Agent Zero AI framework
Fallback when Responses mock parses SSE
Detect LiteLLM JSONDecodeError failures caused by the Responses mock streaming iterator trying to parse a real SSE stream. Fall back to Chat Completions before any output is emitted, keeping custom OpenAI-compatible proxy prefixes provider-neutral. Add a regression test for SSE-shaped JSON decode failures and update the transport DOX contract. Verified with: PYTHONPATH="/home/eclypso/a0/agent-zero" conda run -n a0 pytest tests/test_stream_tool_early_stop.py tests/test_responses_architecture.py -q; PYTHONPATH="/home/eclypso/a0/agent-zero" conda run -n a0 python -m py_compile helpers/litellm_transport.py; docker exec -i -w /a0 9c436228a4a2 /opt/venv-a0/bin/python -m py_compile helpers/litellm_transport.py; git diff --check.
Alessandro committed
Jul 1, 2026 at 17:23 UTC
038f88848d53515031b0335e0de7ed4d7d18d86b
3 files changed
+73
helpers/litellm_transport.py
+22
@@ -1715,6 +1715,8 @@ def _is_responses_not_supported_error(exc: Exception) -> bool:
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text = _exception_text(exc).lower()
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if any(marker in text for marker in ("429", "too many requests", "rate limit")):
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return False
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+ if _is_sse_json_decode_error(exc):
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+ return True
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if _is_bad_request_error(exc) and _looks_like_responses_request_rejected(text):
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return True
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if _is_server_error(exc) and _looks_like_responses_endpoint(text):
@@ -1777,6 +1779,26 @@ def _is_server_error(exc: Exception) -> bool:
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)
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+def _is_sse_json_decode_error(exc: Exception) -> bool:
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+ current: BaseException | None = exc
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+ while current is not None:
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+ if isinstance(current, json.JSONDecodeError) and _looks_like_sse_payload(
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+ current.doc
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+ ):
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+ return True
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+ current = current.__cause__ or (
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+ current.__context__ if current.__context__ is not current.__cause__ else None
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+ )
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+ return _looks_like_sse_payload(_exception_text(exc))
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+
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+
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+def _looks_like_sse_payload(text: Any) -> bool:
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+ if not isinstance(text, str):
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+ return False
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+ lowered = text.lstrip().lower()
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+ return lowered.startswith("event:") and "\ndata:" in lowered
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+
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+
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def _looks_like_responses_request_rejected(text: str) -> bool:
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if "/v1/responses" in text or "responses api" in text:
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return True
helpers/litellm_transport.py.dox.md
+1
@@ -29,6 +29,7 @@
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- Prefer Responses API when configured, but fallback to Chat Completions when the provider does not support Responses.
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- Fall back to Chat Completions when a Responses request is rejected before any output by an endpoint-specific or shape-specific Bad Request indicating the provider cannot parse Responses payloads.
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- Fall back to Chat Completions when a Responses endpoint fails before output with an endpoint-specific server error, proxy path-unavailable error, or LiteLLM proxy-extra import error.
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+- Fall back to Chat Completions when LiteLLM's Responses mock streaming path tries to JSON-decode a real SSE stream before any output.
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- Preserve Chat Completions tool calls from both non-streaming responses and streaming deltas as canonical `LLMResult` function-call items.
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- Preserve provider-state metadata when Responses API calls succeed, and fall back to local replay when provider state is unsupported.
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- Keep prompt-cache markers only for providers that accept them.
tests/test_stream_tool_early_stop.py
+50
@@ -1,3 +1,4 @@
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+import json
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import sys
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from pathlib import Path
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@@ -643,6 +644,55 @@ async def test_unified_call_falls_back_for_proxy_responses_failures(
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assert calls == ["responses", "chat"]
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+@pytest.mark.asyncio
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+async def test_unified_call_falls_back_when_responses_mock_reads_sse_as_json(
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+ monkeypatch,
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+):
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+ calls: list[str] = []
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+ sse_error = json.JSONDecodeError(
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+ "Expecting value",
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+ 'event: response.output_text.delta\ndata: {"delta":"hello"}\n\n',
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+ 0,
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+ )
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+ failing_stream = _FailingAsyncChunkStream(sse_error)
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+
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+ async def fake_aresponses(*args, **kwargs):
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+ calls.append("responses")
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+ return failing_stream
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+
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+ async def fake_acompletion(*args, **kwargs):
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+ calls.append("chat")
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+ assert kwargs["stream"] is True
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+ assert kwargs["drop_params"] is True
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+ return _AsyncChunkStream([_chunk("fallback")])
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+
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+ async def fake_rate_limiter(*args, **kwargs):
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+ return None
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+
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+ monkeypatch.setattr(litellm_transport, "aresponses", fake_aresponses)
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+ monkeypatch.setattr(litellm_transport, "acompletion", fake_acompletion)
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+ monkeypatch.setattr(models, "apply_rate_limiter", fake_rate_limiter)
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+
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+ wrapper = models.LiteLLMChatWrapper(
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+ model="omniroute/test-model",
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+ provider="openai",
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+ model_config=None,
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+ )
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+
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+ async def response_callback(chunk: str, full: str):
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+ return None
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+
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+ response, reasoning = await wrapper.unified_call(
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+ messages=[],
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+ response_callback=response_callback,
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+ )
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+
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+ assert response == "fallback"
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+ assert reasoning == ""
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+ assert calls == ["responses", "chat"]
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+ assert failing_stream.closed is True
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+
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+
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@pytest.mark.asyncio
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async def test_unified_call_falls_back_when_responses_bad_request_rejects_shape(
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monkeypatch,