feat: force read-write for listener connection

CHANGELOG.md

@@ -39,6 +39,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #3478, Media Types are parsed case insensitively - @develop7
  - #3533, #3536, Fix listener silently failing on read replica - @steve-chavez
     + If the LISTEN connection fails, it's retried with exponential backoff
+ - #3414, Force listener to connect to read-write instances using `target_session_attrs` - @steve-chavez
 
 ### Deprecated
 

src/PostgREST/AppState.hs

@@ -64,6 +64,7 @@ import Data.Time.Clock    (UTCTime, getCurrentTime)
 
 import PostgREST.Config                  (AppConfig (..),
                                           addFallbackAppName,
+                                          addTargetSessionAttrs,
                                           readAppConfig)
 import PostgREST.Config.Database         (queryDbSettings,
                                           queryPgVersion,
@@ -560,7 +561,7 @@ retryingListen appState@AppState{stateObserver=observer, stateMainThreadId=mainT
       let delay = fromMaybe 0 rsPreviousDelay `div` oneSecondInUs in
       observer $ DBListenRetry delay
 
-    connection <- acquire $ toUtf8 (addFallbackAppName prettyVersion configDbUri)
+    connection <- acquire $ toUtf8 (addTargetSessionAttrs $ addFallbackAppName prettyVersion configDbUri)
     case connection of
       Right conn -> do
 

src/PostgREST/Config.hs

@@ -25,6 +25,7 @@ module PostgREST.Config
   , toURI
   , parseSecret
   , addFallbackAppName
+  , addTargetSessionAttrs
   ) where
 
 import qualified Crypto.JOSE.Types      as JOSE
@@ -480,6 +481,18 @@ readPGRSTEnvironment :: IO Environment
 readPGRSTEnvironment =
   M.map T.pack . M.fromList . filter (isPrefixOf "PGRST_" . fst) <$> getEnvironment
 
