool:
-        return net.is_physical(devname)
+        """
+        Is ``devname`` a physical network device?
+
+        Examples of non-physical network devices: bonds, bridges, tunnels,
+        loopback devices.
+        """
+        pass
 
     def is_renamed(self, devname: DeviceName) -> bool:
         return net.is_renamed(devname)
@@ -103,7 +111,8 @@ class Networking(metaclass=abc.ABCMeta):
 class BSDNetworking(Networking):
     """Implementation of networking functionality shared across BSDs."""
 
-    pass
+    def is_physical(self, devname: DeviceName) -> bool:
+        raise NotImplementedError()
 
 
 class LinuxNetworking(Networking):
@@ -126,3 +135,6 @@ class LinuxNetworking(Networking):
 
     def is_netfail_standby(self, devname: DeviceName) -> bool:
         return net.is_netfail_standby(devname)
+
+    def is_physical(self, devname: DeviceName) -> bool:
+        return os.path.exists(net.sys_dev_path(devname, "device"))
diff --git a/cloudinit/distros/tests/test_networking.py b/cloudinit/distros/tests/test_networking.py
new file mode 100644
index 00000000..2acb12f4
--- /dev/null
+++ b/cloudinit/distros/tests/test_networking.py
@@ -0,0 +1,42 @@
+from unittest import mock
+
+import pytest
+
+from cloudinit.distros.networking import BSDNetworking, LinuxNetworking
+
+
+@pytest.yield_fixture
+def sys_class_net(tmpdir):
+    sys_class_net_path = tmpdir.join("sys/class/net")
+    sys_class_net_path.ensure_dir()
+    with mock.patch(
+        "cloudinit.net.get_sys_class_path",
+        return_value=sys_class_net_path.strpath + "/",
+    ):
+        yield sys_class_net_path
+
+
+class TestBSDNetworkingIsPhysical:
+    def test_raises_notimplementederror(self):
+        with pytest.raises(NotImplementedError):
+            BSDNetworking().is_physical("eth0")
+
+
+class TestLinuxNetworkingIsPhysical:
+    def test_returns_false_by_default(self, sys_class_net):
+        assert not LinuxNetworking().is_physical("eth0")
+
+    def test_returns_false_if_devname_exists_but_not_physical(
+        self, sys_class_net
+    ):
+        devname = "eth0"
+        sys_class_net.join(devname).mkdir()
+        assert not LinuxNetworking().is_physical(devname)
+
+    def test_returns_true_if_device_is_physical(self, sys_class_net):
+        devname = "eth0"
+        device_dir = sys_class_net.join(devname)
+        device_dir.mkdir()
+        device_dir.join("device").write("")
+
+        assert LinuxNetworking().is_physical(devname)