Merge ~troyanov/maas:backport-54f3e5e-3.5 into maas:3.5

[Anton Troyanov]

fix: return 0 bytes for non-existing .lst

Resolves LP:2067793

(cherry picked from commit 54f3e5e544d998465ca7fd94b5c3e74b58ccc097)

[MAAS Lander (maas-lander)]

UNIT TESTS
-b backport-54f3e5e-3.5 lp:~troyanov/maas/+git/maas into -b 3.5 lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas-tester/5693/console
COMMIT: 1e3ae400dab0ad8dfd808bd07c2a1a51ccb27b4c

review: Needs Fixing

[Anton Troyanov (troyanov)]

jenkins: !test

[MAAS Lander (maas-lander)]

UNIT TESTS
-b backport-54f3e5e-3.5 lp:~troyanov/maas/+git/maas into -b 3.5 lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas-tester/5695/console
COMMIT: 1e3ae400dab0ad8dfd808bd07c2a1a51ccb27b4c

review: Needs Fixing

[Anton Troyanov (troyanov)]

jenkins: !test

[MAAS Lander (maas-lander)]

UNIT TESTS
-b backport-54f3e5e-3.5 lp:~troyanov/maas/+git/maas into -b 3.5 lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas-tester/5697/console
COMMIT: 1e3ae400dab0ad8dfd808bd07c2a1a51ccb27b4c

review: Needs Fixing

[Anton Troyanov (troyanov)]

jenkins: !test

[Anton Troyanov (troyanov)]

jenkins: !test

[MAAS Lander (maas-lander)]

UNIT TESTS
-b backport-54f3e5e-3.5 lp:~troyanov/maas/+git/maas into -b 3.5 lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: 1e3ae400dab0ad8dfd808bd07c2a1a51ccb27b4c

review: Approve

diff --git a/src/provisioningserver/rackdservices/tests/test_tftp.py b/src/provisioningserver/rackdservices/tests/test_tftp.py
index 07b71b8..f7b65ea 100644
--- a/src/provisioningserver/rackdservices/tests/test_tftp.py
+++ b/src/provisioningserver/rackdservices/tests/test_tftp.py
@@ -640,7 +640,7 @@ class TestTFTPBackend(MAASTestCase):
             client, GetBootConfig, **params_okay
         )
 
-    def test_get_cache_reader(self):
+    def test_get_cache_reader_200(self):
         params_okay = {
             name.decode("ascii"): factory.make_name("value")
             for name, _ in GetBootConfig.arguments
@@ -656,6 +656,11 @@ class TestTFTPBackend(MAASTestCase):
 
         filename = factory.make_name()
 
+        mock_result = Mock()
+        mock_result.code = 200
+
+        backend._cache_proxy.request.return_value = mock_result
+
         backend.get_cache_reader(f"/grub/{filename}")
 
         backend._cache_proxy.request.assert_called_once_with(
@@ -681,11 +686,11 @@ class TestTFTPBackend(MAASTestCase):
         mock_result.code = 404
 
         backend._cache_proxy.request.return_value = mock_result
-        result = yield backend.get_cache_reader(f"/grub/{filename}")
-        self.assertEqual(result.read(0), b"")
+        with self.assertRaisesRegex(FileNotFound, rf"{filename}"):
+            yield backend.get_cache_reader(f"{filename}")
 
     @inlineCallbacks
-    def test_get_cache_reader_file_not_found_for_pxelinuxcfg(self):
+    def test_get_cache_reader_zero_size(self):
         params_okay = {
             name.decode("ascii"): factory.make_name("value")
             for name, _ in GetBootConfig.arguments
@@ -696,10 +701,10 @@ class TestTFTPBackend(MAASTestCase):
         client_service.getClientNow.return_value = succeed(client)
         backend = TFTPBackend(self.make_dir(), client_service)
         backend._cache_proxy = Mock()
-        filename = "pxelinux.cfg/0D0001BE"
+        filename = "/grub/x86_64-efi/command.lst"
 
-        with self.assertRaisesRegex(FileNotFound, rf"{filename}"):
-            yield backend.get_cache_reader(f"{filename}")
+        result = yield backend.get_cache_reader(f"/grub/{filename}")
+        self.assertEqual(result.read(0), b"")
 
 
 class TestTFTPService(MAASTestCase):
diff --git a/src/provisioningserver/rackdservices/tftp.py b/src/provisioningserver/rackdservices/tftp.py
index 85f3550..b933c9c 100644
--- a/src/provisioningserver/rackdservices/tftp.py
+++ b/src/provisioningserver/rackdservices/tftp.py
@@ -317,15 +317,15 @@ class TFTPBackend(FilesystemSynchronousBackend):
         if resp.code != 200:
             # legacy BIOS mode is expecting to get `TFTP file not found error`
             # for any `pxelinux.cfg/` that do not exist.
-            if str(file_name, encoding="utf-8").startswith("pxelinux.cfg"):
-                raise FileNotFound(file_name)
             # However for anything else (at least for GRUB) things like
             # - command.lst
             # - fs.lst
             # - crypto.lst
             # - terminal.lst
             # Are expected to be 0-sized with no error.
-            return BytesReader(bytes())
+            if ".lst" in str(file_name, encoding="utf-8"):
+                return BytesReader(bytes())
+            raise FileNotFound(file_name)
         body = yield readBody(resp)
         return BytesReader(body)