Fix can_parse_as_json (#5177)

Signed-off-by: harupy <17039389+harupy@users.noreply.github.com>

mlflow/utils/rest_utils.py

@@ -147,10 +147,9 @@ def http_request(
         raise MlflowException("API request to %s failed with exception %s" % (url, e))
 
 
-def _can_parse_as_json(string):
+def _can_parse_as_json_object(string):
     try:
-        json.loads(string)
-        return True
+        return isinstance(json.loads(string), dict)
     except Exception:
         return False
 
@@ -166,7 +165,7 @@ def http_request_safe(host_creds, endpoint, method, **kwargs):
 def verify_rest_response(response, endpoint):
     """Verify the return code and format, raise exception if the request was not successful."""
     if response.status_code != 200:
-        if _can_parse_as_json(response.text):
+        if _can_parse_as_json_object(response.text):
             raise RestException(json.loads(response.text))
         else:
             base_msg = "API request to endpoint %s failed with error code " "%s != 200" % (
@@ -177,7 +176,7 @@ def verify_rest_response(response, endpoint):
 
     # Skip validation for endpoints (e.g. DBFS file-download API) which may return a non-JSON
     # response
-    if endpoint.startswith(_REST_API_PATH_PREFIX) and not _can_parse_as_json(response.text):
+    if endpoint.startswith(_REST_API_PATH_PREFIX) and not _can_parse_as_json_object(response.text):
         base_msg = (
             "API request to endpoint was successful but the response body was not "
             "in a valid JSON format"

tests/utils/test_rest_utils.py

@@ -13,6 +13,7 @@
     _DEFAULT_HEADERS,
     call_endpoint,
     call_endpoints,
+    _can_parse_as_json_object,
 )
 from mlflow.protos.service_pb2 import GetRun
 from mlflow.protos.databricks_pb2 import ENDPOINT_NOT_FOUND, ErrorCode
@@ -312,3 +313,12 @@ def test_numpy_encoder_fail():
     with pytest.raises(TypeError, match="not JSON serializable"):
         ne = NumpyEncoder()
         ne.default(test_number)
+
+
+def test_can_parse_as_json_object():
+    assert _can_parse_as_json_object("{}")
+    assert _can_parse_as_json_object('{"a": "b"}')
+    assert _can_parse_as_json_object('{"a": {"b": "c"}}')
+    assert not _can_parse_as_json_object("[0, 1, 2]")
+    assert not _can_parse_as_json_object('"abc"')
+    assert not _can_parse_as_json_object("123")