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fix(langchain): do not read from streamed chunks when there are none for chat model streams (#14985)
## Description Fixes an issue where an `IndexError` would be raised trying to access a chunk that didn't exist when a streamed chat model operation did not produce any chunks - usually because of a timeout error. ## Testing Verified with the reproduction in the linked issue ## Risks None ## Additional Notes Closes #14688 (cherry picked from commit 99b19b7)
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‎ddtrace/contrib/internal/langchain/patch.py‎

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@@ -320,10 +320,13 @@ def _on_span_started(span: Span):
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integration.record_instance(instance, span)
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def _on_span_finished(span: Span, streamed_chunks):
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joined_chunks = streamed_chunks[0]
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for chunk in streamed_chunks[1:]:
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joined_chunks += chunk # base message types support __add__ for concatenation
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kwargs["_dd.identifying_params"] = instance._identifying_params
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if len(streamed_chunks):
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joined_chunks = streamed_chunks[0]
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for chunk in streamed_chunks[1:]:
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joined_chunks += chunk # base message types support __add__ for concatenation
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else:
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joined_chunks = []
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integration.llmobs_set_tags(span, args=args, kwargs=kwargs, response=joined_chunks, operation="chat")
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return shared_stream(

‎releasenotes/notes/langchain-early-stream-end-fix-af9ca6475b3aaf00.yaml‎

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---
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fixes:
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- |
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langchain: Fixes an issue where streamed responses that end before the first chunk is received would result in an ``IndexError``.

‎tests/contrib/langchain/test_langchain.py‎

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)
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calculator.invoke("2", config={"unserializable": object()})
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@pytest.mark.snapshot(ignores=["meta.error.stack", "meta.error.message"])
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def test_streamed_chat_model_with_no_output(langchain_openai, openai_url):
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from openai import APITimeoutError
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chat_model = langchain_openai.ChatOpenAI(base_url=openai_url, timeout=0.0001)
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result = chat_model.stream("Hello, my name is")
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try:
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next(result)
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except Exception as e:
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if not isinstance(e, APITimeoutError):
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assert False, f"Expected APITimeoutError, got {e}"

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