add: add "Vary" header to responses

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

CHANGELOG.md

@@ -13,9 +13,12 @@ All notable changes to this project will be documented in this file. From versio
 - Optimize requests with `Prefer: count=exact` that do not use ranges or `db-max-rows` by @laurenceisla in #3957
   + Removed unnecessary double count when building the `Content-Range`.
 - Add config `client_error_verbosity` to customize error verbosity by @taimoorzaeem in #4088, #3980, #3824
+- Add `Vary` header to responses by @develop7 in #4609
 
 ### Changed
 
+- All responses now include a `Vary` header by @develop7 in #4609
+
 - Log error when `db-schemas` config contains schema `pg_catalog` or `information_schema` by @taimoorzaeem in #4359
   + Now fails at startup. Prior to this, it failed with `PGRST205` on requests related to these schemas.
 

docs/postgrest.dict

@@ -15,6 +15,7 @@ BOM
 Bytea
 Cardano
 cd
+CDNs
 centric
 CLI
 CMS

docs/references/api.rst

@@ -21,6 +21,7 @@ PostgREST exposes three database objects of a schema as resources: tables, views
    api/aggregate_functions.rst
    api/openapi.rst
    api/preferences.rst
+   api/vary_header.rst
    api/*
 
 .. raw:: html

docs/references/api/vary_header.rst

@@ -0,0 +1,16 @@
+.. _vary_header:
+
+Vary Header
+===========
+
+In order to assist caching proxies and CDNs, PostgREST includes a ``Vary`` header of value
+``Accept, Prefer, Range`` in its responses which should fit most of the bills. As any other
+response header, it's available for override
+by updating ``response.headers`` GUC variable accordingly, for example:
+
+.. code-block:: postgres
+
+   -- Override the Vary header to include Accept, Prefer and X-Test-Vary headers
+   perform set_config('response.headers', '[{"Vary": "Accept, Prefer, X-Test-Vary"}]', true);
+
+In this case PostgREST will use provided value verbatim.

src/PostgREST/App.hs

@@ -60,15 +60,16 @@ import PostgREST.SchemaCache          (SchemaCache (..))
 import PostgREST.TimeIt               (timeItT)
 import PostgREST.Version              (docsVersion, prettyVersion)
 
-import qualified Data.ByteString.Char8  as BS
+import qualified Data.ByteString.Char8     as BS
-import qualified Data.List              as L
+import qualified Data.List                 as L
-import           Data.Streaming.Network (bindPortTCP,
+import           Data.Streaming.Network    (bindPortTCP,
-                                         bindRandomPortTCP)
+                                            bindRandomPortTCP)
-import qualified Data.Text              as T
+import qualified Data.Text                 as T
-import qualified Network.HTTP.Types     as HTTP
+import qualified Network.HTTP.Types        as HTTP
-import qualified Network.Socket         as NS
+import qualified Network.HTTP.Types.Header as HTTP (hVary)
-import           PostgREST.Unix         (createAndBindDomainSocket)
+import qualified Network.Socket            as NS
-import           Protolude              hiding (Handler)
+import           PostgREST.Unix            (createAndBindDomainSocket)
+import           Protolude                 hiding (Handler)
 
 type Handler = ExceptT Error
 
@@ -208,7 +209,17 @@ postgrestResponse appState conf@AppConfig{..} maybeSchemaCache authResult@AuthRe
 
   where
     toWaiResponse :: ServerTiming -> Response.PgrstResponse -> Wai.Response
-    toWaiResponse timing (Response.PgrstResponse st hdrs bod) = Wai.responseLBS st (hdrs ++ ([serverTimingHeader timing | configServerTimingEnabled])) bod
+    toWaiResponse timing (Response.PgrstResponse st hdrs bod) =
+      Wai.responseLBS st (hdrs ++ serverTimingHeaders timing ++ [varyHeader | not $ varyHeaderPresent hdrs]) bod
+
+    serverTimingHeaders :: ServerTiming -> [HTTP.Header]
+    serverTimingHeaders timing = [serverTimingHeader timing | configServerTimingEnabled]
+
+    varyHeader :: HTTP.Header
+    varyHeader = (HTTP.hVary, "Accept, Prefer, Range")
+
+    varyHeaderPresent :: [HTTP.Header] -> Bool
+    varyHeaderPresent = any (\(h, _v) -> h == HTTP.hVary)
 
     withTiming :: Handler IO a -> Handler IO (Maybe Double, a)
     withTiming f = if configServerTimingEnabled

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"