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: 319m 3s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +285
Passed Tests	📈 +284
Failed Tests	📉 -1
Skipped Tests	📈 +2

➖ Removed Tests (1)

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test_circular_references
- File: tests.tracing.test_misc

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2484 uncovered lines.
❌ Project coverage is 89.66%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    89.68%    89.66%    -0.02%
==========================================
  Files          193       193         —
  Lines        24007     24030       +23
  Branches      8342      8348        +6
==========================================
+ Hits         21529     21546       +17
- Misses        2478      2484        +6
- Partials      1387      1386        -1

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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 🙏🏻

sentry · 2026-07-21T15:31:20Z

+                try:
+                    serialized = before_send(serialized, {})  # type: ignore[arg-type]
+                except Exception:
+                    exception_raised_in_before_send_func = True
+                    raise


Bug: The capture_internal_exceptions context manager suppresses BaseException subclasses like KeyboardInterrupt, preventing process termination when raised in before_send callbacks.
_{Severity: CRITICAL}

Suggested Fix

Modify the __exit__ method of CaptureInternalException to not suppress BaseException subclasses. It should check if the exception type ty is a subclass of Exception before suppressing it, allowing critical signals like KeyboardInterrupt and SystemExit to propagate and terminate the process as expected.

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#L1249-L1253 Potential issue: The `capture_internal_exceptions` context manager, used to wrap the `before_send` callback, has an `__exit__` method that always returns `True`. This behavior suppresses all exceptions that propagate to it. While a `try...except Exception` block handles standard exceptions, `BaseException` subclasses like `KeyboardInterrupt` or `SystemExit` are not caught by this block. Instead, they are silently swallowed by `capture_internal_exceptions`, preventing the process from terminating as expected. This is a regression that can make services unresponsive to termination signals like Ctrl+C.

Also affects:

sentry_sdk/utils.py:208~223

The TYPE_CHECKING import of BaseClient from sentry_sdk.client in tracing_utils.py created a circular import when Sphinx evaluated type annotations during the API docs build (sphinx_autodoc_typehints evaluates TYPE_CHECKING imports at runtime). A cold 'import sentry_sdk.client' then cycled through scope -> tracing -> tracing_utils -> client -> integrations.dedupe -> partially-initialized scope. Annotate the client parameter as Any instead.

Reset the serialized span to its original value when before_send_span raises, so partial mutations made by the callback before the exception are discarded and the unmodified span is sent. Strengthen the raise test to mutate the span before raising, asserting the mutation does not leak into the sent span.

cursor

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

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sentry · 2026-07-21T16:03:54Z

+                # functions.
+                if exception_raised_in_before_send_func:
+                    return


Bug: The try...except Exception block for before_send callbacks doesn't handle BaseException. This causes logs/metrics to be sent instead of dropped when a BaseException is raised.
_{Severity: LOW}

Suggested Fix

Modify the exception handling to catch BaseException instead of just Exception. This will ensure that the exception_raised_in_before_send_func flag is correctly set for all types of exceptions, causing the log or metric to be dropped as intended.

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#L1258-L1260 Potential issue: The exception handling for `before_send` callbacks for logs and metrics is incomplete. The code uses a `try...except Exception` block to set a flag, `exception_raised_in_before_send_func`, which determines if the log/metric should be dropped. However, this does not catch `BaseException` subclasses (e.g., `KeyboardInterrupt`). When a `BaseException` is raised in a user's `before_send_log` or `before_send_metric` function, the flag is not set. Consequently, the log or metric is sent to Sentry instead of being dropped, which contradicts the intended behavior of dropping events when the callback fails.

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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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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Comment thread sentry_sdk/client.py Outdated

Comment thread sentry_sdk/tracing_utils.py

actually, do not drop spans

99fe440

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Comment thread sentry_sdk/tracing_utils.py

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Comment thread sentry_sdk/client.py

Comment thread sentry_sdk/tracing_utils.py

ericapisani added 3 commits July 21, 2026 11:50

improve reason

f3e440e

Merge branch 'master' into py-2617-handle-exceptions-combined

b89171c

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sentry Bot reviewed Jul 21, 2026

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.

99fb778

		assert span.sampled is traces_sampler_return_value


		@pytest.mark.parametrize(

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