From c96dc3ee90e28f36149924d3c8facd8c8aec7603 Mon Sep 17 00:00:00 2001
From: "M. Taimoor Zaeem" <mtaimoorzaeem@gmail.com>
Date: Wed, 5 Feb 2025 11:01:11 +0500
Subject: [PATCH] fix: log 503 client error to stderr

---
 CHANGELOG.md              |  1 +
 src/PostgREST/AppState.hs |  5 +++--
 test/io/test_io.py        | 19 +++++++++++++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 62543da460..b26ed38673 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
    + Fixed `"column <json_aggregate>.<alias> does not exist"` error when selecting `?select=...table(aias:count())`
  - #3727, Clarify "listening" logs - @steve-chavez
  - #3795, Clarify `Accept: vnd.pgrst.object` error message - @steve-chavez
+ - #3841, Log `503` client error to stderr - @taimoorzaeem
 
 ### Changed
 
diff --git a/src/PostgREST/AppState.hs b/src/PostgREST/AppState.hs
index f5f0bd36ee..7974009498 100644
--- a/src/PostgREST/AppState.hs
+++ b/src/PostgREST/AppState.hs
@@ -261,8 +261,9 @@ 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
diff --git a/test/io/test_io.py b/test/io/test_io.py
index 7d06ffcaa6..ff5619fb97 100644
--- a/test/io/test_io.py
+++ b/test/io/test_io.py
@@ -1696,3 +1696,22 @@ 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)