From 3875fc59530d7794f80bb650c0d329499aade113 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Tue, 5 Jul 2022 23:08:39 -0500
Subject: [PATCH] Cache the response from config/device_registry/list (#74483)

---
 .../components/config/device_registry.py      | 56 ++++++++++++++-----
 .../components/config/test_device_registry.py | 30 +++++++++-
 2 files changed, 71 insertions(+), 15 deletions(-)

diff --git a/homeassistant/components/config/device_registry.py b/homeassistant/components/config/device_registry.py
index e811d43d502e..587710a8c2a2 100644
--- a/homeassistant/components/config/device_registry.py
+++ b/homeassistant/components/config/device_registry.py
@@ -1,12 +1,23 @@
 """HTTP views to interact with the device registry."""
+from __future__ import annotations
+
 import voluptuous as vol
 
 from homeassistant import loader
 from homeassistant.components import websocket_api
 from homeassistant.components.websocket_api.decorators import require_admin
-from homeassistant.core import HomeAssistant, callback
+from homeassistant.components.websocket_api.messages import (
+    IDEN_JSON_TEMPLATE,
+    IDEN_TEMPLATE,
+    message_to_json,
+)
+from homeassistant.core import Event, HomeAssistant, callback
 from homeassistant.exceptions import HomeAssistantError
-from homeassistant.helpers.device_registry import DeviceEntryDisabler, async_get
+from homeassistant.helpers.device_registry import (
+    EVENT_DEVICE_REGISTRY_UPDATED,
+    DeviceEntryDisabler,
+    async_get,
+)
 
 WS_TYPE_LIST = "config/device_registry/list"
 SCHEMA_WS_LIST = websocket_api.BASE_COMMAND_MESSAGE_SCHEMA.extend(
@@ -29,6 +40,36 @@ SCHEMA_WS_UPDATE = websocket_api.BASE_COMMAND_MESSAGE_SCHEMA.extend(
 
 async def async_setup(hass):
     """Enable the Device Registry views."""
+
+    cached_list_devices: str | None = None
+
+    @callback
+    def _async_clear_list_device_cache(event: Event) -> None:
+        nonlocal cached_list_devices
+        cached_list_devices = None
+
+    @callback
+    def websocket_list_devices(hass, connection, msg):
+        """Handle list devices command."""
+        nonlocal cached_list_devices
+        if not cached_list_devices:
+            registry = async_get(hass)
+            cached_list_devices = message_to_json(
+                websocket_api.result_message(
+                    IDEN_TEMPLATE,
+                    [_entry_dict(entry) for entry in registry.devices.values()],
+                )
+            )
+        connection.send_message(
+            cached_list_devices.replace(IDEN_JSON_TEMPLATE, str(msg["id"]), 1)
+        )
+
+    hass.bus.async_listen(
+        EVENT_DEVICE_REGISTRY_UPDATED,
+        _async_clear_list_device_cache,
+        run_immediately=True,
+    )
+
     websocket_api.async_register_command(
         hass, WS_TYPE_LIST, websocket_list_devices, SCHEMA_WS_LIST
     )
@@ -41,17 +82,6 @@ async def async_setup(hass):
     return True
 
 
-@callback
-def websocket_list_devices(hass, connection, msg):
-    """Handle list devices command."""
-    registry = async_get(hass)
-    connection.send_message(
-        websocket_api.result_message(
-            msg["id"], [_entry_dict(entry) for entry in registry.devices.values()]
-        )
-    )
-
-
 @require_admin
 @callback
 def websocket_update_device(hass, connection, msg):
diff --git a/tests/components/config/test_device_registry.py b/tests/components/config/test_device_registry.py
index f923b3261009..f9289b6e3b3b 100644
--- a/tests/components/config/test_device_registry.py
+++ b/tests/components/config/test_device_registry.py
@@ -29,14 +29,14 @@ def registry(hass):
 
 async def test_list_devices(hass, client, registry):
     """Test list entries."""
-    registry.async_get_or_create(
+    device1 = registry.async_get_or_create(
         config_entry_id="1234",
         connections={("ethernet", "12:34:56:78:90:AB:CD:EF")},
         identifiers={("bridgeid", "0123")},
         manufacturer="manufacturer",
         model="model",
     )
-    registry.async_get_or_create(
+    device2 = registry.async_get_or_create(
         config_entry_id="1234",
         identifiers={("bridgeid", "1234")},
         manufacturer="manufacturer",
@@ -85,6 +85,32 @@ async def test_list_devices(hass, client, registry):
         },
     ]
 
+    registry.async_remove_device(device2.id)
+    await hass.async_block_till_done()
+
+    await client.send_json({"id": 6, "type": "config/device_registry/list"})
+    msg = await client.receive_json()
+
+    assert msg["result"] == [
+        {
+            "area_id": None,
+            "config_entries": ["1234"],
+            "configuration_url": None,
+            "connections": [["ethernet", "12:34:56:78:90:AB:CD:EF"]],
+            "disabled_by": None,
+            "entry_type": None,
+            "hw_version": None,
+            "id": device1.id,
+            "identifiers": [["bridgeid", "0123"]],
+            "manufacturer": "manufacturer",
+            "model": "model",
+            "name": None,
+            "name_by_user": None,
+            "sw_version": None,
+            "via_device_id": None,
+        }
+    ]
+
 
 @pytest.mark.parametrize(
     "payload_key,payload_value",