ETag support for .db downloads, closes #1739

datasette/utils/testing.py

@@ -55,10 +55,21 @@ class TestClient:
 
     @async_to_sync
     async def get(
-        self, path, follow_redirects=False, redirect_count=0, method="GET", cookies=None
+        self,
+        path,
+        follow_redirects=False,
+        redirect_count=0,
+        method="GET",
+        cookies=None,
+        if_none_match=None,
     ):
         return await self._request(
-            path, follow_redirects, redirect_count, method, cookies
+            path=path,
+            follow_redirects=follow_redirects,
+            redirect_count=redirect_count,
+            method=method,
+            cookies=cookies,
+            if_none_match=if_none_match,
         )
 
     @async_to_sync
@@ -110,6 +121,7 @@ class TestClient:
         headers=None,
         post_body=None,
         content_type=None,
+        if_none_match=None,
     ):
         return await self._request(
             path,
@@ -120,6 +132,7 @@ class TestClient:
             headers=headers,
             post_body=post_body,
             content_type=content_type,
+            if_none_match=if_none_match,
         )
 
     async def _request(
@@ -132,10 +145,13 @@ class TestClient:
         headers=None,
         post_body=None,
         content_type=None,
+        if_none_match=None,
     ):
         headers = headers or {}
         if content_type:
             headers["content-type"] = content_type
+        if if_none_match:
+            headers["if-none-match"] = if_none_match
         httpx_response = await self.ds.client.request(
             method,
             path,

datasette/views/database.py

@@ -183,6 +183,13 @@ class DatabaseDownload(DataView):
         headers = {}
         if self.ds.cors:
             add_cors_headers(headers)
+        if db.hash:
+            etag = '"{}"'.format(db.hash)
+            headers["Etag"] = etag
+            # Has user seen this already?
+            if_none_match = request.headers.get("if-none-match")
+            if if_none_match and if_none_match == etag:
+                return Response("", status=304)
         headers["Transfer-Encoding"] = "chunked"
         return AsgiFileDownload(
             filepath,

tests/test_html.py

@@ -401,7 +401,7 @@ def test_database_download_for_immutable():
         assert len(soup.findAll("a", {"href": re.compile(r"\.db$")}))
         # Check we can actually download it
         download_response = client.get("/fixtures.db")
-        assert 200 == download_response.status
+        assert download_response.status == 200
         # Check the content-length header exists
         assert "content-length" in download_response.headers
         content_length = download_response.headers["content-length"]
@@ -413,6 +413,14 @@ def test_database_download_for_immutable():
             == 'attachment; filename="fixtures.db"'
         )
         assert download_response.headers["transfer-encoding"] == "chunked"
+        # ETag header should be present and match db.hash
+        assert "etag" in download_response.headers
+        etag = download_response.headers["etag"]
+        assert etag == '"{}"'.format(client.ds.databases["fixtures"].hash)
+        # Try a second download with If-None-Match: current-etag
+        download_response2 = client.get("/fixtures.db", if_none_match=etag)
+        assert download_response2.body == b""
+        assert download_response2.status == 304
 
 
 def test_database_download_disallowed_for_mutable(app_client):