fix: add send object serialization support (#122) (#123)

* fix: Add Send object serialization support 

Fixes the serialization issue with langgraph.types.Send objects
reported in issue #94. Previously, Send objects were not being correctly
serialized and deserialized, which caused them to be returned as plain
dictionaries after a roundtrip. This led to `isinstance(packet, Send)`
checks failing in LangGraph's `prepare_single_task` function, resulting
in tasks not being added when handling interrupts.

Changes:
- Added Send object serialization in JsonPlusRedisSerializer._default_handler
  with a `__send__` type marker (similar to Interrupt handling)
- Added Send object preprocessing in _preprocess_interrupts method
- Added Send object deserialization in _revive_if_needed method
- Added Send object deserialization in base.py's _recursive_deserialize method
- Added comprehensive test suite (tests/test_send_serialization.py) with 6 tests
  covering various Send object scenarios

The fix ensures that Send objects maintain their type identity throughout
the serialization/deserialization cycle, allowing interrupt handling to
work correctly.

Resolves: #94

* release: bump version for 0.2.1 release

Author: bsbodden

langgraph/checkpoint/redis/base.py

@@ -394,6 +394,25 @@ def _recursive_deserialize(self, obj: Any) -> Any:
                 # Decode base64-encoded bytes
                 return self._decode_blob(obj["__bytes__"])
 
+            # Check if this is a Send object marker (issue #94)
+            if (
+                obj.get("__send__") is True
+                and "node" in obj
+                and "arg" in obj
+                and len(obj) == 3
+            ):
+                try:
+                    from langgraph.types import Send
+
+                    return Send(
+                        node=obj["node"],
+                        arg=self._recursive_deserialize(obj["arg"]),
+                    )
+                except (ImportError, TypeError, ValueError) as e:
+                    logger.debug(
+                        "Failed to deserialize Send object: %s", e, exc_info=True
+                    )
+
             # Check if this is a LangChain serialized object
             if obj.get("lc") in (1, 2) and obj.get("type") == "constructor":
                 try:

langgraph/checkpoint/redis/jsonplus_redis.py

@@ -48,6 +48,16 @@ def _default_handler(self, obj: Any) -> Any:
                 "id": obj.id,
             }
 
+        # Handle Send objects with a type marker (issue #94)
+        from langgraph.types import Send
+
+        if isinstance(obj, Send):
+            return {
+                "__send__": True,
+                "node": obj.node,
+                "arg": obj.arg,
+            }
+
         # Try to encode using parent's constructor args encoder
         # This creates the {"lc": 2, "type": "constructor", ...} format
         try:
@@ -69,14 +79,14 @@ def _default_handler(self, obj: Any) -> Any:
             raise TypeError(f"Object of type {type(obj)} is not JSON serializable")
 
     def _preprocess_interrupts(self, obj: Any) -> Any:
-        """Recursively add type markers to Interrupt objects before serialization.
+        """Recursively add type markers to Interrupt and Send objects before serialization.
 
         This prevents false positives where user data with {value, id} fields
         could be incorrectly deserialized as Interrupt objects.
 
         Also handles dataclass instances to preserve type information during serialization.
         """
-        from langgraph.types import Interrupt
+        from langgraph.types import Interrupt, Send
 
         if isinstance(obj, Interrupt):
             # Add type marker to distinguish from plain dicts
@@ -85,6 +95,13 @@ def _preprocess_interrupts(self, obj: Any) -> Any:
                 "value": self._preprocess_interrupts(obj.value),
                 "id": obj.id,
             }
+        elif isinstance(obj, Send):
+            # Add type marker to distinguish from plain dicts (issue #94)
+            return {
+                "__send__": True,
+                "node": obj.node,
+                "arg": self._preprocess_interrupts(obj.arg),
+            }
         elif isinstance(obj, set):
             # Handle sets by converting to list for JSON serialization
             # Will be reconstructed back to set on deserialization
@@ -277,6 +294,28 @@ def _revive_if_needed(self, obj: Any) -> Any:
                         "Failed to deserialize Interrupt object: %s", e, exc_info=True
                     )
 
