net/dhcp: surface type of DHCP lease failure to caller

cloudinit/net/dhcp.py

@@ -28,16 +28,24 @@
 NETWORKD_LEASES_DIR = "/run/systemd/netif/leases"
 
 
-class InvalidDHCPLeaseFileError(Exception):
+class NoDHCPLeaseError(Exception):
+    """Raised when unable to get a DHCP lease."""
+
+
+class InvalidDHCPLeaseFileError(NoDHCPLeaseError):
     """Raised when parsing an empty or invalid dhcp.leases file.
 
     Current uses are DataSourceAzure and DataSourceEc2 during ephemeral
     boot to scrape metadata.
     """
 
 
-class NoDHCPLeaseError(Exception):
-    """Raised when unable to get a DHCP lease."""
+class NoDHCPLeaseInterfaceError(NoDHCPLeaseError):
+    """Raised when unable to find a viable interface for DHCP."""
+
+
+class NoDHCPLeaseMissingDhclientError(NoDHCPLeaseError):
+    """Raised when unable to find dhclient."""
 
 
 class EphemeralDHCPv4(object):
@@ -89,12 +97,7 @@ def obtain_lease(self):
         """
         if self.lease:
             return self.lease
-        try:
-            leases = maybe_perform_dhcp_discovery(
-                self.iface, self.dhcp_log_func
-            )
-        except InvalidDHCPLeaseFileError as e:
-            raise NoDHCPLeaseError() from e
+        leases = maybe_perform_dhcp_discovery(self.iface, self.dhcp_log_func)
         if not leases:
             raise NoDHCPLeaseError()
         self.lease = leases[-1]
@@ -165,16 +168,16 @@ def maybe_perform_dhcp_discovery(nic=None, dhcp_log_func=None):
         nic = find_fallback_nic()
         if nic is None:
             LOG.debug("Skip dhcp_discovery: Unable to find fallback nic.")
-            return []
+            raise NoDHCPLeaseInterfaceError()
     elif nic not in get_devicelist():
         LOG.debug(
             "Skip dhcp_discovery: nic %s not found in get_devicelist.", nic
         )
-        return []
+        raise NoDHCPLeaseInterfaceError()
     dhclient_path = subp.which("dhclient")
     if not dhclient_path:
         LOG.debug("Skip dhclient configuration: No dhclient command found.")
-        return []
+        raise NoDHCPLeaseMissingDhclientError()
     with temp_utils.tempdir(
         rmtree_ignore_errors=True, prefix="cloud-init-dhcp-", needs_exe=True
     ) as tdir:

tests/unittests/net/test_dhcp.py

@@ -5,10 +5,14 @@
 from textwrap import dedent
 
 import httpretty
+import pytest
 
 import cloudinit.net as net
 from cloudinit.net.dhcp import (
     InvalidDHCPLeaseFileError,
+    NoDHCPLeaseError,
+    NoDHCPLeaseInterfaceError,
+    NoDHCPLeaseMissingDhclientError,
     dhcp_discovery,
     maybe_perform_dhcp_discovery,
     networkd_load_leases,
@@ -334,15 +338,21 @@ class TestDHCPDiscoveryClean(CiTestCase):
     def test_no_fallback_nic_found(self, m_fallback_nic):
         """Log and do nothing when nic is absent and no fallback is found."""
         m_fallback_nic.return_value = None  # No fallback nic found
-        self.assertEqual([], maybe_perform_dhcp_discovery())
+
+        with pytest.raises(NoDHCPLeaseInterfaceError):
+            maybe_perform_dhcp_discovery()
+
         self.assertIn(
             "Skip dhcp_discovery: Unable to find fallback nic.",
             self.logs.getvalue(),
         )
 
-    def test_provided_nic_does_not_exist(self):
+    @mock.patch("cloudinit.net.dhcp.find_fallback_nic", return_value=None)
+    def test_provided_nic_does_not_exist(self, m_fallback_nic):
         """When the provided nic doesn't exist, log a message and no-op."""
-        self.assertEqual([], maybe_perform_dhcp_discovery("idontexist"))
+        with pytest.raises(NoDHCPLeaseInterfaceError):
+            maybe_perform_dhcp_discovery("idontexist")
+
         self.assertIn(
             "Skip dhcp_discovery: nic idontexist not found in get_devicelist.",
             self.logs.getvalue(),
@@ -354,7 +364,10 @@ def test_absent_dhclient_command(self, m_fallback, m_which):
         """When dhclient doesn't exist in the OS, log the issue and no-op."""
         m_fallback.return_value = "eth9"
         m_which.return_value = None  # dhclient isn't found
-        self.assertEqual([], maybe_perform_dhcp_discovery())
+
+        with pytest.raises(NoDHCPLeaseMissingDhclientError):
+            maybe_perform_dhcp_discovery()
+
         self.assertIn(
             "Skip dhclient configuration: No dhclient command found.",
             self.logs.getvalue(),
@@ -794,4 +807,50 @@ def test_ephemeral_dhcp_setup_network_if_url_connectivity(
         m_dhcp.called_once_with()
 
 
+@pytest.mark.parametrize(
+    "error_class",
+    [
+        NoDHCPLeaseInterfaceError,
+        NoDHCPLeaseInterfaceError,
+        NoDHCPLeaseMissingDhclientError,
+    ],
+)
+class TestEphemeralDhcpLeaseErrors:
+    @mock.patch("cloudinit.net.dhcp.maybe_perform_dhcp_discovery")
+    def test_obtain_lease_raises_error(self, m_dhcp, error_class):
+        m_dhcp.side_effect = [error_class()]
+
+        with pytest.raises(error_class):
+            net.dhcp.EphemeralDHCPv4().obtain_lease()
+
+        assert len(m_dhcp.mock_calls) == 1
+
+    @mock.patch("cloudinit.net.dhcp.maybe_perform_dhcp_discovery")
+    def test_obtain_lease_umbrella_error(self, m_dhcp, error_class):
+        m_dhcp.side_effect = [error_class()]
+        with pytest.raises(NoDHCPLeaseError):
+            net.dhcp.EphemeralDHCPv4().obtain_lease()
+
+        assert len(m_dhcp.mock_calls) == 1
+
+    @mock.patch("cloudinit.net.dhcp.maybe_perform_dhcp_discovery")
+    def test_ctx_mgr_raises_error(self, m_dhcp, error_class):
+        m_dhcp.side_effect = [error_class()]
+
+        with pytest.raises(error_class):
+            with net.dhcp.EphemeralDHCPv4():
+                pass
+
+        assert len(m_dhcp.mock_calls) == 1
+
+    @mock.patch("cloudinit.net.dhcp.maybe_perform_dhcp_discovery")
+    def test_ctx_mgr_umbrella_error(self, m_dhcp, error_class):
+        m_dhcp.side_effect = [error_class()]
+        with pytest.raises(NoDHCPLeaseError):
+            with net.dhcp.EphemeralDHCPv4():
+                pass
+
+        assert len(m_dhcp.mock_calls) == 1
+
+
 # vi: ts=4 expandtab