transfer-encoding: chunked for DB downloads, refs #749

This should get >32MB downloads working on Cloud Run.

datasette/views/database.py

@@ -169,6 +169,7 @@ class DatabaseDownload(DataView):
         headers = {}
         if self.ds.cors:
             headers["Access-Control-Allow-Origin"] = "*"
+        headers["Transfer-Encoding"] = "chunked"
         return AsgiFileDownload(
             filepath,
             filename=os.path.basename(filepath),

tests/test_html.py

@@ -1028,6 +1028,7 @@ def test_database_download_for_immutable():
             download_response.headers["content-disposition"]
             == 'attachment; filename="fixtures.db"'
         )
+        assert download_response.headers["transfer-encoding"] == "chunked"
 
 
 def test_database_download_disallowed_for_mutable(app_client):