Fix coroutine warning in JSONEncoder

[nishkarshs1]

Fixes #3967

What changed

This updates JSONEncoder to handle objects with async json() methods more safely.

Previously, the encoder checked inspect.iscoroutinefunction(json_method) before calling .json(). In the case of starlette.requests.Request, this check did not reliably detect the async method, which caused the coroutine to be created without being awaited and produced:

RuntimeWarning: coroutine 'Request.json' was never awaited

The updated logic checks whether the returned value is a coroutine after calling the method and closes it safely before falling back to the class name.

Verification

Tested locally using a FastAPI endpoint decorated with @workflow and passing a Request object. The warning no longer appears.

Summary by CodeRabbit

• Bug Fixes
  • Improved JSON serialization robustness: safer invocation of custom serializers, better handling and cleanup of asynchronous serialization results, suppressed serialization errors with a reliable fallback to type names, and more accurate handling of dataclass instances.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7adcc934-a2b5-443d-88ff-ae3f8da663de

📥 Commits

Reviewing files that changed from the base of the PR and between 9f51f1c and 41b4bd0.

📒 Files selected for processing (1)

• packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py

🚧 Files skipped from review as they are similar to previous changes (1)

• packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py

---

📝 Walkthrough

Walkthrough

The JSONEncoder.default method is refactored to detect and safely close coroutines returned by async json() methods. Instead of guarding calls with inspect.iscoroutinefunction(), the code now invokes json() and checks the result with inspect.iscoroutine(), then closes any coroutine found. This prevents RuntimeWarning: coroutine was never awaited when serializing objects like FastAPI Request with async methods.

Changes

JSONEncoder coroutine safety

Layer / File(s)	Summary
Dataclass instance guard packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py	Dataclass serialization now applies only when dataclasses.is_dataclass(o) and not isinstance(o, type).
to_json callable lookup and invocation packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py	Lookup of to_json uses getattr(..., None) and callable() and invokes it only when callable.
json invocation, exception guard, and coroutine cleanup packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py	Lookup of json uses getattr(..., None) and callable(); json() is invoked inside try/except; after calling, inspect.iscoroutine(result) detects coroutines which are closed and cause a fallback to class-name serialization; otherwise the call result is returned.
Fallback behavior packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py	If __class__ exists return type(o).__name__; else delegate to super().default(o).

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

A rabbit hops through async streams so bright,
Where coroutines once wandered through the night,
Now caught and closed before they float away,
JSON encodes them safely, come what may! 🐰✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix coroutine warning in JSONEncoder' accurately describes the main change: addressing the coroutine warning issue in the JSONEncoder by implementing safer handling of async json() methods.
Linked Issues check	✅ Passed	The pull request directly addresses issue #3967 by modifying JSONEncoder to safely handle async json() methods, preventing the 'coroutine was never awaited' warning when @workflow decorates async FastAPI endpoints with Request parameters.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the JSONEncoder coroutine issue; the modifications to json_encoder.py directly address the linked issue with no extraneous changes.

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🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py (1)

21-34: ⚡ Quick win

Consider an iscoroutinefunction fast-path before invoking json_method().

The current "call then inspect" pattern correctly fixes the reported warning, but it always invokes the callable — even when we can cheaply determine ahead of time that it's async. For objects whose json callable has side effects on invocation (resource acquisition, logging, state mutation in __call__), this is unnecessary work. Checking inspect.iscoroutinefunction(json_method) first as a fast path, and keeping the post-call inspect.iscoroutine(result) check as a fallback, gives defense-in-depth: the fast path covers the common case, and the post-call check still catches wrapped/decorated callables that iscoroutinefunction misses (the case this PR explicitly motivates).

♻️ Proposed defense-in-depth refactor

         if callable(json_method):
+            if inspect.iscoroutinefunction(json_method):
+                return o.__class__.__name__
             try:
                 result = json_method()

                 if inspect.iscoroutine(result):
                     result.close()
                     return o.__class__.__name__

                 return result

             except Exception:
                 pass

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py` around lines 21 -
34, Add a cheap async fast-path before invoking the object's json callable: in
json_encoder.py, when you obtain json_method (the attribute on the object),
first check inspect.iscoroutinefunction(json_method) and if True, avoid calling
it and return o.__class__.__name__; keep the existing try/except and the
post-call inspect.iscoroutine(result) fallback intact so decorated/wrapped async
callables are still detected after invocation (referencing json_method, result,
and the existing exception handling).

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py`:
- Line 39: The file packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py
is missing a trailing newline (Ruff W292); add a single newline character at EOF
so the file ends with a newline, e.g., after the final line containing "return
super().default(o)" in the default(self, o) implementation of your JSONEncoder
subclass.

---

Nitpick comments:
In `@packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py`:
- Around line 21-34: Add a cheap async fast-path before invoking the object's
json callable: in json_encoder.py, when you obtain json_method (the attribute on
the object), first check inspect.iscoroutinefunction(json_method) and if True,
avoid calling it and return o.__class__.__name__; keep the existing try/except
and the post-call inspect.iscoroutine(result) fallback intact so
decorated/wrapped async callables are still detected after invocation
(referencing json_method, result, and the existing exception handling).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 8c8c43ca-7b5c-4aaf-b24b-9a63281d4ba8

📥 Commits

Reviewing files that changed from the base of the PR and between 6d3e696 and 9f51f1c.

📒 Files selected for processing (1)

• packages/traceloop-sdk/traceloop/sdk/utils/json_encoder.py

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All committers have signed the CLA.

[nishkarshs1]

@cla-bot recheck

[nishkarshs1]

Looks like this issue was already addressed in #3968 and I missed the merged PR while reading the timeline. Closing this PR