From 96fe78f96ecb6d0a5f92a6b7e68a3b770bb25213 Mon Sep 17 00:00:00 2001 From: Kerry Lu Date: Wed, 28 Oct 2026 16:32:45 -0700 Subject: [PATCH] fix(router): reject string fallback targets at Router init (LIT-10238) (#48943) * fix(router): reject string fallback targets at Router init (LIT-10238) * fix(router): keep direct target fallback entries when rejecting string targets * test(router): set string fallbacks after init in cooldown tolerance tests --------- Co-authored-by: devin-ai-integration[bot] <158243242+devin-ai-integration[bot]@users.noreply.github.com> --- litellm/router.py | 15 +++++- .../router_utils/test_cooldown_handlers.py | 7 +-- tests/unit/test_router/test_router.py | 48 +++++++++++++++++++ 3 files changed, 63 insertions(+), 7 deletions(-) diff --git a/litellm/router.py b/litellm/router.py index 5ca09499c3b..408cb20945f 100644 --- a/litellm/router.py +++ b/litellm/router.py @@ -1370,7 +1370,7 @@ class Router: }, ] - router = Router(model_list=model_list, fallbacks=[{"azure-gpt-3.5-turbo": "openai-gpt-3.5-turbo"}]) + router = Router(model_list=model_list, fallbacks=[{"azure-gpt-3.5-turbo": ["openai-gpt-3.5-turbo"]}]) ``` """ @@ -1596,6 +1596,10 @@ class Router: if default_fallbacks is not None or litellm.default_fallbacks is not None: _fallbacks = default_fallbacks or litellm.default_fallbacks + if isinstance(_fallbacks, str): + raise TypeError( + f"default_fallbacks must be a list of model names, got '{_fallbacks}'. Use ['{_fallbacks}']" + ) if self.fallbacks is not None: self.fallbacks.append({"*": _fallbacks}) else: @@ -2839,7 +2843,7 @@ class Router: self._initialize_core_endpoints() self._initialize_specialized_endpoints() - def validate_fallbacks(self, fallback_param: list | None): + def validate_fallbacks(self, fallback_param: Sequence[Mapping[str, object]] | None): """ Validate the fallbacks parameter. """ @@ -2852,6 +2856,13 @@ class Router: raise ValueError( f"Dictionary '{fallback_dict}' must have exactly one key, but has {len(fallback_dict)} keys." ) + ((model_group, targets),) = fallback_dict.items() + if isinstance(targets, list) or check_non_standard_fallback_format(fallbacks=[fallback_dict]): + continue + raise TypeError( + f"Fallbacks for '{model_group}' must be a list of model names, got '{targets}'. " + f"Use {{'{model_group}': ['{targets}']}}" + ) def _add_encrypted_content_affinity_check(self, enable_global_affinity: bool) -> None: def _move_before_deployment_affinity( diff --git a/tests/unit/router_utils/test_cooldown_handlers.py b/tests/unit/router_utils/test_cooldown_handlers.py index 24459a5a250..2e1e3acaabb 100644 --- a/tests/unit/router_utils/test_cooldown_handlers.py +++ b/tests/unit/router_utils/test_cooldown_handlers.py @@ -3150,8 +3150,6 @@ BENCHED: Final = (litellm.Timeout, litellm.Timeout, RouterRateLimitError, Router {}, BENCHED, ), - ({"allowed_fails": 1, "fallbacks": [{"test-model": "backup-model"}]}, {}, BENCHED), - ({"allowed_fails": 1, "default_fallbacks": "backup-model"}, {}, BENCHED), ], ids=[ "allowed_fails", @@ -3160,8 +3158,6 @@ BENCHED: Final = (litellm.Timeout, litellm.Timeout, RouterRateLimitError, Router "policy_names_timeout", "allowed_fails_with_a_fallback_group", "allowed_fails_with_a_dict_fallback_target", - "allowed_fails_with_a_string_fallback_target", - "allowed_fails_with_a_string_default_fallbacks", ], ) @pytest.mark.asyncio @@ -3207,7 +3203,8 @@ async def test_router_allowed_fails_benches_a_lone_deployment_only_when_the_poli def test_has_fallback_group_reads_string_targets_and_skips_unparseable_entries( fallbacks: Sequence[Mapping[str, object]], expected: bool ) -> None: - router: Final = Router(model_list=[TIMED_OUT_DEPLOYMENT], fallbacks=list(fallbacks)) + router: Final = Router(model_list=[TIMED_OUT_DEPLOYMENT]) + router.fallbacks = list(fallbacks) assert _has_fallback_group(router, "test-model") is expected diff --git a/tests/unit/test_router/test_router.py b/tests/unit/test_router/test_router.py index 3c7a222d9a1..300c9cff6ff 100644 --- a/tests/unit/test_router/test_router.py +++ b/tests/unit/test_router/test_router.py @@ -31228,3 +31228,51 @@ async def test_anthropic_caller_rate_limit_does_not_block_other_credentials( finally: await GLOBAL_LOGGING_WORKER.flush() await client.close() + + +_FALLBACK_VALIDATION_MODEL_LIST: Final = ( + {"model_name": "gpt-4", "litellm_params": {"model": "openai/gpt-4", "api_key": "fake-key"}}, + {"model_name": "gpt-3.5", "litellm_params": {"model": "openai/gpt-3.5-turbo", "api_key": "fake-key"}}, +) + + +@pytest.mark.parametrize( + ("router_kwargs", "expected_message"), + [ + ({"fallbacks": [{"gpt-4": "gpt-3.5"}]}, "Fallbacks for 'gpt-4' must be a list of model names, got 'gpt-3.5'"), + ({"default_fallbacks": "gpt-3.5"}, "default_fallbacks must be a list of model names, got 'gpt-3.5'"), + ( + {"content_policy_fallbacks": [{"gpt-4": "gpt-3.5"}]}, + "Fallbacks for 'gpt-4' must be a list of model names, got 'gpt-3.5'", + ), + ], + ids=["string_fallback_target", "string_default_fallbacks", "string_content_policy_fallback_target"], +) +def test_router_rejects_a_string_fallback_target_at_init( + router_kwargs: Mapping[str, object], expected_message: str +) -> None: + with pytest.raises(TypeError, match="must be a list of model names") as excinfo: + Router(model_list=list(_FALLBACK_VALIDATION_MODEL_LIST), **router_kwargs) + + assert expected_message in str(excinfo.value) + + +@pytest.mark.parametrize( + ("router_kwargs", "expected_fallbacks"), + [ + ({"fallbacks": [{"gpt-4": ["gpt-3.5"]}]}, [{"gpt-4": ["gpt-3.5"]}]), + ({"default_fallbacks": ["gpt-3.5"]}, [{"*": ["gpt-3.5"]}]), + ( + {"fallbacks": [{"gpt-4": [{"model": "gpt-3.5", "api_key": "other-key"}]}]}, + [{"gpt-4": [{"model": "gpt-3.5", "api_key": "other-key"}]}], + ), + ({"fallbacks": [{"model": "gpt-3.5"}]}, [{"model": "gpt-3.5"}]), + ], + ids=["list_fallback_target", "list_default_fallbacks", "dict_override_fallback_target", "direct_target_entry"], +) +def test_router_keeps_supported_fallback_shapes( + router_kwargs: Mapping[str, object], expected_fallbacks: list[dict[str, object]] +) -> None: + router: Final = Router(model_list=list(_FALLBACK_VALIDATION_MODEL_LIST), **router_kwargs) + + assert router.fallbacks == expected_fallbacks