+data PGConnString = PGURI | PGKeyVal
+
+-- Uses same logic as libpq recognized_connection_string
+-- https://github.com/postgres/postgres/blob/5eafacd2797dc0b04a0bde25fbf26bf79903e7c2/src/interfaces/libpq/fe-connect.c#L5923-L5936
+pgConnString :: Text -> Maybe PGConnString
+pgConnString conn | uriDesignator `T.isPrefixOf` conn || shortUriDesignator `T.isPrefixOf` conn = Just PGURI
+                  | "=" `T.isInfixOf` conn                                                      = Just PGKeyVal
+                  | otherwise                                                                   = Nothing
+  where
+    uriDesignator = "postgresql://"
+    shortUriDesignator = "postgres://"
+
 -- | Adds a `fallback_application_name` value to the connection string. This allows querying the PostgREST version on pg_stat_activity.
 --
 -- >>> let ver = "11.1.0 (5a04ec7)"::ByteString
@@ -519,7 +532,32 @@ readPGRSTEnvironment =
 -- addFallbackAppName ver "postgresql:///postgres?host=/run/user/1000/postgrest/postgrest-with-postgresql-16-BuR/socket&user=some_protected_user&password=invalid_pass"
 -- "postgresql:///postgres?host=/run/user/1000/postgrest/postgrest-with-postgresql-16-BuR/socket&user=some_protected_user&password=invalid_pass&fallback_application_name=PostgREST%2011.1.0%20%285a04ec7%29"
 addFallbackAppName :: ByteString -> Text -> Text
-addFallbackAppName version dbUri = dbUri <>
+addFallbackAppName version dbUri = addConnStringOption dbUri "fallback_application_name" pgrstVer
+  where
+    pgrstVer = "PostgREST " <> T.decodeUtf8 version
+
+-- | Adds `target_session_attrs=read-write` to the connection string. This allows using PostgREST listener when multiple hosts are specified in the connection string.
+--
+-- >>> addTargetSessionAttrs "postgres:///postgres?host=/dir/0kN/socket_replica_24378,/dir/0kN/socket"
+-- "postgres:///postgres?host=/dir/0kN/socket_replica_24378,/dir/0kN/socket&target_session_attrs=read-write"
+--
+-- >>> addTargetSessionAttrs "postgresql://host1:123,host2:456/somedb"
+-- "postgresql://host1:123,host2:456/somedb?target_session_attrs=read-write"
+--
+-- >>> addTargetSessionAttrs "postgresql://host1:123,host2:456/somedb?fallback_application_name=foo"
+-- "postgresql://host1:123,host2:456/somedb?fallback_application_name=foo&target_session_attrs=read-write"
+--
+-- adds target_session_attrs despite one existing
+-- >>> addTargetSessionAttrs "postgresql://host1:123,host2:456/somedb?target_session_attrs=read-only"
+-- "postgresql://host1:123,host2:456/somedb?target_session_attrs=read-only&target_session_attrs=read-write"
+--
+-- >>> addTargetSessionAttrs "host=localhost port=5432 dbname=postgres"
+-- "host=localhost port=5432 dbname=postgres target_session_attrs='read-write'"
+addTargetSessionAttrs :: Text -> Text
+addTargetSessionAttrs dbUri = addConnStringOption dbUri "target_session_attrs" "read-write"
+
+addConnStringOption :: Text -> Text -> Text -> Text
+addConnStringOption dbUri key val = dbUri <>
   case pgConnString dbUri of
     Nothing  -> mempty
     Just PGKeyVal -> " " <> keyValFmt
@@ -528,20 +566,6 @@ addFallbackAppName version dbUri = dbUri <>
       (_, "?") -> uriFmt
       (_, _)   -> "&" <> uriFmt
   where
-    uriFmt = pKeyWord <> toS (escapeURIString isUnescapedInURIComponent $ toS pgrstVer)
-    keyValFmt = pKeyWord <> "'" <> T.replace "'" "\\'" pgrstVer <> "'"
-    pKeyWord = "fallback_application_name="
-    pgrstVer = "PostgREST " <> T.decodeUtf8 version
+    uriFmt = key <> "=" <> toS (escapeURIString isUnescapedInURIComponent $ toS val)
+    keyValFmt = key <> "=" <> "'" <> T.replace "'" "\\'" val <> "'"
     lookAtOptions x =  T.breakOn "?" . snd $ T.breakOnEnd "@" x -- start from after `@` to not mess passwords that include `?`, see https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING-URIS
-
-data PGConnString = PGURI | PGKeyVal
-
--- Uses same logic as libpq recognized_connection_string
--- https://github.com/postgres/postgres/blob/5eafacd2797dc0b04a0bde25fbf26bf79903e7c2/src/interfaces/libpq/fe-connect.c#L5923-L5936
-pgConnString :: Text -> Maybe PGConnString
-pgConnString conn | uriDesignator `T.isPrefixOf` conn || shortUriDesignator `T.isPrefixOf` conn = Just PGURI
-                  | "=" `T.isInfixOf` conn                                                      = Just PGKeyVal
-                  | otherwise                                                                   = Nothing
-  where
-    uriDesignator = "postgresql://"
-    shortUriDesignator = "postgres://"

test/io/config.py

@@ -60,7 +60,7 @@ def replicaenv(defaultenv):
         "replica": {
             **defaultenv,
             **conf,
-            "PGHOST": os.environ["PGREPLICAHOST"],
+            "PGHOST": os.environ["PGREPLICAHOST"] + "," + os.environ["PGHOST"],
             "PGREPLICASLOT": os.environ["PGREPLICASLOT"],
         },
     }

test/io/test_replica.py

@@ -20,12 +20,7 @@ def test_sanity_replica(replicaenv):
         response = postgrest.session.get("/items?select=count")
         assert response.text == '[{"count":10}]'
 
-    working_replica_env = {
-        **replicaenv["replica"],
-        "PGRST_DB_CHANNEL_ENABLED": "false",  # LISTEN doesn't work on read replicas
-    }
-
-    with run(env=working_replica_env) as postgrest:
+    with run(env=replicaenv["replica"]) as postgrest:
         response = postgrest.session.get("/rpc/is_replica")
         assert response.text == "true"