From b993f3c9a20cfd2208db07fcda8c46d6a8843bac Mon Sep 17 00:00:00 2001
From: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Date: Thu, 10 Apr 2025 09:02:55 +0000
Subject: [PATCH] Return a HTTP404 message when the Metadata instance is not
 present

If the Metadata instance (network, router) is not present, now the
Metadata proxy handler writes a HTTP 404 error message in the socket
file that is received by the client (virtual machine) that requests
the metadata.

Closes-Bug: #2106713
Change-Id: Ic717de94f2c483c08e2aa8fe688fe2e88d17d035
---
 neutron/agent/metadata/agent.py             | 20 ++++++++++++++++----
 neutron/agent/metadata/proxy_base.py        |  9 +++++++--
 neutron/agent/ovn/metadata/server_socket.py | 20 ++++++++++++++++----
 3 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/neutron/agent/metadata/agent.py b/neutron/agent/metadata/agent.py
index 0868f32034a..34488517807 100644
--- a/neutron/agent/metadata/agent.py
+++ b/neutron/agent/metadata/agent.py
@@ -24,7 +24,6 @@ from oslo_log import log as logging
 from oslo_service import loopingcall
 import requests
 import webob
-from webob import exc as webob_exc
 
 from neutron._i18n import _
 from neutron.agent.common import base_agent_rpc
@@ -169,9 +168,22 @@ class MetadataProxyHandler(MetadataProxyHandlerBaseSocketServer,
                 res = self._proxy_request(instance_id, project_id, req)
                 self.wfile.write(res)
                 return
-            # TODO(ralonsoh): change this return to be a formatted Request
-            # and added to self.wfile
-            return webob_exc.HTTPNotFound()
+
+            network_id, router_id = self._get_instance_id(req)
+            if network_id and router_id:
+                title = '400 Bad Request'
+                msg = _(f'Both network {network_id} and router {router_id} '
+                        f'defined.')
+            elif network_id:
+                title = '404 Not Found'
+                msg = _(f'Instance was not found on network {network_id}.')
+                LOG.warning(msg)
+            else:
+                title = '404 Not Found'
+                msg = _(f'Instance was not found on router {router_id}.')
+                LOG.warning(msg)
+            res = common_metadata.encode_http_reponse(title, title, msg)
+            self.wfile.write(res)
         except Exception as exc:
             LOG.exception('Error while receiving data.')
             raise exc
diff --git a/neutron/agent/metadata/proxy_base.py b/neutron/agent/metadata/proxy_base.py
index 11f0af06ccc..29ba0f03fce 100644
--- a/neutron/agent/metadata/proxy_base.py
+++ b/neutron/agent/metadata/proxy_base.py
@@ -91,11 +91,16 @@ class MetadataProxyHandlerBase(metaclass=abc.ABCMeta):
             explanation = str(msg)
             return webob.exc.HTTPInternalServerError(explanation=explanation)
 
-    def _get_instance_and_project_id(self, req, skip_cache=False):
-        forwarded_for = req.headers.get('X-Forwarded-For')
+    def _get_instance_id(self, req):
+        """Returns the network ID and the router ID from the request"""
         network_id = req.headers.get(self.NETWORK_ID_HEADER)
         router_id = (req.headers.get(self.ROUTER_ID_HEADER)
                      if self.ROUTER_ID_HEADER else None)
+        return network_id, router_id
+
+    def _get_instance_and_project_id(self, req, skip_cache=False):
+        forwarded_for = req.headers.get('X-Forwarded-For')
+        network_id, router_id = self._get_instance_id(req)
 
         # Only one should be given, drop since it could be spoofed
         if network_id and router_id:
diff --git a/neutron/agent/ovn/metadata/server_socket.py b/neutron/agent/ovn/metadata/server_socket.py
index 3d10e833e48..2445c4e3677 100644
--- a/neutron/agent/ovn/metadata/server_socket.py
+++ b/neutron/agent/ovn/metadata/server_socket.py
@@ -21,7 +21,6 @@ from oslo_config import cfg
 from oslo_log import log as logging
 import requests
 import webob
-from webob import exc as webob_exc
 
 from neutron._i18n import _
 from neutron.agent.linux import utils as agent_utils
@@ -145,9 +144,22 @@ class MetadataProxyHandler(MetadataProxyHandlerBaseSocketServer,
                 res = self._proxy_request(instance_id, project_id, req)
                 self.wfile.write(res)
                 return
-            # TODO(ralonsoh): change this return to be a formatted Request
-            # and added to self.wfile
-            return webob_exc.HTTPNotFound()
+
+            network_id, router_id = self._get_instance_id(req)
+            if network_id and router_id:
+                title = '400 Bad Request'
+                msg = _(f'Both network {network_id} and router {router_id} '
+                        f'defined.')
+            elif network_id:
+                title = '404 Not Found'
+                msg = _(f'Instance was not found on network {network_id}.')
+                LOG.warning(msg)
+            else:
+                title = '404 Not Found'
+                msg = _(f'Instance was not found on router {router_id}.')
+                LOG.warning(msg)
+            res = common_metadata.encode_http_reponse(title, title, msg)
+            self.wfile.write(res)
         except Exception as exc:
             LOG.exception('Error while receiving data.')
             raise exc