Disable caching of index.html

Disable caching of `index.html` on purpose so that the browser is always loading the latest app code, otherwise changes to the app are not taken into account when the browser is loading the file from the cache.

Fixes: https://github.com/aquarist-labs/s3gw/issues/730

Signed-off-by: Volker Theile <[email protected]>

src/backend/tests/unit/test_app.py

@@ -0,0 +1,50 @@
+# Copyright 2023 SUSE LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+from s3gw_ui_backend import NoCacheStaticFiles
+
+
+def test_static_files_1() -> None:
+    app = FastAPI()
+    app.mount(
+        "/",
+        NoCacheStaticFiles(no_cache_files=["/test_api.py"], directory="api"),
+        name="static",
+    )
+    client = TestClient(app)
+    resp = client.get("/test_api.py")
+    assert resp.status_code == 200
+    assert (
+        resp.headers["cache-control"] == "no-cache, max-age=0, must-revalidate"
+    )
+    assert resp.headers["expires"] == "0"
+    assert resp.headers["pragma"] == "no-cache"
+
+
+def test_static_files_2() -> None:
+    app = FastAPI()
+    app.mount(
+        "/",
+        NoCacheStaticFiles(no_cache_files=["/test_api.py"], directory="api"),
+        name="static",
+    )
+    client = TestClient(app)
+    resp = client.get("/test_api_admin.py")
+    assert resp.status_code == 200
+    assert "cache-control" not in resp.headers
+    assert "expires" not in resp.headers
+    assert "pragma" not in resp.headers

src/frontend/src/index.html

@@ -4,9 +4,6 @@
   <meta charset="utf-8">
   <title></title>
   <meta name="viewport" content="width=device-width, initial-scale=1">
-  <meta http-equiv="cache-control" content="no-cache">
-  <meta http-equiv="pragma" content="no-cache">
-  <meta http-equiv="expires" content="0">
   <link rel="icon" type="image/x-icon" href="favicon.ico">
   <link rel="apple-touch-icon" href="favicon_180x180.png">
   <link rel="icon" href="favicon.svg" sizes="any" type="image/svg+xml">

src/s3gw_ui_backend.py

@@ -16,18 +16,44 @@
 
 import os
 import sys
-from typing import Awaitable, Callable
+from typing import Awaitable, Callable, List
 
 import uvicorn
-from fastapi import FastAPI
+from fastapi import FastAPI, Response
 from fastapi.logger import logger
 from fastapi.staticfiles import StaticFiles
+from starlette.types import Scope
 
 from backend.api import admin, auth, buckets, config, objects
 from backend.config import Config
 from backend.logging import setup_logging
 
 
+class NoCacheStaticFiles(StaticFiles):
+    """
+    Add HTTP headers to do not cache the specified files.
+    """
+
+    def __init__(self, no_cache_files: List[str], *args, **kwargs):
+        """
+        :param no_cache_files: The list of files that should not be cached.
+        """
+        self.no_cache_files = no_cache_files
+        super().__init__(*args, **kwargs)
+
+    async def get_response(self, path: str, scope: Scope) -> Response:
+        resp = await super().get_response(path, scope)
+        if scope["path"] in self.no_cache_files:
+            resp.headers.update(
+                {
+                    "Cache-Control": "no-cache, max-age=0, must-revalidate",
+                    "Expires": "0",
+                    "Pragma": "no-cache",
+                }
+            )
+        return resp
+
+
 async def s3gw_startup(s3gw_app: FastAPI, s3gw_api: FastAPI) -> None:
     setup_logging()
     logger.info("Starting s3gw-ui backend")
@@ -89,8 +115,16 @@ async def on_shutdown():  # type: ignore
 
     s3gw_app.mount("/api", s3gw_api, name="api")
     if static_dir is not None:
+        # Disable caching of `index.html` on purpose so that the browser
+        # is always loading the latest app code, otherwise changes to the
+        # app are not taken into account when the browser is loading the
+        # file from the cache.
         s3gw_app.mount(
-            "/", StaticFiles(directory=static_dir, html=True), name="static"
+            "/",
+            NoCacheStaticFiles(
+                no_cache_files=["/"], directory=static_dir, html=True
+            ),
+            name="static",
         )
 
     return s3gw_app