Skip compressing HTTP JSON responses below 1 KiB (#175560)

Co-authored-by: Claude <noreply@anthropic.com>

homeassistant/components/api/__init__.py

@@ -46,6 +46,7 @@ from homeassistant.exceptions import (
     Unauthorized,
 )
 from homeassistant.helpers import config_validation as cv, recorder, template
+from homeassistant.helpers.http import MIN_COMPRESSED_RESPONSE_SIZE
 from homeassistant.helpers.json import json_dumps, json_fragment
 from homeassistant.helpers.service import async_get_all_descriptions
 from homeassistant.helpers.typing import ConfigType
@@ -223,12 +224,14 @@ class APIStatesView(HomeAssistantView):
                 for state in hass.states.async_all()
                 if entity_perm(state.entity_id, POLICY_READ)
             )
+        body = b"".join((b"[", b",".join(states), b"]"))
         response = web.Response(
-            body=b"".join((b"[", b",".join(states), b"]")),
+            body=body,
             content_type=CONTENT_TYPE_JSON,
             zlib_executor_size=32768,
         )
-        response.enable_compression()
+        if len(body) > MIN_COMPRESSED_RESPONSE_SIZE:
+            response.enable_compression()
         return response
 
 

homeassistant/helpers/http.py

@@ -27,6 +27,10 @@ from .json import find_paths_unserializable_data, json_bytes, json_dumps
 
 _LOGGER = logging.getLogger(__name__)
 
+# Responses smaller than this fit within a single network packet, so
+# compressing them wastes event-loop CPU without reducing round-trips.
+MIN_COMPRESSED_RESPONSE_SIZE: Final = 1024
+
 
 type AllowCorsType = Callable[[AbstractRoute | AbstractResource], None]
 KEY_AUTHENTICATED: Final = "ha_authenticated"
@@ -160,7 +164,8 @@ class HomeAssistantView:
             headers=headers,
             zlib_executor_size=32768,
         )
-        response.enable_compression()
+        if len(msg) > MIN_COMPRESSED_RESPONSE_SIZE:
+            response.enable_compression()
         return response
 
     def json_message(

tests/components/api/test_init.py

@@ -51,6 +51,33 @@ async def test_api_list_state_entities(
     assert remote_data == local_data
 
 
+@pytest.mark.parametrize(
+    ("entity_count", "expect_compression"),
+    [
+        pytest.param(1, False, id="small-body-not-compressed"),
+        pytest.param(50, True, id="large-body-compressed"),
+    ],
+)
+async def test_api_states_compression_threshold(
+    hass: HomeAssistant,
+    mock_api_client: TestClient,
+    entity_count: int,
+    expect_compression: bool,
+) -> None:
+    """Test that only state list responses above the size threshold are compressed."""
+    for i in range(entity_count):
+        hass.states.async_set(
+            f"test.entity_{i}", "on", {"friendly_name": f"Entity {i}"}
+        )
+
+    resp = await mock_api_client.get(
+        const.URL_API_STATES, headers={"Accept-Encoding": "gzip, deflate"}
+    )
+
+    assert resp.status == HTTPStatus.OK
+    assert ("Content-Encoding" in resp.headers) is expect_compression
+
+
 async def test_api_get_state(hass: HomeAssistant, mock_api_client: TestClient) -> None:
     """Test if the debug interface allows us to get a state."""
     hass.states.async_set("hello.world", "nice", {"attr": 1})

tests/helpers/test_http.py

@@ -0,0 +1,40 @@
+"""Tests for the HTTP helpers."""
+
+from http import HTTPStatus
+
+from aiohttp import web
+import pytest
+
+from homeassistant.helpers.http import MIN_COMPRESSED_RESPONSE_SIZE, HomeAssistantView
+
+from tests.typing import ClientSessionGenerator
+
+
+@pytest.mark.parametrize(
+    ("body_size", "expect_compression"),
+    [
+        pytest.param(8, False, id="small-body-not-compressed"),
+        pytest.param(
+            MIN_COMPRESSED_RESPONSE_SIZE * 2, True, id="large-body-compressed"
+        ),
+    ],
+)
+@pytest.mark.usefixtures("socket_enabled")
+async def test_json_response_compression_threshold(
+    aiohttp_client: ClientSessionGenerator,
+    body_size: int,
+    expect_compression: bool,
+) -> None:
+    """Test HomeAssistantView.json only compresses bodies above the threshold."""
+
+    async def handler(request: web.Request) -> web.Response:
+        return HomeAssistantView.json({"data": "x" * body_size})
+
+    app = web.Application()
+    app.router.add_get("/", handler)
+    client = await aiohttp_client(app)
+
+    resp = await client.get("/", headers={"Accept-Encoding": "gzip, deflate"})
+
+    assert resp.status == HTTPStatus.OK
+    assert ("Content-Encoding" in resp.headers) is expect_compression