fix(langchain): keep objects out of association properties - #4467
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Metadata values reached span attributes through str(): any non-primitive was stringified, so an object's repr became the attribute value. A model, client or config object renders its constructor state, which routinely includes an API key, and association properties are copied onto every descendant span, so one such value spread across the whole trace. This path is also not gated by TRACELOOP_TRACE_CONTENT, so turning content capture off did not suppress it. Forward plain data only. Primitives are unchanged, lists keep their primitive elements, and a mapping is kept as JSON when every value in it is serializable (json.dumps with no default, so a mapping holding an object raises and the key is dropped). Anything else sanitizes to None and the key is dropped rather than recorded as a stringified object. Documented usage is unaffected: string and numeric labels such as user_id and session_id are primitives and still populate association properties.
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📝 WalkthroughWalkthroughLangChain metadata sanitization now preserves supported scalar values, stringifies selected standard-library types, filters unsupported objects, and omits unsanitized entries from span metadata. Unit and end-to-end tests cover these behaviors. ChangesLangChain metadata sanitization
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix · Severity of issue fixed: Medium Suggested reviewers: Merge Risk: 🔵 Low · up to Affected LangChain runs with non-JSON-compatible metadata keys can lose their spans, but the trigger is narrow and localized. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
Comment |
The end-to-end test asserted the marker was absent from every span attribute, which also covered traceloop.entity.input. That path dumps the caller's whole input, metadata included, and is gated by TRACELOOP_TRACE_CONTENT -- documented content capture, not the ungated trace-wide leak this fix addresses. Assert on the association-property attributes instead: user_id still propagates, the object key is gone.
| return json.dumps(value) | ||
| except (TypeError, ValueError): | ||
| return None | ||
| return None |
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This catch-all is a silent regression for metadata types that carry no credential risk. Probed against this branch:
| value | before | after |
|---|---|---|
uuid.uuid4() |
"3f2b…" |
dropped |
datetime.now() |
"2026-09-16T…" |
dropped |
Enum.A |
"E.A" |
dropped |
Decimal("3.14") |
"3.14" |
dropped |
It also reaches the dict branch above: json.dumps has no default, so {"tenant": "acme", "sid": uuid4()} raises and the whole mapping is discarded, losing tenant because of an unrelated key. The list branch right above keeps its good elements, so the two are asymmetric.
Worth noting the history here: the str() fallback this replaces was added deliberately in bfb761f (#2608) to fix #2537, where non-primitive metadata was silently missing from spans — OTel's validator rejected the raw value and logged Invalid type ... for attribute. cc2bf14 (#2665) then tightened the list branch for OTel's homogeneous-sequence rule. Dropping instead of stringifying reinstates the original #2537 symptom, now without the warning that used to make it visible.
The leak this PR targets is real and worth closing. A narrower rule would close it without the regression: stringify known-safe stdlib scalars (UUID, datetime, Decimal, Enum, Path) and drop only genuinely arbitrary objects. That also fixes the dict case, since those values would then serialize.
Also note session_id in the PR description is only a primitive when it is a string; as a UUID, which is common, it is now dropped.
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Right. I've attended all three.
bfb761f added that str() deliberately, so a blanket drop re-opens #2537. Fixed in 6c0f9fd9: one _metadata_scalar predicate that every branch routes through, primitives pass through, UUID/datetime/Decimal/Enum/Path stringify, arbitrary objects drop. The dict branch now keeps its serializable keys and loses only the object-valued ones, so {"tenant": "acme", "sid": uuid4()} survives intact and {"tenant": "acme", "client": } keeps tenant. The session_id line in the description was wrong and I've corrected the behaviour rather than the wording.
The catch-all drop went too wide. UUID, datetime, Decimal, Enum and Path render as their own value, not as constructor state, so they carry none of the credential risk the drop exists for -- and a UUID session_id is the common case, not an edge one. Dropping them reinstated the traceloop#2537 symptom that bfb761f set out to fix, now without the "Invalid type" warning that used to make it visible. Route every branch through one predicate: primitives pass through, those stdlib scalars stringify, anything else is dropped. The dict branch keeps its serializable keys and loses only the object-valued ones, the way the list branch already did -- an unrelated key no longer discards the mapping.
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Inline comments:
In
`@packages/opentelemetry-instrumentation-langchain/opentelemetry/instrumentation/langchain/callback_handler.py`:
- Around line 154-159: Update the mapping serialization logic around
_metadata_scalar so entries are retained only when their scalar values are
JSON-serializable, excluding unsupported bytes entries before json.dumps(kept).
Preserve JSON-safe sibling values and add a regression test covering a mapping
containing both bytes and a JSON-safe value.
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bytes is a metadata primitive but not JSON-serializable, so json.dumps
raised on {"tenant": "acme", "payload": b"x"} and the except returned None,
taking the safe tenant value down with the unsupported one -- the same
sibling-discards-sibling behaviour the per-key filter was meant to end.
Filter dict values to what JSON can carry rather than catching the failure
afterwards, which makes the try/except unreachable.
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Inline comments:
In
`@packages/opentelemetry-instrumentation-langchain/opentelemetry/instrumentation/langchain/callback_handler.py`:
- Line 159: Update _sanitize_metadata_value to validate mapping keys along with
their sanitized scalar values before adding entries to kept, skipping entries
that cannot be JSON-serialized; preserve the existing final serialization and
None result for empty mappings.
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json.dumps rejects a non-string key, and this runs before tracer.start_span inside a @dont_throw caller -- so one tuple key in a metadata mapping was swallowed as a failed callback and the chain produced no span at all, not just a missing attribute. Constrain keys the way values are already constrained rather than catching the failure, which keeps the single serialization.
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_sanitize_metadata_valuepassed any non-primitive throughstr(), so an object'srepr became the span attribute value. A model, client or config object renders its
constructor state, which routinely includes an API key. Association properties are
copied onto every descendant span, so one such value spread across the whole trace —
and this path is not gated by
TRACELOOP_TRACE_CONTENT, so turning content captureForward plain data only, through a single
_metadata_scalarpredicate that everybranch routes through:
bool,str,bytes,int,float) pass through unchanged;UUID,datetime,Decimal,Enum,Path— arestringified. Their
str()renders the value itself rather than constructor state,so they carry none of the credential risk. A
session_idpassed as a UUID is thecommon case here, and dropping it would have reinstated the 🐛 Bug Report: Invalid type NoneType for attribute 'traceloop.association.properties.ls_temperature' value. #2537 symptom that
bfb761f set out to fix;
homogeneous-sequence shape cc2bf14 established;
object-valued or
byteskey no longer discards its siblings;Noneand the key is dropped rather than recordedas a stringified object.
Documented usage is unaffected:
user_idandsession_idstill populate associationproperties, whether they arrive as strings, numbers or UUIDs.
Also tick two boxes that are now true: I have added tests (tests/test_metadata_sanitization.py, 10 cases) and PR name follows conventional commits.
feat(instrumentation): ...orfix(instrumentation): ....Summary by CodeRabbit
Bug Fixes
Tests