+            # Check if this is a serialized Send object with type marker (issue #94)
+            # Send objects serialize to {"__send__": True, "node": ..., "arg": ...}
+            if (
+                obj.get("__send__") is True
+                and "node" in obj
+                and "arg" in obj
+                and len(obj) == 3
+            ):
+                # Try to reconstruct as a Send object
+                try:
+                    from langgraph.types import Send
+
+                    return Send(
+                        node=obj["node"],
+                        arg=self._revive_if_needed(obj["arg"]),
+                    )
+                except (ImportError, TypeError, ValueError) as e:
+                    # If we can't import or construct Send, log and fall through
+                    logger.debug(
+                        "Failed to deserialize Send object: %s", e, exc_info=True
+                    )
+
             # Recursively process nested dicts
             return {k: self._revive_if_needed(v) for k, v in obj.items()}
         elif isinstance(obj, list):

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "langgraph-checkpoint-redis"
-version = "0.2.0"
+version = "0.2.1"
 description = "Redis implementation of the LangGraph agent checkpoint saver and store."
 authors = ["Redis Inc. <applied.ai@redis.com>", "Brian Sam-Bodden <bsb@redis.io>"]
 license = "MIT"

tests/test_send_serialization.py

@@ -0,0 +1,195 @@
+"""Test Send object serialization fix for issue #94.
+
+This test validates that langgraph.types.Send objects are properly serialized
+and deserialized by the JsonPlusRedisSerializer.
+
+Before the fix, Send objects were not serialized correctly, which led to issues
+with handling Interrupts - namely the user's response would not be treated as
+the response to the Interrupt.
+
+The issue occurs in `prepare_single_task` in pregel._algo.py where:
+```
+if not isinstance(packet, Send):
+    logger.warning(
+        f"Ignoring invalid packet type {type(packet)} in pending sends"
+    )
+    return.          <<<<< task not added
+```
+
+The fix adds custom serialization/deserialization for Send objects similar to
+how Interrupt objects are handled.
+"""
+
+import pytest
+from langgraph.types import Send
+
+from langgraph.checkpoint.redis.jsonplus_redis import JsonPlusRedisSerializer
+
+
+def test_send_object_serialization():
+    """Test that Send objects are properly serialized and deserialized.
+
+    Before the fix, Send objects would not serialize correctly, causing
+    isinstance(packet, Send) checks to fail after deserialization.
+    """
+    serializer = JsonPlusRedisSerializer()
+
+    # Create a Send object
+    send_obj = Send(node="my_node", arg={"key": "value"})
+
+    # Serialize
+    type_str, blob = serializer.dumps_typed(send_obj)
+    assert type_str == "json"
+    assert isinstance(blob, bytes)
+
+    # Deserialize
+    deserialized = serializer.loads_typed((type_str, blob))
+
+    # Critical check: the deserialized object must be an instance of Send
+    assert isinstance(deserialized, Send), (
+        f"Expected Send instance, got {type(deserialized)}. "
+        "This will cause isinstance(packet, Send) checks to fail!"
+    )
+    assert deserialized.node == "my_node"
+    assert deserialized.arg == {"key": "value"}
+    assert deserialized == send_obj
+
+
+def test_send_object_in_pending_sends_list():
+    """Test that Send objects in pending_sends lists are properly handled.
+
+    This simulates the scenario where Send objects are stored in checkpoint
+    pending_sends and must be correctly deserialized for interrupt handling.
+    """
+    serializer = JsonPlusRedisSerializer()
+
+    # Create multiple Send objects as they would appear in pending_sends
+    pending_sends = [
+        Send(node="node1", arg={"data": "first"}),
+        Send(node="node2", arg={"data": "second"}),
+        Send(node="node3", arg={"data": "third"}),
