core: Tap output of sync iterators for astream_events (#21842)

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libs/core/langchain_core/runnables/base.py

@@ -1716,6 +1716,9 @@ class Runnable(Generic[Input, Output], ABC):
         """Helper method to transform an Iterator of Input values into an Iterator of
         Output values, with callbacks.
         Use this to implement `stream()` or `transform()` in Runnable subclasses."""
+        # Mixin that is used by both astream log and astream events implementation
+        from langchain_core.tracers._streaming import _StreamingCallbackHandler
+
         # tee the input so we can iterate over it twice
         input_for_tracing, input_for_transform = tee(input, 2)
         # Start the input iterator to ensure the input runnable starts before this one
@@ -1742,6 +1745,17 @@ class Runnable(Generic[Input, Output], ABC):
             context = copy_context()
             context.run(var_child_runnable_config.set, child_config)
             iterator = context.run(transformer, input_for_transform, **kwargs)  # type: ignore[arg-type]
+            if stream_handler := next(
+                (
+                    cast(_StreamingCallbackHandler, h)
+                    for h in run_manager.handlers
+                    # instance check OK here, it's a mixin
+                    if isinstance(h, _StreamingCallbackHandler)  # type: ignore[misc]
+                ),
+                None,
+            ):
+                # populates streamed_output in astream_log() output if needed
+                iterator = stream_handler.tap_output_iter(run_manager.run_id, iterator)
             try:
                 while True:
                     chunk: Output = context.run(next, iterator)  # type: ignore

libs/core/langchain_core/tracers/_streaming.py

@@ -1,6 +1,6 @@
 """Internal tracers used for stream_log and astream events implementations."""
 import abc
-from typing import AsyncIterator, TypeVar
+from typing import AsyncIterator, Iterator, TypeVar
 from uuid import UUID
 
 T = TypeVar("T")
@@ -22,6 +22,10 @@ class _StreamingCallbackHandler(abc.ABC):
     ) -> AsyncIterator[T]:
         """Used for internal astream_log and astream events implementations."""
 
+    @abc.abstractmethod
+    def tap_output_iter(self, run_id: UUID, output: Iterator[T]) -> Iterator[T]:
+        """Used for internal astream_log and astream events implementations."""
+
 
 __all__ = [
     "_StreamingCallbackHandler",

libs/core/langchain_core/tracers/event_stream.py

@@ -9,6 +9,7 @@ from typing import (
     Any,
     AsyncIterator,
     Dict,
+    Iterator,
     List,
     Optional,
     Sequence,
@@ -102,10 +103,10 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
         self.send_stream = memory_stream.get_send_stream()
         self.receive_stream = memory_stream.get_receive_stream()
 
-    async def _send(self, event: StreamEvent, event_type: str) -> None:
+    def _send(self, event: StreamEvent, event_type: str) -> None:
         """Send an event to the stream."""
         if self.root_event_filter.include_event(event, event_type):
-            await self.send_stream.send(event)
+            self.send_stream.send_nowait(event)
 
     def __aiter__(self) -> AsyncIterator[Any]:
         """Iterate over the receive stream."""
@@ -119,7 +120,26 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             run_info = self.run_map.get(run_id)
             if run_info is None:
                 raise AssertionError(f"Run ID {run_id} not found in run map.")
-            await self._send(
+            self._send(
+                {
+                    "event": f"on_{run_info['run_type']}_stream",
+                    "data": {"chunk": chunk},
+                    "run_id": str(run_id),
+                    "name": run_info["name"],
+                    "tags": run_info["tags"],
+                    "metadata": run_info["metadata"],
+                },
+                run_info["run_type"],
+            )
+            yield chunk
+
+    def tap_output_iter(self, run_id: UUID, output: Iterator[T]) -> Iterator[T]:
+        """Tap the output aiter."""
+        for chunk in output:
+            run_info = self.run_map.get(run_id)
+            if run_info is None:
+                raise AssertionError(f"Run ID {run_id} not found in run map.")
+            self._send(
                 {
                     "event": f"on_{run_info['run_type']}_stream",
                     "data": {"chunk": chunk},
@@ -155,7 +175,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             "inputs": {"messages": messages},
         }
 
-        await self._send(
+        self._send(
             {
                 "event": "on_chat_model_start",
                 "data": {
@@ -192,7 +212,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             "inputs": {"prompts": prompts},
         }
 
