add: add "Vary" header to responses

Co-authored-by: Steve Chavez <stevechavezast@gmail.com>

test/io/test_io.py

@@ -1811,3 +1811,23 @@ def test_client_error_verbosity_config(defaultenv):
             "details": None,
             "hint": "Perhaps you meant the table 'public.items'",
         }
+
+
+def test_vary_custom_header_set(defaultenv):
+    "Test default Vary header value is overridden in pre-request database function"
+
+    env = {**defaultenv, "PGRST_DB_PRE_REQUEST": "custom_vary_hdr"}
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.get("/projects")
+
+        assert response.headers["Vary"] == "X-Test-Accept"
+
+
+def test_vary_default_header_set(defaultenv):
+    "Test default Vary header value matches default one"
+
+    with run(env=defaultenv) as postgrest:
+        response = postgrest.session.get("/projects")
+
+        assert response.headers["Vary"] == "Accept, Prefer, Range"