fix: log 503 client error to stderr

CHANGELOG.md

@@ -5,6 +5,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Fixed
+
+ - #3841, Log `503` client error to stderr - @taimoorzaeem
+
 ## [12.2.7] - 2025-02-03
 
 ### Fixed

src/PostgREST/AppState.hs

@@ -265,8 +265,9 @@ usePool AppState{stateObserver=observer, stateMainThreadId=mainThreadId, ..} ses
         SQL.ServerError{} ->
           when (Error.status (Error.PgError False err) >= HTTP.status500) $
             observer $ QueryErrorCodeHighObs err
-    SQL.SessionUsageError (SQL.QueryError _ _ (SQL.ClientError _)) ->
-      pure ()
+    err@(SQL.SessionUsageError (SQL.QueryError _ _ (SQL.ClientError _))) ->
+      -- An error on the client-side, usually indicates problems wth connection
+        observer $ QueryErrorCodeHighObs err
     )
 
   return res

test/io/test_io.py

@@ -1644,3 +1644,22 @@ def test_jwt_cache_purges_expired_entries(defaultenv):
         response = postgrest.session.get("/authors_only", headers=hdrs3)
 
         assert response.status_code == 200
+
+
+def test_pgrst_log_503_client_error_to_stderr(defaultenv):
+    "PostgREST should log 503 errors to stderr"
+
+    env = {
+        **defaultenv,
+        "PGAPPNAME": "test-io",
+    }
+
+    with run(env=env) as postgrest:
+
+        postgrest.session.get("/rpc/terminate_pgrst?appname=test-io")
+
+        output = postgrest.read_stdout(nlines=6)
+
+        log_message = '{"code":"PGRST001","details":"no connection to the server\\n","hint":null,"message":"Database client error. Retrying the connection."}\n'
+
+        assert any(log_message in line for line in output)