+    ]
+
+    # Serialize the list
+    type_str, blob = serializer.dumps_typed(pending_sends)
+
+    # Deserialize
+    deserialized = serializer.loads_typed((type_str, blob))
+
+    # Verify all items are still Send instances
+    assert isinstance(deserialized, list)
+    assert len(deserialized) == 3
+
+    for i, send_obj in enumerate(deserialized):
+        assert isinstance(
+            send_obj, Send
+        ), f"Item {i} is not a Send instance: {type(send_obj)}"
+
+    assert deserialized[0].node == "node1"
+    assert deserialized[1].node == "node2"
+    assert deserialized[2].node == "node3"
+
+
+def test_send_object_with_complex_args():
+    """Test Send objects with complex nested arguments."""
+    serializer = JsonPlusRedisSerializer()
+
+    # Create Send with complex nested arg
+    complex_arg = {
+        "messages": ["msg1", "msg2"],
+        "metadata": {
+            "step": 1,
+            "config": {
+                "model": "gpt-4",
+                "temperature": 0.7,
+            },
+        },
+        "nested_list": [
+            {"a": 1, "b": 2},
+            {"c": 3, "d": 4},
+        ],
+    }
+
+    send_obj = Send(node="processor", arg=complex_arg)
+
+    # Serialize and deserialize
+    type_str, blob = serializer.dumps_typed(send_obj)
+    deserialized = serializer.loads_typed((type_str, blob))
+
+    # Verify type and structure
+    assert isinstance(deserialized, Send)
+    assert deserialized.node == "processor"
+    assert deserialized.arg == complex_arg
+    assert deserialized.arg["metadata"]["config"]["model"] == "gpt-4"
+
+
+def test_send_object_in_checkpoint_structure():
+    """Test Send objects embedded in checkpoint-like structures.
+
+    This simulates how Send objects appear in actual checkpoint data.
+    """
+    serializer = JsonPlusRedisSerializer()
+
+    # Simulate checkpoint structure with pending_sends
+    checkpoint_data = {
+        "v": 1,
+        "id": "checkpoint_1",
+        "pending_sends": [
+            Send(node="task1", arg={"task_data": "A"}),
+            Send(node="task2", arg={"task_data": "B"}),
+        ],
+        "channel_values": {"messages": ["msg1", "msg2"]},
+    }
+
+    # Serialize and deserialize
+    type_str, blob = serializer.dumps_typed(checkpoint_data)
+    deserialized = serializer.loads_typed((type_str, blob))
+
+    # Verify Send objects are preserved correctly
+    assert "pending_sends" in deserialized
+    assert len(deserialized["pending_sends"]) == 2
+
+    for send_obj in deserialized["pending_sends"]:
+        assert isinstance(
+            send_obj, Send
+        ), f"pending_sends contains non-Send object: {type(send_obj)}"
+
+
+def test_send_object_equality_after_roundtrip():
+    """Test that Send objects maintain equality after serialization roundtrip."""
+    serializer = JsonPlusRedisSerializer()
+
+    send1 = Send(node="test_node", arg={"value": 42})
+
+    # Serialize and deserialize
+    type_str, blob = serializer.dumps_typed(send1)
+    send2 = serializer.loads_typed((type_str, blob))
+
+    # Send objects should be equal
+    assert send1 == send2
+
+    # Test hash equality with hashable args
+    send_hashable1 = Send(node="test", arg="hashable_string")
+    type_str, blob = serializer.dumps_typed(send_hashable1)
+    send_hashable2 = serializer.loads_typed((type_str, blob))
+    assert hash(send_hashable1) == hash(send_hashable2)
+
+
+def test_send_object_with_none_arg():
+    """Test Send object with None as argument."""
+    serializer = JsonPlusRedisSerializer()
+
+    send_obj = Send(node="null_handler", arg=None)
+
+    # Serialize and deserialize
+    type_str, blob = serializer.dumps_typed(send_obj)
+    deserialized = serializer.loads_typed((type_str, blob))
+
+    assert isinstance(deserialized, Send)
+    assert deserialized.node == "null_handler"
+    assert deserialized.arg is None
+
+
+if __name__ == "__main__":
+    # Run tests
+    pytest.main([__file__, "-v"])