add: add "Vary" header to responses

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

test/io/__snapshots__/test_cli/test_schema_cache_snapshot[dbRoutines].yaml

@@ -196,6 +196,23 @@
       pdSchema: public
       pdVolatility: Volatile
 
+- - qiName: custom_vary_hdr
+    qiSchema: public
+  - - pdDescription: null
+      pdFuncSettings: []
+      pdHasVariadic: false
+      pdName: custom_vary_hdr
+      pdParams: []
+      pdReturnType:
+        contents:
+          contents:
+            qiName: void
+            qiSchema: pg_catalog
+          tag: Scalar
+        tag: Single
+      pdSchema: public
+      pdVolatility: Volatile
+
 - - qiName: get_postgres_version
     qiSchema: public
   - - pdDescription: null

test/io/fixtures/schema.sql

@@ -258,3 +258,10 @@ $_$ language sql;
 create or replace function notify_pgrst() returns void as $$
   notify pgrst;
 $$ language sql;
+
+
+create or replace function custom_vary_hdr() returns void as $$
+  begin
+    perform set_config('response.headers', '[{"Vary": "X-Test-Accept"}]', false);
+  end
+$$ language plpgsql;

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"