Make sure to use the default decimal context in our code (#4231)

Fixes #4213

Author: antonpirker

sentry_sdk/tracing.py

@@ -1,3 +1,4 @@
+from decimal import Decimal
 import uuid
 import warnings
 from datetime import datetime, timedelta, timezone
@@ -1198,10 +1199,8 @@ def _set_initial_sampling_decision(self, sampling_context):
             self.sampled = False
             return
 
-        # Now we roll the dice. self._sample_rand is inclusive of 0, but not of 1,
-        # so strict < is safe here. In case sample_rate is a boolean, cast it
-        # to a float (True becomes 1.0 and False becomes 0.0)
-        self.sampled = self._sample_rand < self.sample_rate
+        # Now we roll the dice.
+        self.sampled = self._sample_rand < Decimal.from_float(self.sample_rate)
 
         if self.sampled:
             logger.debug(

sentry_sdk/tracing_utils.py

@@ -5,7 +5,7 @@
 import sys
 from collections.abc import Mapping
 from datetime import timedelta
-from decimal import ROUND_DOWN, Context, Decimal
+from decimal import ROUND_DOWN, Decimal, DefaultContext, localcontext
 from functools import wraps
 from random import Random
 from urllib.parse import quote, unquote
@@ -872,10 +872,13 @@ def _generate_sample_rand(
 
     # Round down to exactly six decimal-digit precision.
     # Setting the context is needed to avoid an InvalidOperation exception
-    # in case the user has changed the default precision.
-    return Decimal(sample_rand).quantize(
-        Decimal("0.000001"), rounding=ROUND_DOWN, context=Context(prec=6)
-    )
+    # in case the user has changed the default precision or set traps.
+    with localcontext(DefaultContext) as ctx:
+        ctx.prec = 6
+        return Decimal(sample_rand).quantize(
+            Decimal("0.000001"),
+            rounding=ROUND_DOWN,
+        )
 
 
 def _sample_rand_range(parent_sampled, sample_rate):

tests/tracing/test_sample_rand.py

@@ -1,4 +1,5 @@
 import decimal
+from decimal import Inexact, FloatOperation
 from unittest import mock
 
 import pytest
@@ -58,14 +59,19 @@ def test_transaction_uses_incoming_sample_rand(
 
 def test_decimal_context(sentry_init, capture_events):
     """
-    Ensure that having a decimal context with a precision below 6
+    Ensure that having a user altered decimal context with a precision below 6
     does not cause an InvalidOperation exception.
     """
     sentry_init(traces_sample_rate=1.0)
     events = capture_events()
 
     old_prec = decimal.getcontext().prec
+    old_inexact = decimal.getcontext().traps[Inexact]
+    old_float_operation = decimal.getcontext().traps[FloatOperation]
+
     decimal.getcontext().prec = 2
+    decimal.getcontext().traps[Inexact] = True
+    decimal.getcontext().traps[FloatOperation] = True
 
     try:
         with mock.patch(
@@ -77,5 +83,7 @@ def test_decimal_context(sentry_init, capture_events):
                 )
     finally:
         decimal.getcontext().prec = old_prec
+        decimal.getcontext().traps[Inexact] = old_inexact
+        decimal.getcontext().traps[FloatOperation] = old_float_operation
 
     assert len(events) == 1