-        await self._send(
+        self._send(
             {
                 "event": "on_llm_start",
                 "data": {
@@ -241,7 +261,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
         else:
             raise ValueError(f"Unexpected run type: {run_info['run_type']}")
 
-        await self._send(
+        self._send(
             {
                 "event": event,
                 "data": {
@@ -295,7 +315,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
         else:
             raise ValueError(f"Unexpected run type: {run_info['run_type']}")
 
-        await self._send(
+        self._send(
             {
                 "event": event,
                 "data": {"output": output, "input": inputs_},
@@ -340,7 +360,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
 
         self.run_map[run_id] = run_info
 
-        await self._send(
+        self._send(
             {
                 "event": f"on_{run_type_}_start",
                 "data": data,
@@ -373,7 +393,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             "input": inputs,
         }
 
-        await self._send(
+        self._send(
             {
                 "event": event,
                 "data": data,
@@ -408,7 +428,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             "inputs": inputs,
         }
 
-        await self._send(
+        self._send(
             {
                 "event": "on_tool_start",
                 "data": {
@@ -432,7 +452,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             )
         inputs = run_info["inputs"]
 
-        await self._send(
+        self._send(
             {
                 "event": "on_tool_end",
                 "data": {
@@ -470,7 +490,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             "inputs": {"query": query},
         }
 
-        await self._send(
+        self._send(
             {
                 "event": "on_retriever_start",
                 "data": {
@@ -492,7 +512,7 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
         """Run when Retriever ends running."""
         run_info = self.run_map.pop(run_id)
 
-        await self._send(
+        self._send(
             {
                 "event": "on_retriever_end",
                 "data": {

libs/core/langchain_core/tracers/log_stream.py

@@ -8,6 +8,7 @@ from typing import (
     Any,
     AsyncIterator,
     Dict,
+    Iterator,
     List,
     Literal,
     Optional,
@@ -252,6 +253,25 @@ class LogStreamCallbackHandler(BaseTracer, _StreamingCallbackHandler):
 
             yield chunk
 
+    def tap_output_iter(self, run_id: UUID, output: Iterator[T]) -> Iterator[T]:
+        """Tap an output async iterator to stream its values to the log."""
+        for chunk in output:
+            # root run is handled in .astream_log()
+            if run_id != self.root_id:
+                # if we can't find the run silently ignore
+                # eg. because this run wasn't included in the log
+                if key := self._key_map_by_run_id.get(run_id):
+                    if not self.send(
+                        {
+                            "op": "add",
+                            "path": f"/logs/{key}/streamed_output/-",
+                            "value": chunk,
+                        }
+                    ):
+                        break
+
+            yield chunk
+
     def include_run(self, run: Run) -> bool:
         if run.id == self.root_id:
             return False

libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py

@@ -1650,27 +1650,22 @@ EXPECTED_EVENTS = [
 ]
 
 
-@pytest.mark.xfail(
-    reason="This test is failing due to missing functionality."
-    "Need to implement logic in _transform_stream_with_config that mimics the async "
-    "variant that uses tap_output_iter"
-)
 async def test_sync_in_async_stream_lambdas() -> None:
     """Test invoking nested runnable lambda."""
 
-    def add_one_(x: int) -> int:
+    def add_one(x: int) -> int:
         return x + 1
 
-    add_one = RunnableLambda(add_one_)
+    add_one_ = RunnableLambda(add_one)
 
-    async def add_one_proxy_(x: int, config: RunnableConfig) -> int:
+    async def add_one_proxy(x: int, config: RunnableConfig) -> int:
-        streaming = add_one.stream(x, config)
+        streaming = add_one_.stream(x, config)
         results = [result for result in streaming]
         return results[0]
 
-    add_one_proxy = RunnableLambda(add_one_proxy_)  # type: ignore
+    add_one_proxy_ = RunnableLambda(add_one_proxy)  # type: ignore
 
-    events = await _collect_events(add_one_proxy.astream_events(1, version="v2"))
+    events = await _collect_events(add_one_proxy_.astream_events(1, version="v2"))
     assert events == EXPECTED_EVENTS
 
 
@@ -1694,11 +1689,6 @@ async def test_async_in_async_stream_lambdas() -> None:
     assert events == EXPECTED_EVENTS
 
 
-@pytest.mark.xfail(
-    reason="This test is failing due to missing functionality."
-    "Need to implement logic in _transform_stream_with_config that mimics the async "
-    "variant that uses tap_output_iter"
-)
 async def test_sync_in_sync_lambdas() -> None:
     """Test invoking nested runnable lambda."""