fix(tracing): handle exceptions raised within traces_sampler and other callbacks by ericapisani · Pull Request #6853 · getsentry/sentry-python

ericapisani · 2026-07-20T18:57:10Z

When a user-provided traces_sampler callback raises, catch the exception,
log a warning, and fall back to the parent sample rate or the configured
traces_sample_rate instead of propagating the error.

Wrap the before_send callback invocation in capture_internal_exceptions()
so that exceptions raised by user-provided before_send_log,
before_send_metric, and before_send_span callbacks do not crash the
application. When a callback raises, the original, unmodified telemetry
item is sent.

Fixes PY-2617
Fixes #6850

When a user-provided traces_sampler callback raises, catch the exception, log a warning, and fall back to the parent sample rate or the configured traces_sample_rate instead of propagating the error. Refs PY-2617 Refs #6849

Wrap the before_send callback invocation in capture_internal_exceptions() so that exceptions raised by user-provided before_send_log, before_send_metric, and before_send_span callbacks do not crash the application. When a callback raises, the original, unmodified telemetry item is sent. Refs PY-2617 Refs #6849

linear-code · 2026-07-20T18:57:14Z

PY-2617

github-actions · 2026-07-20T19:07:03Z

Codecov Results 📊

✅ 92197 passed | ⏭️ 6304 skipped | Total: 98501 | Pass Rate: 93.6% | Execution Time: 323m 36s

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2475 uncovered lines.
✅ Project coverage is 89.7%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.68%    89.70%    +0.02%
==========================================
  Files          193       193         —
  Lines        24007     24028       +21
  Branches      8342      8346        +4
==========================================
+ Hits         21529     21553       +24
- Misses        2478      2475        -3
- Partials      1387      1384        -3

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alexander-alderman-webb

Nice !

sentrivana

Looks good, just a couple places where the behavior or tests need some tweaking.

Re: dropping/keeping the metrics/logs/spans that went through a faulty before_send_*: might need more alignment on this. Spans likely shouldn't be dropped, but metrics and logs we might want to drop. There's a convo on slack about this.

sentrivana · 2026-07-21T08:04:57Z

-                sample_rate = propagation_context.parent_sampled
-        else:
-            sample_rate = client.options["traces_sample_rate"]
+        sample_rate = _get_fallback_sample_rate(


I'd change the name of the helper function since in the context of this else branch, it's not really a fallback.

Maybe something like _get_effective_sample_rate?

sentrivana · 2026-07-21T08:17:20Z

+    # parent said "don't sample", but its propagated sample rate of 0.75
+    # combined with sample_rand 0.5 should win over both the flag and
+    # traces_sample_rate=0.0


This is actually not correct. If the parent sample decision is 0, that should take precedence over anything else.

Can we remove this test? I think I know where this needs fixing (it's not something you've introduced in this PR), and I can follow up with a fix after we've merged this. (I expect some other tests to break so don't want to tack this onto your PR.)

sentrivana · 2026-07-21T08:18:13Z

+        _experiments={
+            "trace_lifecycle": "stream",
+        },


Suggested change

_experiments={

"trace_lifecycle": "stream",

},

trace_lifecycle="stream",

sentrivana · 2026-07-21T08:18:31Z

+        _experiments={
+            "trace_lifecycle": "stream",
+        },


Suggested change

_experiments={

"trace_lifecycle": "stream",

},

trace_lifecycle="stream",

sentrivana · 2026-07-21T08:19:50Z

+    # The exception in before_send_log is swallowed and the original,
+    # unmodified log is sent.
+    assert len(logs) == 1
+    assert logs[0]["body"] == "This is an error log..."
+    assert logs[0]["attributes"]["sentry.severity_text"] == "error"


We should drop the log in this case

sentrivana · 2026-07-21T08:20:01Z

+    # The exception in before_send_metric is swallowed and the original,
+    # unmodified metric is sent.
+    metrics = [item.payload for item in items]
+    assert len(metrics) == 1
+    assert metrics[0]["name"] == "test.keep"


Same here -- the metric should not be sent

sentrivana · 2026-07-21T08:27:50Z

+    "traces_sample_rate,expected_decision",
+    [(0.0, False), (0.25, False), (0.75, True), (1.00, True)],
+)
+def test_traces_sampler_raising_falls_back_to_traces_sample_rate_span_streaming(


Can we also add a span streaming test case with no incoming trace propagation headers/no continue_trace and check that we fall back to traces_sample_rate?

sentrivana · 2026-07-21T08:28:37Z

        assert span.sampled is traces_sampler_return_value


+@pytest.mark.parametrize(


[not related to this specific line or testcase] One case I'm not quite sure of: there is no incoming trace, traces_sampler is defined and throws, and there is no traces_sample_rate defined. We should have a test case (or two: streaming and non streaming) for that too.

