Fix Redis caching always returning False due to unhandled string values (#7022)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ekzhu <320302+ekzhu@users.noreply.github.com>
Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>

Author: Copilot

python/packages/autogen-ext/src/autogen_ext/models/cache/_chat_completion_cache.py

@@ -223,6 +223,31 @@ def _check_cache(
                 except ValidationError:
                     # If reconstruction fails, treat as cache miss
                     return None, cache_key
+            elif isinstance(cached_result, str):
+                # Handle case where cache store returns a string (e.g., Redis with decode errors)
+                try:
+                    # Try to parse the string as JSON and reconstruct CreateResult
+                    parsed_data = json.loads(cached_result)
+                    if isinstance(parsed_data, dict):
+                        cached_result = CreateResult.model_validate(parsed_data)
+                    elif isinstance(parsed_data, list):
+                        # Handle streaming results stored as JSON string
+                        reconstructed_list_2: list[CreateResult | str] = []
+                        for item in parsed_data:  # type: ignore[reportUnknownVariableType]
+                            if isinstance(item, dict):
+                                reconstructed_list_2.append(CreateResult.model_validate(item))
+                            elif isinstance(item, str):
+                                reconstructed_list_2.append(item)
+                            else:
+                                # If item is neither dict nor str, treat as cache miss
+                                return None, cache_key
+                        cached_result = reconstructed_list_2
+                    else:
+                        # If parsed data is not dict or list, treat as cache miss
+                        return None, cache_key
+                except (json.JSONDecodeError, ValidationError):
+                    # If JSON parsing or validation fails, treat as cache miss
+                    return None, cache_key
             # If it's already the right type (CreateResult or list), return as-is
             return cached_result, cache_key
 

python/packages/autogen-ext/tests/models/test_chat_completion_cache.py

@@ -1,4 +1,5 @@
 import copy
+import json
 from typing import Any, Dict, List, Optional, Tuple, Union, cast
 
 import pytest
@@ -482,6 +483,128 @@ def test_check_cache_already_correct_type() -> None:
     assert cache_key is not None
 
 
+def test_check_cache_string_json_deserialization_success() -> None:
+    """Test _check_cache when Redis cache returns a string containing valid JSON.
+    This tests the fix for the Redis string caching issue where Redis returns
+    string data instead of dict/CreateResult, causing cache misses.
+    """
+    _, prompts, system_prompt, replay_client, _ = get_test_data()
+
+    # Create a JSON string representing a valid CreateResult
+    create_result_json = json.dumps(
+        {
+            "content": "response from string json",
+            "usage": {"prompt_tokens": 12, "completion_tokens": 6},
+            "cached": False,
+            "finish_reason": "stop",
+            "logprobs": None,
+            "thought": None,
+        }
+    )
+
+    # Mock cache store that returns the JSON string (simulating Redis behavior)
+    mock_store = MockCacheStore(return_value=cast(Any, create_result_json))
+    cached_client = ChatCompletionCache(replay_client, mock_store)
+
+    # Test _check_cache method directly
+    messages = [system_prompt, UserMessage(content=prompts[0], source="user")]
+    cached_result, cache_key = cached_client._check_cache(messages, [], None, {})  # type: ignore
+
+    # Should successfully reconstruct the CreateResult from JSON string
+    assert cached_result is not None
+    assert isinstance(cached_result, CreateResult)
+    assert cached_result.content == "response from string json"
+    assert cached_result.usage.prompt_tokens == 12
+    assert cached_result.usage.completion_tokens == 6
+    assert cache_key is not None
+
+
+def test_check_cache_string_json_list_deserialization_success() -> None:
+    """Test _check_cache when Redis cache returns a string containing valid JSON list.
+    This tests the fix for streaming results stored as JSON strings in Redis.
+    """
+    _, prompts, system_prompt, replay_client, _ = get_test_data()
+
+    # Create a JSON string representing a streaming result list
+    streaming_list_json = json.dumps(
+        [
+            "streaming chunk 1",
+            {
+                "content": "streaming response from json",
+                "usage": {"prompt_tokens": 8, "completion_tokens": 4},
+                "cached": False,
+                "finish_reason": "stop",
+                "logprobs": None,
+                "thought": None,
+            },
+            "streaming chunk 2",
+        ]
+    )
+
+    # Mock cache store that returns the JSON string (simulating Redis streaming)
+    mock_store = MockCacheStore(return_value=cast(Any, streaming_list_json))
+    cached_client = ChatCompletionCache(replay_client, mock_store)
+
+    # Test _check_cache method directly
+    messages = [system_prompt, UserMessage(content=prompts[0], source="user")]
+    cached_result, cache_key = cached_client._check_cache(messages, [], None, {})  # type: ignore
+
+    # Should successfully reconstruct the list from JSON string
+    assert cached_result is not None
+    assert isinstance(cached_result, list)
+    assert len(cached_result) == 3
+    assert cached_result[0] == "streaming chunk 1"
+    assert isinstance(cached_result[1], CreateResult)
+    assert cached_result[1].content == "streaming response from json"
+    assert cached_result[2] == "streaming chunk 2"
+    assert cache_key is not None
+
+
+def test_check_cache_string_invalid_json_failure() -> None:
+    """Test _check_cache gracefully handles invalid JSON strings.
+    This ensures the system degrades gracefully when Redis returns corrupted
+    string data that cannot be parsed as JSON.
+    """
+    _, prompts, system_prompt, replay_client, _ = get_test_data()
+
+    # Create an invalid JSON string
+    invalid_json_string = '{"content": "test", invalid json}'
+
+    # Mock cache store that returns the invalid JSON string
+    mock_store = MockCacheStore(return_value=cast(Any, invalid_json_string))
+    cached_client = ChatCompletionCache(replay_client, mock_store)
+
+    # Test _check_cache method directly
+    messages = [system_prompt, UserMessage(content=prompts[0], source="user")]
+    cached_result, cache_key = cached_client._check_cache(messages, [], None, {})  # type: ignore
+
+    # Should return None (cache miss) when JSON parsing fails
+    assert cached_result is None
+    assert cache_key is not None
+
+
+def test_check_cache_string_invalid_data_failure() -> None:
+    """Test _check_cache gracefully handles JSON strings with invalid data structure.
+    This ensures the system handles JSON that parses but doesn't represent valid CreateResult data.
+    """
+    _, prompts, system_prompt, replay_client, _ = get_test_data()
+
+    # Create a JSON string that parses but has invalid structure
+    invalid_data_json = json.dumps({"invalid_structure": "not a CreateResult"})
+
+    # Mock cache store that returns the invalid data JSON string
+    mock_store = MockCacheStore(return_value=cast(Any, invalid_data_json))
+    cached_client = ChatCompletionCache(replay_client, mock_store)
+
+    # Test _check_cache method directly
+    messages = [system_prompt, UserMessage(content=prompts[0], source="user")]
+    cached_result, cache_key = cached_client._check_cache(messages, [], None, {})  # type: ignore
+
+    # Should return None (cache miss) when validation fails
+    assert cached_result is None
+    assert cache_key is not None
+
+
 @pytest.mark.asyncio
 async def test_redis_streaming_cache_integration() -> None:
     """Integration test for Redis streaming cache scenario.