core[minor]: Add v2 implementation of astream events

libs/core/langchain_core/language_models/chat_models.py

@@ -52,7 +52,7 @@
 from langchain_core.prompt_values import ChatPromptValue, PromptValue, StringPromptValue
 from langchain_core.pydantic_v1 import Field, root_validator
 from langchain_core.runnables.config import ensure_config, run_in_executor
-from langchain_core.tracers.log_stream import LogStreamCallbackHandler
+from langchain_core.tracers._streaming import _StreamingCallbackHandler
 
 if TYPE_CHECKING:
     from langchain_core.pydantic_v1 import BaseModel
@@ -608,7 +608,7 @@ def _generate_with_cache(
                     (
                         True
                         for h in run_manager.handlers
-                        if isinstance(h, LogStreamCallbackHandler)
+                        if isinstance(h, _StreamingCallbackHandler)
                     ),
                     False,
                 )
@@ -691,7 +691,7 @@ async def _agenerate_with_cache(
                     (
                         True
                         for h in run_manager.handlers
-                        if isinstance(h, LogStreamCallbackHandler)
+                        if isinstance(h, _StreamingCallbackHandler)
                     ),
                     False,
                 )

libs/core/langchain_core/tracers/_streaming.py

@@ -0,0 +1,28 @@
+"""Internal tracers used for stream_log and astream events implementations."""
+import abc
+from typing import AsyncIterator, TypeVar
+from uuid import UUID
+
+T = TypeVar("T")
+
+
+class _StreamingCallbackHandler(abc.ABC):
+    """For internal use.
+
+    This is a common mixin that the callback handlers
+    for both astream events and astream log inherit from.
+
+    The `tap_output_aiter` method is invoked in some contexts
+    to produce callbacks for intermediate results.
+    """
+
+    @abc.abstractmethod
+    def tap_output_aiter(
+        self, run_id: UUID, output: AsyncIterator[T]
+    ) -> AsyncIterator[T]:
+        """Used for internal astream_log and astream events implementations."""
+
+
+__all__ = [
+    "_StreamingCallbackHandler",
+]