fix(langfuse_otel): read string mask flags the way the classic callback does

The langfuse_mask_input / langfuse_mask_output headers arrive as strings,
so "false" redacted the derived trace io. Parse them with str_to_bool and
fall back to truthiness, as the classic langfuse callback does

litellm/integrations/langfuse/langfuse_otel.py

@@ -16,6 +16,7 @@ from litellm.integrations.langfuse.langfuse_otel_attributes import (
 from litellm.integrations.opentelemetry import OpenTelemetry, OpenTelemetryConfig
 from litellm.litellm_core_utils.safe_json_dumps import safe_dumps
 from litellm.litellm_core_utils.safe_json_loads import safe_json_loads
+from litellm.secret_managers.main import str_to_bool
 from litellm.types.integrations.langfuse_otel import (
     LangfuseSpanAttributes,
 )
@@ -54,6 +55,12 @@ def _preset_cache_key(kwargs: Mapping[str, object]) -> object:
     return litellm.cache.get_preset_cache_key_from_kwargs(**kwargs)
 
 
+def _mask_flag(value: object) -> bool:
+    """A mask flag as the classic langfuse callback reads it: "true" / "false" strings parse, anything else by truthiness."""
+    parsed: Final = str_to_bool(value) if isinstance(value, str) else None
+    return bool(value) if parsed is None else parsed
+
+
 def _caller_tag_list(value: object) -> tuple[str, ...]:
     """Caller tags as Langfuse ingestion reads a raw tags value: a list, a JSON array string, a comma list or one tag."""
     parsed: Final = (
@@ -248,7 +255,7 @@ class LangfuseOtelLogger(OpenTelemetry):
                 safe_set_attribute(
                     span,
                     LangfuseSpanAttributes.TRACE_INPUT.value,
-                    REDACTED_BY_LITELLM if metadata.get("mask_input") else input_json,
+                    REDACTED_BY_LITELLM if _mask_flag(metadata.get("mask_input")) else input_json,
                 )
 
         output_json: Final = LangfuseOtelLogger._observation_output(response_obj)
@@ -258,7 +265,7 @@ class LangfuseOtelLogger(OpenTelemetry):
                 safe_set_attribute(
                     span,
                     LangfuseSpanAttributes.TRACE_OUTPUT.value,
-                    REDACTED_BY_LITELLM if metadata.get("mask_output") else output_json,
+                    REDACTED_BY_LITELLM if _mask_flag(metadata.get("mask_output")) else output_json,
                 )
 
     @staticmethod

tests/integration/observability/test_langfuse_otel_trace_fields.py

@@ -337,6 +337,26 @@ def test_mask_flags_redact_the_derived_trace_io(v1: Rig) -> None:
     assert attributes.get("langfuse.trace.name") == "litellm-acompletion", attributes
 
 
+@pytest.mark.parametrize(
+    ("headers", "masked"),
+    [
+        pytest.param({"langfuse_mask_input": "true", "langfuse_mask_output": "true"}, True, id="true"),
+        pytest.param({"langfuse_mask_input": "false", "langfuse_mask_output": "false"}, False, id="false"),
+    ],
+)
+def test_mask_flag_headers_parse_as_booleans(v1: Rig, headers: Mapping[str, str], masked: bool) -> None:
+    marker: Final = "lit8281-mask-header-" + uuid.uuid4().hex
+    _chat(v1, marker, headers=headers)
+    attributes: Final = v1.sink.one(marker).attributes
+    expected: Final = (
+        (REDACTED, REDACTED)
+        if masked
+        else (attributes.get("langfuse.observation.input"), attributes.get("langfuse.observation.output"))
+    )
+    assert (attributes.get("langfuse.trace.input"), attributes.get("langfuse.trace.output")) == expected, attributes
+    assert marker in str(attributes.get("langfuse.observation.input")), attributes
+
+
 @pytest.mark.parametrize(
     "tags",
     [

tests/unit/integrations/test_langfuse_otel.py

@@ -1127,6 +1127,9 @@ class TestDerivedTraceFields:
             ({"mask_input": True}, {"langfuse.trace.input"}),
             ({"mask_output": True}, {"langfuse.trace.output"}),
             ({"mask_input": True, "mask_output": True}, {"langfuse.trace.input", "langfuse.trace.output"}),
+            ({"mask_input": "true", "mask_output": "TRUE"}, {"langfuse.trace.input", "langfuse.trace.output"}),
+            ({"mask_input": "false", "mask_output": "False"}, set()),
+            ({"mask_input": False, "mask_output": None}, set()),
         ],
     )
     def test_mask_flags_redact_the_derived_trace_io(self, mask_flags, masked_trace_keys):