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,