[FIX] Show malformed XML response details

openml/_api/clients/http.py

@@ -453,14 +453,17 @@ def _validate_response(
             code, message = self._parse_exception_response(response)
 
         except (requests.exceptions.JSONDecodeError, xml.parsers.expat.ExpatError) as e:
+            extra = f"Status code: {response.status_code}\n{response.text}"
+            parse_error = OpenMLServerError(
+                f"Unexpected server error when calling {url}. Please contact the "
+                f"developers!\n{extra}"
+            )
+
             if method != "GET":
-                extra = f"Status code: {response.status_code}\n{response.text}"
-                raise OpenMLServerError(
-                    f"Unexpected server error when calling {url}. Please contact the "
-                    f"developers!\n{extra}"
-                ) from e
+                raise parse_error from e
 
-            exception = e
+            parse_error.__cause__ = e
+            exception = parse_error
 
         except Exception as e:
             # If we failed to parse it out,

tests/test_api/test_http.py

@@ -6,7 +6,7 @@
 from pathlib import Path
 from urllib.parse import urljoin, urlparse
 from openml.enums import APIVersion
-from openml.exceptions import OpenMLAuthenticationError
+from openml.exceptions import OpenMLAuthenticationError, OpenMLServerError
 from openml._api import HTTPClient, HTTPCache
 import openml
 
@@ -160,10 +160,31 @@ def test_get_with_api_key(http_client, sample_path, test_apikey_v1):
 
 @pytest.mark.test_server()
 def test_get_without_api_key_raises(http_client):
-    with openml.config.overwrite_config_context({"apikey": None}), pytest.raises(OpenMLAuthenticationError):
+    with openml.config.overwrite_config_context({"apikey": None}), pytest.raises(
+        OpenMLAuthenticationError
+    ):
         http_client.get("task/1", use_api_key=True)
 
 
+def test_get_with_invalid_error_xml_shows_response(http_client, sample_url_v1):
+    response = Response()
+    response.status_code = 500
+    response._content = b"<invalid"
+    response.headers = {"Content-Type": "text/xml", "Content-Encoding": "gzip"}
+
+    with (
+        openml.config.overwrite_config_context({"connection_n_retries": 1}),
+        patch.object(Session, "request", return_value=response),
+        pytest.raises(OpenMLServerError) as exc_info,
+    ):
+        http_client.get("task/1")
+
+    assert str(exc_info.value) == (
+        f"Unexpected server error when calling {sample_url_v1}. Please contact the developers!\n"
+        "Status code: 500\n<invalid"
+    )
+
+
 @pytest.mark.test_server()
 def test_download_creates_file(http_client, sample_download_url_v1):
     dummy_content = b"this is dummy content"