Will add a couple, where the assertion is that the span/transaction isn't sampled

sentrivana

Approving to not block -- as long as the comments have been addressed feel free to merge 🙏🏻

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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cursor · 2026-07-21T15:03:34Z

+                    raise
+
+            if exception_raised_in_before_send_func:
+                return


Span dropped on callback exception

Medium Severity

The early return on a before_send exception applies to spans as well, so a raising before_send_span drops the span. That conflicts with the nearby rule that spans cannot be dropped, and with invalid-return handling that keeps the original span. Review feedback only asked to drop logs and metrics; the PR description still says the unmodified item is sent. A buggy sanitizer can silently break traces.

Additional Locations (1)

tests/tracing/test_span_streaming.py#L382-L384

^{Reviewed by Cursor Bugbot for commit 0f8a64a. Configure here.}

sentry · 2026-07-21T15:04:52Z

+            if exception_raised_in_before_send_func:
+                return


Bug: If the telemetry before_send callback raises an exception, the telemetry item is silently dropped instead of sending the original item.
_{Severity: MEDIUM}

Suggested Fix

Remove the early return statement if exception_raised_in_before_send_func: return. This will allow execution to continue after the before_send callback fails, sending the original serialized data that was preserved.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not valid. Location: sentry_sdk/client.py#L1255-L1256 Potential issue: In `_capture_telemetry`, if the user-provided `before_send` callback raises an exception, the code sets a flag `exception_raised_in_before_send_func` and the exception is suppressed. An `if` statement then checks this flag and executes an early `return`, which silently drops the telemetry item. This contradicts the intended behavior of sending the original, unmodified telemetry item when a callback fails.

sentry · 2026-07-21T15:04:52Z

+) -> "Union[float, bool]":
+    if propagation_context.parent_sampled is not None:
+        propagation_context_sample_rate = propagation_context._sample_rate()
+
+        if propagation_context_sample_rate is not None:
+            return propagation_context_sample_rate
+        else:
+            return propagation_context.parent_sampled
+    else:
+        return client.options["traces_sample_rate"]
+


Bug: When traces_sampler raises an exception, the fallback can return None as the sample rate, causing all associated traces to be silently dropped.
_{Severity: HIGH}

Suggested Fix

Modify _get_effective_sample_rate to ensure it does not return None when the traces_sampler fails. The fallback logic should return a valid float, such as 0.0, if traces_sample_rate is not set, to prevent traces from being dropped.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not valid. Location: sentry_sdk/tracing_utils.py#L1579-L1591 Potential issue: The function `_get_effective_sample_rate` can return `None` if `traces_sampler` raises an exception and `traces_sample_rate` is not explicitly configured by the user. The downstream function `is_valid_sample_rate` treats `None` as an invalid rate, logs a misleading warning, and causes all traces for that context to be silently discarded. This affects users who only configure `traces_sampler`.

ericapisani added 2 commits July 20, 2026 14:55

fix(tracing): Handle traces_sampler raising by falling back

bfe9623

When a user-provided traces_sampler callback raises, catch the exception, log a warning, and fall back to the parent sample rate or the configured traces_sample_rate instead of propagating the error. Refs PY-2617 Refs #6849

ericapisani requested a review from a team as a code owner July 20, 2026 18:57

sentry Bot reviewed Jul 20, 2026

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Comment thread sentry_sdk/client.py Outdated

alexander-alderman-webb approved these changes Jul 21, 2026

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sentrivana requested changes Jul 21, 2026

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address CR comments

0f8a64a

sentrivana approved these changes Jul 21, 2026

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cursor Bot reviewed Jul 21, 2026

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sentry Bot reviewed Jul 21, 2026

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		assert span.sampled is traces_sampler_return_value


		@pytest.mark.parametrize(

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