From 9a1eac78acfa327a5f27d49b3ea1c47264362941 Mon Sep 17 00:00:00 2001
From: Emanuel <emanuelsdsj@gmail.com>
Date: Thu, 30 Apr 2026 14:30:53 -0300
Subject: [PATCH] Retry on HTTP 200 with empty response body

When Trino returns HTTP 200 with an empty body under load, the
client was crashing with a bare JSONDecodeError. Treat this as
a transient condition and retry using the existing backoff
mechanism, consistent with how 429/502/503/504 are handled.
If retries are exhausted, raise TrinoConnectionError with a
descriptive message.

Fixes #596
---
 tests/unit/test_client.py | 26 ++++++++++++++++++++++++++
 trino/client.py           |  7 +++++++
 2 files changed, 33 insertions(+)

diff --git a/tests/unit/test_client.py b/tests/unit/test_client.py
index f011a54d..07b5b68d 100644
--- a/tests/unit/test_client.py
+++ b/tests/unit/test_client.py
@@ -1094,6 +1094,32 @@ def test_429_error_retry(monkeypatch):
     assert post_retry.retry_count == 3
 
 
+def test_empty_200_response_retry(monkeypatch):
+    http_resp = TrinoRequest.http.Response()
+    http_resp.status_code = 200
+    http_resp._content = b""
+
+    post_retry = RetryRecorder(result=http_resp)
+    monkeypatch.setattr(TrinoRequest.http.Session, "post", post_retry)
+
+    get_retry = RetryRecorder(result=http_resp)
+    monkeypatch.setattr(TrinoRequest.http.Session, "get", get_retry)
+
+    attempts = 3
+    req = TrinoRequest(
+        host="coordinator",
+        port=8080,
+        client_session=ClientSession(user="test"),
+        max_attempts=attempts,
+    )
+
+    req.post("SELECT 1")
+    assert post_retry.retry_count == attempts
+
+    req.get("URL")
+    assert get_retry.retry_count == attempts
+
+
 @pytest.mark.parametrize("status_code", [
     501
 ])
diff --git a/trino/client.py b/trino/client.py
index 97ef11ae..adf53766 100644
--- a/trino/client.py
+++ b/trino/client.py
@@ -641,6 +641,9 @@ def max_attempts(self, value: int) -> None:
                 # need retry when there is no exception but the status code is 429, 502, 503, or 504
                 lambda response: getattr(response, "status_code", None)
                 in (429, 502, 503, 504),
+                # need retry when the server returns 200 with an empty body (transient under load)
+                lambda response: getattr(response, "status_code", None) == 200
+                and not getattr(response, "text", "").strip(),
             ),
             max_attempts=self._max_attempts,
         )
@@ -723,6 +726,10 @@ def process(self, http_response: Response) -> TrinoStatus:
             self.raise_response_error(http_response)
 
         http_response.encoding = "utf-8"
+        if not http_response.text.strip():
+            raise exceptions.TrinoConnectionError(
+                "received empty response from server (status 200)"
+            )
         response = json.loads(http_response.text)
         if "error" in response and response["error"]:
             raise self._process_error(response["error"], response.get("id"))